Irregular circular motion imparted to wheel, A. C is an elliptical spur-gear rotating round center, D, and is the driver. B is a small pinion with teeth of the same pitch, gearing with C. The center of this pinion is not fixed, but is carried by an arm or frame which vibrates on a center, A, so that as C revolves the frame rises and falls to enable pinion to remain in gear with it, notwithstanding the variation in its radius of contact. To keep the teeth of C and B in gear to a proper depth, and prevent them from riding over each other, wheel, C, has attached to it a plate which extends beyond it and is furnished with a groove, g, h, of similar elliptical form, for the reception of a pin or small roller attached to the vibrating arm concentric with pinion, B.