.143 is a DARN NARROW brush ! -- esp for a .285 comm

That's .050 off of a new brush -- I've never trimmed more than about .010.

I liked your first formula better :)

Hey guys question for you.
I have the putnam jig, that allows you to drill holes in the middle of the brush. When I get brushes that are a fraction wider that are tough to get in the jig my motors all dyno and run better on the track, versus brushes that slide right into the jig.
This is with Putnam and 767 brushes.

Anyone else experience this?

Which brings me to another question. if the ever-so-slightly wider brush works then why would you want to time the brush. i have tried taking some of the trailing edge off and it only reduced the numbers on my dyno.

It's probably because those tight fit brushes are getting less brush cock then the looser ones.

I work on large DC motors in the 300 to 600 amp draw size with many segments on the comm. The one thing that is for sure if we want to increase RPM and Reduce Torque, we have a SHUNT across the fields to weaken the magnets and create a larger amp draw to the motor.

SO, think of the reedy MVP, its a high RPM motor. Reduce brush overlap like Big Jim recomends and you have torque again. I think this could work on the moster stock too.

All this makes sense to me. Strong magnets make more torque, Lots of brush overlap makes for more RPM. Cut down on the magnet strength and RPM comes up while torque goes down. Cutting brush overlap will reduce amp draw (ask any 1/12 scaler trying to make run time) and torque will go up. "narrow the brushes and gear it to the moon"

David Root

tourque x rpm= power,so you have to find a happy medium as far as brush overlap is concerned.
I hope the new reedy stock motor is decent the MVP was a sad specimen indeed.

Here is my preliminary drawing...

No explination of the Trig yet... but I have a start, and it should make some
things clearer I hope.

http://www.wiltse.net/nb.pdf

.148" X .190" is what the first 6 or so brushes measured when I picked some old ones at random from my box.

.020" comm slot on the first arm I looked at...

TRinity 4379 dual shunt P-94 brush... .175" X .200" ( I thought those were suposed to be square?? )

Goodwrench... that last formula comes out to .160" brush width... .143" is for a comm with comm slots that have no measureable width... when you figure the .020" slots, it adds about .017" to the imaginary brush size. Imaginary because there is no way to have a comm slot that is .00000" wide...

I still think that having some overlap can be good, so .175 is probably pretty good in many cases... what's .015" ??? less then the width of the comm slots themselves...

Ok, I've got a slightly more detailed drawing and explination of how I come up with my formula... I've also created a new term that better describes what I'm really after... Non Shorting Brush Width (NSBW)

http://www.wiltse.net/pdf/nsbw.pdf

Looks like I'm going to need a second page to explain how I'm accounting for the addtional brush width that comes about by figuring in the width of the comm slots. I'm not done with that part yet.

Dyno - You have way too much time on your hands LOL

I was thinking that same thing, LOL
My question is if you cut the brush width down so it doesn't short does it make the motor better? if not then why all the work trying to figure this term out?
You would think brush manufacturers would have caught onto this and design brushes like that.

Page 2...

http://www.wiltse.net/pdf/p2nsbw.pdf


Narrowing the brushes down from full size lay down deffintely helps the proformance in many cases. In my humble opion, one thing is for sure... taking a brush down to less then NSBW is not good, and should be avoided at all costs.

Some manufacturers have though about this... Trinity came up with .175" wide P-94 brush... how they came up with .175" is not known to me.

Reedy made a 'mid sized' comm to match their comm to the size of a laydown brush....

They've thought about it... maybe not as much as I have :), but they have thought about it.

By the way... my Reedy Quad Magnet 19 turn motor has a .350" comm, the comm slots are .025". Using my calculations... the non shorting brush width would be...

.197" The lay down brush is .190" wide which is too narrow in my opion.

The comm will have to get smaller then .336" before it starts to have any overlap.

Why not just turn it down to about .335 or so and run it there. Just a curious obversation.

Well... I could do that. However I think at that point, at least half the life is gone out of it. My understanding is that the thickness of the metal on those comms are not any diffent then the thickness of the metal on a standard comm. Standard coms start about .300 and can go down to .270... If I can go down .030 from .350 on the big comm, that means .320 is about as low as you should go.

You can always cut a brush down to size, it seems like it'd be better to start with a brush that had slight overlap, and allow the user too cut it down as needed.

I'm going to be doing some testing on some P-94 brushes soon. Not many people have much good to say about these... I'm thinking they offer lots of possiblitys in terms of cutting them in differnt ways, etc... The 4379 compound seems to be fairly easy on the comm, and produces good power too.

