This animation realistically illustrates the cycle of a rotary engine. Each face of the rotor is marked with a color, so you can keep track of it's orientation with respect to the eccentric shaft and the housing. Notice that the eccentric shaft turns three times for each turn of the rotor. The rotor's motion is complex, in the sense that it both rotates on a journal of the eccentric shaft and orbits the center of the eccentric shaft's rotation. The rotor orbits at full eccentric shaft speed, but rotates at one-third the speed. The combination of the two motions results in the rotor apexes following the path of a "two lobe peritrochoid", which, not coincidentally, happens to be the shape of the housing. As it turns, the rotor creates three distinct "working chambers" that expand and contract, in turn, in such a way as to facilitate the four strokes of it's combustion cycle. Please refer to the Rotary Engine 101 section to understand the process better.