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Old Feb 17, 2012, 12:57 AM
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Joined Mar 2011
97 Posts
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Motor Brushes and Commutator run out in short time?

My friends why motor brushes and commutator run out in short time?guarantee is about 2 years but some brushes of motors are run out in short time. Commutator run out too. What can be reason of this?
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Old Feb 17, 2012, 08:18 PM
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Chattanooga, Tennessee, United States
Joined May 2003
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Typically too much voltage and/or too many amps... arcing burns pits in the comm, and destroys the brushes quickly.
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Old Feb 21, 2012, 01:52 AM
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how can i realize that motor takes too much voltage and too many ampers?
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Old Feb 21, 2012, 10:28 AM
Jack
USA, ME, Ellsworth
Joined May 2008
17,218 Posts
Some years back a grizzled old motor re-builder I talked to explained a little to me about the needs for re-cutting commutators. He said that all of the current is focused on the leading edges of the brush and the commutator segment as they "meet" with the motor running. And that there is some inevitable spark erosion as that happens.

We were really discussing the process of using a lathe and commutator recutting tool and how using those revealed new clean surfaces and sharp corners on the commutator. That and replacing the brushes with new brushes took the motor back to start anew on the process of wearing itself out again...

So when I first read of brushless motors and their use in RC to replace brushed motors, it was obvious to me what one of the immediate advantages would be for the brushless motors.

Beyond all of that, brushes were available in various grades of hard and soft and that altered the wear and tear on the commutator too. And then the springs that apply pressure to the brushes were another variable too and that also impacted on both how well motors ran and for how long.

I still have a small soft abrasive stick that I got from that gentleman. He explained how I could use that to "seat" or "bed in" newly installed brushes to get the best contact with the commutator. And could even use them to "freshen up" those surfaces for a short term recovery between the re-cutting cycles.

Just another of the fascinating details of how things work and are used and repaired. There is so much to learn...

Jack
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Last edited by jackerbes; Feb 21, 2012 at 10:35 AM.
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