Clockwork toys do not require electricity, as the motion is caused by simple stored energy. Regardless of the ultimate function of the contraption, every clockwork device works in essentially the same way. Clockwork toys consist of four basic parts: key, spring, gears and mechanism.
In a clockwork toy, the key is the lever or other trigger used to operate the device. The key is attached to a spring inside the device. The spring stores the energy used to make the toy move or perform its other functions. The bigger and sturdier the spring, the more energy it can hold. The more the key is wound, the more the spring tightens, storing more energy.
The spring is connected to a series of interlocking gears. Once the key is released, the gears begin to turn. One gear turns another, which turns another. These turn the mechanism, the part that is supposed to move, and the toy starts to perform its function. In a wind-up car, the wheels are the mechanism. Most clockwork toys generate rotational power; they cause wheels to move. Even in a wind-up robot that appears to walk, the walking motion is typically generated by wheels using rotational power inside the robot's legs.