Pop up crankshaft

The use of books for education (although becoming outdated) is a very important aspect of them. This mechanism inside a mechanism (a meta-mechanism, a metachanism) provides a way to learn about crankshafts, which are important to many machines. this particular one is set up in a similar way to the one in a car's engine. You can turn it with the gear on the right. Both halves of the crankshaft are connected with a universal joint which enables them to both turn simultaneously despite being at an angle to each other.