[hankster]

Welcome to the most extensive collection of RC electric motor information available anywhere. Never before has there been one place to find all the motor information you need to get the most out of your RC motors. Big Jim’s RC Motor Black Book eliminates the need to scour years of magazines, search the Internet for information of questionable nature and pick the brains of the local hotshots. You will find the answers and information you need on all aspects of electric motors that are used in RC. Everything from basic maintenance to detailed tuning information, design theories and dyno setup are in Big Jim’s RC Motor Black Book.

Most of the advanced tuning and theory information is provided by Big Jim Greenemeyer. Jim has been in the RC motor business since 1978 and is the premiere motor designer in the world. The Trinity D4 modified and P2K motors are just a couple of the latest designs that he helped bring to market. Besides his own motor tuning and winding business, Big Jim also winds modified motors for Integy and is consulting with Reedy on the MVP2 stock motor that will be on the market in 2002.

Never one to pull punches, Big Jim tells it like it is. You won’t find hear-say or maybes here, just straight forward information that has proven to work through extensive on-track testing.

The RC Motor Black Book eliminates the need to scour years of magazines, search the Internet for information of questionable nature and pick the brains of the local hotshots. You will find 160+ pages of answers and information that you need on all aspects of electric motors that are used in RC. Everything from basic maintenance to detailed tuning information, design theories and dyno setup are in the RC Motor Black Book.

You can purchase Big Jim's RC Motor Black Book directly from the publisher or from any of the major booksellers such as Barns & Nobel or Borders. The Motor Black Book is no longer in print

Note: In June 2005 Big Jim passed away. While not everyone may have gotten along with him, he did provide great information on motors and helped a lot of racers "go faster". Hopefully the information provided below will also help you as you try to get the most out of your RC motor!

 

[hankster]

Motor Anatomy

If you are new to RC, the electric motor that powers your vehicle may be a mystery to you. You'll hear other RCers talk about winds, comms, brushes and other things that you have no idea what they mean. We will dissect a modern electric RC motor and show you what all of these terms mean and help you better understand how your power plant works.

Here is what a new motor looks like from the outside. This motor is a rebuildable stock motor based on a design by Yokomo. There are designs by other companies that you may find at your local hobby shop, but basically they are all the same. Let's take a look at what makes up a modern rebuildable stock motor.

Motor Can: The motor can is manufactured out of steel. It holds the magnets and the bushing for the pinion end of the armature. At the end where the shaft extends, there are two sets of mounting holes for mounting the motor in your RC vehicle.

End Bell: The is the end of the motor that takes care of the electrical connections to your motor. The wires from your speed controller connect to it and through the brushes passes the electricity from your battery to your motor. Made of a non-conducting material, on it is mounted the brush hoods, an armature bushing and capacitors. In a motor that can be rebuilt, two screws hold the end bell to the motor can.

Brushes: The brushes are what actually pass the battery power to your motor and makes it go. They are generally made out of a graphite compound and can have mixtures of silver added for better conductivity. With use, brushes do wear out and will be one of the items that need to be periodically replaced.

End Bell
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The end bell is the end of the motor that takes care of the electrical connections to your motor. The wires from your speed controller connect to it and through the brushes passes the electricity from your battery to your motor. Made of a non-conducting material, on it is mounted the brush hoods, an armature bushing and capacitors. In a motor that can be rebuilt, two screws hold the end bell to the motor can.

Wiring Lugs: This is where your speed control connects to the motor. Each motor is marked a little differently, but if you look closely, one of them will have a + sign next to it. That is the one that you connect your speed control positive motor wire to. The negative wire connects to the remaining lug. Read your speed control instructions closely so you know which wires connect to the motor.

Brush Spring: The brush springs hold the brushes tightly against the armature allowing electricity to pass from your speed controller to the armature while it turns. The brush spring can easily be removed with your fingers by just moving the end of spring out from under the small tab that is on top of the brush hood. You can then just lift it off of the brush spring post to complete the removal.

Brushes: The brushes are what actually pass the battery power to your motor and makes it go. They are generally made out of a graphite compound and can have mixtures of silver added for better conductivity. With use, brushes do wear out and will be one of the items that need to be periodically replaced. They can be removed and replaced once the brush spring is removed as noted above.

Motor Screws: These are used to hold the end bell onto the motor. remove these to remove the armature from the motor

Capacitors: Capacitors are mounted to the motor to help keep radio interference to a minimum. Every electrical motor makes electrical "noise" when they are run. The capacitors absorb this noise so it does no interfere with the operation of your transmitter. You can learn more about mounting capacitors on your motor by reading our How To's where we give easy to follow steps on how to mount them.

Brush Hood: The brush hoods holds the motor brushes in place on the motor and keeps them in proper alignment with the armature. They also include the wiring lugs for connecting your speed control wires and the mounting post for the brush springs.

Bushing: The bushing holds the commutator end of the motor and is what the spinning armature uses as a bearings. Some motors use a ball bearing instead of the stock motor's solid oillite bushing. You should put one drop of oil on each bushing every few runs to make sure it is properly lubricated.

Motor Can
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The motor can holds the armature, the magnets and is what the end bell mounts to. Stock motors such as this one has "fixed timing" and the end bell is "keyed" to the motor can so it can not be changed. Some motors have adjustable timing that allows you to "tune" the performance for the motor.

The timing on most stock motors is fixed at 24 degrees. The more timing (up to 45 degrees max) gives the motor more RPM and power, but this also means that it will draw more power and your batteries will not give as much "run time", plus it also shortens the life of the motor.

Magnets: The magnets are glued to the motor can and are what produces the magnetic field that causes the motor to work.

Endbell Mounting Key: Rebuildable stock motors are fixed with 24 degrees of timing. A key on the endbell fits into the slot on the motor can to insure this timing is maintained and that you can only fit the endbell on one way.

Bushing: The bushing holds the end of the motor and is what the spinning armature uses as a bearings. Some motors use a ball bearing instead of the stock motor's solid oillite bushing. You should put one drop of oil on each bushing every few runs to make sure it is properly lubricated.

Motor Can: The motor can is manufactured out of steel. It holds the magnets and the bushing for the pinion end of the armature. At the end where the shaft extends, there are two sets of mounting holes for mounting the motor in your RC vehicle.

Armature
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The armature is what spins in the motor and makes you RC vehicle go. Some may shorten the name of this piece to just "arm".

Electricity flows through the brushes into the commutator, the slotted commutor then passes this electricity into the windings. Since the windings are wrapped into a coil, they create a magnetic field when current is passed through them. This magnetic field is repelled and attracted to the magnets in the can causing the armature to turn.

Armature Stack: The armature stack is constructed of laminated steel. It holds the windings of the motor and helps increase the magnetic force created by the windings when current is passed through them.

Label: Rebuildable stock motors are labeled so it is easy to tell if this armature was made for this motor. This is for racing purposes to make it easy to examine the motor to make sure the motor is legal for stock racing.

Commutator: Many times this is called the "comm" by RCers. The comm takes current from your brushes which ride on this part of the armature and sends it to the windings. The comm is not one solid piece, but is actually made up of 3 separate pieces and this allows the current to be switched to the different windings on the armature as it spins. Because it rubs against the brushes as the armature spins, the comm needs to be cleaned after every few runs. You can purchase comm cleaning sticks from your local hobby shop.

Balancing Holes: Armatures are balanced when they are manufactured so they run smoother. This is needed since it is almost impossible to get exactly the same amount of wire on each armature pole. Without balancing, your motor would not run as fast and would wear out quicker.

Windings: Each pole of the armature was wire wound around it. This lacquer coated (for insulation) wire is what the battery current passes though and creates a magnetic field so the motor will run. Stock motors have 27 wraps (or turns) of 22 gage wire. You may hear some RCers refer to this as "winds or turns". Less winds generally means a faster motor and the smaller number of the gage means bigger diameter wire. You will see motors with as few as 8 "winds or turns" and as many as 35 or more.

Here is an "exploded" view of a modern rebuildable stock motor. You can use this as a guide in case you need to find out how to reassemble your motor once you have taken it apart to clean or rebuild.

If you have any questions on motors or need any help on how to rebuild or clean, we have many articles on the subject and you can always get help in our discussion Forums.

Good luck and have fun... that's what RC is all about!

 

[hankster]

Motor Cleaning

I was cleaning some P2K endbells last night and realized I have been cleaning and scrubbing motors and parts for a long time. But I don't think I've ever posted any of my tips for cleaning and what to use This is an important step in rebuilding your motor. If you're one of those racers who just spray the endbell and can out with motor spray and that's it, let me explain why you should do it better.

THE most important area on the motor that has to be clean is the one most overlooked. That is the inside of the brush hoods. This area is responsible for flowing current from the hoods and base plate (or heatsink) to the brush. That little shunt wire is rated at 10A peak so not much help there. The contact area that the brush slides on inside the hood is most important for getting power to the armature. Take extra steps to make sure it's clean and corrosion free. And also free of burrs that could hang up a brush.

Cleaning the Endbell
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An endbell gets really dirty with a variety of contaminants. Solder blobs, old solder flux, oil, tire dust, brush dust, corrosion, tarnish, etc, are some of them. The first thing you do is take your iron and get rid of the excess solder on the tabs and remove the brushes (if they're soldered on the way they should be). I just heat the area up and sling it in the waste can before the solder sets. Instant gone. You could use that de-solder braid but this is easier.

Now you'll need an old toothbrush, your alignment bar, and (this is the best stuff for this) LYSOL Basin Tub and Tile Cleaner. This stuff gets rid of everything on the endbell, even tarnish. This is a time saver if you're doing some Epic stuff. Cleans the copper like new again. Old flux gone, everything. Spray it inside and out of the endbell especially inside the hoods. Let it sit for a few minutes. The scrub it with the toothbrush. Now take your alignment bar and slide it back and forth inside each hood. If your hoods are aligned properly, you won't be able to shove it through both sides at the same time easily. Just do one side at a time. This polishes the inside, removes dirt and corrosion and gets rid of any burrs that popped up. Rinse in warm water. Shake it, then dry with a hair dryer.

If you have the Epic copper hardware, it looks good now but by the time you get it back together it's already starting to look tarnished. What you need to do is get some AEROPLATE. It comes in a spray bottle from Aerotrends Co. www.aerotrend.com. It's a light oily kinda stuff that stops tarnish on any metal surfaces. Just spray it on and brush the excess off with a brush. Let dry. It can't be removed with solvents but soap and water works just fine.

Check the tightness of the spring posts and screws, straighten the metal timing ring and set the endbell aside.

Cleaning the Can and Armature
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Yeah, you're thinking the cleaning is about over right? Well, for sure, you have the important part done. Cleaning the can is easy but do you inspect it after? The LYSOL BTTC works good for the can too. Use the toothbrush to clean around the edges of the magnets where they suck up metal chips from everywhere through the holes.

When it's clean and dry, check the mounting holes for any thread damage. Check the magnets for cracks and push on the ends with a srewdriver. You'll catch loose magnets this way. Check for those small metal chips that hang on the magnets and only come loose when you put the arm in. Instant lock up. If you see any, take your dry toothbrush and stick it in the can and drag the chips outward with a flicking motion. Keep doing it until you can't see any more steel chips. Set can aside.

The armature doesn't need much but as long as you have the Lysol out, spray the windings and especially the comm area. Use your toothbrush on the coils and scrub the comm slots well. That's where all kinds of crap hides. When it's rinsed and dry, chuck the arm in a drill and polish the shafts with #2000 wet or dry sand paper. If you have any scoring around the area that the bushing rides on, you may have to use #400 first and then finish with the #2000 grit. Check for loose or burnt wires. True and set aside. A side note, if you have that scoring, you wouldn't if you used the Tribotech IJP Oil Treatment (the makers of the TRIBO Power Matrix comm lube) I have recommended on my forums for awhile now. Don't use the Prolong for bushings. It's viscosity is too thin.

Motor Ball Bearings
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I have one of those bearing cleaner things where you put the bearing in and spray motor spray through it. But I use that at the track only. If I'm home, dish soap and hot water works the best. You'll also need an old armature.

Dirty bearings can rob power. I have cleaned some really gritty bearings with the following procedure. Do this after the LYSOL rinse. It case you're wondering why don't you just use the the Lysol, that's pretty harse stuff. It seems the dish soap (Dawn, my favorite) polishes the inside races of the bearings. Maybe just my imagination but it does something.

Take the dish soap and pour it in the bearing from both sides. Now take your old armature and stick it in the bearing and spin it. Spin it both directions. Now let the armature spin the bearing while you hold it under the hot running water. Do both sides. This will flush out most grit, oil and crud from your motor bearings. You may have to do this procedure again if they're really bad. If you've done this twice and the bearing still feels notchy, it's not dirt. The balls have dented the inner race. It happens sometimes. You'll have to replace the bearing.

Now just reassemble your motor in the usual way.

 

[hankster]

Brush Basics

One of the best ways to extent the life of your motor and to keep it running at top performance is by paying attention to the motor brushes. The brushes are the lifeline of the motor. With use they get worn and burnt. If you don't clean and change your brushes often your motor will perform poorly and will have a much lower then expected lifetime. Brushes are easy to clean and change, are inexpensive and can triple (or more) the life of your motor. Follow along as we give you a few tips on brushes, how to clean them and how to change them.

Remove the Brushes
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The motor brush is held into the motor by the brush spring. It is easy to remove the spring by unhooking it from the tab on the brush hood and then removing it from the spring post. Be careful that you do not lose the spring as it can fly off when removed and you will need to use it again when you are done cleaning or replacing the brush.

Here you can see that the end brush spring has been removed from the spring tab. You can just use your finger to remove the end of the spring from the tab. Completely remove the spring and the brush will then slide out of the brush holder.

The brushes are attached to the brush hood by two different methods. On most stock motors, the brush is equipped with an eyelet and this is held in place by a the brush hood screw. Just remove this screw and you can completely remove the brush from the motor.

On high performance or team motors, the brushes are soldered to the brush hood. You will need to use a soldering iron to remove and replace brushes that are attached this way. If you are not racing in competition, you can replace a soldered on brush with a brush that has an eyelet to make subsequent brush changes easier and it will make little or difference in the speed of your motor.

Clean the Brushes
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Here you can see a brush that has been used next to a new brush. Note that the used brush is shorter and shows signs of burning along the edges. This used brush is not so bad and can be cleaned and reused.

I like using a Parma Fiberglass Comm Cleaning Stick (part #11050) to clean brushes. It is inexpensive and does a great job. Just use the end of the stick on the face of the brush to clean off the glaze and any deposits.

Clean the Motor
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Now is a great time to clean the motor. Use can use the same Parma Comm Cleaner stick to clean the comm on the motor. Just stick the cleaning stick in the brush hood, apply a little pressure to the end of it and spin the motor a few times. You may want to put a pinion gear on the end of the motor to make it easier to spin.

Use a motor cleaner spray to completely flush out the motors making sure you get the bearings clean of any dirt and gunk. Be sure you use motor spray designed for RC use and to wear safety glasses to prevent the spray from getting into your eyes.

In these before and after shots, you can see how the comm on the motor was burnt, glazed and scarred before the Parma Comm Cleaning Stick was used on it.

With just a few turns of the motor, the comm is now shiny and ready to go. If your comm is extra worn and gouged, then the comm stick will not completely clean it up. It would be best if you could find someone to "turn" the comm for you. In all cases, it is better to use the comm cleaning stick no matter how bad of shape the comm is in.

Put a drop or two of oil on each bushing on the ends of the motor and you are ready to reinstall the brushes and springs, put the motor back in your car or truck and go out and have a blast!

 

[hankster]

Soldering Capacitors

Mod or Rebuildable Stock Motors
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Tools Required: The following tools & items will be needed: Soldering Iron (a 40 watt iron will work well), Solder (60/40 rosin core solder works well), 3 Capacitors (0.1 microfarad ceramic capacitors (50V)).

1) Take the soldering iron, heat the solder tabs on the motor and melt a small amount of solder on them.
2) Take one of your capacitors and solder one of the legs of it on the positive (+) side of the motor and one on the negative (-) side of the motor (use picture above as a guide).
3) Take the other two capacitors and twist one of each of their legs together.
4) Solder the free leg of each cap to one of the solder tabs. One leg goes on the positive (+) side of the motor, the other to the negative (-) side.
5) Solder the legs that you twisted together to the the tab in the center with the screw in it.
6) Snip off any extra wire that may be hanging off the capacitors with a pair of clippers and you are done installing your motor capacitors.


Tips: Always wear safety glasses when soldering. Melted solder can splatter and get into your eyes. Installing capacitors help in preventing radio interference.

Non-Rebuildable Stock Motors
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Tools Required: The following tools & items will be needed: Soldering Iron (a 40 watt iron will work well), Solder (60/40 rosin core solder works well), 3 Capacitors (0.1 microfarad ceramic capacitors (50V)), Metal File.

1) Take the soldering iron, heat the solder tabs on the motor and melt a small amount of solder on them.
2) Rough up the motor can between the solder tabs with the metal file so the solder will stick easier.
3) Apply a small amount of solder to the motor can in the place you roughed up in step 3.
4) Taker one of your capacitors and solder one of the legs of it on the positive (+) side of the motor and one on the negative (-) side of the motor (see picture above as a guide).
5) Take the other two capacitors and twist one of each of their legs together.
6) Solder the free leg of each cap to one of the solder tabs. One leg goes on the positive (+) side of the motor, the other to the negative (-) side.
7) Solder the legs that you twisted together to the spot on the motor can that you previously filed and melted the solder on.
8) Snip off any extra wire that may be hanging off the capacitors with a pair of clippers and you are done installing your motor capacitors.


Tips: Always wear safety glasses when soldering. Melted solder can splatter and get into your eyes. Installing capacitors help in preventing radio interference.

 

[hankster]

Armatures

Question: How do you center the armature?

BJ's Answer: Assemble the motor first with no shims at all. Hold the motor horizontal. Pull the arm back and forth an notice where it wants to rest when you spin it. Start putting thin shims on the ends of the arm and slowly take up the play noticing each time where the arm wants to rest. Put the appropriate number of shims on each side to keep it in the center. One shim one way or the other is not going to make much difference. When you take it apart again for rebuild, just keep the shims separate off each end, and reassemble the same way it came apart.

Question: Why are all motor manufacturers & relabelers still using a brass shims against a bronze bushing? Cost?

BJ's Answer: I don't really see anything wrong with the brass washer. What would you suggest?

