External rotation as morphological bootstrapping for emergence of biped walking

Many researchers are interested in the onset and learning of bipedal walking, but still not much is known how a human (and even a robot) can acquire the ability. In this paper, we hypothesize that external rotation of the hip joint plays an essential role for emergence of bipedal walking in human infancy. We build an infant robot “Pneu-born 13” driven by pneumatic artificial muscles so that we would get biologically plausible results. The robot can walk without any intention to move forward by utilizing the external rotation of the hip. We also analyze a quasi-static model of the robot and find that the joint compliance plays an important role in this scheme.