Leonardo's self-propelled cart
The machine is powered by two symmetric springs. While one spring would be enough to move the device, two symmetric springs probably looked like a more "logically perfect" solution. Leonardo had been well aware that the powering force provided by the springs drops significantly they unwind. In order to deliver smooth and stable motion, the machine features a balance wheel, as used in clocks. The control mechanism is quite complex and allows it to follow a pre-programmed path automatically. The machine also features a mechanism similar to a differential that also allows the turning angle to be set.