This is a functional model of a rotary (Wankel) engine. While it may not be entirely accurate, it is useful as a demonstration of the engine's basic mechanism. The cut-away shows all four rotors operating where the compression stroke would be. This is entertaining to watch when sped up with an electric drill. And sorry about the large space between the rotors and chamber wall; I had to increase the clearance from the original design to prevent jamming (consumer 3D printed plastic does not allow nearly the precision of machined metal). There are two options to print: 1 - Simplified version - no gluing/assembly; single chamber; easy to print and use 2 - Full version - requires gluing/assembly; four chambers + more detail; may require graphite lubricant Good Luck :)