Question: Just pondering along the metallurgical lines of thought... bronze is an alloy of some of the same composition as brass... so why do we want to put to like materials against each other and hope the get along (they don't). Plastic, fiberglass, chrome plated (p2k).... or???

BJ's Answer: Well, this is one motor question that I'll have to say, I don't know. It must not make any difference what the material is with all the oil around it and all. Just my guess.

Question: The only item that I have noticed... if using a fiber or Teflon washer.. the endplay is kept in check. Seems that metal, bronze, and even the chrome plated tend to wear a little or cut into the back of the bushing slightly.

Seems that the armature is fighting against itself with any time spent having the arm shoved against one end when spooling up.... instead of being kept in the center of the magnetic field.

BJ's Answer: The armature slams up against the can under acceleration and slams up against the endbell on deceleration anyway. It's always going back and forth on the track. Exact arm centering is not real important, in my opinion. I think you'll find that the arm spacer is getting shorter with all this slamming, accounting for the increased

endplay. Bushing wear does play a part in this too, though. I use some Tribotech mixed with a little 40w Pennzoil on my bushings. Cuts wear almost to zero.

D4 Armature Design
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Question: I have seen the pictures, but what are the actual design differences between the D4 "RPM" blank and the "torque" blank and why do they favor one or the other ?

BJ's Answer: The "rpm" blank was my exclusive brain child. It has what I call a reverse tapered web. Meaning the web (the part of the armature the wire is wrapped around) is tapered smaller toward the shaft. This allows more flux to build up closer to the crown (the part of the armature closest to the magnets), while still allowing room for lots of wire. The crown area is the part that reacts with the magnets the most and this taper directs the flux that way. Also the tips of the crown are closer together for more torque, although it does make it harder to wind.

The "torque" blank is the result of a collaboration between me an Jim Dieter, probably the best tuner in the world, in my opinion. It has a "fat" web design. This makes for lots of flux build-up, which in turn, makes lots of torque, hence the name. We decided to go with the two designs to optimize the performance of every wind from 6 to 16 turns. With these two designs, it is possible to get the right power curve with any wind, at any track, with any number of cells.

In our testing, the "rpm" blank produced the most amount of power with a 12 turn arm and above. However, below 10 turns, the "torque" blank produced more power.

Our type motors gain rpm as the turns are dropped off, but lose torque. Since HP=rpm x torque, you gain horsepower when you drop off turns down to about 10 turns. With most motors at that point, you lose more torque than the rpm you gain. In other words, an 11 turn would have more power than a 10 turn. But if you can offset the torque loss with a "torque" blank, you can get very good HP all the way down to 6 turns. With the "rpm" blank you can get good HP all the way up to 16 turns and even higher because it revs so well. Hopefully, you can see with two different type blanks, it's possible to have maximum horsepower through a wide variety of winds.

P2K Armature Design
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Question: Motor theory question..... are the P2K and Paradox arms better for torque because of.... the armature is heavier (mass)... or because more area of the arm is exposed to the magnetic field?

BJ's Answer: It's because of the Z-speed arm (I didn't name it) we designed. The armature web is asymmetrical as is the can side holes and the indentation around them. They all help for power by increasing the magnetic timing of the motor. At least that's my theory anyway, but it seems to work.

Question: What's the difference on the P2K VS. Paradox arm?

BJ's Answer: There are two important differences in the two arms. Most important is the asymmetrical web ( the part the wire is wrapped around) along with the inside of the crown (the part that looks like the top of a mushroom) in the armature. In other words, one side of the armature stack is thicker than the other. This shifts the magnetic field to the advanced side giving the armature more effective magnetic time, the same thing the off-set holes and the one sided dent in the can does. This arm design has been shown for many months in RCCA mag.

Also, the flat areas on the outside of the arm are less pronounced. We (Dieter and myself) felt because of our web design, we didn't need as great a "shift" this way as in the Paradox. This is why the P2K has so much torque. There are other ways to make even more torque and power in a stock motor as we all will see later this year.

Armature Testing
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*** This topic is updated and covered in-depth in the print version of Big Jim's RC Motor Black Book. ***

Armature Weight
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Question: How about the weight of the armatures?

BJ's Comments: I find armature weight is something to be considered when winding mod arms. A lightly wound arm will spool up quicker than a heavy wound one of the same number of turns. But a high circular mil arm (fully packed) will produce more total power because of its lower resistance, and is the arm of choice for bigger tracks where spool up is not as important as top end power. If one arm is heavier than another because of the amount of steel in the blank, the one with the most "iron mass" will usually have more torque, all other things being equal.

Armature Magnetism
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Question: What effect do you think a magnetized armature has on performance. I've seen some of the armatures in my brand "T" motors would become magnetized after setting around for awhile. Would this just go away after the motor runs a little or should I take them to the shop and demagnetize them?

BJ's Comments: I think you'll find that residual magnetism is non-directional and is quickly dissipated once the arm is run.

Armature Winds
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Question: Mabuchi vs. Hemi wind - any advantage for oval racing ? Do the Hemi's actually end up with a half-turn less wind, e.g., an eleven turn hemi-wind is actually like a ten and a half regular wind ?

BJ's Answer: A hemi style wind does cut a half a turn off electrically but not resistance wise, although that is a little less too. The hemi wind, so named from an old Japanese slot car motor, works very well on a motor that has a lot of magnetic flux both in the armature and the can, like the D4. Although it might not be as effective on a motor with a lot of flux loss like the Yokomo and the Orion thing. Holes

between the magnets kill the magnetic flux and the thin web on the arm doesn't help either. For oval racing I'd definitely get the "rpm" blank. All D4's are wound hemi.

Question: Split winds - any use for oval racing ?

BJ's Answer: By split winds, I assume you mean the high-variance split wind, where one big wire is wound with one or two small ones. This type wind works best with a light wind or where the arm isn't very full. The secret is to run one or two winds hotter than you normally would because these winds are very efficient on the lower end of the power curve and spool-up very quick but lack top end. But you get the top back by the hotter wind and taller gear. A very effective way to get HP everywhere but a Velodrome type track. There you'd want as full an arm as you could get for the top end HP you need for that type of track.

Question: You've said that the only things about winds that matter are the circular mil and the number of turns. So what's so good with those HSV winds?

BJ's Answer: The High-variance split wind or HVW, so named by yours truly, but first made by Mike Reedy. This is something on the cutting edge. When I mentioned that nothing matters but circular mils and number of turns, I was referring to basic motor theory.

We motor designers are on a constant quest for even the slightest increase in power. There are many theories on why or how this works but without going into this advanced hypothesis here, let's just say that it does work under certain circumstances and at certain tracks.

Question: When running 14 cells, is it necessary to run higher turns because of the weight of the batteries.

BJ's Answer: The reason you run a higher wind with a high number of cells is because of the voltage of those cells. A low wind with a lot of cells would draw too much current and over-saturate the armature steel. Also, the motor's brush system can only carry so much current. This is why Steve Saik only set the car up with 17 cells and not higher. 20 cells wouldn't produce any more power and the car would weight more.

Question: I was wondering what causes a mod arm in a stock can to run in the reverse direction? Is the polarity of the magnets reversed or are modified armatures wound the opposite direction as stock ones

BJ's Answer: The direction an arm is wound has nothing to do with

it's direction of rotation. The way the wires go up to the commutator is what determines that. Stock motors are wound cross-over style. Most mod arms are wound Hemi style. Each style will run in opposite directions from each other. However, just reversing the leadwires is all that's required to fix the problem or rotate the endbell 180 degrees.

Question: Would you mind explaining how a hemi wind and a cross over wind is wound??

BJ's Answer: I don't know if I can explain how the different styles are wound without showing you. Probably the best thing is to take a modern mod arm (Epic or Reedy preferably) and a stock motor arm and lay them down side-by-side with the comms up. On the stock arm, you will see the wire comes off the coil and crosses over itself to the comm tab on the opposite side which it goes through and down to the start of the next coil and so on. You will notice the starting wire of one coil crosses over the ending wire of the same coil. This is called a cross-over wind for obvious reasons. It's also called the Mabuchi wrap to the less informed.

The hemi wind, so named after a slot car motor from the '60's, starts on one tab and winds around the stack and up to the other comm tab on the other side without crossing wires. In order to make a complete magnetic loop, the wire has to cross itself on every turn. However, with a hemi wind, the last turn doesn't cross itself so that loop is incomplete. This, in essence, creates the effect of only 1/2 a turn. So a 12 turn hemi wound motor is really a 11 and 1/2 turn as far as the field strength of that coil. With the modern magnets we have now and the batteries, we can get more performance from this type of wind over the antiquated cross-over style. However, because this type of wind doesn't hold the comm as secure from moving if not epoxied, stock motor rules have mandated that they all be wound cross-over.

Question: You know about the new EFRA regulations with the 12T limit. There are some manufactures that are bringing out some kind of EFRA special motor. In case of Orion this are two 12 singles, one with a high rpm blank and one with a high torque blank. I have a question about the high rpm motors. Is it possible that a 12 single can beat a stuffed 12 hex on a very fast circuit ??

BJ's Answer: Everything in a motor is a trade off. A high rpm motor trades rpm for torque and visa-versa. On the big tracks you guys race on over there and with the 12 turn limit, I'd say the rpm (thin web) arm is the way to go.

I never really liked singles. That big wire just uses up too much space and they tend to be rather snappy out of the corners due to their lighter weight but lack top end power because of their extra resistance. This is because the space between the big single wire fills up with epoxy. Epoxy is a lot lighter than copper. Copper conducts current, epoxy doesn't. With the light winds we use now days I would think singles would be thing on the past. But not having tuned at a track like that with a mild wind like a 12 turn, there might be something I'm missing in my theory.

I have made some motors for racing over there. I use either a triple or double that is sort of full but not packed on a thin web blank. Packed arms make a lot of top-end power but are really hard on magnets due to the extra field they generate. With the cells we have now, it's easy to make the field so strong, and run so much timing that the magnets don't even last 4 minutes. I've seen it.

On the type of tracks you race on and with the 12 turn limit I see no detrimental effects of using a single but no extra benefits either. It's just someone else's idea to get the job done.

A sextuple wind (6 strands or hex) uses very little space for the amount of copper surface area. It's a lot easier to pack the wire in using a bunch of small wires than one big one. If getting the most amount of copper on an arm is the winders goal then yes, smaller wires is the way to go. But there is a point of diminishing returns. An octuple (8 strands) seems to be the limit for packing although I have used as many as 19 strands.

Armature Air Gap
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Question: You said you didn't put a lot of emphasis on perfect vertical centering of the armature, but how about "air gaps" in terms of performance, especially RPM's. I have always concentrated on matching arms and cans for minimal air gap. Is this worth it or am I just wasting time ?

BJ's Answer: In my opinion, there is an optimum air gap on these motors and it isn't always the closest one. I purposely made the D4 arms .005" smaller than the D3.5 or the D3. My testing showed more horsepower was obtained by a wider air gap. As far as air gap is concerned, the magnetic field goes up by the square of the distance.

A .910" armature choked the rpm too much. Also, the tighter the air-gap the more eddy currents build up, which hurts efficiency. Average winds actually respond better with a .900" arm but this would hurt 7 and 8 turn stuff. Also, the version 1 armature design (marketed as the "rpm" blank) has more total power but it's at a higher rpm level. The version 3 (or "torque" blank) should be chosen for any wind below 10 turns. 10 turns is kind of a gray area and depends on the track. Anyway, keeping the air-gap the way it is will probably be the best choice.

Armature Balancing
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Question: Epoxy vs. drill balancing - any advantages ?

BJ's Answer: I'm not a fan of epoxy balancing. The balance on those arms change as they are run, plus it has a tendency to come off, and it adds centrifugal mass to the arm making it spool-up slower. True, drill balancing takes metal away from the arm, but it doesn't really matter much in the place on the arm where it's drilled. Of course if the arm is not wound properly and a big crater hole has to be drilled to balance it, that's a different story. In that case, a small amount of epoxy could be used to bring it down to a certain tolerance and then finished by drill balance. I used to do it both ways on the team arms I did at Trinity, but there I couldn't eliminate the epoxy altogether because they started this epoxy balance deal. I'd epoxy balance down to a point, then touch it up by drill after the epoxy was cured. I see no benefit from one or the other in any type of racing.

Question: Is it possible to check and adjust an armature's balance at home? I've been tinkering with a magnetic prop balancer. This seems to work, however I'm guessing that I'm just performing static (not dynamic) balancing. I have an old magnetic mayhem that has been a real workhorse but is now shaking like a poorly tuned Harley. The arm is drilled with no epoxy that may have fallen off.

BJ's Answer: There's no way I know of that you can dynamically balance at home, but you don't need to. There are many motor shops that will do it for you, mine included.

LCR Meter Use
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Question: In the ISTC world cup and in the English touring car championship they have a 12 turn motor limit. I know that they use an LCR meter to test the motors. Is it possible to know the inductance value for each wind or is it different from manufacturer to manufacturer? How do they tell if a motor is legal or not?

BJ's Answer: Good question. Measuring the inductance is probably the only way of telling what wind for sure is on a armature, but you have to have some sort of standard to go by. The type of blank and how full the armature is will effect the readings. A 12 turn will have about 18 uh's (or micro-henrys) of inductance on an wide leg Epic blank, at the commutator, if I remember from my records. But a 12 turn wound on a Yokomo blank will read lower, as will a very high circular mil armature (fully packed), and a light wire arm will read higher but only by about 1uh or so up or down. An 11 turn, will read about 3uh's lower and a 13 turn 3uh's higher. So it still is easy to tell the difference in winds, theoretically.

A problem arises because they measure the inductance of the arm through the brushes and all the possible carbon build-up on the comm. If all the variables build up, mistakes can happen. The wind on the arm (single, double, etc.) has little effect on inductance, or much of anything else for that matter.

Question: On the topic of LCR meters... inductance, capacitance, + resist. I would appreciate it if you could go a little deeper in detail... I was curious as how to check the inductance of an arm and what the #'s might be for a stock and mod.??? Can you simply check the SMD caps in the can??? If so what should they read on a capacitor meter?? I tried today and got .265 stk, and .001 mod. I was connecting the black lead to the arm shaft. It would be nice to know how to check the arm, brushes and caps.

BJ's Answer: Well, without getting too windy, measure the armature from comm segment to comm segment. The reading for every wind, arm blank, and fullness of the arm with wire is different. A 12 turn will read between 18 and 19 uH's or microhenrys. Every wind will go up or down by approximately 3uh. In other words, a 13 turn will read about 22-23uH. An 11 turn will read 15-16uH.

Measuring the caps works fine. One lead to the solder tab, the other leads to the end bell screw. The SMD caps are rated at .1uf but actually read .98pf, which is close enough. The cap that goes between plus and minus will read different, as it is in series with the other two. Be sure and short out the caps with a screwdriver or some other small

metal tool before measuring or your readings could be off. Also zero your machine before each reading. Stock and modified are the same caps.

Armatures for 3000 mAh Packs
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Question: We hear a lot about modified motors from different manufacturers being "tuned" to run with the new 3000 cells.

Are there design differences that you did make or will make to motors, depending upon whether you are running 2000, 2400 or 3000 cells ? And what about tuning differently for Panasonics vs. Sanyo 3000's?

BJ'S Answer: I can't see doing anything different for 3000's as far as design, but obviously, with more run time, you can run more timing and/or spring tension if necessary to get more HP.

However, I would wind and use different arms for a 3000 than for less capacity batteries. It used to be that maximum efficiency was necessary. This was done by winding arms that were very full of wire for a given number of turns. But they also worked best with higher voltage packs for quicker spool-up because of their excessive weight and it's effects on centrifugal mass. Now, with the added run time of the new batteries, we can use lighter winds for really quick spool-up because efficiency is not the primary goal- power is. This is what the new High-Variance Split Winds were designed for (HVW). They are wound light for quick spool up and the big wire, small wire make-up lessens inductance and adds to efficiency. You can make maximum use of the extra capacity by running a hotter wind that spools up quick.

Can't see any difference in tuning/winding for the two different brands of cells, at least at this point in time.

Armature Cutting
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Question: Is it better to run the arm at it's full dia. or does it need to be cut down to a certain dia., or does this all depend on how much gap is left in the can after the magnets have been installed.

BJ'S Answer: It depends on gap after magnets and arm are installed.

Armature Troubleshooting

Question: Is there a good way to tell if an armature is bad?

BJ'S Answer: I will assume that you mean bad electrically, verses bad balance, bent shaft, etc.

They are a variety of things that can go wrong with an armature. The most likely things are shorts, grounds and open coils.

If an arm is shorted (like two bare wires touching each other,) it will not rotate in a magnetic field, even without brushes. This is a trick I learned from Neal McCurdy. Try it. Dig out an old mod can and clean the bearings really well. Put the suspected arm in the motor, but do not install the brushes. Spin the armature by hand. A good arm will spin quite easily. A shorted arm will spin maybe two revolutions no matter how hard you try to turn it. I know this sounds weird but try it with an old arm. Solder the comm plates together on one pole. It will then be shorted and not spin. Unsolder it. It spins again. Of course if you apply power to a motor with a shorted arm it will draw amps like crazy, if it runs at all, depending on the severity of the short, but the above test saves maybe blowing something up.

This test works for all arms except for high multiple strand mod arms. If one wire is shorted in a quad wind, for example, it will be hard to tell if it spins well or not because if only one wire is shorted, it will only be a 25% short. To test these arms you have to put power to it.

A grounded arm means that there is continuity between the comm and the shaft or stacks. This is easily tested with a meter. A grounded arm will sometimes sound OK but be off on the dyno and/or track.

An open coil probably means a bad weld at the comm tabs or a broken wire. Usually the first evidence of this is you have to push the car to get it to run, or spin the armature by hand and then the motor runs but not well. This is because only two of the coils are connected.

All of the above can be found easily with an inductance meter, but they're expensive and I couldn't afford one when I was young and learned these tricks.

There is one other condition that happens once-in-awhile and can drive you up the wall. It's called a heat short. This is a short that happens

only when the arm gets hot like in a race, and then unshorts when the arm cools. I've changed speed controls, battery packs, transmitters, and everything else I could think of the first time it happened to me. The best test is let it run on the bench or dyno it until it's too hot to hold. Usually this type of condition is not a dead short even when it's hot, but will draw serious amps anyway.

Purchasing Advice
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Question: When buying a new stock armature, what should we look at to determine if one will work better than another?

