shiming motors

Old 08-29-2004, 12:59 PM
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Default shiming motors

how do you shim a motor
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Old 08-29-2004, 01:17 PM
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you just add shims to each pole of the armature intill theirs not to much play in it but just enough
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Old 08-29-2004, 01:18 PM
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make sure you get the brushes in the centre of teh armature also..i have seena lot of peoples motors with the brushes right at the bottom (to many shims on teh bottom) or the brushes right at the top of the motor (to many shims at the top)
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Old 08-29-2004, 01:33 PM
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Try assembling the motor with no brushes, push the arm and let the magnetic field bring it back, then pull the arm the opposite way, it should be centered in the magnetic field and have equal movement in both directions. I usually set it for a total of .02" movement..
-Wayne
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Old 08-29-2004, 04:44 PM
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the proper way to do it is on a dyno
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Old 08-29-2004, 08:48 PM
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1.remove all shims and brushes but leave the insulater (make sure its all the way in ) on and screw the endbell back on

2hold the motor horizontaly and spin the armature in dir. of rotation and it should stop at the "Neutral pos." then pull the shaft towards the can side and feel the gap to place porper shims in between and repeat 1 2 untill theres no space between, finally add washers to endbell side of armature and leave just veeery small play so that it doesnt bind.

hope this helps and please correct if im wrong
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Old 08-29-2004, 09:05 PM
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HeY!!!


No offense to al those who do all this but i sorta think it's over rated i'd just play w/ brushes and springs mainly, as long as it aint all the way at bottom of comm your all good then. and also play w/ the setup for your car, bcuz u could have fastest motor, but worst car.
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Old 08-30-2004, 07:03 AM
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whether it matters to you or not, the most logical way to shim a motor is as wayne or rc_square pointed out. why?

because when the motor is energized, the armature is pulled to it's magnetic center. this is the same as where it sits at rest. it isn't pulled very hard to this center, and dyno pulls won't change if you miss the center, but if you are going to shim, do it right. let the motor spin where it won't be pushed up against either bushing unless you give it some extraneous forces (ie, centripetal, gears, impacts, etc.)

there is still some speculation about how large of a gap to leave. if a large gap is beneficial, i suspect it has to do with periodically letting the armature move to a spot were there is fresh comutator contacting the brushes. this is only something that can really occur when the serrations are still present on the brush. or a large gap works better if you miss the gap altogether when shimming tighter.

the above has nothing to do with the position of the brushes on the com. that is dictated by the relative placement of the magents in the can. and where the center of the stack is relative to the comutator. that is the reason every motor will get shimmed differently.
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Old 08-30-2004, 07:36 AM
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i just finished playing with a bunch of motors and shimming them and there is definitely a sweet spot where the motor works best, not sure if its where the magnets pull the arm when its stationary but there is a difference. one thing i did notice that the arm moved as the motor spooled up initially then moved back.



as for the proper gap i will have a play with that aswell to see what happens. i will let you know what happens.
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Old 08-30-2004, 09:59 AM
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Shimming the arm in the center of the magnetic field is the best way to do it. There are some instances, with some motors that more power can be made by shimming the arm out of the field, but unless you know why, or when to do that, is just going to be a waist of your time trying to find that situation, especially on the dyno.

Shimming the brushes in the center of the comm is very pointless. If you cut your comm straight, then there is no difference in where the brushes ride on the comm.
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Old 08-30-2004, 07:44 PM
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yes it does not make a diffrence where the brushes ride on the comm as long as they make full contact with it your good to go!
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