Self-contained rotary actuator provides motive power in automated mechanical systems and includes cross-roller bearing as a structural joint. Outer attachment shell rigidly interfaces the mechanical system and contains motor stator and internal bull gear. Internal bull gear, with internal gear teeth, interfaces cross-roller bearing, and provides stiffness. Output attachment plate mechanism includes internal ring gear and supports drive shaft bearings. Internal ring gear, with internal gear teeth, rigidly interfaces output attachment plate. Drive shaft holds prime mover rotor and eccentric and associates output attachment plate via the drive shaft bearings. Gear train includes circular arc, external teeth meshing gear for meshing with internal teeth of internal bull and internal ring gears and walks minimal external gear teeth per prime mover rotor rotation. Cross-roller bearing, outer attachment shell, drive shaft, and meshing gear train provide a self-contained, integrated, actuation torque transmitting force from the prime mover along shortest-possible transmission path.