# Motor question



## J_Bone (Nov 17, 2004)

I have a Return of the Monster quad magnet and a Fantom quad magnet motors.
Now, when I put a pinion gear on and spin it, it spins to good and when it comes to a stop, it bobbles. It just doesn't stop. I checked it with a brand new motor and it just stops. 
Now are the magnets done? Why do they wobble or bobble to a stop when I spin it?? Never seen this before.

Thanks,


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## smojoe (May 17, 2002)

I am confused on the problem. Does the motor spin more when you spin it; as in there is less resistance on the arm? are the brushes making good contact with the comm?


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## J_Bone (Nov 17, 2004)

I spin it by hand with a pinion gear on it. It seems to have more rotations than the brand new one. 

The brushes are brand new with new springs. The COMM is freshly cut and the arm is seated and shimmed on both ends. I rebuilt it just like all the other motors I have. 
More details..hhmmm I can't think of any thing else. It's one detail.

OK, so spin a motor. Watch the arm inside the can. And when the arm stops it's rotation it will bobble (rock back and forth the stopping point) to a stop. The rotation axis will bobble to a stop, not side to side. When I spin my other motors they all come to a stop. They don't bobble when they stop. Hope that helps.

With all the info on this web site I thought more people would be able to help.

Thanks


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## Guest (Dec 15, 2004)

If armature rotates freely or longer it usually an indication that magnetic has lost it's strength. Normally you can also tell the difference in magnet strength when removing or installing the armature - there is good resistance when removing it and during installation magnets will pull it back into can. The wobbling probably is due to the bushings also being worn or became misaligned.
While Epic motors are good for racing, the one weak area has always seemed to be the magnets loosing their strength sooner than some other brands.


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## bojo (May 6, 2002)

If the motor runs good and it rocks when it stops that means you are shim pefect.you like to see that


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## Luckyman4 (Sep 26, 2001)

Yep, most likely the magnets have lost some of their oomph ... possibly from the motor getting too hot at some time. Or the motor spent some time in contact with other metal when out of the car. You need to get the motor's mags rezapped or buy a new can.


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## tfrahm (Nov 14, 1998)

I'm with bojo on this one...

A new motor will sometimes be shimmed wrong (either off center or too tight), creating friction. The armature will not rock/wobble when you spin it because of that friction.. A new motor will also normally have more bind/friction in the bushings, as they are usually not broken in and/or seated properly yet. Both things contribute to a lack of rocking or "wobble" when the armature is spun by hand...

A broken in (not "worn out") motor will have been properly shimmed and will have the bushings free (but not slopply). This will allow the armature to rotate freely with minimal bind or friction. The wobble/rocking motion as the armature spins to a stop is a GOOD thing (within reason), because of some basic laws of physics. An object in motion tends to remain in motion, so when you spin the armature, and it prepares to stop, it will tend to rotate past a point of magnetic balance (due to it's momentum), then rock/wobble back toward that magnetic balance point... The interaction of angular momentum (spinning/rocking) and magnetic forces will cause a dampened back and forth oscillation that we see as that rocking/wobbling motion. Of course, this is all more visible when the brushes are removed to minimize friction, but it is always there...

Of course, as John (Luckyman) noted, the magnets may have lost some of their strength, which can change the visible wobble action. The simplest way for me to "feel" the magnetic strength is to SLOWLY rotate the armature in the assembled motor, and feel how firm the "thunk" is as each pole of the armature cogs from one magneticly neutral point to the next. Of course, you cannot compare traditional 2-magnet motors with the 4-magnet motors, as the cogging is much less obvious in the quad magnet cans.


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## J_Bone (Nov 17, 2004)

Awsome, THANK YOU! :thumbsup: 
I did spin it to feel how strong the magnets are and they seem a little weak, even for a quad magnet can. Maybe that's why the wobble is more noticable now. 
I'm gonna try to find some one out here who can zap the magnets.

thanks again!


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## bojo (May 6, 2002)

If you cant fine someone to do it I can just pay shipping both ways no charge for zapping them.


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## J_Bone (Nov 17, 2004)

Thanks!! I might have to take you you up on that. 
I will keep looking for a while. There is a new motor builder out here in AZ and I'm waiting for a reply.


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