BJ'S Answer: Neat, tight windings are always good. You might check to see how the comm tabs line up down the center of the stacks. Looking at the arm with the comm up, the tab should be dead center or slightly to the left. This would be zero or slightly advanced. If it's to the right, it will run retarded. I know it has a comm lock but there are tolerances. Trust me.

Also, look for big holes on one side of the arm. This is bad and indicates the arm was not wound evenly or even have a missing or added wind, although this is rare. Big holes all over the arm is not necessarily bad on a stock arm. It should rev higher with less steel. Personally, I would prefer to have no holes at all because I could balance it right myself but I realize most of you aren't in the motor builder's situation (you all have full time, decent jobs but that's another story, ha).

Another thing, look at the tag. Make sure it seems secure. If the tag falls out not only will the arm be questionable for racing (from a tech inspector point of view) but if a tag flies off, it will make the arm REALLY out of balance and that's bad.

Look to see if the comm had to be cut down smaller than normal. You can tell by the lip above the tabs. Even if you like to cut the comm down smaller, wouldn't you like that choice?

On everything else, it's really hard to tell in the package.

 

[hankster]

Motor Break-in

Bushing Break-in
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Question: I have been using tooth paste to break in my bushing's and it seem to work just fine.

BJ's Answer: Modern toothpaste has very little, if any, abrasive in it. Just try to scrub the tarnish off a penny and you'll see what I mean. You really should use something a little harsher like metal polish or valve grinding compound.

Question: Using a 1/8" reamer is there any benefit to reaming out the bushings of a stock motor?

BJ's Answer: A reamer would work if you had one with really long cutting flutes so that it could ream both can and e/b bushings at the same time. This would be like line-boring and would work. Unfortunately, reamers don't come that long in the right size so you're better off just to break your bushings in with some heavy metal polish and an old armature.

Break-in Voltage
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*** This topic is updated and covered in-depth in the print version of Big Jim's RC Motor Black Book. ***

.Water dipping
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Question: I also heard about the water dip break in. Is that still being done?

BJ's Answer: "Water dipping" was the way we motor builder's at races use to take care of our whining team that just had to get out on the track in a big hurry. It breaks in the brush really fast. The serrated

brushes we use nowadays would be wiped out in seconds if we used this method today. There are some motors used in racing that do benefit from "water-dipping", in fact I know of no other way to do it efficiently. The Johnson and Mabuchi 540 are two of the motors. The Trinity Street Spec with the spec brushes is another. Those brushes are so hard, I doubt if they'd ever break-in fully if you didn't water dip. This is very tricky and can ruin a motor in a matter of seconds if you don't know what you're doing. Therefore, I feel it's best not to go further with this.

Break-in Using a Slave Motor
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Question: Would it be better to break in a fresh cut com and new brushes with a slave motor or just run them in at low voltage?

BJ's Answer: Breaking the brushes in with a slave motor turns the motor you're breaking-in into a generator causing current to flow out of the brushes instead of in, and still arcs the brushes. This method is supposed to save the commutator from arcing up during break-in. The only way to do this is one brush at a time. This is the only way I know to eliminate all arcing.

 

[hankster]

Brushes Part 1

BJ's Comments: The absolute best way to break-in your brushes (on a stock motor) is 500 seconds at 3 volts or until the serrations are seated all the way across. Then take the arm out and take a skim cut across the comm, removing the break-in grooves from the serrations. Your brushes will last a lot longer this way too because that abrasive "skin" on the outside of the brushes is worn off. Now you have the ideal power situation-seated brushes on a freshly cut comm. You don't have to replace your brushes every time you re-true the comm. Just clean and de-glaze the sides and face with one of those comm sticks. I like the Racer's Edge ones.

Question: I had a P2K that had been quick, then I recur the comm and re-brushed it - motor was "off" after the rebuild... Turns out I had just gotten in a hurry and failed to fully seat the brushes -- I just broke them in until they were "close enough" (or so I thought).. Wrong! I went back and did a careful brush break-in, and the motor was back to life...

BJ's Answer: Here's something I do that might help. I don't always put new brushes in when I cut the comm. I find that after the brushes are deglazed they work just fine, as long as they are not discolored from too much heat. Just cut the comm. This way, your brushes are already seated and the comm is really why it needs to be rebuilt anyway. If you really do need brushes, cut the comm and let the brushes break-in for a long time, so there's not doubt. Then take a light cut on the comm. Now you have a motor putting out maximum power for sure. You have a fresh comm and perfectly seated brushes. Just a thought.

Question: The term "full seated", does that mean no serration’s visible... or the brush does not arc excessively but serration’s are visible?

BJ's Answer: What I mean by "fully seated" I mean that all the brush face is touching the comm. Yeah, don't waste the serrations on break-in.

Question: You replied "don't waste the serrations on break-in". This wasn't clear to me. Are you saying that I shouldn't bother breaking-in the brush?

BJ's Answer: No, just make sure they're seated. Make sure the serrations make contact all across the face of the brush.

Some racers/tuners change the brushes as soon as the serrations are gone. Some just use the serrations for breaking in the brush quickly. Either way, the entire surface of the brush should be making contact with the comm.

Question: Would it be better to break in a fresh cut com and new brushes with a slave motor or just run them in at low voltage?

BJ's Answer: Breaking the brushes in with a slave motor turns the motor you're breaking-in into a generator causing current to flow out of the brushes instead of in, and still arcs the brushes. This method is supposed to save the commutator from arcing up during break-in. The only way to do this is one brush at a time. This is the only way I know to eliminate all arcing.

Question: I also heard about the water dip break in. Is that still being done?

BJ's Answer: "Water dipping" was the way we motor builder's at races use to take care of our whining team that just had to get out on the track in a big hurry. It breaks in the brush really fast. The serrated brushes we use nowadays would be wiped out in seconds if we used this method today.

Changing Brushes
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Question: How often should I change my brushes?

BJ's Answer: Most racers change brushes much too often, in my opinion. When you change brushes, you have to go through all the trouble to break them in again and by that time, the comm has a lot of wear on it. I cut the comm a lot and otherwise rebuild the motor, but I usually just deglaze the brushes with a comm stick. If you have to put new brushes in the motor, break them in really well on a fresh comm so they are fully seated, even if it's just the serrations. Then take the motor apart again, take a light cut across the comm, and reassemble it. Now you have the best performance situation possible-seated brushes and a fresh comm.

Brush Cutting
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Question: How important is it that the hole is centered in the face of the brush when tuning for a P2K motor? I've read about people putting the hole offset toward the trailing edge, any reasoning behind this? Again I haven't noticed any difference here.

BJ's Answer: I always try to keep it in the center, and that's hard enough to do. You'd have to use a smaller bit than #42 if you wanted to off-set it much. I can't see what difference it would make, though.

Question: In your advice for tuning the P2K, you call out the drill bit as a #42. What is that in standard dimensions for that bit (3/32)? How critical is that hole diameter. I would suspect not that important but then that is why I am asking the question

BJ's Answer: A #42 drill bit is .093" or the same as 3/32". 1/16" is slightly smaller than an .067", #51 bit.

You're right. It's not that critical. But I do use a smaller bit, a #50 for mods. I think the reason I started using a #42 was it was the sharpest bit in my box that was about the size I wanted. I know guys that have used a #40 bit on stock and said it works great. I hope I didn't imply that this is the only size that works, but this is a good place to start. The bit will get dull really quick, so have some extras around handy.

Question: Your advice about drilling a hole in the center of the face of the brush to create sharp edges, does the slotted brush have the same effect?

BJ's Answer: A horizontal slot would work close to the same, but a vertical slot works on a whole different principle. It requires different springs and may not work for all tracks.

Question: I have also heard of people using a diagonal cut on brushes to change motor performance. Any insight on this?

BJ's Answer: I've seen that too but can't see any difference between that and horizontal cut. But like everyone else I guess, I tend to find something that works really well and stick with it.

Question: What will the difference be with a slot down the middle of the brush (same direction as the slots in the com) then drilling the hole? Will they both be the same or will one give you more rpm or torque?

BJ's Answer: The slot down the middle works well also. It makes a lot of torque if used with lighter springs. The hole and heavier springs

produce more top-end power I believe. I will say that every stock motor I ever personally ran had either a hole or a slot in the brush. You just have to try them both and decide what works best for you. Both "cuts" make really good HP.

A special note from Big Jim: When I originally posted this answer on the HobbyTalk Forum, the hole and slot were my cuts of choice. Now days however, with the cells we have now, I prefer to just use the serrations. That doesn't mean the serrations work better, it's just that they negate allot of the extra benefits of other cuts.) I must add that a vertical slot does not work the same as a horizontal slot.

Question: What does a horizontal slot do? Any word on diagonal or X (diagonal) cut brushes?

BJ's Answer: The horizontal slot does pretty much what the hole does except leaves a funny comm track and reduces brush surface area a little more.

The diagonal or "X" cut is just a gimmick. It doesn't do anything different other than reduces brush contact area even more than the horizontal cut.

Question: Do you suggest timing the brush when you need more rpm?

BJ's Answer: Never use a timed brush. You can cut the trailing edge of the brush away and the motor will see more timing, but to do this you have to narrow the brush which reduces overlap, and any rpm gain is negated by the narrower brush. Now you are right back where you started from except now the motor commutates poorly due to the offset brush.

Question: What is the best cut to use on the Reedy MVP stock motor?

BJ's Answer: The way I tune my MVP's is cut equal amounts off both sides so the face that rides on the comm is square or about .140" wide. Here is a picture of what the brush should look like once it is cut.

Question: I have been working with motors for 1/12 on road stock. I have been cutting a small amount from the leading and trailing edges of the brush, drilling a hole and running green on + and blue on -. I

am getting more RPM, better torque and way better efficiency. I found this just playing around. What is the theory as to why this happens. P2K's seem to respond better to this than Paradox motors. This works well for 1/12th but not for touring car. Why is that?

BJ's Answer: By cutting back the trailing and leading edges of the brush you are reducing the comm overlap which reduces arcing and adds torque and efficiency at the sacrifice of rpm. You didn't say but I assume you are running a 4 cell class as most 1/12th classes are now days. Running 4 cells in a light 1/12th scale car doesn't put that much load on the motor. Because of this it doesn't arc much, especially with the narrowed brush. This is why you can get by with such light springs. Less arcing, less spring tension. More arcing, more tension. For the type of small tracks that 1/12th cars usually run on, this is a good combination.

Touring cars on the other hand are total different. They are 6 cell, heavy cars with a lot of drive train drag compared to a 1/12th pan car. This puts a lot of load on a stock motor, hence more brush arc. It needs the load handling capabilities of a full face brush with stiffer springs.

Polarized Brushes
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*** This topic is updated and covered in-depth in the print version of Big Jim's RC Motor Black Book. ***

Brush Theory
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Question: You made a comment that your theory for the electrical flow through a brush to the comm, was primarily around the edges of the brush.

This brings me to question the use serrated brushes. In theory, there are more edges of the brush for electrical flow to the comm. The problem that I see is that this is not the outer surface of the brush. Also I assume that the same spring tension will generate a greater pressure against the comm. since there is less surface area. I do not have a dyno to confirm whether the brush drag is greater or less and or if the power and amp draw is improved with serrated brushes.

BJ's Answer: I didn't exactly say the current transfers only by the

edges. I believe I said it likes to travel that way. Kind of like path of less resistance and all that. This is my theory why a hole works well in a brush. There might be other reasons, but this is just what I think. The serrations do flow current very well. This is why they work so well not even fully seated. It ads more edges for current to flow

You're right about the quicker break-in. I think this is the original reason for the serrations, but it was found out they have other benefits as well. Yes, reducing contact area with the same force will, effectively increase spring tension. By how much I don't know. I like to put a hole in with the serrations. That way I can still get the benefit of more edges after the serrations are gone.

Brushes have an effect on switching. The narrower the brush the more torque the motor will have. The wider the more rpm. This is why most stock motors have laydown brushes-for more rpm. The exception to this is the last, and discontinued, Epic 36 degree stocks. It was found that 36 degrees is rpm-ish enough and stand-up brushes commutate better. All mod motors, other than the Epic Chameleon, have stand-up style brushes.

Question: What does "lay down" and "standup" mean in brush terms?

BJ's Answer: The terms "laydown" and "stand-up" refers to the position of the brush in the motor. "Stand-up" means that the brush is taller than it is wide in the motor. "Laydown" means the brush is laying on it's side and is wider than it is tall. Both types of brushes are the same dimensions. The only difference is the curvature on the face which is 90 degrees from the other to match the shape of the commutator in that position.

Laydown brushes are mostly used in stock motors and mild-wind spec modifieds. They receive extra rpm and mid-range power from the increased brush/comm overlap. But this benefit comes at the sacrifice of bottom end torque.

Stand-up brushes are used almost exclusively on full modifieds. They need the extra torque this type of brush provides.

BJ's Comments on Brush Reversing: I have run into a phenomenon most people won't believe. Sometimes, I just swap the brushes around from positive to negative and visa-versa, providing they aren't polarized brushes.

It seems the copper molecules align themselves in a certain direction under high current, and heat conditions. This causes resistance in the brush. By reversing them, current can flow even better than a new brush. I know this sounds weird and unscientific. So strange in fact, I don't do it very often. Just doesn't seem right. But I thought I'd share this with you.

I discovered this one time when I was having trouble with my comm welder. I cleaned all the cables and connections and I just didn't seem to have the power it use to. Just out of curiosity, I swapped the pos and neg cables around. Everything worked great after that.

BJ's Comments on Brush Cutting: Narrowing the brush will give you more torque but not necessarily more power. You can knock the trailing edge off a little but that only cuts the amps down a little. It has little effect on the power, however. The best thing you can do to gain torque and power is to have clean, seated brushes on a fresh comm cut. An out-of-round comm will still have the rpm but the torque will be way down, therefore, power.

BJ’s Comments on Brush Replacement: Ideally, the brushes should stay the same color as when they're new except at the very tip, but this isn't always the case. A lot has to do with the ambient temperature as well as how much load the motor sees. And believe it or not, driving style can be important too. If a certain racer is on and off the throttle a lot, using a lot of brakes, it will cause the brushes to got hotter than a driver that has a smoother driving style and uses less brakes. Gearing, of course, plays a major roll in brush temperature. Over-geared motors get hotter because the motor strains more around the track and pulls more current. The condition of the comm also is a factor. If the comm is worn and out-of-round, it arcs more creating more heat.

If most of the brush is a natural color after a run, then I will use the brush again. I'll just clean it up by rubbing the sides on a Formica table top and deglaze the face with a ProEdge comm stick. If it's too silvery or even worse, red or blue, it's definitely replaced. If a brush gets too hot and the end of the brush crystallizes, it ruins the brush. If it's just around the face of the brush, you may get away with it depending on the importance of the race you're at. Just a weekly race then yeah, you can use it again. But if you're at the Nationals and your brushes are blue or red even at the tips, replace them and cut the

comm.

You don't have to replace the brushes every time you cut the comm, in fact, it's not advisable that you do, if their in good shape. I see it a lot though. Racers will throw away a set of brushes that are just getting seated well to the comm. They put new ones in and have to start the seating process all over again. But ALWAYS cut the comm before installing new brushes. Trying to get new brushes to seat on a worn comm just arcs a lot and will eventually destroy the comm. If a comm lathe is not available at the time, it's better to leave the old brushes in.

Brush Soldering
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Question: Any advice for soldering on brushes? I often have problems with the shunts stiffening. I have a clamp that is supposed to keep this from happening but it doesn't work very well.

BJ's Answer: I put a small pool of solder on the hood where I want the shunt to be. I then take the brush and straighten the shunt out. I barely dip the very end of the shunt in a can of rosin flux, the paste kind. I then remelt the pool and stick the shunt right down into it while it's liquid. The shunt sticks straight up out of the pool and you can put it anywhere you want that way. Too much flux will cause the shunt to fill up. Practice with an old brush and keep cutting the shunt shorter and retrying. That way you don't waste a bunch of brushes.

Radio Shack 60/40 solder is the best I've ever used and I've used them all. It's cheap and easy to find.

Question: Do you think it makes a difference to solder the brush leads directly to the tab with the motor wire (even on the wire) versus someplace on the hood? What about fatter brush shunts or the dual shunts from a while back?

BJ's Answer: It doesn't really matter where you solder the brush shunts on. The little shunt wire on the brush is only rated at 10A max and won’t make any difference in placement. The motor gets most of it's power from the contact of the brush inside the hood. This is why I always recommend cleaning this area really well when rebuilding a motor. The double shunt thing fizzled out when brush dampeners got put on all the motors. That and it became known how little current they really carry and for the added complexity and brush hang up possibilities

, it wasn't worth it. Trinity is going to bring back the double shunt on their new motors, at an increase in price, of course. But the new motor will have bigger brushes and more room for the shunts.

Question: I was wondering if placing the shunt of the brush between the spring and the hood instead of soldering the brush to the hood affects the performance. I have seen a lot of guys do this but I continue to solder mine for piece of mind. I also wonder if this also may increase spring tension.

BJ's Answer: My opinion is that a good solder joint is always more conductive than a mechanical one. I think the guys that do this are just lazy. It might increase spring tension slightly but not much.

 

[hankster]

Brushes Part 2

Comm Drops
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BJ's Comments: Use Prolong straight, but Tribotech can be mixed with mineral spirits to thin it down a little. The stuff seems to vary in viscosity from bottle to bottle so start with 30% mineral spirits (turpentine). I have heard that some use it straight also.

Comm drops only work with certain types of brushes at best. Most comm drops on the market are crap. Try Prolong or Tribotech. These are oil treatment additives and work excellent with #4500's or 767's but not with a high silver content brush like the #4499's. And never for off-road. To much dirt. Use one of the above brushes with a red spring on the pos and a green on the neg. Drill a hole 1/8" deep in the center of the brush with #42 drill. Never put new brushes in a motor without cutting the comm first.

You can get Prolong Engine Treatment at most auto parts stores. You can get Tribotech at their web site at http://www.tribotech.com

A special note from BIG JIM:</u> Since these original posts from the Team RCV forums, the Tribotech Company, the makers of the oil additive mentioned above, have released their own formula of commutator lubricant especially made for R/C motors. Their formulation far exceeds the usefulness of any automotive oil additive for comm drops. The TRIBO R/C Power Matrix Commutator Lubricant is the best stuff I have ever used. It works with <u>any</u> brush compound and is great for off-road too, since it has no petroleum products in it. It is 100% synthetic and doesn't attact dirt and dust nearly as badly as oily

products. And the TRIBO Power Matrix works great for bushings and bearings too. Go to their R/C web site for more info. www.triborc.com.

