Trotting and Pacing Locomotion of a Position-Controlled Quadruped Robot

Compared with torque-control techniques, a position-controlled quadruped robot is lower cost, easier to build, and more direct to drive. However, the stiff actuation of position-controlled actuators makes it difficult for the quadruped to achieve dynamically stable locomotion. This paper presents an implementation of joint velocity programming technique to regulate the body’s moving speed and orientation for a position-controlled quadruped robot that performs trotting or pacing locomotion. The robot model is mapped to a new coordinate space in order to decouple the control of its body. In one plane of the new coordinate space, the robot is simplified to an inverted pendulum model to generate attitude and velocity tracking actions. In the other planes, body regulating problems are formulated in velocity forms and solved by designing support leg motions. The controllers in these planes are integrated to produce joint velocities that enable robust trotting and pacing locomotion at a variety of speeds and directions, despite lacking force control or feedback techniques. Physical test results as well as simulating results demonstrate control of the quadruped robot SmarQ to perform omni-directional locomotion, impact recovery, and adaptability to uneven terrains.