Where can I find *hard* brushes?

[JohnRobHolmes]

If you have an amp limiting power supply, throw 1 amp over the brush and measure voltage drop across it for ohms. I generally repeat at 5 and 10 amps and average out.

Originally Posted by fyrstormer

After trying to hunt down reliable suppliers for various different brushes, I decided to try some 20% silver brushes from Team Trinity. Hopefully they will be able to strike a balance between reducing comm wear without accelerating brush wear too much. I ran-in the brushes with the throttle trim turned up for a couple minutes, then took the car outside for a couple top-speed runs. My multimeter says the 20% silver brushes rate at 0.2 ohms from the face of the brush to the end of the shunt, whereas the Reedy Plutonium brushes rate at 0.05 ohms, but that slightly increased resistance wasn't enough to slow down the car I installed them in for initial testing. After 3 top-speed runs, the serrations haven't worn-down completely, so hopefully the brushes will have a decent lifespan. We'll see how my Traxxas Slash responds tomorrow; that truck has a Holmes TorqueMaster Pro 550 11t motor in it, and it's a brush-devouring monster; slightly higher resistance might actually be a good thing in that respect.

[Waitwhatsthat?]

So I just read this whole thread. First off it's very informative and I enjoy the sharing of knowledge that goes on. Secondly, I'd have to say, why not go brushless? It seams the ideal solution for your situation. You want to be able to run you rc's without having to teardown and maintain the motors so often. You can run a good brushless motor for years with only needing to oil the bearings every now and then.

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[fyrstormer]

Originally Posted by Waitwhatsthat?

So I just read this whole thread. First off it's very informative and I enjoy the sharing of knowledge that goes on. Secondly, I'd have to say, why not go brushless? It seams the ideal solution for your situation. You want to be able to run you rc's without having to teardown and maintain the motors so often. You can run a good brushless motor for years with only needing to oil the bearings every now and then.

For the same reason some people insist on running carburetors on their hot rod engines. I have plenty of brushless vehicles, but I like variety in my RC experiences.

- - -

That being said, something very strange is going on with my TorqueMaster Pro 550. It's running a custom-wound 11t armature, so it's definitely not a crawler motor, but it's in a RWD short course truck so there's a reason it has a low turn-count. I was running Reedy Plutonium brushes in it, as with all of my brushed motors, and because it's heavily-loaded compared to my other brushed motors, the Plutonium brushes were inflicting pretty significant wear on the comm. I decided it should be one of the first to test the Trinity 4403 brushes in, to see if they would be any kinder to the comm.

After a short on-road run to seat the brushes, I took it off-road for a full pack. Afterwards I saw this:



I've only once seen a commutator that badly burned, and it was in an old Tamiya motor that had really weak brush springs. (stiffening the springs solved the problem on that old Tamiya motor, but I don't know if that's what I need to do here as well.) After the run I saw temperatures around 180F at the brush hoods, and that was with an endbell cooling fan blowing on the endbell the entire run. Oh, and the brush shunts got so hot they melted their solder joints.

I lathed the comm, gave it a mirror-smooth finish, re-faced the brushes with a Fussy Brush tool from Holmes, cleaned everything thoroughly with aerosol electronics cleaner, reassembled the motor, touched-up the solder joints on the shunts, and reinstalled the motor in my Slash. I geared-down from 17/58 to 15/58, re-seated the brushes again, and took it for a second off-road run.

I haven't taken the motor apart yet to see what the damage is, but I know there's more damage. This time I saw temperatures around 208F at the brush hoods, even higher than before, and the brushes are nearly annihilated. The solder joints on the shunts are fine, no sign of melting this time, so I guess that's a silver lining. (pardon the pun.) The solder joints remaining intact suggests the maximum amperage being pushed through the motor has decreased, which is exactly what I'd expect from gearing-down, but that doesn't seem to have saved the brushes and commutator from a gruesome death.

I have no idea why this is happening. For the comm to be that badly burned, the brushes must be arcing like crazy, but for the Trinity 4403 brushes to be so badly worn after two runs they must be much softer than the Reedy Plutonium brushes I used to use. I thought softer brushes arc less? Do I have that backwards?