Brush Marketplace
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BJ's Comments: All r/c companies use to buy all their brushes from the same place - Keystone Brush and Commutator in Ohio. But about 7 or 8 months ago (early 2000), Keystone decided to undertake a massive restructuring. They weren't sure if they ever would sell r/c brushes ever again. This news, of course, sent all the motor companies in a panic, seeking brushes from other brush manufacturers. Two problems existed.

One was, they didn't give the r/c motor people much time. If they didn't have a big stock on hand, they were hurting. I know of one big motor company that bought whatever old brushes they could from another motor companies junk pile, put them in packages and called them their top-line motor brush just to fill orders and saving the good brushes for their production motors. I think most of the big guys have replacement brushes now.

The second problem was, a certain brush made by one brush company cannot be exactly duplicated by another. They each have their own suppliers for raw materials and if the raw materials are different, so will be the brush. So what brushes you use to like, may not work the same even though the part number is the same. You are basically going to have to experiment all over again, to make sure you still like your old favorites.

Brush Hood Alignment
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BJ's Comments: Correct brush hood alignment is still the best way to get more power out of any motor. Most hoods aren't aligned well from the factory.

Before you guys get carried away making alignment bars, just remember that getting the hoods directly across from each other and

centered to the shaft is a good starting point but not the end. Properly aligned hoods are very seldom directly across from each other. If the brushes were the same size as the inside of the hoods then this would work but they're not, not even close. This difference in size causes the brushes to "cock" in the hoods in the direction of armature rotation.

To properly center the brush, the hood must be tweaked in the opposite direction, off center to allow the brush to be centered when it's cocked. To do this, you need to run the motor just a few seconds with new brushes to notice where the comm wear mark is on the face of the brush. If it's off center, the hoods must be tweaked until that wear mark runs right down the center of the brush. Because of this, alignment bars don't have to be the exact size of the brush unless you plan on sizing the hoods. I don't recommend this however, because it will mess up the brush dampener inside the hood (Yokomo's don't have this problem).

You can drill out the hood holes to make alignment easier but usually there's enough play to align. Just move the hoods and heat sinks together as an assembly and don't worry about the dimples. Sometimes you have to bend the hoods slightly in severe cases. When you assemble the motor, just make sure that the comm wear mark on the brush runs right down the center. Just aligning the hoods exactly straight doesn't compensate for the brush "cocking" in the hood. Proper hood alignment will probably not be directly across from each other. It's best to use one of those bars for aligning.

So nothing fancy is really needed. Just a bar that fits inside the hood that allows you to move it around without distorting it. This is also why those screw-together alignment tools don't work.

Get yourself a good bar for bending/aligning the hoods. I have to say that that Racer's Edge makes a good alignment bar. Look for it on their web site.

Mod Motor Brushes
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Question: Any Brush and Spring combo tips for mod motors?

BJ's Answer: If you are a serious hard-core racer who doesn't mind new brushes and truing comms every heat, then there is no better brush than the Trinity #4383. If you're a very competitive racer that

doesn't want to go nuts every week, then I recommend the Trinity #4455's or the Reedy Quasar #729. Both provide excellent power and are easier on the comm. The Quasar's are so good, you'll probably get a whole days worth of racing on them before you have to replace and recut. This would apply to all types of racing and winds aside from that 7 turn you might have in your sedan car. Ha.

Use purple springs on both sides or the harder silver's. For Reedy Ti's, I use Reedy coppers bent 180 degrees. If you want to try a polarized system, try a #4383 on the pos and a #4455 on the neg with purple springs and a harder bend in the pos side. The polarized brush technique is sometimes the best of both worlds but it is kind of a individual thing and you'll have to decide if you want to go that way.

Question: What is the brush you recommend for a 9T modified motor for touring car. Have you try the GM 05 brush? Is it suitable for my application? Will Prolong compatible with these brush?

BJ's Answer: Sorry, never tried that brush. But Tribotech and Prolong are compatible with the T #4455, Reedy #737 brush, Reedy #729 Quasar's and his #737 brush. (Use the TRIBO Comm Lube now-BJ). Don't know about using drops with a 9 turn.

Off-road Brushes
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Question: I race just about every weekend with my Reedy Rage. I just bought some brushes for the Reedy Rage, they are serrated and have a slot. I heard they do good but you are the expert. I race off-road stock truck, any suggestions?

BJ's Answer: Because of your off-road truck, you can use either of two brush compounds. The Reedy #767 or the long-wearing #766. The #767 has a little more silver in it and therefore has more rpm. But it wears the comm a little more too. The slotted brush, #768, is made from the #767 silver brush. However, the #766 brush has gained so much in popularity, the new #768 and #769 (with a hole) will be made from that brush instead. You won't notice much difference from slot, hole or just the serrations in your type of vehicle.

Brush Cleaning
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Question: Is it ok for motor spray to hit the brushes? I always thought that it would suck the lube from them (not sure where I heard/saw that) and that's not a good thing!

BJ's Answer: I may be wrong but I always thought the lubrication was in the form of graphite, which is throughout the brush. I don't believe that the type of motor spray made for r/c motors is detrimental to the brushes. If it bothers you, soak them in Prolong or Tribotech.

Putnam Propulsion Brushes
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Product Test: Putnum Propulsion:

#EFB-170 Silver Serrated Laydown Brushes, (Green Shunt=High Silver)

#EFB-140 Silver Serrated Laydown Brushes, (Blue Shunt=Medium Silver)

I had a couple of P2K's I was setting up for one of my customers so I thought I'd give these brushes a try. Since they are both very high in silver, I put the lesser content, blue shunt brush on the negative and the high content, green shunt on the positive. I figured it would be a little easier on the comm this way and still get maximum power. No brush modifications.

After aligning the hoods breaking in the bushings, re-balancing and cutting the comms, I reassembled the motors. I was a little concerned about the blue and green coating making the shunts hard to solder, so I put a little extra solder on the hoods and held the iron a little longer on the shunts to make sure they soldered well. Bad Idea! I filled up the shunt about 1/4" up, so I had to throw that brush away and start over. This time I did it like the shunt coating wasn't there and it soldered fine. The coating does solder well.

I started out with Integy P2K springs which were a little harder than the combination I normally use. After breaking in at 3 volts for 300 seconds, I found the brushes to be well seated, with the serrations shiny all the way across. On the dyno it went. After oiling the bushings with 50-50 Tribotech and Pennzoil 30W, I did two runs on the CE TurboDyno and looked at the numbers. I was only getting 95 watts @20A load. Not that good. To see which way to go, I put a light gold spring on the neg. Power went up to 98 watts. After tweaking

on the springs with a pair of long nose, and several more runs, I got the watts up to 99. Then I put on my old favorites red on the pos and green on the neg , but I tweaked the red just a little softer. And the power stayed the same, both rpm and torque. Not bad, but could be better.

I took it off the dyno and pulled the brushes out. The brushes looked real good but the comm had deep grooves where the serrations dug into the comm. Wow. These brushes are hard. I recut the comm, leaving everything else the same. I reassembled and put it back on the dyno. Now we're talkin'. With the voltage set at 7.00, it pulled 102 watts @20A load, 18,865 rpm, 7.2oz torque, 72% EF. Now that's a motor. At a 28A load, in pulled 126 watts, 16,280 rpm, 10.4oz torque and 62% EF. Not quite my record, but definitely up there. The 20A number is definitely the most important, as you can see by the EF number's. This shows where the power band of the motor will be.

The torque and rpm is exactly where it should be. With this power band, it will be easy to gear and go fast. After 4 dyno runs, the comm still looked pretty good. I seems that getting the sharp edges worn away on the brushes really helps. I pulled the brushes out again, smoothed the sharp edges of the brush by rubbing them on my Formica work bench. I also touched up the serrations with my tool. I put the brushes back in, cleaned and oiled it up and after putting on some Big Jim holographic motor stickers, shipped both motors off the my customer.

I case you're wondering about the other motor, it was off by 1 watt from the first one at the same rpm. Torque was also down by .1oz. Still a very good motor. Also, I don't want to give the impression that it was necessary to recut the comm to get good numbers. I always use this procedure. Putting a clean, seated brush on a fresh comm cut is the best racing condition.

In conclusion, I find the Putnam Propulsion brushes to be at least as good as any other brush on the dyno. How the comm holds up to this hard brush is something only a good night of racing can tell. Will keep you informed.

The price of the Green high-silver's are $5.50 a pair. The Blue's are $4.99 a pair. This is kind of marketing thing because I doubt if there is any difference in price from Keystone. A little pricey, yes, but at least you know you'll get a good product.

Can I put the Big Jim recommendation on these brushes? YES!

Brush Contouring
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Question: Do you know of any company who sells a brush contouring system other than the RACEtech Clyde brush grinder? It has grinder bits in .280, .285, .290, .295, .300 This seems like it would make a huge difference in power if you could put a fresh cut on the comm and then reinstall brushes that were almost to the same size. Wouldn't it make awesome power with the brush making full contact on a clean comm?

BJ's Answer: In theory, it sounds good but brush hoods are never exactly in the center no matter how close we try to make them. If you use the tool in the same motor to cut your brushes that you're going to be running them in, it might work, but it's doubtful if your brush will be the same size as your comm after using the tool. It would take that hard skin off the outside of the brush face though.

Discolored Brushes
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Question: I have been checking my brushes when I remove them from the hoods. I have noticed a 1/16 to 3/16 area on the trailing edge of the brush that is darker in color as if from arcing. Is this normal? If not what should I do to minimize this effect.

BJ's Answer: I hope you were mistaken on those 1/16" to 3/16" measurements because the largest amount would be most of the brush. Brushes are typically .150"+-. Anyway, you shouldn't have any more than maybe the very tip of the trailing edge of each brush black like you were talking about. Assuming you are using the brand of brushes I recommend here and assuming again you aren't using any weird brand of comm drops or getting oil on the comm, your hoods are definitely out of alignment. If you are absolutely convinced your hoods are off-set properly to match the cocking of the brush, there is something definitely wrong there. I have never encountered anything like you mentioned unless one or more of the situations I mentioned above exist.

Question: Several days ago someone asked about black deposits on a

fraction of the brush near the trailing edge. I made a comment that it seemed to be incomplete break-in of the trailing edge when it happened to me. I now take that back. That isn't what it is, but I'm not sure exactly what it really is. It's too large an area to be brush overlap.

BJ's Answer: That area is what happens when your bush hoods aren't aligned properly. That part of the brush is not pushing on the comm hard enough and since that edge usually arcs the most anyway, that dark area happens. If you just let it go, it will eventually seat and the dark area will go away but the hoods are still misaligned. Usually the motor has too much rpm and not enough torque if this condition is not rectified. It just take a little tweak to the hood with your tool to make the comm push on that part of the brush more.

The blackened area at the trailing edge of the brush is most noticeable during the first few minutes of break-in. But it may or may not be noticeable after the brushes fully seat. It depends on the degree of misalignment. The brushes, even though misaligned, will eventually wrap themselves around the comm when they seat fully and then you'll have to look for the discoloring of that edge to diagnose it properly. It's kinda like reading spark plugs on a real car.

Brush Serrations
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Question: Is there any value to serrated brushes and if so, how do you cut the serration into the brush after it wears out?

BJ's Answer: It seems all the good brushes have them. They were originally put there to ease brush break-in but then it was found that good current flow could be obtained from the exposed edges of the serrations riding on the comm, kinda like what a hole provides. But with the added benefit of less friction. The brushes seem to still work OK with the serrations gone but not quite the same. This is where the problem arises. Do you put new serrations back on the brush, put a hole in the brush at that time, start out with a hole in the serrated brush, or simply replace the brush.

My choice is re-serrate the brushes and cut the comm, although I have done all the other stuff too. It seems a shame to get rid of a brush just when it's perfectly seated on the comm. After all, a perfectly seated brush on a fresh comm is your best racing condition. I tend to cut the comm 2 maybe 3 times before I change the brushes. But you must deglaze them before reinstalling if you don't re-serrate. I use one of

those Pro-Edge comm sticks, the red or green one. This stick also lets you clean up the inside of the hoods too. That's where most of your current flows is from the contact of the brush to the inside of the hood. Not that little shunt that's only rated at 10 amps.

There are several companies now making re-serrating tools. I use a Trinity serration tool off their brush cutter. The machine itself is basically junk but the serrater tool works killer. It's not just a knurl like some others. I use it to touch up the serrations before they're gone by just turning it in the brush by hand. If the serrations are totally gone, I chuck the tool in an electric drill and hold the brush on the tool for a second or two.

Hung Brushes
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BJ’s Comments: I think if I had to count the number of times a brush has hung up in one of my motors it would be about 3 times. That's not bad for 23 years in the r/c motor business. Here's the secret to never getting a hung brush. You have to thoroughly clean, size and keep deburred the inside of the brush hood. This doesn't mean just spraying it out with motor spray.

First, you must get a brush hood alignment tool. This is nothing more than a piece of steel shaped like a brush (slightly oversize is best) but about 3-6 inches long. RACEtech, Parma, Niftech, and I heard Pro Match sells them. I personally recommend you check out the Racer's Edge alignment tool on their web site. It's hard to beat for $8.95

When the motor is apart, go to the sink and squirt some dishwashing liquid (I use Dawn) in and around the brush hoods. Holding the endbell under warm water from the tap, slide the alignment tool back and forth in each brush hood. This not just cleans the inside of the hood where most of the power is transferred to the armature but polishes and deburrs as well as sizes the hood to the brush. Don't try to slide the tool through both hoods at the same time. I you can, then your hoods aren't aligned properly but that's a different story. Rinse thoroughly and finish assembling the motor.

When you put your brushes in, make sure the shunt can't hang up on any corners of the hood as the brush wears.

Your sticking brush problem is a thing of the past.

1/12th Scale Mod Motor Brushes
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BJ’s Comments: Tuning 1/12th scale motors, years ago, was quite a science. We use to run half-cut brushes, really light springs and timing was critical. Winds were somewhere in the 13-14 turn range. Nowadays, with the batteries we have, running 8 minutes is a lot easier. For the last two years, Cleveland was won with 10 turn motors with just regular serrated brushes and a lighter tension spring than you'd use in a TC and that's about it. The drivers can concentrate more on driving instead of dumping. Dieter would be the one who knows 1/12th scale but I haven't been able to persuade him to stop by our forum. I have built some 1/12th motors lately for some customers and they seem to like the way I set them up.

The best advice I can give is, don't get too fancy. A special cut in a brush is not going get a C main car into the A main. My favorite mod brush of late is a Reedy #737 on the pos and a Quasar on the neg. I do put an off-set slice in brushes and install them one up and one down. Red springs or equivalent on both sides. Timing 1 to 2 notches, depending on wind. The always powerful Trinity #4383's are good also but extra comm maintenance is required.

 

[hankster]

Commutators

BJ's Comments: Use Prolong straight, but Tribotech can be mixed with mineral spirits to thin it down a little. The stuff seems to vary in viscosity from bottle to bottle so start with 30% MS. I have heard that some use it straight also.

Comm drops only work with certain types of brushes at best. Most comm drops on the market are crap. Try Prolong or Tribotech. These are oil treatment additives and work excellent with #4500's or 767's but not with a high silver content brush like the #4499's or 4383's. And never for off-road. To much dirt. Use one of the above brushes with a red spring on the pos and a green on the neg. Drill a hole 1/8" deep in the center of the brush with #42 drill. Never put new brushes in a motor without cutting the comm first.

You can get Prolong Engine Treatment at most auto parts stores. You can get Tribotech at their web site at http://www.tribotech.com

A special note from BIG JIM</u>: Since these original posts from the Team RCV forums, the Tribotech Company, the makers of the oil additive mentioned above, have released their own formula of commutator lubricant especially made for R/C motors. Their formulation far exceeds the usefulness of any automotive oil additive for comm drops. The TRIBO R/C Power Matrix Commutator Lubricant is the best stuff I have ever used. It works with any brush compound and is great for off-road too, since it has no petroleum products in it. It is 100% synthetic and doesn't attact dirt and dust nearly as badly as oily products. And the TRIBO Power Matrix works great for bushings and bearings too. Go to their R/C web site for more info. www.triborc.com.

Question: The only store in my area that carries Tribotech doesn't have it in stock, so I got Prolong. Should I thin it 30% with mineral sprits too??? Lastly is there quite a difference between the two???

BJ's Answer: No, run Prolong straight. Tribotech IJP is kind of a west coast thing (we love our cars out here), but you can order it right from their web site. Tribotech seems to add more torque and Prolong is more RPM-ish. Both keep the comm and brushes much cooler. Be

sure and spray out the brush area after your heat to remove accumulated brush particles. Just re-apply before your next heat. Make sure your brushes like comm drops. Some don't.

Question: In regards to Prolong/Tribotech, do you recommend using those in mod-motors, too?

BJ's Answer: I can't really recommend using comm drops. I just suggest try it. Some brushes don't like any sort of comm drops. I want people to have all the information they need to go fast. Drops can make the motor faster. But they can eat up the brushes. But the Prolong and Tribotech work the best I've found. When comm drops work, they work real well. Extra caution should be used when using drops on mod motors. Comm drops, of any sort, don't seem to like high silver content brushes either.

Question: One other question, that I believe hasn't been mentioned. That is the use of silicone spray lubricant on brushes. The brushes were soaked in this. Any benefits to this over the Prolong?

BJ's Answer: Don't use silicone. It doesn't work. You need the chemicals that are in the Prolong or Tribotech. Silicone will just gum up your motor.

Question: About the Prolong you said... Just be sure and spray out the end bell after every heat... does that mean to leave the brushes in the motor while spraying? I usually remove the brushes after every run and deglaze them with a comm stick along with cleaning off any graphite dust with a Pentel white eraser stick. I will also lightly clean the comm with the comm stick also and spray out and contaminates. Would you recommend I keep doing this or leave the brushes alone and just spray the motor out?

BJ's Answer: If you do use the comm drops and they work out well, they should keep the comm shiny and the brushes in good shape. So try just spraying the end bell out first. If you feel you need more cleaning, then go ahead.

Comm Size
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*** This topic is updated and covered in-depth in the print version of Big Jim's RC Motor Black Book. ***

Comm Cutting
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Question: When you cut the comm, are you supposed to run a ball point pen down the "cracks" of the comm to round the edges? Does this reduce arcing or does it cause other problems?

