3-DOF passive dynamic walking of compass-like biped robot with semicircular feet generated on slippery downhill

The authors demonstrated that a stable passive compass gait can be generated on a slippery downhill, and showed that the 2-DOF constraint conditions for the contact point are not always necessary for it. The generated walking gait while sliding on the slope becomes 3-DOF increased by addition of the positional coordinate of the contact point. This paper then investigates the effects of semicircular feet on the 3-DOF passive compass gait. First, we develop the equations of a 4-DOF passive compass-like biped robot with semicircular feet that slides on a slippery downhill. Second, we derive the term of the sliding friction force and discuss the complexity and relationship with holonomic constraint condition. Third, we perform numerical simulations to observe the typical 3-DOF passive walking motion and change in the gait properties according to the foot radius.