BottleCapWheel

Build a robot wheel with this part. You need a plastic cap from a juice or milk bottle, double sided tape and a screw to mount the wheel on the motor. The design allows to use a wheel encoder based on the ITR8307 optocoupler for rough control of the motor movement.
In order to get more grip a small piece of an old bicycle tube can be put on the outside of the bottle cap. Double side tape might help to keep the rubber in place.