Brushmobile

...or perhaps "dentipede", since it is driven by toothbrushes.

Al and Sim hypothesised that with such a vehicle one could control both speed and direction with a single degree of freedom. The vehicle rolls on unpowered wheels (from Ikea set of drawers). 2 toothbrushes (Colgate) are vibrated against the ground powered by an unbalanced electric motor (Ann Summers). By controlling the voltage supply, the speed of vibration is varied. Both brushes are constrained to vibrate at the same frequency, and both are angled slightly backwards, pushing the vehicle forwards . However they're also angled slightly outwards in opposite directions. With slightly different inertias the toothbrushes will have different resonant frequencies. At a certain frequency, one toothbrush will be vibrating more strongly and transferring more energy to the ground, pushing the vehicle round in one direction. With the motor running slightly faster the other toothbrush will then get closer to its resonant frequency and the vehicle will be driven in the opposite direction. This far we just about got the theory into action - see it sort of working here:

http://www.youtube.com/watch?v=Wk8Pp7XDtj8

Crank up the motor further and in theory the range of directions will repeat with the toothbrushes hitting higher harmonics, all the time the vehicle will be being driven faster along the ground. So it would be as if there were a number of different gears, within each of which there would be a range of directions available. The beast we created though barely got through the first cycle before the motor maxed out. But we think there's potential there, for a very rainy day.

Someone was saying that brushed motion was used in some toys in the 50's - more info anyone?