Design, Simulation, and Stability of a Hexapedal Running Robot

Animals are the current gold standard of locomotion ability. Their ability to navigate rough terrain is unmatched by their man-made counterparts. Recent studies by biologists have begun to demonstrate some of the principles behind their remarkable capabilities. In particular, studies of cockroaches have shown that they use a feed-forward motor actuation pattern that is virtually unchanged, even when running over very rough terrain. It appears that their considerable structural compliance contributes significantly to their stability when running. Their sprawled posture and tuned impedance in their musculoskeletal system enable an instantaneous or preflex response to disturbances. This allows for rapid response to the large perturbations experienced when interacting with irregular terrain. Consideration of these principles has led to the design of the Sprawl family of robots, which features one active thruster and one entirely passive rotary joint on each leg. Without these spring elements the robots would not be able to run. With them, they can easily overcome hip-height obstacles without any alteration of their open-loop controller. The robots function as tuned oscillating systems and small changes in their physical parameters (e.g. leg stiffness and damping) can produce large changes in their speed and stability. Simple conceptual models of hopping have been used to analyze the effects of modifying the open-loop control system on system performance. These simple onelegged models have proven effective in helping to tune the actuation dynamics of the robot, but their simplicity precludes their use in tuning the sprawled self-stabilizing posture of the robot. This thesis describes the development, calibration, and analysis of a three-dimensional