In particular, the positive brush is several millimeters shorter than the negative brush, and this isn't the first time this has happened. The Reedy Plutonium brushes had the same problem -- but strangely, only in this motor, not in any of my other motors. I tried swapping the springs, and after I replaced the brushes I replaced the springs completely, but the positive brush is still wearing significantly faster. This makes no sense to me, but it's only one problem among many.

Maybe I should go back to the Reedy Plutonium brushes and accept the higher comm wear. They seem to work better in all other respects, which is the opposite of what I expected based on the conversation in this thread.

[EddieO]

That arm is toast....Multiple issues I can see in the pic, first...the wire insulation is melting. When its flaking off like that, that far down from the tabs, the means the wire has gotten so hot that its melting it. It appears to have burned more along the top as well, though sometimes that can be brush dust.

On top of that, look closer at your own pictures of the comm. Those jagged edges on the slots, that is showing massive arching that is burning the edges. Its always gonna happen some, but that is beyond what is normal. The comm has also gotten so hot that the phenolic core reached its softening point and started to expand, which has now left you with extremely wide comm slots. You can also see where the copper has basically slid down a bit, exposing phenolic at the top.

So all the brushes burning up is because the arm has a short. It may still run, but it will run hot (which you have already stated temps well above whats acceptable) and will burn through brushes.

The positive brush wearing faster is normal, just like the negative getting pitted faster. This is a long standing arguement from way back. Big Jim used to get into massive flame wars on hobbytalk (may still be available), rccars.com (no longer available), and such about how power flowed through a motor. I am not taking either side, the arguement was one that was never settled...these scenarios worsen when the armature has an issue typically or something else is amplifying it (excessive timing, comm drops, etc)

At this point, any results of your brush testing doesn't really matter because the arm is toast and burning them up. Install a new armature and then test....you will probably find much different results.

Maybe go to a more safe gearing. I think the slash stock is like a 18/86, which is like 4.75...yer at like 3.29 with first gearing and now at like a 3.73...

Later EddieO

[fyrstormer]

Originally Posted by EddieO

That arm is toast....Multiple issues I can see in the pic, first...the wire insulation is melting. When its flaking off like that, that far down from the tabs, the means the wire has gotten so hot that its melting it. It appears to have burned more along the top as well, though sometimes that can be brush dust.

The grey on the windings near the comm is indeed brush dust. I took this picture before I cleaned anything; the grey disappeared after I cleaned the motor. Interestingly the windings *look* fine except for the peeling enamel near the solder joints -- no visible discoloration anywhere else.

Originally Posted by EddieO

On top of that, look closer at your own pictures of the comm. Those jagged edges on the slots, that is showing massive arching that is burning the edges. Its always gonna happen some, but that is beyond what is normal.

Oh, believe me, I noticed that straightaway. I was able to clean it up somewhat, but yes, there is erosion of the phenolic under the copper, so it will never really work right again.

Originally Posted by EddieO

The comm has also gotten so hot that the phenolic core reached its softening point and started to expand, which has now left you with extremely wide comm slots. You can also see where the copper has basically slid down a bit, exposing phenolic at the top.

I wish I could remember whether the phenolic has always stuck out from the end of the comm on this particular armature, but I didn't bother to pay attention to that particular detail when the armature was new.

Agreed about the phenolic swelling. I had issues with that early-on with this armature, which caused one of the pads to raise up and caused hugely uneven wear until I lathed the comm after a few runs. Unfortunately that problem doesn't seem to have settled-down.

Originally Posted by EddieO

So all the brushes burning up is because the arm has a short. It may still run, but it will run hot (which you have already stated temps well above whats acceptable) and will burn through brushes.

I tested each coil with my multimeter, but I don't see a meaningful difference in resistance between them. Is there some reason this wouldn't be an effective test?

Anyway, yes, the armature is shot to hell. After the second run the edges of the comm pads are so badly eroded there's no possible way to clean them up.

Originally Posted by EddieO

The positive brush wearing faster is normal, just like the negative getting pitted faster. This is a long standing arguement from way back. Big Jim used to get into massive flame wars on hobbytalk (may still be available), rccars.com (no longer available), and such about how power flowed through a motor. I am not taking either side, the arguement was one that was never settled...these scenarios worsen when the armature has an issue typically or something else is amplifying it (excessive timing, comm drops, etc)

Now that you mention it, I do remember seeing old discussions about positive brushes wearing faster. I guess I assumed people were noticing a pattern that didn't exist because they were subconsciously ignoring observations that didn't fit the pattern.

