Nico found an old camera in our junk drawer - I told him to take it apart and look around. He and Ryan had a hey day. motors and batteries and gears and wires and things I don't know the names of.
They used the motor and gears in the old camera in combination with a AA battery and some "tiny jumper cables" to make gears and pinwheels spin. This went on for a good hour and 1/2.