Fisher Price Brush Arching??

[Andy4Hawks]

We've just got our transmissions up and running tonight. We're using the Fisher Price motors (teamed with the drills) and we noticed when we powered it tonight that the Fisher Price motors displays a fair amount of arcing under a light load from the brushes. We ran it for them for a few minutes, and it doesn't seem to be a problem but we are curious if others have noticed this?

[aaronbr28040]

We have hooked up our fisher prices under no load and we did not notice any arcing at all. I dont think that you should be noticing arcing unless something is wrong. If I get a chance I will check the motors with a load in the morning to see if ours arc. Good luck with motor troubles (my team knows how that is right now, our drill motors have a really bad wobble when the left hand threaded bolt is screwed into the coupler and gearbox).
-Aaron

[Rickertsen2]

I don't know about arching. That sounds a bit unusual, but most motors arc a little bit. Ahh who am i to complain about spellellining. Is it both you motors or jsut one? If it is both of them then what you are seing is pretty normal.

[kiracofe8]

Originally Posted by Andy4Hawks

We've just got our transmissions up and running tonight. We're using the Fisher Price motors (teamed with the drills) and we noticed when we powered it tonight that the Fisher Price motors displays a fair amount of arcing under a light load from the brushes. We ran it for them for a few minutes, and it doesn't seem to be a problem but we are curious if others have noticed this?

I have seen a significant amount of arcing on the FPs (the can practically glows) but only under heavy load (near stall). The only recommendation that I have is to put an ammeter on the motors and make sure that what you think is a light load is really a light load. If they are drawing 20 or 30 A, you may have some significant side loads or misalignment.

[Al Skierkiewicz]

Andy,
Arcing in brush type motors is normal. It is occurs when the brush just leaves a commutator segment, opening a winding in the motor. The collapsing magnetic field generates a high voltage which jumps across the gap from the commutator to the brush. At high RPM and high loads, the arcing is at it's worst. As the motor wears in, the arcing also grows worse as the arc is able to jump across (through?) all the debris built up on the commutator and brush.

[shawny963]

We have been having these problems too and a member of our electrical team pointed out a problem with the fp's provided to FIRST. It seems the brushes, in every fp we have seen, are turned 90 degrees. They are contoured incorrectly to the commutator. This results in low contact and an ineffecient motor with a shorter life span. This can be fixed with a simple trick from the rc racing community. It is questionable as to whether this is legal under FIRSTs rules on motor modifications. Anyhow, if anyone would like i can put you in contact with our electrical guy that can explain how to fix in a matter of minutes. Just email me at shawny963@wi.rr.com.

[Al Skierkiewicz]

Originally Posted by shawny963

It seems the brushes, in every fp we have seen, are turned 90 degrees. They are contoured incorrectly to the commutator.

Shawn,
I will check our motors and get back to you on this one. Nice find on your motors though! Are you able to make the change?

[Joe Ross]

Originally Posted by shawny963

This can be fixed with a simple trick from the rc racing community. It is questionable as to whether this is legal under FIRSTs rules on motor modifications.

Shawn, I do not beleive that this would be allowed under <R62>. However, if this is a real problem, then FIRST may allow it, but you would have to ask in the Q/A forums first.

[shawny963]

Joe, by logic this would be allowed under that ruling. This break in process does occur on its own, you can merely speed it up using our method. So we really arent modifying the motor, we dont even open it.

[Al Skierkiewicz]

I have checked our motors and it appears that that the brushes are turned 90 degrees when looking from the outside. However, one of ours burned up after a continuous stall condition, so I disassembled the motor. I found that the brushes are actually contoured in two directions. I am guessing this allows the brush to be used in a variety of different motors. (i.e. a production efficient design) However, in checking past year's motors, they also have the exact same brush design. The conclusion then is that the brushes are not the cause of the failures encountered. Please remember that this year's motor is different than last year's. Please see Paul Copioli's motor report from earlier this month for the exact data.