Abstract：Inspired by the unique body configuration when a baby crawls, a quadruped crawling robot with flexible spine and elastic knees is designed, named BabyBot. The spine is a variable cross-section structure of elastic material and the knees are passively deformable joints without active DOFs (degrees of freedom). The flexible spine and elastic knees are designed using pseudo rigid body modeling approach. The central pattern generator (CPG) is employed to generate trot gait trajectories for BabyBot. Combining the compliant mechanical structure with the biologically-inspired control approach, the “supporting on knees and waist-hip motion coupling” gait in baby crawling is developed. The dynamic simulations and physical experiments are conducted to evaluate the feasibility of Babybot's mechanical configuration and the influence of the flexible spine on its performance of the baby-mimic insufficient-DOF robot. The results show that the insufficient-DOF quadruped crawling robot with passive elastic knees is capable of crawling stably. Variable cross-section flexible spine can reduce the trunk's postural instability in roll and yaw directions when the robot crawls. That means the flexible spine enables the robot to crawl naturally and to maintain its direction. And it implies the spine's compliant swinging has active role on stabilizing the vision of a baby.
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