Effect of flexible spine on stability of a passive quadruped robot: Experimental results

In rapid quadruped animals, the flexibility of spine is obviously observable while running. In this paper, we introduce a 3D passive dynamic quadruped robot, Fanari, that is capable to gallop down a slope without any external energy. We study the effect of spine flexibility on improvement of stability, adaptability and achievement of rapid leg locomotion. So a flexible spine that is capable to bend both outward and downward, a flexible spine that is only capable to bend outward and a rigid spine are designed and tested on the robot. Based on the case studies, we discuss about the challenges and the roles of spine stiffness on the gallop action. A simulation model is also made in order to corroborate the experimental results of the robot. It is concluded that the robot with the spine that is flexible in both outward and downward directions, has the most stability, adaptability and fastest velocity in its gallop action.