A rotary actuator for use in surgical instruments is provided, including a plurality of engine elements placed symmetrically around a rotation axis a disk in contact with the engine elements, centered on the rotation axis, the engine elements providing a first rotation to the disk an input shaft coupled to the disk to rotate with the first rotation and a coupling mechanism to provide a second rotation to an output shaft from the first rotation of the input shaft. A surgical manipulator is also provided, including a base to provide stability and support a first rotary actuator as above coupled to the base and a first arm coupled to the rotary actuator.
