What you see above is a Flash animation of an Oldham coupling. You can change the rotation speed or direction of the rotation. I made a model of an Oldham coupling which can be seen in the video shown below.
Below is the 3D animation of Oldham coupling I made by using Sketchup.
Below is exploded view of an Oldham Coupling.
An Oldham coupler is a method to transfer torque between two parallel but not collinear shafts. It has three discs, one coupled to the input, one coupled to the output, and a middle disc that is joined to the first two by tongue and groove. The tongue and groove on one side is perpendicular to the tongue and groove on the other. Often springs are used to reduce backlash of the mechanism. The coupler is much more compact than, for example, two universal joints.
The coupler is named for John Oldham who invented it in Ireland, in 1820, to solve a paddle placement problem in a steamship design. The middle disc rotates around its center at the same speed as the input and output shafts. Its center traces a circular orbit, twice per rotation, around the midpoint between input and output shafts.