Oh, another interesting tid bit I noticed while making my drawings... the width of a .020 comm slot is about 9 degrees on a .300 comm. If you trim the leading edge of the brush by 20 thousands, your losing around 9 degrees of timing. I don't know many people who'd willingly give up 9 degrees of timing. So I highly suggest if you do try narrowing your brushes... stick to triming just the trailing edge, that way you won't be losing timing...

I've tried triming just the trailing edge on just about every stock motor there is. None suffered at all as long as I didn't remove more then about .020". In my opion, even MVPs will run better with just the trailing edge trimed. P2K2s, GM3s, and Monsters all do well with .015" to .020" off the trailing edge.

Been intereesting reading all of this. I have a Fantom and I take it to the track every weekend for anyone to use. If they don't know how I'll run the motor for them. I have seen everyones motor and the numbers they produce including a couple of really fast racers that place well at National events.. at first glance their motors don't seem any better than what I or most of the others run.. I've been watching one fella in particular and try to question him about what he's looking at when he runs a motor. He's not after the highest power number or the highest RPM. The last ROM he ran had a 53% effeciency with 21,000 max RPM. The higher effeciency number he has the more gear he can put to it and it'll perform the way he wants. He's fast, very fast and always has the track records where he runs.

A fella that pits beside me brings his CE45 occasionally and he's also used mine.. he's used to the data his spits out but also knows by the numbers he gets on mine what to do to change his motor or gear his car at. I'm still a rookie at the DYNO info but it's been a really good tool for working with motors.

I've been doing more contemplating about NSBW... I've got a slight flaw in my formula, probably causes a error of less then .001" when the comm size is close to what we have on our motors. I've got a solution... though... :)

It's really insignficant for our purposes... so don't no one loose any sleep over it... I do that, so you don't have to. Seriously... last night about 4AM i woke up thinking about this flaw... Man I need a new hobby to get my mind of this stuff.

But MiniCAD has become my new hobby... :)

Is it because you can't just measure brush width, you have to measure the curve length?? I was looking at all your diagrams and that is the only thing I didn't see. To me it looks like you are figuring width for a flat object riding on a curved surface? Just curious.

It has to do with the way I'm calculating the additional brush width allowable as a result of the comm slot. It's slightly more complex then what I did... the error between the way I did it, and the way it needs to be done is proabably something like .0001" or something that's basicly very insignfiicant for our purposes. I just want to get it right, so that no one points out that I'm wrong... :)

For our puposes

NSBW = ( (slot width * .9) + radius of comm)

heck... " NSBW = radius + slot width " is close enough...

The first part where calculating NSBW without considering the width of the slot, is fully accurate as far as I know...

Didn't get to finish last night, power went out and I sent the post before the battery backup died...

He also looks at the 18 amp settings, seems to be the one he's most worried about.. Will have to corner him this weekend and get some Dyno secrets as to what he's looking for when he runs a motor.

Topstrap

Dyno numbers can be inerpeted many differnt ways. The numbers from one dyno to another can not be compared directly. This forces you to learn more about the dyno you are using and try to understand the numbers it gives. All dynos give numbers that could easily be misinturpted, if the user is not carefull. I know my Robitronic numbers pretty well by now, but I don't think I could tune with a Fantom to save my life. If I had a Fantom, and no other dyno, I'm sure I could figure out a way to use it eventualy. I've owned a CE TurboDyno, and I could use one of those right now pretty well if that was my only option.

What dynos are still being produced?
Stevent

Robitronic, Fantom, and CS are the only dynos I know of that are still in production. However there are plenty of CE TurboDynos for sale used, and you can still get service on them.

Ok, for those who just can't wait for the new improved formula...

"Non Shorting Brush Width" = D * sin((arcsin(S/D) +30))

Where...

D is the Diameter of the comm
S is the width of the slot between comm segments

The error in my other formula would result in about .00033" on a .300" comm, about .00037" error on a .270" comm... Now that would have ruined your whole day if you'd had that kind of error, wouldn't it? :)

Pictures to follow... :)

Yup I think that last formula is about as accurate as can be...

"Non Shorting Brush Width" = D * sin((arcsin(S/D) +30))


I sure am glad I don't have to write math text books for a living... Here's my best effort at explaining this...

http://www.wiltse.net/pdf/p3nsbw.pdf

For all those skeptics... do the math... or just trust me. :)

Now just make a handy chart for us with all the NSBW of all the comm diameters!!!!! Thanks.

