When quadrupedal robots execute locomotion, their interactions with the ground surface will make themselves unstable without careful compliance control for each leg. This paper presents a control method which uses a virtual leg compliance with instantaneous reflexes to external disturbance to obtain the self-stabilization for legged robots. Each leg was modeled as two sets of virtual spring and damper systems. And as the robot walks, the impulse imposed by collisions with the ground surface will make its leg shrink as a spring and then return its balance according to the desired foot trajectory. This is verified by simulation results from the single leg robot. For further evidence, the corresponding experimental results were also obtained under the same control conditions. It is found that the single leg robot is able to move to its desired balance position automatically, and if its thigh or calf is forced to leave the balance position, the leg robot will return balance like a spring and damper system after the force is relieved.
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