Experiment and analysis of quadrupedal quasi-passive dynamic walking robot “Duke”

Much attention has been paid to passive dynamic walking as an approach to investigate the walking of human beings and animals. As for quadrupedal passive dynamic walking, it is confirmed that walking resembles that of animals, and that the gait of the robot changes depending on the structure of robot or the environment. Based on these facts, it is conceivable that quadrupedal passive dynamic walking is related to walking of animals, and the walking principle is inherent in passive dynamic walking. In this research, we approach the walking principle through realization of a walking on the level ground by rational-energy input and investigation how gait changes depending on the input. In this paper, a quadrupedal quasi-passive dynamic walking robot named Duke has been developed by applying passive dynamic walking. This robot has only two rolling actuators, which simply provide with rocking motion and not drive the knee or hip joint directly. We conduct walking experiments by Duke with various inputs, and observe its gaits. As a result of walking experiments, it was verified that walking speed was related to the frequency and the phase difference of rocking motion. In addition, through analysis of a shape of soles, we revealed Duke has a nonholonomic constraint that is comparable to that of “two-wheeled robot” on its sole. As a result of analyses based on the nonlinear control theory, we conclude that the sole shape contributes to the transition of walking speed accompanying with change of a phase difference.