Today's New York Times has a feature about how Italian scientists built a working model of "L'automobile di Leonard da Vinci," a self-propelled vehicle powered by a motor made of coiled springs. Pushing the machine backwards or turning the wheels counterclockwise would wind up the motors like a toy car that you pull back and then release. The car has no seats and was designed as a special effects prop for a theatrical production. It's currently on display at the Institute and Museum for the History of Science in Florence.
"While a scale model of the Da Vinci-mobile has been observed... to move, change direction, start and stop - thus proving that the design works - the full-size model weighing hundreds of pounds is seen, even by its own builders, as too hazardous to set loose on an unsuspecting public."Link (free NYT reg. required)