Can anyone explain the need for the metal jacket found on the Drill and FP motors? Can it be removed with no effect to motor performance?
The extra metal case is there to help strengthen the magnetic field in the path of the armature. It helps increase the output of the motors by a small but significant amount (10% is a good rule of thumb as I recall).
The normal case of the motor is not sufficient for the Mabuchi and the Johnson Electric motors to direct all the magnetic flux from the permanent magnets toward the armature. This extra magnetic material around the outside makes the PM magnets more effective. There is no benefit to having such extra pieces on motor housings that are thicker (such as all the other motors in the kit).
I may be wrong but I think these bits of metal are called flux yokes – I was sure until I started to type this message and I got cold feet. Some other motor guru help me out here.
You can take them off if you like, but your are giving up motor performance if you do.
I can tell you that you aren’t likely to see a Chief Delphi robot without them any time soon