Cutting a motor commutator & motor tweaks

[killswitch]

i always thought you shimmed the armature to center it in the magnetic field, not to center the brushes on the comm

Thats what I learned from pitting beside Big Jim Greenmeyer at an oval race when I was a kid. I watched him build mod and stock motors for a few top level racers and he built them to center the arm in the magnetic field. He would take all of the shims out of motor and throw some voltage at it and mark the shaft while it was spooled up. After he that he would do the push/pull centering method and mark it. He would then shim it using the marks as a reference. He also said that the magnetic field center would change due to the voltage being applied and thats why he used both methods and found a "happy median" center. I learned more about electric motors that weekend than I have in the rest of my 20+ years in RC racing and crawling. If you can find it, Big Jim's black book about electric motors is an excellent source of info on brushed motors, but its been out of print for a long time.

heres a link to some older motor info that I found a while ago while trying to find another copy of his book (mine disappeared at a local race a few years ago...)

http://www.hobbytalk.com/bbs1/showthread.php?t=126994

 

[EeePee]

Killswitch! That's awesome. Thanks. I must be getting lucky with what I've done. I seem to end up with some float both ways when I'm done. But I'm not putting voltage through it so I could be off. Good to know, and I'll try it that way next time. Or just redo this motor. :ror:

Got the other brush all good so the comm hits in the center.

Water break in. Couple drops of dish soap, maybe about 7 minutes in the drink.

 

[Duuuuuuuude]

You'd never think a "new" motor would throw out so much crap.




I'll give you $1 to drink that. :mrgreen:

 

[killswitch]

It should float both ways a bit. You never want to shim a motor tight. It just cant be super loose either or the bearings and comm can be damaged. If its too loose the arm will slam into the can end on acceleration and smash into the endbell on deceleration. You should also be careful on doing the water dip trick. its really best used on extremely hard brushes that were used in spec racing (bolink legends, trinity street and touring spec motors) or closed endbell motors. Water break in can actually wear softer, higher silver content brushes out faster than just letting them break in dry on 4 cells. I dont know what it is thats so relaxing about throwing an arm on the lathe and seeing what kind of power you can create. I do have a ? for ya about the integy motor that you cant believe how good it is... did you happen to notice if the windings were tight to the stack? Ive rebuilt a ton of those motors and it always seems that the best ones have tighter wraps and fewer/smaller balancing holes in the stack.

 

[EeePee]

That black crap is the serration cuts wearing off. Yes, I'm impatient and water is faster. And the bonus of the water suspending the garbage away from the comm is a good reason to use water no matter what the brush hardness. In my opinion of course. Just like motor oil in an engine, minus the filter.

Hang around enough touring guys and youll learn all kinds of tricks

I'd like to learn some tricks. I think what I'm doing is simply getting the motor to where it should be initially.

I do have a ? for ya about the integy motor that you cant believe how good it is... did you happen to notice if the windings were tight to the stack?

I can't say I noticed, but I wasn't looking. I will however take it apart and compare it to some other arms/winds I have here. Might be a while, but I will.

Good words man, thanks.

 

[killswitch]

Try running a harder brush on the negative pole. The additional lubricant in the harder brush should help the softer brush last longer and keep you from rebuilding as often with no difference in performance.

 

[Manning]

If you don't want to cut the comm as often, put a set of Trinity XXX Lemans brushes in the motor. They are great, very low wear on either the brush or comm, and they still make great power. Unfortunately they are expensive, about $13 a pair.

The XXX brushes were the only ones that I could get a full day of mod 4wd racing (using a killer 10 single) in with little to no loss of power.

 

[ericinMD]

Like Killswitch said, you should try to get a copy of Big Jim's book. I have one around here somewhere but have been unable to locate it. I got a chance to know Jim on a personal level and the RC community took a big hit when he passed away. What a great guy! He helped more people than anyone will ever know.

 

[EeePee]

Off and on I've been looking for that book. "thumbsup"

Trinity P2K Pro 2. Laydown brushes.

 

[slobin3d]

I have one of those P2k motors I'd let your work on for more practice if you want. It's out of my Sc-10. I also have a nearly new novak 55t you could tweek too if you wanted to compare it to a integy"thumbsup"

 

[BlueMonster]

Damn, I will have document my cuts now too, I have the same lathe. You are right, it's great to sit there and cut comms, hahaha.

I will have to check my Integy arms now to see how tight the windings are.

