A rotary device containing a housing with two side plates, a shaft, an eccentric connected to the shaft, a rotor mounted on the shaft, a first gear, and a second gear. The rotor contains at least 3 sides, the housing has an interior surface defined by at least a first lobe and a second lobe, the first gear is an internal gear which is connected to the rotor, the second gear is an external gear connected to the housing, the difference between the pitch diameter of the first gear and the pitch diameter of the second gear is is equal to twice said eccentricity of the eccentric, and the ratio between the pitch diameter of the first gear and the pitch diameter of the second gear is equal to the ratio between the number of said sides in said rotor divided by the number of lobes in the interior surface of said housing.