Pure rolling cycloid transmissions with variable effective diameter rollers and roller constraints

A variety of transmissions, and improvements thereof, are provided having improved efficiency and other benefits. The transmissions include one or more inner members that are driven by one or more cams or other means to engage in precessional rotation about an axis of rotation that, itself, orbits about a primary axis of rotation. A plurality of shaped rollers are in contact with shaped cutouts on the inner member(s) and on a ground member such that an input rotation/torque applied via the cam is realized as an output rotation/torque at an output member that is coupled to the inner member(s). Tire rollers and contact surfaces are shaped such that the rollers engage in rolling motion relative to the contact surfaces, providing improved efficiency. Multiple inner members, and corresponding sets of shaped rollers, can be provided to increase power capacity, reduce torque ripple, reduce wobble, or provide other benefits.