Whether they walk, roll, hop, spin or play the drums, all wind-up toys operate on the same basic mechanism. In the age before cheap batteries, these simple mechanical devices were the most common moving toys for children. Wind-up toys are still a favorite with kids, while vintage tin toys are sought after by collectors.
Winding the Toy
The central feature of any wind-up toy is a key or crank connected to a thin, coiled metal strip called the mainspring. The spring normally rests in an unwound position, but as the key turns, it gets tighter and tighter. Once it is fully wound, the spring is full of potential energy, ready to be released to power the toy. A bend in the end of the spring hooks into a gear next to the wheel to stop the spring from unwinding immediately.
Releasing Potential Energy
In some wind-up toys, a mechanism stops the spring from unwinding until a button is pushed or a switch flipped. In others, the spring starts to uncoil as soon as the key is released. Either way, the uncoiling spring turns a gear, which rotates other gears or spins axles, making the toy roll forward, spin, flip or buzz.
Although the basic principles of wind-up toys are the same, there are some variations in design. Some wind-up toys have a small rotating knob rather than a key, while in others, part of the actual toy turns. Pull-back toys rely on the same principle as wind-up toys; the spring winds when the toy's wheels are rotated backward.
What Can Go Wrong
One reason working vintage wind-up toys are valuable is that wind-up mechanisms aren't known for durability. The most common problem is the connection between the spring and the gear snapping after repeated use. When this occurs, the spring simply unwinds freely after winding without turning the gears. It's also possible for the connection between the key and the spring to fail; when this happens, the key simply rotates in its socket without tightening the spring at all.