On the effect of semielliptical foot shape on the energetic efficiency of passive bipedal gait This paper studies the effects of varying rollover curvature on the passive dynamic gait of a biped walker. The dynamic model of a compliant biped robot is extended with the implementation of semielliptical feet, to mimic human rollingradius progression during a step. The process of modeling the semielliptical foot shape and integrating its kinematics to the bipedxe2x80x99s dynamics is presented in detail. The passive dynamic behavior of the biped for elliptic feet of various dimensions is investigated through numerical simulations to provide results about gait stability, walking speed, energetic efficiency, and impact force levels. The concept of energetic efficiency in passive walking is discussed thoroughly, and an efficiency comparison methodology is proposed. Finally, it is shown that the biomimeticallyinspired semielliptical foot profile can lead to higher gait efficiency. The results of this study can be used to optimize energetic efficiency in biped walking machines andor gait assisting prosthetic equipment by means of foot shape optimization.

Toward a Bipedal Robot with Variable Gait Styles: Sagittal Forces Analysis in a Planar Simulation and a Prototype BallTray Mechanism Variable walking styles in bipedal robots may be used to communicate information about purpose andor 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 gravitydriven 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 underactuated planar model. Then, a traylike 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 variablexe2x80x93 bipedal gaits using this hardware design.