Piston in cylinder without reciprocation. The big end of the connecting rod rotates around the fixed crank journal. Combustion pressure pushes the cylinder head away from the piston, just the opposite of a reciprocating engine.
Now reverse the pistons and have them backwards of the illustration. No connecting rods, both pistons and cylinders oscillate relative to the crank journal as they rotate around the different eccentrics.
Piston in cylinder compression ignition without reciprocation. The engine block is the flywheel.
Animated Engines - Gnome Rotary
regards
Mech