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Old 11-28-2008, 10:42 PM   #1
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Default How to determine lifespan of commutator

Simple question for the brushed motor experts out there, how can I determine the condition and lifespan of a used brushed motor ?

Meaning how can I determine how many more runs does the commutator have or how much longer can I keep on running the armature ?

Is there an indication that the comm has finished?
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Old 11-28-2008, 10:54 PM   #2
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i haven't run brushed, but a good rule of thumb was that once the diameter gets down to .270" it's pretty much toast. most motors start out around .300" and if you cut every 2~3 runs you'll only need to cut about .001" off each time.
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Old 11-29-2008, 12:32 AM   #3
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.270" for laydown brushes...standup will be smaller, closer to .240" or so. Technically the motor should still run as long as the brushes are touching the comm, but performance will be substantially reduced once it gets below those numbers.

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Old 11-29-2008, 01:45 AM   #4
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I have used one motor right down until the metal came off the comm as I cut it

I don't reccomend it though, I was lucky not to damage my cutting bit

Anyone remember the stock 36deg race prep motors back in their day? H cut brushes, sealed can but kept going for ages!

To a certain degree, the lifespan depends on how often you are cutting the comm and how hard it's being worked.

From new i've had a stock motor last about 6 months, but I couldn't tell you how many minutes use the motor had seen in total.
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Old 11-29-2008, 04:02 AM   #5
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Originally Posted by tc3team View Post
I have used one motor right down until the metal came off the comm as I cut it

I don't reccomend it though, I was lucky not to damage my cutting bit

Anyone remember the stock 36deg race prep motors back in their day? H cut brushes, sealed can but kept going for ages!

To a certain degree, the lifespan depends on how often you are cutting the comm and how hard it's being worked.

From new i've had a stock motor last about 6 months, but I couldn't tell you how many minutes use the motor had seen in total.
I'm not particularly keen on knowing how long a motor will last as it depends on how much we use them... the matter now is, is there an indication that the motor is at the end of its lifespan?

Like those post up there that states the diameter of the comm reduces up to a certain sizes... I can definitely use that indication as a guide to my motor's lifespan...

But is there other kind of indication ? Is it possible to use the indication of the gap in between every comm section ? I've read somewhere that if the gap between the 3 comm section is no longer visible, that shows that the motor is no longer able to be use as the diameter of the comm has finished... is this true ?
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Old 11-29-2008, 04:36 AM   #6
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Usually you can tell when the motor is almost at the end of its life by looking inbetween the comm segments and seeing how much copper is left on it.

There is no set way of working out how many turns it will do before the copper peels off and the comm is dead. There are several things to factor in, and these would include how its looked after between use, the gearing used and probably even how much current is passing though it.

hth
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Old 11-29-2008, 11:52 AM   #7
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I still use brushed motors as i have still got boxes of them left, now what i have always done is run the motor until i start to see a noticeable drop off in performance i.e my lap times are starting to drop, if a rebuild(skim,new brushes, mag zap rest timing etc.) doesn't sort this out then it get turned into a paper weight. Using this method i have had motors that literally run till the com comes off whilst running, sometimes the motors only run down to .280" and then get binned or just used for practice. If your just racing for fun then run it till it dies!

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Old 11-29-2008, 01:52 PM   #8
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Quote:
Originally Posted by Tpg racer View Post
Is it possible to use the indication of the gap in between every comm section ? I've read somewhere that if the gap between the 3 comm section is no longer visible, that shows that the motor is no longer able to be use as the diameter of the comm has finished... is this true ?
The gaps between the comm segments will not be any indication of wear. The gaps are going to be there, and remain pretty much constant right up unto the motor dies.

The .270" diameter advice is sound. I've run them maybe a bit smaller, but any time you try to get one more cut out of a comm that has gotten down to .270 or smaller, you're taking the risk of having it peel apart during the cut or the next time it runs. You might get to run motors down to .265 if you're lucky, but once I see the motor gets to .270, I won't do any more cuts on it. If the comm decides to peel in the lathe, most times it takes your diamond bit with it.
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Old 11-29-2008, 02:35 PM   #9
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Quote:
The .270" diameter advice is sound.
My experience seconds this.

I've cut a LOT of stock motor arm comms... once it's at .270 it's either time for a new arm or a whole new motor.

Brushless is the way of the future for sure but for the time being, I've just come away from over 3.5 years not racing to race a Mabuchi in a local vintage trans am-style control tire/body/motor series using tc chassis. It's a blast! and I don't have to eff with the motor (although that was an enjoyable part of the SoCal R/C Raceway club racing ritual...)
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Old 11-29-2008, 02:45 PM   #10
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Quote:
Originally Posted by SQUIER
My experience seconds this.....
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Old 11-29-2008, 02:53 PM   #11
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^ Don't you have some 1/8 scale shocks to rebuild?





Quote:
RussB

i haven't run brushed, but a good rule of thumb was that once the diameter gets down to .270" it's pretty much toast. most motors start out around .300" and if you cut every 2~3 runs you'll only need to cut about .001" off each time.
Quote:
Trips

The .270" diameter advice is sound.
Acutally, my experience thirds this. rofl.
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Old 11-30-2008, 02:57 AM   #12
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Quote:
Originally Posted by SQUIER View Post
^ Don't you have some 1/8 scale shocks to rebuild?







Acutally, my experience thirds this. rofl.
I suppose I'll fourth this....is it good posting etiquette to fourth an original post with the preceding seconding and thirding posts between

Quote:
I still use brushed motors as i have still got boxes of them left, now what i have always done is run the motor until i start to see a noticeable drop off in performance i.e my lap times are starting to drop, if a rebuild(skim,new brushes, mag zap rest timing etc.) doesn't sort this out then it get turned into a paper weight. Using this method i have had motors that literally run till the com comes off whilst running, sometimes the motors only run down to .280" and then get binned or just used for practice. If your just racing for fun then run it till it dies!

steve
Good info for you here as well.
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