Sorry, I know this post is almost a decade old but I can't believe no one has said anything....I've had coreless motors apart and they are nothing like a servo motor. They are a conventional brushed motor with a variation on the windings. The windings form a cup on the armature which rotates around the fixed permanent magnets attached to the end of the case. There are brushes contacting the commutator as in a conventionally wound brushed motor. This light weight winding (with no ferrous core...hence the name) is quick to start up and stop. (Centering has to do with the output which is after the gear train and determined by the servo electronics; amplifier and servo potentiometer.)

Jerel