When DynoMoHum listed the three dyno's still in production, what does the "CS" stand for? Do they have a website.

I used to own a Robitronic...I sold when I got out of the hobby 5 years ago. Now that I'm back in, I really wish I still had it. I do have access to two Fantom dynos that their owners never use. I've just never used a Fantom before!

Thanks for keeping up a great thread!

Mitch

Problem fixed...

CS is CS electronic, the dyno is known as Power Check. It's basicly a poor mans Robitronic. I don't really mean that in a truely offensive way. People who own them tend to like them, they are cheaper then the Robitronic, which is a big attraction because as we all know the Robitronic is not cheap.. (about $750 new these days I think). My understanding is that the CS can be had for about the same price as a Fantom when new. (something like $450 or so.). The CS does not have a regulated power source, it basicly is designed to use a rechargable RC battery as the power source for the test motor. They seem to market this as one of the most desireable features of their dyno... that it uses the same power source as the motor would use in your vehicle... That's all interesting in concept, and may indeed have some value as a test... However in my opion, it's also a draw back to the dyno, and potentialy a problem for the users. It's also very likely the reason they are able to sell the dyno much cheaper then the Robitronic.

http://www.cs-electronic.com/CS-Produkte/Power_Check/power_check.php

Anyway... potential users of the CS dyno should be prepared to deal with the fact that the power souce's voltage may not repeat itself very well, depending on what exactly is used as the power source. If it's a rechargable RC battery... the voltage will drop with each dyno run you make, untill you recharge the pack. Some users report they get at least 6 consistant runs, and maybe even more. Other users use two packs in paralell, so the voltage stays consistant longer. Still others use 6 volt lead acid batterys that they keep a trickle charger on, etc... Many ways to try and deal with the issue...

Then there is also just buying a differnt dyno that doesn't have the issue.

I fully admit that it would be nice to be able to ocasionaly test a motor with the RC battery pack as the power source. I just think it's better as a option, then the norm.

DynoMoHum, It's nice to see someone that sees things the way I do. I came to a simmilar conclusion 6 years ago (the last time a raced). The only problem with your equation is that it is right on if you trim the same amount from each side of the brush, however if you "time" the brush by removing only the trailing edge of the brush the numbers are not right (the brush orientation is no longer at 90 deg to the comm, it has now advanced several deg.). My equation as follows takes this rotation into account. I know it could be simplified however it is stored in my calculator. I also know I have way to many operators however this is to make sure my trusty calculator doesn't choke on it.

Where
B = Brush width
D = Comm diameter
G = Gap between poles of the comm

(sin(180-(arcsin((B/2)/(D/2)))-(60-(arcsin(G/D)/2)))*(2((D/2)sin((60+arcsin(G/D))/2)))

This equation will yield a brush width of .1489. As I said before it is really great to see someone on the same page as me. I hope to be racing again soon. My oldest son will turn 7 early next year and I think santa will be bringing him his first rc car (ok so that will just give me a reason to get back into it, I miss it).

Dave

Well thank you for doing what I wasn't going to do... Figure out what it would be if the brushes weren't trimed evenly on both sides... I knew my equation didn't work, but I had made up my mind that it was close enough... and I wasn't going to do any more math to figure it out... It's not really something I enjoy all that much, and I just simply had, had enough... :)

Thanks for the follow up on the issue.

Oh, one more thing... if your still in the mood... Think about what happens if/when your brush hoods are not aligned perfectly...

Or when your brushes get shorter and cock more

Well, lets see. This is a set-up I would only use at a large race. At these races when you only make several runs a day and they are hours apart you have plenty of time to make sure your brush hoods are aligned properly. If you are looking for a formula to describe intentionally shifting the brush hoods to advance timing it would be fairly complicated as many times the misalignment is caused by a slightly deformed brush hood and not just the gaps between the screw and the brush hood and the spring perch and the brush hood being uneven. Also to the best of my knowledge this would be illegal by ROAR rules. ROAR states that the brush hoods must be aligned at 90 deg. As far as the brushes getting shorter and cocking more the result would be similar with or without the brushes being cut as the depth of the cut would not have to be deep enough to actually enter the brush hood. Also I wouldn't expect to run a set of these brushes more than two runs before changing them or shelving the motor. By the way, the following equation will tell you how much the cut of the brush has advanced the timing of your motor.

arcsin((B/2)/(D/2))+(60-(arcsin((G/D)/2)))-90

In the case of our comm being .285, brush width being .190 and the gap being .020, the new timed brush width would be .1489 wide and the advance would be 9.7995 deg. If you were to cut the comm to .273 and your brush to .1419 you would then have a 36 deg motor in a 24 deg can. Just something to think about.

