How do you center the armature?
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.
Why are all motor manufacturers & relabelers still using a brass shims against a bronze bushing? Cost?
I don't really see anything wrong with the brass washer. What would you suggest?
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???
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.
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.
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 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 ?
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 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?
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.
What's the difference on the P2K VS. Paradox arm?
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.
*** This topic is updated and covered in-depth in the print version of Big Jim's RC Motor Black Book
Armature Weight Question:
How about the weight of the armatures?
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 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?
I think you'll find that residual magnetism is non-directional and is quickly dissipated once the arm is run.
Armature Winds 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 ?
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.
Split winds - any use for oval racing ?
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.
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?
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.
When running 14 cells, is it necessary to run higher turns because of the weight of the batteries.
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.
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
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.
Would you mind explaining how a hemi wind and a cross over wind is wound??
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.
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 ??
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 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 ?
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 Question:
Epoxy vs. drill balancing - any advantages ?
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.
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.
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 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?
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.
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.
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 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?
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 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.
It depends on gap after magnets and arm are installed.
Is there a good way to tell if an armature is bad?
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 Question:
When buying a new stock armature, what should we look at to determine if one will work better than another?
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.