A leg system with the proposed actuators was fabricated, as shown in Fig. 2. Two linear actuatorswere installed at the hip and stifle joints. A programmable dc power supply (Agilent 6573A (2000 W) [17]) was used to provide electric power for the linear actuators, and the electric current was switched by H-bridge amplifiers according to PWM input signals. The PWM signals were generated from a laptop computer with 15 bit resolution at 40 MHz. One cycle of the PWM takes 0.8192 ms, and thus the minimum sampling rate was about 1 ms.