Thinking about it a bit...the positive brush is positively charged when the motor is running forward, obviously, so if there's any humidity in the air, electrolysis from the electricity passing between the brush and the comm will split the water molecules and the negatively-charged oxygen atoms will be attracted to the positive brush but repelled from the negative brush. That would cause the positive brush to oxidize more, which could explain why it wears faster.

Stll, it's odd that I've only ever noticed it with this specific motor.

Originally Posted by EddieO

At this point, any results of your brush testing doesn't really matter because the arm is toast and burning them up. Install a new armature and then test....you will probably find much different results.

I'm sad now.

Well...I was sad already, but I'm still sad.

Originally Posted by EddieO

Maybe go to a more safe gearing. I think the slash stock is like a 18/86, which is like 4.75...yer at like 3.29 with first gearing and now at like a 3.73...

Gearing is always a compromise, and sometimes a very difficult compromise to figure out. At 15/58, this truck has an on-road top speed of 30mph. I haven't checked what it's off-road top speed is. The ratio you mentioned is equivalent to 12/58, which would drop its on-road top speed to about 24mph; I'd rather not lose the extra speed, but I may have to. The reason I got this 550 motor was so I could run this truck off-road sometimes without having to worry about frying the motor, but I guess that didn't work out anyway.

[fyrstormer]

I pulled the armature out of my spare motor, installed it, and geared-down the truck to 13/58. I forgot about the square-root rule when calculating estimated speed changes from gearing changes; the speed didn't drop to 26mph, it dropped to 29mph -- much more reasonable. (the off-road top speed is 20mph.) The motor still got hot, but not as hot (max temp at the brush hoods was 180°F and max temp on the surface of the can was 140°F), and after a full pack the commutator looks fine. I think the serrations on the brush faces are focusing the heat (and wear) on too small of an area, but hopefully after a couple more runs that issue will go away.

[fyrstormer]

>_<

And now, after three runs, my spare armature is behaving like it has a dead coil. The motor makes a trilling sound when it accelerates and brakes, like it's accelerating and braking unevenly, the top speed of the truck on flat pavement has dropped by 20%, and the motor is suddenly running much cooler.

This is ridiculous. These armatures are $50 apiece!

[kongluc]

Are you running 2s or 3s? Not that i have any advice...just curious... I run 550's in my slash on 3s(closed endbell) and they seem to be asking for 4s...

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[fyrstormer]

2S. It looks like I could just barely jam two 2S packs into the battery tray, side by side, and if absolutely all else fails I can do that, but I'll have to replace the ESC to get 4S compatibility, and I'd rather not do that if I can help it. Also, if I went to 4S, the 11-turn motor would suddenly be WAAAY too fast, even with the lowest possible gearing, so I'd have to replace the motor too.

Anyway that wouldn't fix the dead coil in my spare motor.

[kongluc]

How fast did it normally go before you changed brushes?

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[fyrstormer]

32mph with 17/58 gearing. The motor got hot, but it didn't burn the comm like it did after I changed the brushes.

After replacing the damaged armature and the worn-out brushes, I geared it down to 13/58 and only lost 3mph, down to 29mph, and naturally it behaved much better off-road. However, after only a couple runs the spare armature appears to have a dead coil. As a result the speed has dropped to 23mph. I am not amused.

EDIT: I just gave the commutator another thorough inspection and cleaning, and the motor is still misbehaving. It has to be a dead coil at this point.

[kongluc]

Originally Posted by fyrstormer

32mph with 17/58 gearing. The motor got hot, but it didn't burn the comm like it did after I changed the brushes.

After replacing the damaged armature and the worn-out brushes, I geared it down to 13/58 and only lost 3mph, down to 29mph, and naturally it behaved much better off-road. However, after only a couple runs the spare armature appears to have a dead coil. As a result the speed has dropped to 23mph. I am not amused.

EDIT: I just gave the commutator another thorough inspection and cleaning, and the motor is still misbehaving. It has to be a dead coil at this point.

