Abstract— For robotic manipulation tasks in uncertain environments, good force control can provide significant benefits. The design of force-controlled actuators typically revolves around developing the best possible software control strategy. Discussions about the passive dynamics are often imprecise, lacking comprehensive details about the physical limitations. This paper develops relationships between an actuator’s passive dynamics (stiffness, damping, motor inertia and torque limits) and the resulting performance, for the purpose of better understanding how to select the passive dynamics for a force-control task. We present two distinct scenarios for the actuator system and calculate the required input to produce the desired output. These exact solutions provide the basis for understanding how the parameters effect bandwidth. Our model does not include active control; we computed the optimal input to the system to produce the required torque at the load with zero error. This ...