View Full Version : How to properly shim an armature

2009.01.15, 03:38 PM
I have been experimenting with tranfaringan armature from a non BB case to a BB case. I noticed there were small black spacers on either end of the shaft. although the motor armature has these shims, once assembled the motor shaft stiff has play.

I noticed that the stock kyosho motors allot you to "pull" the shaft where as the atomic motors allow you to "push" the shaft. What determines which way to shim a MOD motor, and how do you know where to place the shims and how many to place.


2009.01.15, 06:59 PM
The shims are for centering the brushes in the commutator. One reason the Kyosho motors have a lot of "play" is they use bushings, not ball-bearings. So to reduce the chance of binding, and keep the armature free and smooth while spinning, there is quite a bit of play. Whether the armature has play when you "push" or "pull" does not matter, this is just due to the way the magnets pull on the armature inside.
When shimming an armature, the two main points are:
1.) Try to get the brushes to touch the "sweet spot" on the comm, not too close to the edge and not too close to the windings, and
2.) Allow for a little bit of "push/pull" play with the armature when the motor is assembled. This will keep pressure off the can's bearings or bushings and allow the armature to spin its easiest. Only a tiny bit of play is necessary for BB cans, 0.3mm-1mm is fine. If the armature just barely fits in a motor can, then 0.1mm is still OK. To keep the arm from binding is the main goal.

2009.01.15, 10:30 PM
thanks for the response felix,
so basically i can shim the front or back ?

I removed some shims tonight not knowing anything (I didnt have any play before). My motor was running very very hot, but now that it has some play it was much cooler.

I am going to take it apart once more and shim it right.

2009.01.15, 11:23 PM
Sounds like the armature was binding some before you removed some shims. Glad your motor is running better.:)
Yes, you can shim either side; If you can get the brushes to sit right in the center of the comm, using one shim on both ends, then that is what I recommend. This is because the shims on either side of the armature will act as a spacer that only contacts the inner race of the can's ball bearings, which will reduce the chance of the armature binding up against the ball bearings' metal shields.
If you cannot fit a shim on both ends of the arm without getting the necessary back&forth "play" with the armarure inside the motor can, then I would focus on making sure you have some play, and that the brushes sit on/near the comm's center.

2009.01.16, 10:22 AM
You should ideally have something at either end of the shaft that is SMALLER than the outer race of the can's bearing so it doesn't rub against the race and introduce friction. If you can't get one shim at either end, the small brass piece on the winding end of the arm can be moved slightly to get you the extra clearance. Don't damage the outside surface of it though...


2009.01.16, 10:58 AM
great input eveyone. thanks =)
I am waiting on a new can