How about some tips and tricks concerning mixing cans and arms? I ran a set of Brood 65 turn cans with some 45t arms in my Berg, I loved em.

 

[Robbob]

Big Jim was a great man when it came to electric motors. Read his blackbook many times and learned a lot from guys like Dieter when he worked for Trinity and Putnam when he started his own company.

Heres some more small tricks ....

check your comm top and bottom to see how straight your lathe is cutting. digital linears is the best. the straighter it is the easier brush break in is.

after you cut the comm use a razor blade to clean the slots out between the poles. then take a small ball point pen and slowly run it up and down the slots. it helps debur the edges and keeps them from tearing up or burning them when running. go slow though and dont press to hard, its only copper.

serrated brushes are useless in crawling in my opinion. they only add to comm wear and dont last long enough to notice anything.

one big thing i learned from Putnam is power flows on edges. yes serrated brushes seem faster in the racing world but as the serrates wear down and the comm gets grooved you increase the contact surface. power doesnt flow on the surface so your losing.

When I raced Modified oval we would run serrated brushes once, pull the motor, cut the comm, drop new brushes in and spin for 15 seconds then back in the car. race for 4 minutes and repeat it.

you would get similar performance with less rebuilds by drilling a 1/16 hole in the center of a full face brush and using red springs or for racing conditions a red + and green - spring setup. Associated 767's were a great choice for us in touring car for power and efficiency. When you had the battery to support it you could do the same to something like a Reedy Quasar or Trinity E-brush.

Also using a hood tool like Niftech makes is the best. Its a rectangular piece of steel that gos through both hoods and has a rod that gos through the bearings. it centers everything as its assembled.

when building a new motor use assembly lube, the red liquid crap, on the bearings. it helps break them in and keep them cool while your building it and it doesnt fling off into your brushes on the hood side. little trick i use to do when building stock bushing motors, nothing was worse then a burnt brass bushing and a vibration. after that use something like synthetic oil for the bearings, the lower the viscosity the better.


also when your cutting those you should put one of those phenolic washers on the pinion side of the arm. it helps so you dont tear up the plastic piece there.
sorry for the book, hope you made another sandwich. :mrgreen:

 

[Rockcrawler]

Been playing around with them myself a little. :mrgreen:

And some old motors. :mrgreen:

And have this on the way...........

EeePee, are you serrating the brushes? If so, that water will kill them quick.

 

[Rockcrawler]

serrated brushes are useless in crawling in my opinion. they only add to comm wear and dont last long enough to notice anything.


Also using a hood tool like Niftech makes is the best. Its a rectangular piece of steel that gos through both hoods and has a rod that gos through the bearings. it centers everything as its assembled.

If you run a harder brush, the serrated brushes give more torque.

How does that tool work going through both hoods? Hoods have to be angled in the opposite direction that they spin because of the slop between the brush hood and the brush..........

 

[Robbob]

How does that tool work going through both hoods? Hoods have to be angled in the opposite direction that they spin because of the slop between the brush hood and the brush..........

sorry for the picture size, its right from Niftechs site.

http://niftech.com/catalog.php?mode=3000

there shouldnt be that much slop in a hood that it walks the brush enough to create a bad trailing edge.

 

[cartronicshn]

8) Great thread Ep"thumbsup", i haven't taken apart a motor in long time, all this great info is making me want to buy a lathe to rebuild all my motors:shock::mrgreen:, keep the info coming, i think this could become a stickie.

 

[TSK]

I;I'm curious as to how bad some of these integy comms are. Are they bad enough to where they don't want to run? I recently installed one, and it doesn't spin off the esc's throttle input, but will spin if hooked up directly to the battery pack. tested the esc with another motor and it works fine. i haven't had time to follow up, but i think it might be a bad brush. like it's not getting enough current to spin when hooked up to the esc, but getting the 9.6 volts straight from the pack gets enough juice to the motor so that it spins...

 

[EGRESSor]

Off and on I've been looking for that book. "thumbsup"

Trinity P2K Pro 2. Laydown brushes.

it runs to hot:twisted:

i like the P94 brushes or the Kyosho 5x5 more

 

[Rockcrawler]

there shouldnt be that much slop in a hood that it walks the brush enough to create a bad trailing edge.

From Big Jim:

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.

 

[Rockcrawler]

Oh, and Rob, not trying to be a know it all. I am just learning all of this again myself. "thumbsup" I have been told that this man knew what he was doing and what he was talking about so I have been "going by the book" on everything I can. "thumbsup"