Investigating balance control of a hopping bipedal robot

Legged robots are dynamic moving machines that are potentially able to traverse through rough terrain which is inaccessible for wheeled or tracked vehicles. For bipedal robots, balancing control while hopping/running is challenging, especially when the foot contact area is small. Servo hydraulics is highly suitable for robot leg actuation due to its high power density and good power-to-weight ratio. This paper presents a controller for a hydraulically actuated bipedal robot, the Bath Bipedal Hopper (BBH). The controller follows the well-established structure of the ‘Three-part’ control algorithm. The three parts are: hopping height control; longitudinal velocity control by changing the leg angle during the flight phase to place the foot in the desired position; and body attitude correction during the stance phase. Simulation results from a detailed non-linear model indicate that this controller can successfully balance the hydraulic robot while hopping with different longitudinal velocities.