An actuator system for articulated mechanism may have a fluid actuator having a displaceable member operating an output configured to apply an output force to the articulated mechanism. A fluid system may be in fluid communication with the fluid actuator to supply the fluid actuator with motive fluid to contribute to the output force. The fluid system may include a pressure reservoir configured for storing fluid, a pumping device for controlling a pressure of the fluid in the reservoir, and a circuit for directing the fluid from the reservoir to the fluid actuator. An actuator device may be operatively connected to the fluid actuator to apply a variable force to the displaceable member to contribute to the output force.