Hah, Allan beat me to the punch, but I was going to suggest just that: hacking an old motor armature and providing power to it as needed through the existing commutator. Seems to me if you energize the teeth in the proper sequence(like a stepper) it would run along the floor. Plus they are already rounded for you!
My thoughts would be that if the tooth that is in most contact with the floor is energized in such a way that the north pole faced the floor, then energizing the adjacent tooth, in the direction of intended travel, to have the south pole facing the floor, would step a smidge in that direction so that both teeth`s pull meets in the middle.
Admittedly, I just had surgery hours ago, and the meds may be clouding my thoughts( even more than normal :-))
But I love your outside the box thinking!
Bc