This is a still from an animation I did for work. The gears were built in the spline room and are several pieces -- each tooth is rotated and duplicated around the outside of the disk it's mounted on. The disk has the ridges and the center pin, too. The center pin doesn't rotate, but the disk does.

Rotations of the gears was pretty simple to calculate based on the number of teeth and the rotational speed I wanted to convey. It's a pretty detailed animation; I'll try to post it at my home site tonight....