Hypocycloidal gearing

Hypocycloidal gearing is like playing with toy trains!

Imagine you have a big train track, and a little train track inside of it. The big train track has a really big circle, and the little train track has a smaller circle inside it. The little train track spins around inside the big train track, and it has these little teeth on it that fit with the big train track's teeth.

When the little train track spins, it moves the big train track too! But the way it moves is really cool. The little train track goes around the big circle once for every few times it goes around the little circle. But because the big track has a lot more teeth than the little track, it makes the little track spin faster than it's going around the big track.

So, each time the little track goes around the big track, it's actually making the big track spin multiple times! This can be really useful for making machines run smoothly and efficiently.