BJ's Answer: Running a ball-point pen down the slots of the comm is an old slot car trick done by the "fiddlers" amounst us. It is suppose to remove the burrs on the edges of the slot caused from cleaning the slots with an Exacto after cutting the comm. In actuality, these burrs are microscopic and are easily wiped away by the break-in procedure of the brushes. Many racers spend a lot of time doing this or getting the finish just right. To me, if it's round, that's all that matters. Other than getting ink on the comm, this procedure doesn't hurt anything though.

Question: When using a comm lathe what should the finished cut look like? I've been told that it should have a mirror finish and I've been told it should have a finish like a CD satin like. I am so confused!!

BJ's Answer: I can understand your frustration with the lathe. The best way to describe how a comm should be is round. It really doesn't matter how the finish looks as long as it ends up that way.

The mirror finish that most racers try to achieve looks pretty but that's about all. This is usually made with a diamond with a rounded tip. This kind of tip pushes the metal away as much as it cuts it off, consequently

you can have a nice shiny finish and it be out-of-round. This is not the most desirable for breaking in brushes on either.

The best comm finish is achieved with a very sharp tip so that it ends up looking very much like a CD, as you described. It should reflect colors when put in front of a strong light. However, this is ideal, but not necessary. I've been at a lot of races where my tip is getting old and the finish isn't as pretty as it once was but it still cuts round, so it works fine. It actually seems to work better if it's a little rougher. Brushes seat quicker.

When you cut a comm, you can test it for roundness by running the motor at about 4-5 volts and holding a pinion wrench or other small tool on the end of the brush where the shunt goes in and feel for vibration. It should feel as if it was not running at all. Most pit lathes are hard to set up just right. Diamond bits can cut very shiny and be cutting out-of-round. This is why I always use a C2 carbide bit. But you need a tool grinder to put the right edge on it. It also never chips when you go too deep and hit the tabs. And it's cheap, about $4 a bit.

I use an old Cobra I've had for years when I'm in the field (I now use an Integy Xipp lathe with carbide V-blocks-BJ). Otherwise, I use a Unimat 3 with a brass collet dedicated to just cutting comms. Lubrication is important too when cutting copper. Unless you have a very fancy set-up like Mike Reedy does for cutting comms, you'll need some sort of lube. Most racers know the Sharpie trick. There's something about the ink in that pen that works for lubricating a comm as you cut it. And it's clean and easy. Just cover the comm in black ink just before you cut. WD-40 also works well as does mineral spirits, or mix the two together.

Hope this helps in your quest for round comms, for that's the most important thing. Heck with the finish.

BJ's Comments: Here's something I do that might help. I don't always put new brushes in when I cut the comm. I find that after the brushes are deglazed they work just fine. Just cut the comm. This way, your brushes are already seated and the comm is really why it needs to be rebuilt anyway. If you really do need brushes, cut the comm and let the brushes break-in for a long time, so there's not doubt. Then take a light cut on the comm. Now you have a motor putting out maximum power for sure. You have a fresh comm and perfectly seated brushes. Just a thought.

Comm Theory

BJ's Comments on Checking Out-of-Round Comms: Check your comm for concentricity by running the motor at 5 volts or so, no load. Hold with one hand and put a small screwdriver or pinion wrench lightly on the brushes right where the shunt goes in. It should feel almost the same way as if the motor isn't running at all. If there's much vibration, you comm is out.

BJ's Comments on Brush Replacement: Here's something I do that might help. I don't always put new brushes in when I cut the comm. I find that after the brushes are deglazed they work just fine. Just cut the comm. This way, your brushes are already seated and the comm is really why it needs to be rebuilt anyway. If you really do nee brushes, cut the comm and let the brushes break-in for a long time, so there's not doubt. Then take a light cut on the comm. Now you have a motor putting out maximum power for sure. You have a fresh comm and perfectly seated brushes. Just a thought.

Comm Overheating
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BJ's Comments on Comm Overheating: After a run and inspecting the comm, anything more than a light brass color is not good. Even that shows things could be better. As the color gets darker, it indicates the severity of the problem. I've never seen a blue or purple comm on a motor where it ran 100% after that no matter what you do. Seems it anneals the comm or wires or something. Yellow, orange or red are fairly common nowadays with the heavy cars and low wind motors or on stockers trying to pull them around the track.

If the comm is red after a run but you think you were geared about right, then the problem is too light a spring. Cut the comm and use heavier ones. If the car was mushy around the track and the comm turned red, then it was probably over-geared and could need heavier springs also. Motors that seem to have good punch seldom have too light a spring. If the car peaked out half way down the straight and the comm turned yellow or orange, it was under-geared. I've never seen a red comm from under-gearing though. These color indicators are not

absolute. There's lots of things that can turn the comm or brushes colors, but assuming the comm is round, the brushes are good and broken-in and the hoods are aligned fairly well, these are the first things I'd think about. You have to know how much time is on your motor and what it's been through to accurately use color changes for tuning and gearing.

Copper goes yellow, orange, red, purple then blue as it heats up. It's as easy to read a motor's condition by reading the comm and brushes as reading spark plugs is to an engine's condition.

Question: My comm is turning a reddish color. What does this mean and how do I fix it?

BJ’s Answer: Your motor is suffering from one of two things or both. Your springs are too light or you are over geared. I would think the first scenario is your problem. Stronger springs should stop the comm from turning red but you should retrue the comm first.

 

[hankster]

Dynos

BJ's Comment: When using a CE TurboDyno for stock, change your load settings around so it goes from low to high. Let the motor build up to that heavy load. Hitting the motor with max load right off the bat could arc up the brushes and comm especially if the brushes aren't quite seated yet, as well as give you false readings. I use 7.0 volts for stock motors but that is not that important as long as you always use the same number and that number is close to what the motor sees on the track. I use a 5 volt setting when running 4 cells and 7 volts with 6 cells with amp settings of 12,15,18,20,22,25 for 24 degree and 15,18,20,22,25,28 for 36 degree. I find the 20 and 22 amp setting is the most important for that's pretty much the most a stock motor will draw on the track in average racing, and I tune for maximum watts and efficiency at that point.

I use three programs for modified. All 6.5 volts:

1) 20,22,25,28,30,35

2)0,25,30,35,40,45

3) 25,35,45,0,0,0

depending on the wind and whether I'm at the track or home. I do most of my tuning at home and I just use the shorter settings at the track after rebuild when I've already got the timing and spring settings.

Dyno Troubleshooting
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Question: I used to run the loads starting with 15 on my TurboDyno but I had problems with the dyno loading the motor right. It hunted around on the 15 and 17 amp loads and let the rpms soar. It would settle down at around 20. I called CE and they didn't know what to think. This would only occur on new P2k's. It would seem like a brush break-in problem, I thought I had run them enough. When I switched to the high load first it helped.

BJ's Answer: It is a motor problem not a dyno one. We had the same problem at Trinity also. I had to start the dynos first reading at 18

amps and then it was OK. They couldn't take the time to do it right. I think it is both a brush break-in problem and a hood alignment problem. Try doing both. You will notice that after a couple of runs on the dyno, the problem goes away right? Now the brushes are broken in all the way.

The easiest way to avoid dyno or Turbo 30 shut down is to rub the sharp sides of the brush face on a Formica table top to flatten them. This allows more of the brush face to contact the comm and shouldn't shut down your equipment

Dyno Voltages
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Question: I have a p2k that is the most powerful that I have seen at 5V on my Robi but at 7.5V it is merely average. It has the standard red/green spring setup and V slotted AG9 brushes. The brushes appear to be lined up well as their wear indicates but there is a small black band on the trailing edge of each brush. 5V-->59w and 7.5V-->123w

BJ's Answer: Testing a motor at 5 volts if your racing 6 cells is a waste of time, in my opinion (you didn't say how many cells you race, 4 cells OK). A motor should be tested at the voltage it will see in the car. So many more things happen at 7.5v that at 5v.

You're right though, 123 watts is only a little above average but not bad. I'd run it one heat and test it again. But remember, a flywheel dyno starts from a dead stop and figures it's power reading from there. In actual racing you don't start from a dead stop more than once. This will cause tuners to over-spring. I would bet that if you put a red spring on both sides, the power numbers would go up. But leave it the way you have it anyway, for the above reason.

A fully charged 6 cell battery pack will sit on the line at about 7.5 to 7.8 volts. The motor will see this maybe for only a moment. The instant on feature of a flywheel dyno takes this into account. I tune a motor for the maximum voltage it will see on the track. If I don't, it could be damaged by the excess voltage (spikes from slamming into the wall, not withstanding). Robitronics recommends the 7.5v setting for 6 cells.

You have to "over-tune" so that your motor doesn't start to degrade

first right at the voltage you need it. Also, the more voltage, the more arcing from the brushes and the more spring tension is needed to overcome that arcing. If you tune your springs for a lower voltage, it won't be able to operate with maximum efficiency during the first minute of the race, causing the brushes to glaze and heat-up. This is the problem with trying to tune with a 5-volt dyno when you're running 6 cells.

A load dyno, like the CE Turbo 45, will simulate the voltage under a specified load. One time I tested a fully charged battery pack and put a 30 amp load across it. The voltage was 6.80 volts at the start. Of course it quickly dropped off. I tune a stock motor on the CE dyno for the best readings at about 20 amps. So I figured if a 30A load drew the batteries down to 6.8 volts, then 20 amps ought to be about 7.0 volts.

This is my setting for this dyno. I never figured the small resistance of the ESC and the wires. It's better to "over-volt" a little than "under-volt" if you know what I mean.

As long as your in that range, I wouldn't figure it to much matter. As long as you don't use, say, 5 volts to tune for 6 cells. This is the major draw-back with a Fantom dyno. I'm not saying don't use your 6.7 volt setting. That should work just fine as long as you always use the same voltage as a standard. Whatever works for you.

Dyno Results Conversions
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*** This topic is updated and covered in-depth in the print version of Big Jim's RC Motor Black Book. ***

Dyno Theory
​

Question: I have to respectfully question your flywheel versus slave motor dyno theories.

I agree with one point that you made, we (should) only accelerate from a dead stop once per race... but... for my driving style, and me how can I tune a motor for

A. Glance off board

B. A triple off the dot (but I do STICK the landing)

C. Going wide in the corners

D. Finishing the race with three wheels in contact with the ground.

A, B, C, & D, is just having fun.... don't take it seriously.

A slave motor dyno can be very inconsistent from pull to pull. Slave motor heating up, difference between rebuilds of your slave motors, magnetic field strength of slave motor changing over time, difference between slave motors across everybody that has bought one (my results are different from yours because we may have the same dyno, but different slave motors).

With the flywheel dyno, you get the same "pull" every time, are consistent with heat variances, and the dyno pulls are (or could be) consistent from dyno to dyno. Comments?

BJ's Answer: This may surprise you but I'm not a real big fan of slave motor dynos either. Both types have their drawbacks. I know, what's left. Well, nothing. If someone says something that is a characteristic of a slave motor dyno, I'd say that's just the way slave motor dynos are. I'm not saying I prefer one to the other.

I agree the weak point of this type of dyno is the slave motor. If someone would make a load dyno that used a propeller in a tub of water with a variable pitch prop to vary the load and all this was controlled and calculated by a CPU like we have now, that would probably be the ideal dyno.

However, in the case of drag racing motors, a flywheel dyno IS the ideal instrument. It measures HP from a dead stop and, with the proper weight flywheel, and the same voltage applied to the motor, can almost exactly duplicate the actual track conditions. Fantom's dyno with the drag program that uses the actual multi-cell battery pack that's in the car to run the motor, can do this. This kind of surprises me that Albie doesn't use this type. Maybe he does, but he's always mentioned the Robitronics dyno, with it's wind and voltage limitations. Not the type of dyno I'd use for motors made for up to 20 cell usage.

I just wanted to set the record straight. Both types of dynos have their respective limitations. But you can work around them if you understand what these limitations are and not take the dyno's reading as "gospel".

BJ's Comments on Using Dynos: Most motor builders don't use a dyno that much at the track. We do most of the testing at the shop and only make small adjustments at the track for different drivers or cell type. When we rebuild a motor at the track, we already have the timing and spring settings we want so we just true the comm, new brushes and reset to the way the motor was. Unless something anomalous has happened to the motor, re-dynoing a motor is really not necessary. Also, with the advent of the Quasar and #766 brushes, rebuilding time is about cut in half because they wear so well and are so easy on the comm.

We can usually tell if something is wrong by the sound of the motor after all these years. I realize most racers may not have developed that knack yet so there is nothing wrong with using a dyno at the track until you feel comfortable without it. As someone gets more and more into this motor thing, a dyno becomes less important.

CE Dyno Slave Motor
​

Question: I've got a question about your CE TurboDyno. Can you use a Stock motor for the Slave motor, or does it need to be a special motor??? Also what effect would it have, if you changed between a Stock motor and a Mod motor. If I can use one of these motor, and take a base reading with it, I would think it would be alright.

BJ's Answer: You can use a stock arm in a mod can set at zero timing.

This is what's in mine. Don't use the whole stock motor because of the timing on the endbell.

Dyno Setup
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Question: Do you solder the leads on your CE dyno? What are the consequences, if any, of using alligator clips?

BJ's Answer: Yes, I solder my leads because it's the recommended way. However, alligator clips can handle a 45 amp load for a few seconds at a time. If you're testing stock motors with a max load of 28 amps, there is no reason why good solid copper alligator clips shouldn't work just fine. Just don't use them with a Fantom or Robitronics.

Interpreting Results
​

BJ's Comments: There are a few subtle differences between the CE and Robotronics dynos and the information you can derive from them. The CE I feel gives you a much more accurate and consistent torque reading as it uses a torque transducer that actually measures the amount of torque, rather than a calculated formula. The Robotronics offers spool up (acceleration) information that is unavailable from the CE. Maybe someday someone will build a complete dyno that offers all the information in one package. But then again, it would probably be too expensive to afford.

When reading dyno numbers for 1/12th scale I look at the performance in the 20-25 amp range Watt output being the prime number. I find most people look at the rpm as their reference. Myself that is number three behind watts and torque.

A lot of racers make the mistake of under gearing torquey stocks like the Orion seems to be by your CE numbers. The next generation Reedy/Yokomo's will have even more torque and may experience a certain period of under gearing also. But when testing on my CE, it was easy to calculate what the gear should be. We geared our test motor 41/88 (64 pitch) in a TC3 and it was an ultra-rocket. This ratio probably wouldn't be normally attempted with a stock motor if other dynos were used. I have always found that if the watts are there on the CE, speed is just a matter of gearing.

The Reedy 19t is another good example. It makes a lot of torque but racers try to gear it like an Epic and it doesn't work that way. The CE picks out this torque difference and doesn't give it a lower power number just because the rpm is down. I sent one of my tuned ones to a friend and he said it looked really bad on his Fantom. I told him to go up on the gearing from what the Fantom was telling him. He did play with it a lot on the track and it got really fast 5.5 teeth HIGHER than his dyno said it should be geared. He said if he had nothing else to go by but his Fantom readings, he would never have tried gearing it that much over the dyno's gearing calculations. He said his Thor Chassis Dyno picked up the taller ratio also.

Trust your CE readings (on your Orion motor). A 102 watt stock motor @ 20A with a 7.0v input should be fast if it's geared properly. Watts is power. I wish somebody would send me one with no strings attached so I could test it.

The way I calculate gearing using the CE is easy. First, you have to have a good stocker at a certain track to be a standard to go by. Say you have a fast GM3. The dyno reads 102 watt at a 20A load and your gear for your track was 4.00. The rpm at that load was 21,000. Now you have a 102 watt Orion but the rpm is only 18,202 at the same 20A load. What do you gear?

Well, first, divide the ratio that you use with the GM3 into the rpm (21,000/4). That gives you a number of 5250. This is your control number for 24D stock motors at this track. Now take that control number (5250) and divide that into the rpm of your new Orion motor. 18202/5250 = 3.47 to 1. This is the ratio you should run the Orion motor to equal the same speed (if tire size remains the same). If you were geared 25/100 with the GM3, you would have to gear the Orion with a 34 or 35 pinion with the same spur. That's at least 9 teeth taller! How many racers would gear one stock motor 9 teeth higher than another. Not many unless they used a CE dyno and my gearing formula.

Dyno Analysis
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BJ's Comments: The Competition Electronics Turbo 45 Dyno is a load dyno. It puts a progressive load on a motor in 6 settable steps.

The programming is simple and so is understanding what it's trying to tell you. It doesn't flood you with a plethora of information that you don't need or can't figure out. It's also a stand-alone unit and requires no PC. Plus you can always ask me questions directly about settings and what certain figures are most important. The main drawback is that the accuracy of the readings are dependent on the condition of the slave motor. You have to rebuild it once-in-awhile. And it won't measure acceleration curves. But it tells you all you need to know accurately. It has an available HP infrared printer that gives you little slips of paper you can keep for your records. A 45A power supply is all that's required. Made by the same US company that makes the famous Turbo 30/35 chargers that are the standard in the industry for reliability and usefulness. If you have a problem, you can call and talk to the guy who designed it and runs the company, if you want.

The Robitronics Dyno is a flywheel dyno and like all flywheel dynos, acceleration curves are it's specialty, but load numbers are easy to misinterpret. The voltage input is completely adjustable up to a 7.5 volt maximum, I believe. Great for 4 or 6 cell testing. It makes some pretty graphs on a PC but works as a stand-alone unit also if you don't want to take your expensive laptop to a race. But the info it gives you is limited in that mode. I've run 8 turn motors, at 7.5 volts, on it with no problems. Listening to an 8 turn HVW double, buzz up at 7.5 volts is like a V12 Ferrari to me. What a sound. It doubles as a neat charger too. The drawbacks are the amount of information it gives you is massive. I had a problem figuring out what area of the graphs to look at that were important for the motor and track is was running. I finally just looked at the power numbers. That's about all I could figure out. Also, it's made in Austria. It's difficult to talk to someone about it if you have problems and repairs/upgrades take awhile. It also likes a special (but easily obtainable) battery power source. Reads out in metric torque numbers. The most expensive of all the ones listed here.

The Fantom Competition Dyno is also a flywheel type. The best part about this dyno is the software. It will tell you what the circular mils on the armature should be if you decide to use that mode. It has gear calculations, graphs, roll-outs, etc, etc, and is fairly easy to use as far as flywheel dynos go. Many pro motor builders as well as serious racers use this machine. Jim Dieter (Team Trinity) likes this machine better than the Robi but he has to use the Robi because Trinity is the importer. The drawbacks are, it's not stand-alone. It requires a PC to run it (a cheap one works just fine though). Also, it only tests at

5.0 volts. Good for 4 cell but for 6 cell it could be better, although it does have conversion factors to calculate the difference in voltage. Like the other flywheel dyno the amount of information it gives you might be overwhelming. Any good 12 volt car battery works just fine for power. This is probably the least expensive of the three, not counting the PC. Made in the good old USA and reads in inch-ounces of torque.

