Practical modeling and system identification of R/C servo motors

An R/C servo motor is a compact package of DC geared-motor associated with position servo controller. They are widely used in small-sized robotics and mechatronics by virtue of their compactness, easiness-to-use and high power/weight ratio. However, in order to improve control performance of mechatronic systems using R/C servo motors, such as biped robots or under-actuated systems, it is crucial to clarify their mathematical model. In this paper, we propose a simple and realistic internal model of R/C servo motors including the embedded servo controller, and estimate their physical parameters using continuous-time system identification method. We also provide a transfer function model of their reference-to-torque characteristics so that we can estimate the internal torque acting on the load.