Dave

I don't have any disagreements with what you've said. However experiance tells me that reducing the brush width to .149", even when it's all removed from the trailing edge... will reduce power output when compared to a brush width of say .170" or so.

I'm just bascily saying that a little bit of brush wrap doesn't seem to hurt much, in fact it seems bennifical in many cases. Even so... my personaly opion is you should never trim the leading edge, as that will clearly retard the timing and I really don't see any point in doing that.

One other thing I've observed... as a motor wears and gets pitted near the comm slots, the motor tends to behave as if the timming is going up. My thinking is that the comm slots are effectively getting larger (as a result of the pitting)... The reason I bring this up here now, is that I'm thinking that when this happens, the brush width can get wider without shorting. So... I think it's best to be conservitive when you start triming the brush width, start small, and maybe none at all unless you feel you need more effciency or have some other purpose behind your desire to trim the brushes.

Wow, I never thought of the pitting actually simulating the increased gap, but I can see that it is logically possible. One thing I do know is that thinking like this can give a huge advantage on the track over others who do not put this much effort into the process. I know that similar thought allowed me to finish 5th at the 91 US Indoor Champs (12th stock) while using 1400SCR's that were like mid 290's (20A) with good voltage (The expensive 1400SCR's were probably 310's - 320's at the time). Most people were using 1700SCE's or the P-170 Panasonics which both had far more run time (and they were using it all even in stock). It just kills me the way people will chuck up big bucks for the best packs on the market while ignoring things like brush overlap which in all actuality is taking the gains from the mega batteries and producing less output (on the track) than using average batteries with an efficient motor. Dyno, What classes do you race. Most of my experience has been in 12th on road and the now almost extinct 10th on road (pan cars). Also the pitting you have noticed, is it only on one side of the comm pole or both. Is it possible that the pitting is actually caused by the huge load of the shorted portion of the comm pole. As far as the Robitronic dyno you use, what do you think of it? That may be a purchase for me when I get back into it. My dyno experience was mostly with the Fantom unit (I was sponsored by them in the early 90's). The Robitronic seems pretty cool the way you don't need to have your laptop connected to use it, and I think i read something about using it as a battery charger. Is it possible to change the voltage to simulate a 4 cell pack as this is what I will be doing again? Nice talking to you again.

Dave

I race 4 cell oval. Lots of stock last year, this year I've moved to 19 turn class with adustable timing. I'm at best a average racer, my cars tend to go fast in a straight line, but I get beat in the corners on a regular basis.

The pitting occurs only on one side of the comm slot, I don't remember which side off the top of my head. Typicaly you will have to cut the comm about .001" or more to remove all the pitting on a motor that has more then a run or two on it. Some times you have to remove .005" or more if you really let your motor go. I never let mine go that far. I know for sure it makes the motor proformance change as this pitting changes (grows). Quite frankly, I think it can actualy inhance proformance in some cases, if it hasn't gone too far. Knowing when to cutt the comm and when to not cut the comm is tricky as a result. I personaly think it's not nessasalry a good thing to cut the comm after every run. Most people don't anyway, but sometimes at big races they will, and I actualy think they may be hurting themselves sometimes if they do that.

I've done some recent dyno runs that I will post sometime soon. Where I took a fresh motor, clean comm, broken in burshes... then ran like 20 consecutive dyno runs... you can see the RPM increase with each run... I've noticed this previously, but I've never really attemted to document the phenomina.

In my opion, the biggest draw back of the Robitrnonic dyno is it's price. THey are about $750 new, and you rarely see them for sale used. I have seen some go for like $400 to $500 on ebay. I personaly bought mine used for $500 about 4 years ago. I have absolutely no regrets with my Robitronic purchase. You can adjust the voltage from like 4 to 8 volts. They claim they 'simulate' the voltage drop of a NiCd, so the higher the load, the lower the voltage as you run the test. In all honesty, the voltage drop of their 'simulated' NiCd is too much... For sure it doesn't simulate a modern NiMh internal resistance, and I'm not even sure it did a very close simulation of a NiCd... But to me it's a very minor issue, I just set the voltage so it achives the voltage I want at a perticular load. For my 4 cell racing, I've found that the 6 volt setting yeilds 4.8 volts at the motor as it is pulling 30 amps. I average 30 amps in my racing, and a modern NiMh cell will easily put out 4.8 volts with a 30 amp load on it... at least for the first 3 minutes or so of the batteries discharge...

