Study on quadruped bounding with a passive compliant spine

In running, legged animals take advantages of their flexible bodies to increase their locomotion performance, resulting in superior mobility and fast motions. Previous works on quadruped robots mostly used the simplified model with massless legs. However, in reality, a leg consists of two or three segments with mass and inertia. We study herein the bounding of quadruped robots with a model closer to a real animal, i.e., a model having articulated legs with joints with stiffness and damping properties, and a passive spinal joint, to obtain an insight into the robot's dynamic behaviors. The effects of spine flexibility were investigated on quadrupedal bounding gait by changing dynamic properties and hardware parameters and then comparing the performance of models with and without a spinal joint. The model comparisons revealed that body flexibility significantly increased stride length and strongly affected the dynamic of the body and the energy efficiency.