Toward a Bipedal Robot with Variable Gait Styles: Sagittal Forces Analysis in a Planar Simulation and a Prototype Ball-Tray Mechanism

Variable walking styles in bipedal robots may be used to communicate information about purpose and/or personality to human viewers- and may also help accommodate features of the environment. This paper presents variable gait in a simulation and results from a hardware prototype for gravity-driven rolling ball mechanism in a previously proposed bipedal design. First, optimal control inputs that produce a range of variable feasible gaits is generated on a simplified under-actuated planar model. Then, a tray-like mechanism that provides a curved path for a ball to roll on is presented. This mechanism is designed to replicate a notion of pelvic shift, described in Bartenieff Fundamentals, with movement of the ball (which is shaped by the tray) creating a shift of weight. Analysis of two gait styles and two tray designs shows comparable ranges of forces in the direction of travel between the simulated planar model and the hardware mechanism. This work is an important first step in generating feasible, stable- and variable- bipedal gaits using this hardware design.