A two-motor actuator for legged robotics applications

Abstract

In many robotics and mechatronics applications, actuators must bear a large load at low speeds and also move at high speeds. A single geared motor with a fixed gear ratio is unable to cover the two extreme load conditions effectively. Here, I propose a dual-motor actuator made by combining two electric motors with different gear ratios. Unlike prior works, where two operation ranges are switched by clutch, brake, and other mechanical means, the proposed design does not require any mechanical switches, but instead uses an electrical switch. At higher speeds, the motor with a high gear ratio, called the torque booster, is electrically disconnected from the drive amplifier, so that it does not generate a reverse current and thereby consume power as a generator. First, the design concept is presented, followed by modeling of the system as a hybrid control system. A basic control scheme for distributing drive currents to the two motors is presented, and an example of time-optimal control of the hybrid system is addressed. A proof-of-concept prototype is built and the control algorithms are implemented and tested experimentally.