Instead of pistons moving up and down, with a crank to convert linear motion into rotary motion, a Wankel engine uses a triangular rotor that turns within a chamber. As the triangle rotates, different areas within the chamber get compressed. When petrol and air are injected, and the mixture ignited, the triangle spins fast enough to power a car, motorbike, or aircraft. Wankel engines have advantages (high power-to-weight ratio, low
vibration) and disadvantages (poor fuel efficiency, a tendency to break down if not maintained) compared with standard piston engines, but we like them mainly because of the clever, original design – which also translates well into 3D printing.