Switchback motion of the fan-shaped disks connected at the arc centers on a slope

“ The passive dynamic biped walker robot ” can walk on a slope due to only the function of gravity. Many researches concerning this walker are executed nowadays. The conventional dynamic model of this walker has two legs connected with its body like a rigid pendulum. The lateral rolling motion of the body causes to swing each floated leg forward alternately. From this, the walker can naturally walk down a slope. But this walker has a possibility of falling down due to the instability by the instant standing with one leg alone. On the other hand, the descending model of this report also has the same particularity that can walk down a slope without active control. But it has the appearance that two fan-shaped disks are connected at the arc centers with free rotation. Consequently, the possibility of falling down almost vanishes. The principle of descending a slope of this model is based on the yawing motion induced by the lateral deviation of the gravity center which the rolling motion of the body generates. These rolling and yawing motions are consequently coupled each other and generate the self-excited swaying motion like a switchback. The purpose of this research is to clarify the conditions of the occurrence of this switchback motion. The author analyzed this interesting dynamic motion of each fan-shaped disk as three dimensional descending movement of the rigid body without a fixed point. From this analysis, he could confirm the occurrence of the switchback motion which also was observed in the experiments.