Tekin makes one for about $350 retail that seems to do a decent job for stock motors. I know guys that can tune well with them in stock.

The CS Dyno is almost identical to the Robi from what I hear. But is really hard to get and service in this country.

Bud's (BRP Products) makes a cleaver unit that sells for less than $100 and actually works better than the price tag might imply, from what I've heard. But can't really compare with the more expensive units.

The Thor Chassis Dyno made by Parma is gaining in popularity because of it's low price and unique ability to measure power right at the rear wheels of your race car. It takes some getting use to but is quite useful. This requires a look-see in my opinion.

Each of these dynos have it's strong and weak points. In my opinion, the best dyno hasn't been made yet.

Remember this! No dyno is worth anything unless you can translate what it tells you into how a motor works on the track.

 

[hankster]

Brush Hoods

Question: Would I slide the brush hood and heat sink horizontally along the end bell (parallel to the other hood), or would I try to rotate the brush hood around the comm in the increased timing direction? This would require elongating the hood holes perpendicular to the heat sink vs. elongating the holes parallel to the heat sinks for sliding along the other hood. I would assume it would be better to slide along the end bell rather than trying to rotate around the comm. (I have tried this with some success but it easy to get out of alignment again. You have to grind away the area of the hood that touches the heat sink in order to "rotate" the brush hood around the comm.)

BJ's Answer: Hood tweaking was the only way I was able to get the early P2K's to perform for me as the hoods were so far off you could easily spot the misalignment by just looking at it. Unfortunately, it was after I had already purchased them. None of my Paradox motors have had their hoods so far off as these P2K's. The brushes in the P2K's would wear rather lopsided with one edge wrapping greatly around the comm and the motors were very soft on the track and would heat up easily. I tried a Paradox endbell on the P2K arm/can and the motor came to life instantly, so I am realizing the importance of proper brush alignment for making HP in these stock motors. And I'm not talking about just using the hood alignment tool without checking the comm wear pattern. The comm should be wearing the brush right down the center or tweak accordingly.

Getting the hoods aligned properly is the single most important thing you can do to get performance from your stocker or any spec motor. If you just run them stock, you could be losing 2-4 degrees of timing. Let alone having them be miss-matched which could be worse.

First, you must have a bar type alignment tool. Those old bolt-together ones won't work. Second, each hood must be aligned separately. Just running the tool through both hoods will align the hoods to each other but not necessarily to the commutator. Also, it will not compensate for each brush "cocking" in the hoods in the direction of armature rotation. This is caused by the difference in size between the brushes and the inside of the hoods. Sizing the hoods won't work because it causes problems with the brush damper.

The only way to do it properly is to align each hood separately to the comm. Dig out some unused old style brushes laying around your pit box that you don't use anymore, either because they aren't the right compound or you've filled the shunt with solder or some other reason you haven't thrown them out. They must be lay down and preferably without serrations or cuts of any kind.

Put these brushes in your motor before you cut the comm. No need to hook the shunts up. Install any spring. Run the motor 15-20 seconds or so on about 4-5 volts. Take the brushes out of the hoods being careful on how they were installed. Notice the comm wear mark on the face of the brush. If it's off to one side, loosen the screws and twist the hood in the needed direction until this wear mark is running right down the center of the brush face. You may have to bend the hoods slightly to achieve this. It is important to always put your brush in the same way or you could be tweaking in the wrong direction. Tighten all the screws and rebuild your motor normally with the right brushes. You will have to check the tightness of the screws periodically or they could spring out of alignment again.

Don't work so hard at aligning. A very small amount of movement is all that's needed. Most of the time, the holes are already big enough to align the hoods properly the way they are. If you loosen the screws and push the hood/heatsink assembly up and pull out the top corner and hold it there while you tighten the screws again is enough. Or you can just run around the holes with a sharp Exacto. Drilling out the holes is the last resort. Rotating the hood or sliding it back and forth, well, just do what is necessary to assure the brush rides down the center of the brush. Remember, you're just correcting for factory intolerances not trying to add more timing.

I will agree that proper brush alignment is the best way to get HP out of a stock motor. The worst things to use were those bolt together alignment plates. Remember those? There was no way to compensate for brush cocking in the hoods with those.

As you say, the only way to align the brushes properly is to go by the wear mark on the brush.

Brush Cocking
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Question: Have you ever tried using small pieces of shim stock to minimize the amount the brushes can cock sideways in the hoods to reduce the burnt area?

BJ's Answer: You are absolutely right about the black marks on the trail edge. It will always be there with lay down brushes and that much timing. Just make sure your brush hoods are aligned properly. You should have no more than 1/4 of the brush face arced up. The Prolong will keep that cleaner also. Some people cut that part of the brush off but that limits your overlap, therefore rpm. But it may work on some tracks. Try it sometime but not everything all at once. Get your Prolong dialed in first, and some good lap times.

If you find that trailing edge gets black badly at first but goes away as the brush seats more, then your hoods are tweaked still in the retarded direction. Re-align more in the advanced direction. If you have to, drill out the holes slightly for more adjustment. I won't tell. Also, move the hood and the heat sink together. This way you won't have to worry about removing those annoying nubs on the hood.

No, I've never tried the shim stock idea. But I don't believe it's necessary.

Brush Hood Cleaning
​

*** This topic is updated and covered in-depth in the print version of Big Jim's RC Motor Black Book. ***

Brush Hood Theory
​

BJ's Comments: Correct brush hood alignment is still the best way to get more power out of any motor. Most hoods aren't aligned well from the factory.

Before you guys get carried away making alignment bars, just remember that getting the hoods directly across from each other and centered to the shaft is a good starting point but not the end. Properly aligned hoods are very seldom directly across from each other. If the brushes were the same size as the inside of the hoods then this would work but they're not, not even close. This difference in size causes the brushes to "cock" in the hoods in the direction of armature rotation.

To properly center the brush, the hood must be tweaked in the opposite direction, off center to allow the brush to be centered when it's cocked. To do this, you need to run the motor just a few seconds with new brushes to notice where the comm wear mark is on the face of the brush. If it's off center, the hoods must be tweaked until that wear mark runs right down the center of the brush. Because of this, alignment bars don't have to be the exact size of the brush unless you plan on sizing the hoods. I don't recommend this however, because it will mess up the brush dampener inside the hood (Yokomos don't have this problem).

The latest crop of motors don't have the dimples on the brush hoods or mounting surface. I had them removed when we decided on the copper hardware. It’s much easier to align that way. If you have some of the old stuff, you can file off the nipples and reassemble. You can drill out the hood holes to make alignment easier but usually there's enough play to align. Sometimes you have to bend the hoods slightly in severe cases. When you assemble the motor, just make sure that

the comm wear mark on the brush runs right down the center. Just aligning the hoods exactly straight doesn't compensate for the brush "cocking" in the hood. Proper hood alignment will probably not be directly across from each other. It's best to use one of those bars for aligning.

So nothing fancy is really needed. Just a bar that fits inside the hood that allows you to move it around without distorting it. This is also why those screw-together alignment tools don't work.

Get yourself a good bar for bending/aligning the hoods. I have to say that Trinity makes a good bar. It's still a little small but better too small than too big.

BJ's Comments: I recommend that the best way to test brush hood alignment, especially on a stock motor, was to install an obsolete brush we all have laying around, with a new face and check the wear comm wear mark on the brush by running the motor for a few seconds on 3 volts or so. And adjust the hood until that wear mark runs directly down the center of the brush. Then install your good brushes.

Well, if you're like me, you're running out of old brushes for testing purposes. You can only use a pair so many times before the wear mark gets obscured by the old marks. So I invented a new trick. Take a new test brush and put a line across it horizontally with a fine tip Sharpie. Assemble the brushes in the motor and chuck the pinion end in an electric drill. Spin the drill in the direction of normal rotation for about 20 seconds. When you pull the brushes out, the Sharpie line will be worn away right where the comm wears without running the motor, saving the comm too.

I also found a few things that could make hood aligning this way difficult. Your old test brushes must have a larger radius than the commutator. I found some brushes that have the same or smaller radius and the comm just wears on the edges which makes the wear mark difficult to position. Also, you should use an old brush that is the same side dimensions as your good brushes, otherwise the degree of "cocking" in the hoods won't be the same, and cause you to misalign the hoods.

What I use for old test brushes are Race Prep "R"s. They are the same side dimensions as the Putnam Pro brushes which is .1885"

Using the above procedure will make one pair of test brushes last through many, many alignments.

I will stress again that proper hood alignment is the single most important factor in tuning a stock motor. If the hoods are left stock or aligned straight across, then you most likely are losing 2-3 degrees of timing.

 

[hankster]

Magnets

BJ's Comment: Taking the magnets out or even shifting them around will seriously diminish their strength and should be remagnetized before use again.

Torque Sleeves
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Question: Speaking of iron sleeves, ever had any luck with them?

BJ's Answer: I never heard of iron sleeves. I have heard of torque sleeves like Trinity sells. They are made out of a special magnetic shielding material, but I don't know if it has iron in it or not. It keeps the magnetic flux in the can where it belongs. However, using a torque sleeve around the motor changes the power curve quite a bit. It does just what the name implies; gives the motor more torque, but at the sacrifice of rpm. Since HP (what we're all after) is, rpm x torque it works out to be about the same in the limited times I've tested it. You just have to gear up.

Question: Can you comment on under what circumstances using a "sleeve" on a modified motor can be beneficial?

BJ's Answer: I tried one one time and I found it added torque but at the sacrifice of rpm, so the total HP was the same. Just had to change my gearing. But I realize this wasn't a good test. My buddy Steve Saik, a drag racer, uses a sleeve on all his motors but now were talking 10+ cells. The new style motors seem to have enough torque though.

Air Gap
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Question: I have always concentrated on matching arms and cans for minimal air gap. Is this worth it or am I just wasting time ?

BJ's Answer: In my opinion, there is an optimum air gap on these motors and it isn't always the closest one. I purposely made the D4 arms .005" smaller than the D3.5 or the D3. My testing showed more horsepower was obtained by a wider air gap. As far as air gap is concerned, the magnetic field goes up by the square of the distance. A .910" armature choked the rpm too much. Also, the tighter the air-gap the more eddy currents build up, which hurts efficiency. Average winds actually respond better with a .900" arm but this would hurt 7 and 8 turn stuff. Also, the version 1 armature design (marketed as the "rpm" blank) has more total power but it's at a higher rpm level. The version 3 (or "torque" blank) should be chosen for any wind below 10 turns. 10 turns is kind of a gray area and depends on the track. Anyway, keeping the air-gap the way it is will probably be the best choice.

Magnet Zappers
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Question: I've seen some magnet zappers and they all operate from AC supply and are quite big but I saw in Vichy in the touring car Euros that LRP and I think also Orion had what I think was a zapper but it was much smaller and I don't think they had to be connected to any source, how do they work? do they have big magnets inside? where did you get those zappers?

BJ's Answer: All the major teams I believe use the magnetizers you are referring to. Reedy and Trinity for sure, and I guess the others you've mentioned also. They are made in Japan from large hunks of neodymium-iron-boron magnets. This stuff supposedly keeps the bullet trains up over there. These magnetizers require no electrical source. The can with a slug is placed on a screw arrangement and slowly allowed to slide down between those powerful magnets. Then the can is rotated back and forth in that field to saturate the can, then unscrewed the way it was put in. This screw arrangement is necessary to be able to get the can out of the machine. They cost about $2500.

Question: Are those magnetizers better than the AC powered ones or is it only more portable?

BJ's Answer: Depends on the brand of magnetizer. Their big advantage is small size and lightweight. They do an adequate job.

Question: Where can one order one of those magnet zappers? And, do they ever need to be replaced?

BJ's Answer: Just a company in Japan is all I know. You'll have to do a little research on your own, I guess. As far as I know, no one has ever replaced the magnets.

Question: Again about those magnetizers: I assume that those zappers have 2 powerful neodymium-iron-boron magnets and the can is placed between them. Why do you need to rotate the can back and forth and not leave it placed there for a while?

Also, the slug is for what? Just to help placing the can or for another purpose? Is it made of steel?

I'm asking these because I might get 2 fairly big neodymium-iron-boron magnets for a good price and would like to know the design of the device so I can build one.

BJ's Answer: I don't know for sure since I've never taken one of those magnetizers apart but I assume the magnets in the can are shorter than the height of the magnets in the zapper. Therefore, it has to be rotated to expose the ferrite magnets in the can completely to the neos in the unit. Otherwise, the neos would have to be a lot bigger and wrap around the can more.

In response to your other question, the magnets in the can are not individual plus and minus magnets. The positive magnet measured on the outside of the can measures negative on the inside of the can and visa-versa. In order to magnetize both magnets together, a steel or iron slug is necessary.

Question: What effect does advancing the timing using zapping do to the motor?

BJ's Answer: What usually happens to a motor that has had the field offset like this is it runs good but the armature tends to want to straighten out the field again but isn't really strong enough so it just makes the magnets go away instead. Therefore, the motor goes away quickly too. I do not recommend doing it.

Question: How long can I run the motors before I need to have them Zapped?

BJ's Answer: There is no way to tell you how often to remagnetize your motors. I've seen magnets never need zapping and I've seen them go away in less than 4 minutes. When you should zap your mags nobody knows for sure, but I do mine every time I rebuild the motor.

Question: How much of a difference do you normally see in zapping a new can?

BJ's Answer: Zapping a new can is just precautionary. The magnets are suppose to be at full charge when new but you never really know. This is why it's a good idea to zap even new motors. But if the magnets are right when you buy it, zapping again won't make a difference on the dyno. You can't fill magnets more than full.

Remagnetizing magnets in the can does put a small charge in the can also and will show a slight increase on a gauss meter but that quickly goes away as soon as the motor is run. That's the nature of the type of steel they use in motors.

Question: One of my newly zapped Rage cans feels like a dog now. I don't know, new cut, fresh brushes, not much RPM. It draws under 5 amps at 5V no load, and not much more with a small break in fan (yeah I know, not much info). I swapped to a older can and the motor ripped.

BJ's Answer: Back in the old days, stock motors used to run better with less magnetic field because the stock cans and armatures we're the same as the mod motors, just the wind was different.

Now days, stock motors are wind specific. They are designed to run best with fully charged magnets. However, zapping the can will put the motor in a different power band than it was before the zap if the magnets were low before. You will have to adjust your gearing with the fresh mags. The Rage is very gearing sensitive. I would bet if you geared up 1-2 teeth, you could go faster than before the zap. This is the best I can do without knowing more.

Drag Motor Magnets
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BJ's Comments: Neodymium-iron-boron or neo, is the world's strongest permanent magnetic material, in it's purest form. Samarium-cobalt or cobalt as it's known is slightly less in magnetic flux at it's best. The difference is cobalt keeps it's strength at high temperatures. Neo's fall off above 350F. Both materials are far stronger than barrium-ferrite or ceramic magnets as we call it that we use in most r/c car applications. Drag racing excluded, except for certain 7 cell econo-classes.

The Trinity loose magnets are full arc cobalts, probably out of the Point Blank cobalt cans they use to sell. The Dragmaster is a small machined can with smaller magnets as well. That motor's overall flux density is less than the other motors you've mentioned but still useful in certain classes.

Installing Magnets
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*** This topic is updated and covered in-depth in the print version of Big Jim's RC Motor Black Book. ***

Measuring Magnet Strength
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Question: In past post you mentioned you could use a milliamp meter to get a reference reading on the magnets in the motor. Could you explain how to do this.

BJ's Answer: You can get a measure of magnetic field strength with an analog milliamp meter. Just hold the meter close to the can with an armature or steel slug in the can. The meter is sensitive enough to pick up the field and move the needle. No physical connection is necessary.

Question: I have been playing with the gauss meter for a while now and I saw some crazy stuff. I have seen some neo mags that have reversed in polarity only on half of the face and the top of the mag will read say 900 gauss + and towards the bottom of the magnet face it will read say 300 gauss -. Now my theory is the arm makes a higher gauss then the mags and it is actually reverse zapping them. What do you have to say about this as I'm puzzled. I never saw it happen with the ferrite magnets even with a lot of cells and old magnets.

BJ's Answer: There are two reasons magnets of any material will demagnetize under normal usage in an r/c motor. One is excessive heat. In that case, the entire magnet would be weak because the heat probably wouldn't be spotty across the magnet. The whole magnet would get hot therefore; it would lose magnetic field evenly across the whole surface.

The second reason is exposure to the reversing field generated by the armature. If this happens, the leading edge of the magnet would lose strength first, since it's this part that attracts the segment of the armature that's energized to the opposite polarity. This exposure during rotation would tend to demagnetize a magnet in this area. The last part of the magnet to demagnetize would be the trailing edge as this part pushes the arm segment away from the magnet because it's energized to a like polarity, which would not demagnetize the magnet.

Since you didn't say what the magnets read when new, and since you said the magnets seem to get weaker the farther down you go, I will have to say that the problem is not in your magnets but in your probe and your technique.

You can not effectively measure accurately the strength of different parts of a magnet while it is still in the can and being influence by the magnet on the opposite side. The farther you stick your probe into the can, the more the probe will pick up BOTH fields and will tend to neutralize your readings. This would account for your lower readings the farther in the can you go.

The best way to measure magnet fields of magnets still in the can is to make a fixture that holds the probe steady and always holds the can the same distance from the probe. Then the can can be rotated from one magnet to the other with the probe staying fixed. And usually the probe only touches one magnet at a time and only goes slightly into the can so that the other magnet can't influence it.

If you are holding your probe by hand and touching it to different places on each magnet while they're still in the can, you can't use these readings to determine much about the strength of your magnets especially on different parts of the surface.

 

[hankster]

Tuning Tips

Trinity GM3
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Brushes: Reedy 767, Trinity 4499 or Putnam Pro's green & blue shunt with a #42 hole in the face. (Special Message from Big Jim: I don't use the hole any more. Not because it doesn't work well, it does. But the serrations seem to do the work of the hole without the bother. In 4 cell, the serrations will last a long time and if you bother putting the hole in, you may not get to the benefits of it for quit awhile, if ever).

Springs: Trinity Red on the positive, Trinity Green on the negative.

