I never had any idea how these engines worked. Now I found this animated video.
That helped me a bit further.
You can adjust the speed, so you can see it real slow. Enjoy!

ANIMATED ENGINES - Gnome

Quote: "I thought the only person crazier than the engine designer was the one who paid money for it."
...yeah... that was my first Impression, too LOL
They've got the Intake-Valve INSIDE the Piston ?!?
Great Find, Olham! I always wondered, how exactly these Things worked...

They are indeed complex motors. I'm sure someone more "inventive" than me could come up with a more complicated piece of machinery, but I don't know how.

The Vintage Aviator has a great video showing the internals here:

http://thevintageaviator.co.nz/projects/oberursel-engine/rotary-engine-detail