[legion]

Interesting. Watching the animation really explained everything to me. It seems that there are two sets of "paddles" that form each combustion chamber. The housing is round (rather than elliptical in a rotary or quasiturbine engine). Each set of paddles is loosley coupled with the crankshaft--they can push it but also have slack not move while the crankshaft is moving.

The only thing I don't understand is what keeps the slack set of paddles from moving forward during the compression stroke?