Anyway... All dynos have their own pros and cons. For my purposes, the Robitronic suits my needs best.

Oval huh, I only did that a few times (I ran for wood racing for years and Mike Sr and Jr talked me into it a few times). What I can say about oval racing is that if your car is not dialed in perfect all the motor in the world will not help. I always had problems with this. I could take my car out, feel like it is rippen (it may have been fast, but not dialed) only to find I would be like .5 sec / lap off the pace. oval races (in my opinion) are really won in the pits with countless hours spent working on the chassis and motor. I almost think, believe it or not that the chassis is more important than the motor. You can be the best driver in the world but without the car being dialed you'll probably be in the middle of the pack. In other words if you are not the fast guy it's probably not the driving (with your thoughts on motors it doesn't appear to be that either) it's probably the chassis (just some thoughts).

If you get a chance try using my equation on a stock motor and see if the pitting still occurs. If it works for a 4 cell oval racer I'll know for sure that it makes power.

As far as the dyno goes, thanks for your thoughts. I do have one other question though. Which curve on the Robitronic best relates your motor's ability to accelerate. For example on a tight twisty track I would probably be looking at this curve to be the highest (in relation to other setups/motors) from 1/4 to 3/4 of the RPM band as where on a more open track 1/2 to 100% would probably be the area to look at. Which curve am I most interested in. Thanks again.

Dave

Hey Dyno!
I have been reading this therad since the begining. I just wanted to thank you for all the great info and wanted to ask you a question.
I'm haveing a hard time understanding this formula. I have put it in excell and can not make it work. =sin(arcsin(.020/.275)+30) Is this how it should go in? What am I missing? Please Help.

Again Thanks for all your effort!
SB

Somewhere I had a typo... I know on the pdf file I last posted there was/is.... I'll go back and look at my postings here and correct if needed.

the formula really should be what you have... times the diamter of the comm...

'NSBW' = D * sin(arcsin(S/D)+30)

Where D is diameter of the comm, and S is the width of the slot.

Man I am sure glad there are people out there like you because math wizzard I'm not. If sin=.866 what is arcsin. I think this is what I am missing!
Thanks
SB

man you had to ask that didn't you? Me, I'm no math wizard... I barely made it though college algabra, and a intro to calculus... I rarely do math in my daily life. I strugled just to get as far as I did...


arcsin is the inverse of sin, more then that... I can't say...

LOL you sound like me! I have been playing around with Excel and found out that arcsin is not listed as a function. Instead you have to use ASIN which the same thing I think. Here is its definition (Returns the arcsine of a number in radians, in the range -pi/2 to pi/2. If I enter this formula "=SIN(ASIN(0.02/0.27))+30" this is what I get (30.074). When you have time do a copy & paste and see what you come up with. That formula is right out of your PDF file. Which is very nicely done by the way. You ever have one of those things’s you just have to figure out or it drives you nuts!
Thanks
SB

Hi all,

I just purchased a Fantom dyno, even though I haven't got it yet, I'm looking for some advice on set-up and usaage. I have never used a dyno before so anything that you could offer is greatly appreicated. If you know of a web site or something that would be great also. As I have no idea of what I'm even going to be looking at. If it matters we run mostly oval.

Thanks,
Tom

I have been reading alot of the older posts here, and I downloaded the DynoViewer, from Mike, my question is how do I get some of the Fantom data, that I also downloaded into it? I just can't figure it out. I know it's so simple, but I'm lost.

Thanks,
Tom

I'm not sure if this thread is strictly motor dyno's but I just recently got a Thor chassis dyno (without instructions) and need some help with it. If anyone wants to share some instructions, it would be most appreciated.

1Loosenut,

Email me at tech@parmapse.com with your address and I will send them to you.

Paul

Chicky, I sent you an email and thanks for the help. Also thanks to Hobby Talk for such a great forum. This site has helped me tremendously :thumbsup:

Anyone know anything abuot this?

http://www.land-and-sea.com/images/dyno/auto/chassis/chassis_dyno_rc-car.htm

No, but that is pretty cool though!!!!

Looks cool. Did you call them for info yet?