Tuning Procedure: Align the brush hoods using my Hood Alignment guide.

Fully break in the brushes using 3 volts. I use a Turbo 30 set for 300 seconds. Once fully broke in, disassemble the motor and cut the comm. Recutting the comm is not mandatory. Unless you're at a big and/or important race, you may not feel the need to do this for the small amount extra it gives you.

Reassemble the motor centering the armature in the magnetic field.

Reinstall the brushes and run the motor for 30 seconds at 3 volts to reset the brushes.

Install the motor in your car or truck and put it in the "A" main!

Reedy MVP
​

Brushes: Reedy 766 with the face narrowed so it is the same width as it is high or a little more. The face of the brush will look square. Take equal amounts off of both sides, the final width will be about .140". Cut about 3/32" down the side of the brush.

Springs: Reedy "gray" standard or stock springs. Neg. side tweaked to remove a small amount of tension.

Tuning Procedure: The first thing I do is remove the endbell screw that has the capacitor tab on it and cut the lockwasher away with a pair of *****, then screw it in a little. This will lengthen the screw enough to allow you take the endbell off with the ring attached. Then I disassemble the motor.

Next, I take the brush hoods off and, with a sharp Exacto, slightly elongate the spring post hole toward the endbell. This is just a slight amount and not noticeable. But will be enough to allow you to kick out that end of the hood to align the brushes. Then I reassemble the endbell keeping the hoods pushed against that new part of the spring post hole.

As for the brushes, I cut the hole off the eyelet leaving the crimped part still attached. This leaves the brush shunt as long as possible and solder it on next to the hood. Some tuners just solder the eyelet while it's still under the screw. This works OK until you have to take the brush off. Kinda hard to get the screw out to take the brush off if it's soldered to the hood.

After soldering on the .140" narrowed #766 brushes, I reassemble the motor with a skim cut done on the comm and a good balance. One brass washer on the shaft in back and the fiber washer with the thicker silver washer on the comm end. This is pretty much the way it came apart, as it comes well spaced from the factory.

Check the spacing and then lightly tap the ends of the shaft with the flat part of a pair of pliers. This seats and centers the bushings and makes breaking them in with polish or toothpaste unnecessary, especially if you reassemble with Tribotech or the new TRIBO comm lube.

I install the stock gray spring on the positive and remove a little tension off the neg side. This is a tuning thing and really should be checked at the track. You could start with a red on the pos and a green on the neg, or just put the stock springs back on. Or the coppers like I mentioned before. Better to over-spring than under-spring.

I oil the bushings with Tribotech IJP and run the motor on my T30 for about 20 seconds then check to make sure the comm is wearing the brushes in the middle. Adjust if necessary. Then run the motor for 300 secs at 3 volts with a little fan blowing on the motor. Recheck the motor and let it cool. If the brushes aren't seated all the way, do it again until the #766's are fully seated.

On the CE dyno you should get numbers of 97-99+ watts at 20A @7.00 volts. High load should be 120+ @28A. This is enough HP to get you competitive anywhere if the rest of your car is up to it. I have done lots of motors this way and they all come out about the same. If the 28A numbers aren't 120+, then usually the brushes aren't fully seated yet. A couple of more runs on the dyno and the numbers come right up. A shot of motor spray helps this.

You can also use the higher-silver compound brushes cut this way as long as they're full face to start (no holes or cuts), but the comm wear will be greater. Those #766's seem to run forever and polish the comm.

If you bought your motor from a tuner other than the Reedy version, you'll have to redo it but if you get the Reedy, you don't have to buy any other parts to super-tune your MVP.

This is all my secrets for this motor, and it's pretty much foolproof. Just be sure and adjust your gearing. You'll have to gear it about the same as a P2K (or one tooth down) with these modifications.

Trinity P2K & Paradox
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Brushes: Reedy 767, Trinity 4499 or Putnam Pro's green & blue shunt with a #42 hole in the face. (See the above on GM3 tuning for a new message since this posts was originally written from Big Jim about the hole.

Springs: Trinity Red on the positive, Trinity Green on the negative.

Tuning Procedure: Align the brush hoods using my Hood Alignment guide.

Fully break in the brushes using 3 volts. I use 300 seconds on a Turbo 30. Once fully broke in, disassemble the motor and cut the comm. Recutting may not be necessary unless you're at a big race.

Reassemble the motor, centering the armature in the magnetic field.

Reinstall the brushes and run the motor for 30 seconds at 3 volts to reset the brushes.

Install the motor in your car or truck and put it in the "A" main!

12th Scale
​

Stock Motors: Use the tuning guide for the stock motor you are using.

You will generally need less spring tension. Try two green springs on GM3 or P2K motors and a green/blue combo on the MVP.

Just follow the rest of the Tuning Setup guidelines for proper brush hood alignments and break-in procedures.

Mod Motors: These motors require less spring tension (than 6 cell mod motors), less timing and probably a 1/2 brush cut. Install them one up and one down. (Special message from Big Jim: Since the advent of the 3000mah high voltage cells, cutting the brush really isn't necessary. I now recommend you leave the brushes full-face.)

Mod motors are much more difficult to give one-size-fits-all brush and spring setups. This will vary by motor, battery, car and track that you are running. All of the same brushes that work for 6 cell will work just fine on 4. Your spring tension, for maximum run-time for 8-minute races, will be the only thing that you will need to change as far as brushes and springs.

General Mod Motor Tuning
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BJ’s Comments: For the Yokomo "Ti" based motor, use #729 Quasar brushes. Get the hard Reedy copper springs and gently bend about 7-10 degrees more tension in the positive spring. For really low winds, bend both springs to 180-degrees apart. You can put the motor together one spacer at a time so you can space the arm properly. However, I find most Ti's are very consistent with the spacing. Put one brown fiber washer on the comm first. This helps to keep fingerprints off the comm while you're assembling. Those magnets will put the arm hard as you put it in the can.

Now take one .020" washer and one .010" washer and put it on the pinion end of the arm and carefully put the arm in the can, holding the shaft up so the washers don't fall off. When the arm is installed, put two, .020" washers on the comm end along with the fiber washer. When you put the endbell on, this should be close. With ball bearings, any play at all is enough. You can tap the shaft on the bench and that helps seat the endbell bearing. If it's too tight or too loose, shim accordingly.

Once you're satisfied with your spacing, turn the endbell to zero advance. This is important (I'll tell you why later). The zero mark on the can will line up with the mark on the endbell. When you have your brushes and springs on, oil the bearings with Tribotech or so other good oil like Mobil One if you can't find any Tribo. Now you can check alignment of the hoods but on mod motors, it's not off enough to make much difference. This is due to the tighter tolerances and the narrower brush (verses stock laydown type). Now lets break the brushes in.

The reason I say set it at zero advance is, this is where you want the timing to break in the brushes. This is the position that is easiest of the comm. If you put it at race advance to seat the brushes, your comm will need truing before you run it on the track (well, almost).

That black area on the trailing edge of the comm slot won't appear if you break in at zero timing.

I run the motor at 3 volts for 300 seconds with a fan blowing on the motor. For low winds, like 9 turns or below, use 2 volts. But you probably have your own method but do something close to this. At the end of that time, pull the brushes and check to see if they are fully seated. If they almost are seated with just little edges that are not worn yet, this should be close enough. You can break it in the rest of the way on the track. If they need more time, let it run some more.

If you are going to dyno tune this motor, you should seat the brushes fully first.

Now the important part. Loosen the endbell screws and advance the timing two notches. Looking down at the endbell, you want to turn it counter-clockwise. Tighten the screws. Don't run it anymore until you have it in your car. Running that much advance (24 degrees) on a mod motor at no-load rpm isn't real good for the comm or brushes. The AE boys were running about 6.70 or 6.80 overall on the gear with their TC3's at Ripon with that wind. You shouldn't have any trouble going the time with this set up if your batts are at least decent.

This is a lot of timing, I'll admit, but the Quasar brushes are real easy on the comm and this is a proven set up. You should take a light cut on the comm after every race day so it's fresh the next time. You can just deglaze the brush faces with a comm stick and use them again. Yeah, you can practice with it to check your gear ratio (and scare the competition) but don't wear it out.

You now have a race prepared team motor. If the comm is round and the brushes are seated well, it will be fast. You now know how to set up a Ti better than most racers (and some motor guys, ha).

Special message from Big Jim: The above setup works for the D4, P-94 or any of the new motors with a high magnetic flux. For other modified motors without the high-grade magnets or cans that aren't made for low magnet flux leakage like the D4, you can't run as much timing. Just back the timing down to 1.5 notches maximum but start at one notch and test first. Also, I like to use the type of brush made by the company who makes the brand of motor I'm using. I always use the Reedy #729 Quasar or #737 brushes in the Ti or any Yokomo motor. For the EPIC brand motors by Trinity, the brush choice is more individual. For high-end racing, where maximum power is most important, use the Trinity #4383 brush but the comm wear will require more maintenance. For Off-Road racing, use the #4380 brush. For general purposes or if you just want to run 99% of what is possible, I recommend the #4455 brush. This brush gives excellent power but doesn't require frequent commutator retruing. The P-94 has it's own limited brush sets since the brushes are larger.

Modified Touring Car
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A special message from Big Jim: For a modified motor in a Touring Car or commonly known as sedans, the strain on a motor is great. Spring tension, brush overheating and commutator wear will be of prime concern. Pulling a heavy car, with a lot of drive-train drag, running on 6 cells on high traction tracks, the motor will require extra maintenance if you want to remain competitive.

Question: Should I buy a few multipe arms of different turns?

BJ's Answer: Buying multiple arms is a good idea but not the kind you think. Contrary to popular belief, the number of strands the arm is wound with means almost nothing to performance. The three most important things that relate to motor performance, as far as the winding go are Resistance (or how big the wire or wires are), Ampere-turns (or the number of times the wire wraps around the stack) and Centrifugal Mass (or weight that accounts for spool-up time).

A fully packed arm of the same number of turns would have bigger wire. Bigger wire equals less resistance. Less resistance means more power. This is not to be confused with the diameter of each wire. You must consider the total surface area of all the strands together. This resistance is determined by the circumference of the wire(s), measured in circular mils.

However, there's a physical factor called centrifugal mass. Something heavy accelerates slower than something light. A fully packed, high circular mil arm, may ultimately have more power, but it will take longer to get there due to it's own weight.

A light-wound arm would accelerate very quickly so it would be perfect for tight twisty tracks with short straights but it would lack top end. For long straightaway tracks with lots of sweepers or very large oval tracks, I'd go with as much wire as I could fit on the arm. It might accelerate slower but if you can keep your speed up, you'd have killer top end and mid-range. A track of medium length, well, you get the idea.

I'd get some arms wound lightly, fully packed, and somewhere in the middle of different turns. This way you can have the right arm for the right track. There is some overlap in this theory too. A medium packed arm can work well on a long track with the right tuning, but that's another story. The number of turns determines resistance more than any other factor. This is a choice made by the racer for a type of track or for the type of racing he does. It should also be taken into consideration with the type of battery packs one has.

Gearing
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Question: Is there anything wrong with "under gearing" your car? By this I mean using a smaller pinion. Other than maybe not optimizing performance, will the motor suffer at all? I am thinking of getting a wilder wind motor and under gearing it to maximize run time. I'm not sure but I may have read something about under gearing a car will get the motor hot - sounds contradictory to me. Maybe it's one of those old motor myths you're trying to dispel!

BJ's Answer: Over-revving the motor can hurt the comm and brushes, because it's mostly at maximum rpm. This applies to any motor.

Special message from Big Jim: How you should gear your motor, either stock or modified has far too many variables to go into here. Track layout, number of turns on the motor, number and type of cells used, car weight, driver's ability etc, etc, are but just a few of them. My general rule for gearing is, gear the motor so it just peaks out as you let off for the turn at the end of the longest straight. This is how you get your maximum chute speed. You can adjust your gearing then for infield punch, run-time or motor temp once you have established this baseline.

General Tuning Guidelines
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*** This topic is updated and covered in-depth in the print version of Big Jim's RC Motor Black Book. ***

Timing
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Question: You said: "all motors have a "sweet spot" for timing regardless of wind". How can I found that sweet spot without a dyno.

BJ's Comments: This "spot" is the amount of timing in the motor that produces the most amount of power at the load most useful in our type of racing. But it is not absolute. It is just a starting point. Motors used in drag or boat racing where lots of cells are used, this spot will change. Also, if you're running hot winds, like 7 or 8 turns, you shouldn't run two notches of timing unless you are prepared for a rigorous maintenance schedule.

For instance, 4-6 cell modified cars draw between 25-38 amps average throughout the race. At that load level, a D4, P-94 or Ti puts out the most power with two notches of timing, regarless of wind. This is about 24 degrees. Less timing makes more torque and less rpm on the dyno, but the power is lower in the load area I look at. More timing makes more power at 45A but lower in that area. Higher timing also is very hard on the magnets and brushes/comm. As I stated earlier, running that much timing on a low turn motor shouldn't be normally done because of the high maintenance involved. But it does make more power.

When I build a motor for a customer, I really don't know all the variables that a motor will be used. I rarely know the track. I do know that most races are 4-5 minutes and the batteries are 2400-3000mah. This combination makes a formula of power used during a race and this is where I came up with the load settings I use.

This is what I found after building hundreds of these motors on the dyno and the track. I agree that the above is a "generic" setting and it may not be optimum under all conditions. But I will say that timing a motor like this will make the motor competitive (timing wise) almost everywhere and is certainly a good place to start.

 

[hankster]

Tuning Secrets

Secret Ice Cube Trick
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Question: I played with some freeze spray on a 53 pwr motor... after 5 min of sitting I dyno'd it and it woke up to 56 and the rpm jumped from 17800 to 19000...I can imagine if I give it a top notch rebuild and try it again. I am trying to get a time span of effectiveness.

BJ's Answer: I found that freeze spray is much to "surface" oriented. Try putting an ice cube directly on the motor for a nice deep freeze.

Question: How exactly does cooling the motor with ice work? Won't the motor get wet and cause any damage? I can get my hands on dry ice. Does that work better than ice? Sorry to bring up this topic again but another small explanation on how to properly perform this motor secret for us slow learners would be helpful. Thanks for all of your useful info!!

BJ's Answer: Take an ice cube and place it on your motor and motor plate. Put some paper towels or a rag on your chassis to hold it. In a few minutes, you won't have to hold it anymore. It has melted to the curvature of the motor and plate. Someone said for a TC he had to use two cubes.

The idea is, when you set your car down on the line, your motor and plate are ice cold. It takes about half the race for your motor to warm up to ambient temperature. After your race, the motor is just warm instead of smoking' hot. I'm sure you know how detrimental heat is to a motor. An added benefit is that the motor loves cold. You won't believe how fast an ice-cold stock motor is.

The motor internals should have enough lubrication on them to shed any water that happens to get inside it but even still, there's nothing in there that will be hurt by a little water. Keep the water off your tires and electronics, of course.

Dry ice should work but I haven't tried it personally. Let us know how it works for you.

Don't try this with your batteries. They don't release good voltage when ice cold.

Question: I tried the ice thing on my mod in my street weapon. It was cool. I noticed it would actually eat a few cubes before it was cold though. It was nice to have a warm motor after my heat rather than a cooked one.

BJ's Answer: I guarantee that going from cold to warm is better for a motor than going from ambient to cooked. Notice how much more HP you have throughout the race, especially at the start. Motors like cold. Try dry ice too.

Secret Brush Hood Alignment Trick
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*** This topic is updated and covered in-depth in the print version of Big Jim's RC Motor Black Book. ***

Secret Comm Drops
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BJ's Comments: Use Prolong straight, but Tribotech can be mixed with mineral spirits to thin it down a little. The stuff seems to vary in viscosity from bottle to bottle so start with 30% Mineral Spirits. I have heard that some use it straight also.

Comm drops only work with certain types of brushes at best. Most comm drops on the market are crap. Try Prolong or Tribotech. These are oil treatment additives and work excellent with #4500's or 767's but not with a high silver content brush like the #4499's. And never for off-road. To much dirt. Use one of the above brushes with a red spring on the pos and a green on the neg. Drill a hole 1/8" deep in the center of the brush with #42 drill. Never put new brushes in a motor without cutting the comm first.

You can get Prolong Engine Treatment at most auto parts stores. You can get Tribotech at their web site at www.tribotech.com

(Special message from Big Jim: I now recommend TRIBO R/C Power Matrix Commutator Lubricant for all motors, brush types and is available from www.triborc.com or one of the companies distributors. It works well for off-road as it is 100% synthetic so there's no petroleum oil to attract dirt more. It also works for any other class of racing or number of cells used.)

Secret Bearing Lube

Question: What can I do to reduce the wear on the output shaft from the bushing in a P2K?

BJ's Answer: The best bushing oil I've found in 22 years of racing is Tribotech IJP. It's available from their website of the same name, www.tribotech.com. It's a trick automotive oil treatment, available in autoparts stores here in CA but not many other places in the country.

You can also use Prolong Oil Treatment, the stuff I recommend for comm drops on stock motors or Mobil 1 works also, available everywhere.

Secret ESC Settings
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Question: In another discussion about limiting current output of a ESC it was suggested that we should not limit the current output when used with a stock motor because we'd just be limiting the power output of our motor. I remember reading somewhere I believe it was in a manual I have for a Tekin Speed controller, that stock motors really aren't capable of using more current then some certain level and that we should limit the current output of the ESC or we'd just be wasting battery power on heat build up in the motor. This info is conflicting obviously, so I want to know from a motor man what the real deal is.

BJ's Answer: Most racers don't realize this but when you get stuffed into a board or slammed into a wall, the motor will draw some serious spikes. I discovered this years ago when Victor had one of those in-car data recorders you hooked up to a DVM after the race and read certain values like current spikes, average voltage and amp draw, etc.

I was surprised to learn that one little tap that sent me into a board gave the motor a 90 amp spike. This would seriously hurt your running time. I never ran my ESC torque limiter wide open again. I just turned it down from full as I was afraid of it hurting my motors performance. I went down about a quarter of the range of adjustment.

Even though running time isn't as important now days with the advent of high mah cells, high-amp spikes can still be detrimental to the motor. I can't see a stock motor ever needing more than about 28-30 amps during any race under normal circumstances. Yeah, from a dead stop maybe, but a 30 amp load on the dyno almost stalls a stock 24 degree motor. In fact, at 4.7v, my CE will not even carry that load. It stops at 28A.

If you set your current limiter at 50A (with a stock motor), I think this would give the motor all it would ever need and keep the motor from having to endure seriously damaging current spikes.

