Various mechanisms are available to convert linear motion to rotational motion. Examples are ratchets, rack and pinion gears, and cranks. Almost all existing hydraulic manipulators use a slider crank mechanism to transform linear motion from a hydraulic actuator to rotary motion of a joint. There are two specific limitations to this approach. First, motion is generally limited to less than 120° of motion. Second, the transmission ratio (conversion of force to torque) is nonlinear and typically varies from about 2:1 to about 1:1 over the 120° workspace. The limitation of the transmission ratio requires that the actuators be oversized to give a specific torque requirement which adversely impacts the efficiency of a hydraulic system. Also, a slider-crank mechanism typically has a pivoting actuator to compensate for the circular motion of the crank center. Fluid powered actuators thus require some kind of flexible tubing or rotary union to pass fluids in and out of the actuator. These kinds of unions are much less reliable than a fixed porting and usually require considerable space. If, on the other hand, the actuator is not allowed to pivot, then an extra linkage is required to compensate for the circular crank motion. This additional linkage adds complexity and volume. What are needed therefore are more efficient and versatile mechanisms to convert linear motion to rotational motion.