That's not much better performance than a regular titan 12t....and it's cheaper...they're rated for 35 on 2s with stock gearing...i got a 21t and it's not even geared that high...and goes faster but i'm running 3s...and more offroad torque 140* temps after about a 45 min run...so i could gear up and go faster, or drop a few teeth and go 4s and go faster, or just buy a bigger motor...they're all cheaper. I can buy at least 3 or more for the price of that motor. I was gonna get one but im not now...I've had the same titan 21t for 3yrs

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[fyrstormer]

The Titan 12T can't come close to touching a TorqueMaster Pro 550. My truck may have only gone 32mph, but it was gearing-limited, not power-limited. It topped-out on flat pavement in maybe 3 seconds or so.

If I were driving on-road only, the Titan 12T would be a viable option, but it lacks the torque-generating capacity of a high-quality rebuildable motor with fancy magnets, and that makes it unsuitable for driving in grass.

[kongluc]

Originally Posted by fyrstormer

The Titan 12T can't come close to touching a TorqueMaster Pro 550. My truck may have only gone 32mph, but it was gearing-limited, not power-limited. It topped-out on flat pavement in maybe 3 seconds or so.

If I were driving on-road only, the Titan 12T would be a viable option, but it lacks the torque-generating capacity of a high-quality rebuildable motor with fancy magnets, and that makes it unsuitable for driving in grass.

HH only recommends running a 10 or 11th pinion with 58th spur in a slash, I've been tempted to try one but being rpm ratings for that motor are like 20,000...not fast enough...and seems a little anemic...the 21t on the other hand makes 26 or 27,000 rpm(which is perplexing that the higher turn motor would produce more rpm) and is 3s compatible but gearing is still "limited"...but like you said..your armatures cost $50...must be nice

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[fyrstormer]

A 21-turn TMP550 would be slow on 2S (I have one in my Wraith and it tops-out at 14mph), but the ones I ordered for my Slash have 11-turn armatures. Unfortunately I over-geared one and the other appears to be defective.

[kongluc]

Originally Posted by fyrstormer

A 21-turn TMP550 would be slow on 2S (I have one in my Wraith and it tops-out at 14mph), but the ones I ordered for my Slash have 11-turn armatures. Unfortunately I over-geared one and the other appears to be defective.

So you have a custom made torque master right? I've been tryin to call for about 3weeks to ask about a custom motor...left bout 5 messages still no-one has returned my call...to many specifics to be trying to email about from my phone...

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[fyrstormer]

They're a small operation and they're busy pretty much constantly. Also, they build motors for military drones as I recall, so they're not *just* a hobbyist business. Send an email and wait your turn, that's all I can advise.

Team Brood also builds custom motors. Maybe contact both companies and see who gets back to you first.

[kongluc]

Originally Posted by fyrstormer

They're a small operation and they're busy pretty much constantly. Also, they build motors for military drones as I recall, so they're not *just* a hobbyist business. Send an email and wait your turn, that's all I can advise.

Team Brood also builds custom motors. Maybe contact both companies and see who gets back to you first.

I already talk to the owner of team brood...do they make 550's we only talked about 540's... He gave me some very informative advice...great guy!

Talked with him again..you might like his new offering of 550's

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[JohnRobHolmes]

I'll get a new arm your way for further testing. Just need to get it into the rotation of manufacturing since it was a custom.

Kongluc, we typically shy away from most custom work for logistical and cost reasons. Custom wind isn't a big deal, but we don't have customs beyond what the website offers. Our lack of options reflect what works best. Start changing it, and the end product suffers. If you can't convey what you want in an email, I can almost guarantee we are going to refuse the work.

[kongluc]

Originally Posted by JohnRobHolmes

I'll get a new arm your way for further testing. Just need to get it into the rotation of manufacturing since it was a custom.

Kongluc, we typically shy away from most custom work for logistical and cost reasons. Custom wind isn't a big deal, but we don't have customs beyond what the website offers. Our lack of options reflect what works best. Start changing it, and the end product suffers. If you can't convey what you want in an email, I can almost guarantee we are going to refuse the work.

It's more me understanding what you have that will work not making a completely custom wind or anything

Like being capable of a higher load with out reducing rpm or voltage...58/11 is not my cup of tea...i found a closed endbell can that handles 4s 35,000rpm starting gear ratio is 58/20...see what im sayin?

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