Johnson/Mabuchi Motor Secrets
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Question: How would you achieve the best overall torque and power from these motors?

BJ's Answer: These motors, like the Mabuchi 540, have reverse curvature brushes. Sort of like putting a laydown stock brush in a stand-up brush mod motor. So you have to break the brushes in a lot. The best way I've found is by water dipping. This involves running the motor under water for a few seconds to a few minutes, checking it constantly, to quickly break-in the brushes. This electrolysis effect wears away the brush material without wearing the comm. It's tricky but it is the easiest and best way. Just letting the motor run for a long time causes a lot of heat build-up and wears the comm as well.

Question: What is cranking the comm? and how is it done with this motor?

BJ's Answer: I have never done "cranking" personally because it's cheating under the street spec rules here. But I have seen it done a couple of different ways.

You can stick an allen wrench up through the mounting holes in the can which would hold the laminations still while you clamp vise grips on the shaft flat spot and turn the shaft inside the laminations which turns the comm also.

Or I've seen people stick long nose pliers through the oval hole in the can up by the endbell and hold the comm while turning the shaft with the aforementioned vise grips. I would imagine a few motors would be screwed up before one mastered that technique which is why it should be outlawed. One should not have to chance screwing up the motor just to keep up. That's not the purpose of the class. This is why people drop out of the sport because of the necessity of doing things like this. I would start a campaign to make this procedure outlawed under your rules. This is no fun for anybody but the guy who has the finances to waste a bunch of motors.

Reedy MVP Tuning Secrets
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BJ’s Comments: Here is exactly how I tune the MVP's like this. The first thing I do is remove the endbell screw that has the capacitor tab on it and cut the lockwasher away with a pair of *****, then screw it in a little. This will lengthen the screw enough to allow you take the endbell off with the ring attached. Then I disassemble the motor.

Next, I take the brush hoods off and, with a sharp Exacto, slightly elongate the spring post hole toward the endbell. This is just a slight amount and not really noticeable but will be enough to allow you to kick out that end of the hood to align the brushes. Then I reassemble the endbell keeping the hoods pushed against that new part of the spring post hole.

As for the brushes, I cut the hole off the eyelet leaving the crimped part still attached. This leaves the brush shunt as long as possible and solder it on next to the screw. Some tuners just solder the eyelet while it's still under the screw. This works OK until you have to take the brush off. Kinda hard to get the screw out to take the brush off if it's soldered to the hood.

After soldering on the .140" narrowed #766 brushes (for more on this, see posts #2582 and #2583), I reassemble the motor with a skim cut done on the comm and a good balance. One brass washer on the shaft in back and the fiber washer with the thicker silver washer on the comm end. This is pretty much the way it came apart as it comes well spaced from the factory.

Check the spacing and then lightly tap the ends of the shaft with the flat part of a pair of pliers. This seats and centers the bushings and makes breaking them in with polish or toothpaste unnecessary.

I install the stock gray spring on the positive and remove a little tension off the neg side. This is a tuning thing and really should be checked at the track. You could start with a red on the pos and a green on the neg, or just put the stock springs back on. Or the coppers like I mentioned before. Better to over-spring than under-spring.

I oil the bushings with Tribotech IJP and run the motor on my T30 for about 20 seconds then check to make sure the comm is wearing the brushes in the middle. Adjust if necessary. Then run the motor for 300 secs at 3 volts with a little fan blowing on the motor. Recheck the motor and let it cool. If the brushes aren't seated all the way, do it again until the #766's are fully seated.

On the CE dyno you should get numbers of 97-99+ watts at 20A @7.00 volts. High load should be 120+ @28A. This is enough HP to get you competitive anywhere if the rest of your car is up to it. I have done lots of motors this way and they all come out about the same. If the 28A numbers aren't 120+, then usually the brushes aren't fully seated yet. A couple of more runs on the dyno and the numbers come right up.

You can also use the higher-silver compound brushes cut this way as long as they're full face to start (no holes or cuts), but the comm wear will be greater. Those #766's seem to run forever and polish the comm.

If you bought your motor from a tuner other than the Reedy version, you'll have to redo it but if you get the Reedy, you don't have to buy any other parts to super-tune your MVP.

This is all my secrets for this motor right here and it's pretty much fool-proof. Just be sure and adjust your gearing. You'll have to gear it about the same as a P2K (or one tooth down) with these modifications.

 

[hankster]

Springs

Changing Springs
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Question: How often do you change springs on a motor. I have been changing brushes after about 4 runs but springs? I have heard that the heat from a motor weakens the springs after a while but how long?

BJ's Answer: I certainly wouldn't change them all the time. If there's evidence of heat distortion or discoloration, then change them. Otherwise, use them over. But a spring gauge should be in every rebuilders pit box, if you can find one.

Mod Motor Springs
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Question: Any Brush and Spring combo tips for mod motors?

BJ's Answer: If you are a serious hard-core racer who doesn't mind new brushes and truing comms every heat, then there is no better brush than the #4383. If you're a very competitive racer that doesn't want to go nuts every week, then I recommend the #4455's or Reedy #729 Quasar brushes. They provide excellent power and are easier on the comm. So good, you'll probably get a whole day's worth of racing on them before you have to replace and recut. This would apply to all types of racing and winds aside from that 7 turn you might have in your sedan car. Ha. Use purple springs on both sides. If you want to try a polarized system, try a #4383 on the pos and a #4455 on the neg with purple springs and a harder bend in the pos side. The polarized brush technique is sometimes the best of both worlds but it is kind of an individual thing and you'll have to decide if you want to go that way.

Question: I am running modified 6 cell, 4 min oval, that's 580 ft. Using 12 & 13 triples one of the 12 D4 ate a set of brushes after 3 runs. Setup with 4383, red +, grn - and timing set to 27 degrees, gearing was 128/33 using radial tires 3L and R and 2400 batt. Usually I had been able to get 4-5 runs with a slight skim on the com after 1 or 2 runs.

BJ's Answer: Those springs you are using seems awful light for a D4 of any wind with 27 degrees of timing. What happens if the spring tension isn't strong enough is the motor runs fine for about half the race and then it goes soft and runs in "cruise control mode" as I call it for the rest of the race and beyond. This is what happened to you, I bet.

Sometimes the dyno will show better numbers with lighter springs but on the track, it's a different story. I reaffirmed this in my mind when testing the MVP stocker. The dyno showed super-soft springs make better power but on the track, the comm turned reddish and the brushes glazed. I now run a lot more tension. I give up a few watts on the dyno but I know it works best on the track.

Unless I was running a very mild wind in the D4, for some reason, I'd have purple springs on both sides. At least try a purple on the pos and a red on the neg. This is about as light a tension as I'd go with that motor.

I think you just ran out of tension as the comm and brushes got worn more during the race.

Testing Springs
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*** This topic is updated and covered in-depth in the print version of Big Jim's RC Motor Black Book. ***

Spring Tension
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Question: A stock motor I tuned that on the Roby dyno which is the craziest thing I ever seen as I played all day and found 151 watts with light springs as the heavy springs slowed it up to a 140. The motor dynoed 131 out the box, does this happen often that a motor runs better with softer springs?

BJ's Answer: Most racers do over-spring. The stronger the permanent magnetic field, the less the motor "lugs" under heavy load. The less it lugs, the less it arcs. Less arcing equals less needed spring tension. Too much tension acts like a disk brake on the comm. You only need enough tension to keep the brush seated on the comm when it arcs under racing conditions, whatever type of racing that my be. This goes for both stock and mod.

Question: What do you think of the 15% silver cavity brush's that Cam used to sell and Birdman in California now sells? And when you use a high silver brush, would you use heavy or light springs.

BJ's Answer: The amount of silver in a brush does not dictate the spring tension. The amount of arcing does. The more arcing, the more tension is needed to overcome the arcing. The main factors that increase arcing are, low winds, excess timing, high voltage, high loads, out-of-round comm, glazed brushes and, yes, high silver content brushes.

However, high silver content doesn't necessarily mean the brush is going to arc a lot. It has to do with the kind of lubrication in the brush and particle size. I use Putnam Pros in most of my stock and 19t motors. Todd says they are 13-14% silver. And but I couldn’t say they arc more than any other brush. After the serration tips are worn away, they are not that hard on the comm.

Trinity Spring Tension: Trinity springs go this way. Silver, purple, red, black, green, and blue, from hardest to the softest. The red and the black actually have the same tension. The red being a 7 coil spring and the black being a 6 coil. The black spring is imported from Japan and is the only one in the set that is designed for laydown hoods. When I use any spring other than the black, I put a small "z" bend in the long end so it fits laydown hoods better.

Spring Theory
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Question: Why is it necessary to have a stiffer spring on the pos side? Doesn't the stiffer spring cause unbalanced com wear?

BJ's Answer: The purpose of the springs is to keep the brush in contact with the comm when the arcing wants to blow it away. The more the brush arcs, the more spring tension is needed. The theory is that since the current enters the motor from the pos side, that brush is going to arc more than the neg side. Therefore more spring tension is need on the pos side.

The commutator rotates between the brushes so it would be impossible that a spring tension difference at the brushes could cause uneven comm wear. Possibly, the brushes would wear different do to more tension on the pos side.

Question: I've heard that you should disconnect the springs when the motor is in storage, and I do that. I was wondering why it is that those springs need to be kept that strong, and was looking at my P2K and noticed that they are connected to immovable objects. I disconnected them and tried to run the motor on a stand and it will run without any springs. What exactly do the springs do in the motor?

BJ's Answer: That motor was running simply from the stiction of the brushes in the hoods. Put any load on the motor and the brush arcing will push the spring away and it will stop.

Motor springs do keep the brushes on the comm during the bumps and slams the car makes on the track but more importantly, it keeps the brushes seated when the arcing wants to blow them away. There are lots of reasons for arcing. High current loads, high voltage, out-of-round comm, hoods out of alignment, brushes glazed, high timing are most of them. The more the motor arcs, the more spring tension is needed. Too much spring tension and it puts more drag on the comm than necessary. It also wears brushes faster and, depending on the motor, it may change the power curve, like a stock motor. The older racers here can remember back, there was always somebody at the local track that used those black, crowbar stiff springs on their stock motor. These springs had more tension than a 10-cell car running a 9 turn motor would need, let alone any stock motor. We know better now with the advent of dynos.

Too little tension and the brushes glaze up and in turn arc up the comm. The motor will have a mushy feel on the track. When this happens, the car seems to go into "cruise control" mode at about the 3-minute mark. That's all it takes for the damage to happen.

Obviously, you can see it's better to over-spring instead of under spring. Without a lot of trial-and-error, it's hard to do without a dyno.

Motor design has a lot to do with spring tension also. A motor with a strong magnetic field, like the D4, will need less spring tension than a Reedy-Yokomo Fury, for example, unless you crank the timing up on a D4 to get more top end, but that's another story. A D4, with the "torque" arm blank, will arc less under high loads so you may get by with less tension.

A guy that relaxes the springs by taking them off the hood tang, because he's afraid the springs will lose tension, doesn't have a spring gauge. The only things that would do that would be excessive heat or a lot of flexing. A motor in storage will not encounter any of these conditions.

 

[hankster]

Timing

How Much Timing
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Question: What about modifieds? My questions is about timing. How much timing? Does it vary from motor to motor and if so, when do you know you have the timing just right?

BJ's Answer: The answers aren't so clear on modifieds. Timing, as you probably already know, is the relationship between the brush center and the center of the magnets. When these two centers line up, that is called "zero" degrees of timing. Timing can either be "advanced" or "retarded" by rotating the endbell either clockwise or counter-clockwise to the can. This could get rather complicated if it weren't for the zero markings on the can and endbell. Each degree of timing is about .0125" (0.32mm) off of the center, at the radius of the motor. The "hash" marks molded into the endbell in the advanced direction of most mod motors, is about .150" (3.81mm) apart so each hash mark represents 12 degrees.

The sticker most motor companies put on the motors are not necessarily marked off in degrees. Most are just indicators for timing adjustments and for reassembling after cleaning.

Now for the hard part. This is where dynos come in real handy. Different motor brands (Yokomo, Epic, Orion, etc.), different winds, tracks, types of cars (sedans, off-road, etc) number of cells, even the type of brush compound, all have a factor in motor timing. Any kind of help I could give you without knowing more about the above specifics would have to be so general that it probably wouldn't help you much.

Setting Your Timing
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BJ's Comments: This could get rather complicated if it weren't for the zero markings on the can and endbell. Each degree of timing is about .0125" off of the center, at the radius of the motor. The "hash" marks molded into the endbell in the advanced direction of most mod motors, is about .150" apart so each mark represents 12 degrees. The sticker most motor companies put on the motors are not necessarily marked off in degrees. Most are just indicators for timing adjustments and for reassembling after cleaning.

Timing for Off-road
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Question: I plan on using. Reedy Sonic 12x4 and a Tri-sonic 12x2, 6 cell 4wd and Truck Mod off-road (I race at lake Park FL) I'm using an 82 tooth spur and pinions can vary.

BJ's Answer: With your particular situation, I'd start with 1 to 1 and a half "notches" of timing using the scribed line in the can as a starting point. Or about 12-18 degrees. Start lower and go up noticing the change that takes place in the power band as you do. You can get exact timing degree settings by using a RACEtech timing jig sold by BoLINK. The Yokomo motor doesn't like a lot of timing because of its thinner armature web. The Sonic is one of my favorite Yokomos. It doesn't have the big holes in the can the way the new one does. I've never done anything with the Tri-Sonic. Let me know how it works.

6-cell Oval Timing
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*** This topic is updated and covered in-depth in the print version of Big Jim's RC Motor Black Book. ***

Mod Motor Guidelines
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Question: I'm building up a mod motor from parts I got from a friend. (15x2, GM Racing can and arm, if that makes any difference.) When setting the timing, what should I be looking for? I usually run stock, so this hasn't been an issue before.

BJ's Answer: Good basic question. As you probably know, timing is the relationship between the brushes, magnets, commutator and the poles of the armature. If the comm slots are running down the center of the arm poles, and the brushes are in the center of the magnets, then this is called zero static timing (on our kind of motors anyway). Electrical timing is another subject which we won't go into now.

The only timing we can change is the brush/comm relationship by turning the endbell on the can. Small pointers on the can and endbell mark the zero point. When the pointers are aligned, this is zero degrees. Looking down at the endbell, rotating the endbell CCW from this zero point will advance the timing. Rotating the endbell CW from the zero point will retard the timing. This is assuming the desired direction of armature rotation is CW from the top off the motor (endbell side). This is the direction most r/c motors run.

Under no circumstances is the endbell to be turned past zero in the retarded position. This will cause the motor to arc excessively, run hot and everything else bad.

Now to the "how to" part. After assembling your motor and lining up the two zero markings on the endbell and can, you will notice a polarity marking molded into the endbell. It will either be up by the bearing or on the flat part near the solder tabs or screw. It might be just the positive one or both on either side. Hook up a small amount of voltage to the motor in the marked polarity, enough to allow the motor to run slowly. Notice the direction the armature spins. If it is the correct way then the endbell is on correctly. If the motor spins in reverse then rotate then endbell 180 degrees on the can.

Now to setting the timing. At the radius of the motor, each degree of timing is .012". So if you rotate your endbell CCW so that the zero pointers are .120" (about 1/8") apart, this would be 10 degrees and a good place to start. The amount of timing necessary for maximum performance is dependent on a lot of variables like number of cells used, type of racing, track size, armature wind, driving style etc. A 15 turn might like a little more timing than 10 degrees, maybe 12 degrees or one notch. But go up slowly. If you notice the motor arcing excessively, back off on the timing. I wouldn't go more than 20 degrees advance with this wind under any conditions. Also, the condition of the motor (comm, brushes, etc.) will determine how much timing you can run.

This may be a little more than you needed to know, but now you can time any motor with a little practice now that you know the principles.

Question: Just to ask about the D4 type of motor. I accidentally put some degreaser on the motor which erase the label away, now, I dunno how to adjust the timing of the motor. I noticed that there are some notch on the end-bell which might be able to use as marking. Would you advise how many degree might be one notch. There are 4 notches all together and one look like 0 degree. My guess is 1 notch equal 10 degree.

BJ's Answer: Each degree of timing at the diameter of the can, is .0122". Each notch is about .150" apart. So you pretty much had it right. Each notch is 12 degrees.

Timing Sweet Spot
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Question: You said: "all motors have a "sweet spot" for timing regardless of wind". How can I found that sweet spot without a dyno.

BJ's Comments: This "spot" is the amount of timing in the motor that produces the most amount of power at the load most useful in our type of racing. But it is not absolute. It is just a starting point. In drag or boat racing where lots of cells are used, this spot changes.

For instance, 4-6 cell modified cars draw between 30-38 amp average throughout the race. At that load level, a D4 or Ti works best with two notches of timing regardless of wind. This is about 24 degrees. Less timing makes more torque and less rpm on the dyno, but the power is lower in the load area I look at. More timing makes more power at 45A but lower in that area. Higher timing also is very hard on the magnets and brushes/comm.

When I build a motor for a customer, I really don't know all the variables that a motor will be used. I rarely know the track. I do know that most races are 4-5 minutes and the batteries are 2400-3000mah. This combination makes a formula of power used during a race and this is where I came up with the load settings I use.

This is what I found after building hundreds of these motors on the dyno and the track. I agree that the above is a "generic" setting and it may not be optimum under all conditions. But I will say that timing a motor like this will make the motor competitive (timing wise) almost everywhere and is certainly a good place to start.

 

[hankster]

Conclusion

Motor Theory: In this section Big Jim tells you how motors work, tells you how different designs affect performance and the best way to pick the right wind that suits your type of racing.

The RC World According to Big Jim: In this section Big Jim gives his personal opinions on the world of RC. Find out what he thinks about other motor designs like the brushless motor, the comm drop rip-off, the Team Motor deception and more.

Photo Album: In this section you'll find personal photos from Big Jim. Check out past and present photos of Big Jim, his Checkpoint Motors, pictures & race results from the first ever ROAR Off-road race and more.

*** These topics are updated and covered in-depth in the print version of Big Jim's RC Motor Black Book. ***

This concludes the major excerpts from Big Jim's RC Motor Black Book.

 

[RocketRacer]

the link to the print version of the RC Motor black book doesn't work? is there another link??

 

[hankster]

Sorry, the book is no longer in print. Once Jim died his daughter said she would sue me if I continued to have it printed even though it was printed with Jim's permission.