Gearless Combat Robot Drive - Ask Aaron

Friction drive The shaft of the motor presses directly against the surface of the tire and relies on friction to transmit power to the wheel. You will get some slippage, but if your motor has a 2mm to 3mm shaft the reduction ratio works out about right.

Tiny wheels If direct-drive for a normal sized wheel isn't practical, how about a really tiny wheel? Mount a very small wheel to the motor shaft and mount the motor at an angle to put the wheel in contact with the floor. Unconventional, but a successful antweight full-body spinner used this method as a space and weight-saving measure. The 'wheels' could be something as simple as a small plumbing washer, a short length of small diameter rubber tubing, or even a few layers of electrical tape wound around the shaft. They won't last long, but they're easy to replace.