Pseudo-passive dynamic walkers designed by coupled evolution of the controller and morphology

In this paper we investigated the morphology and controller of biped robots. We viewed them as design components that together can induce dynamically stable bipedal locomotion. We conducted coupled evolution of the morphology and controller of a biped robot, consisting of nine links and eight joints, actuated by oscillators without sensor feedback in three-dimensional simulation. As a result, both pseudo-passive dynamic walkers and active-control walkers emerged, but the pseudo-passive dynamic walkers showed more dynamic stability than the active-control walkers. This is because compliant components in morphology function as noise filters and passive oscillators. Analysis on this latter class of walkers revealed that this was achieved by two novel functions: self-stabilization and self-regulation. Because these functions were handled by the passive dynamics induced in the robot morphology, due to its compliance, we concluded that a computational trade-off between the controller and morphology occurs in these devices. Finally, we have concluded that appropriate compliance is a key to achieving dynamical stability during locomotion.