Generalized Contact Constraints of Hybrid Trajectory optimization for Different Terrains and Analysis of Sensitivity to Randomized Initial Guesses To generate a dynamic bipedal walking with foot rolling motion for bipedal robot, hybrid trajectory optimization is capable of planning level walking with great energetic efficiency. However, the direct implementation of this optimization requires different sets of variables to express different active contact constraints, which can be complicated to implement. To simplify the optimization formulation, we propose the generalized contact constraints where the same set of variables are used through all the walking phases. By changing the variable and constraint bounds, different contact constraints for different contact conditions can be generally expressed. The proposed modifications are applied on the bipedal robot AMBER 3, where the optimization results on different terrains are compared and discussed. On the other hand, it is known that a randomized initial guess can be used to solve this optimization, yet its effect on the gaits on different terrains is unclear. As a result, we analyzed the sensitivity of the optimization to a set of randomized initial guesses. The level and downslope walking gaits are also validated via the experiments on AMBER 3.

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.