The hypocycloid mechanism is used to make a compact, simple gear box that reduces rotational speed. In the case of this animation the reduction is 7:1. Follow one of the lobes of the six pointed rotor with your eye and see how it advances one notch anticlockwise for each rotation of the blue rotor. By adding two similar mechanisms back to back it is possible to multiply up the the gear reduction ratio

The blue piece is an off-centre drive shaft connected to the main drive. The output of the drive would be from the front.