I'm working on a new SketchUp model of a WWI plane. The 110 hp engine in it was an Oberursel Ur.II, a German product copied from a French design. I was vaguely aware that in such rotary engines, much of the machinery went around along with the prop. It wasn't until I began looking at CAD representations that I began to understand why the rotary was considered a good idea at the time, or what made them work. Two CAD depictions in particular make the functioning of rotary engines a lot easier to understand.
The cut-away depiction below is from the marvelous Vintage Aviator site. If you look closely you will see the key feature of the engine, which is that there are two axes of rotation.
How the machinery is linked by the two axes is illustrated with great simplicity by an illustration at the Animated Engines site. Once there, click on the "Gnome Rotary" link to view the animation. Under the "About" link, you will also find an excellent explanation of how the engine animations are produced.
