Parametric models for motion planning and control in biomimetic robotics

We describe the design, testing and tools to build parametric models of a six-legged cockroach-like robot for velocity control without precise knowledge on the robot's geometry or its inertia. Robot legs were made by Shape Deposition Manufacturing and were compliant at the "knee." These kinds of robots usually have a limited number of actuators and a small number of low-cost sensors. Consequently, they are difficult to control with analytic models. Our goal was to design a very fast robot that could run in a straight line over short distances at a desired velocity. We incorporated such legs into a novel body design, where position and orientation of the legs were chosen to enhance static stability. Robot design proved to be robust, as the machine did not suffer any failure in over 20 000 runs. We found that body-pitch angle was a crucial parameter in the control of running speed. To control this angle, we built a parametric model that related leg orientation to pitch angle. We experimented with various leg stiffness parameters, and built a comprehensive parametric model that quantified performance as a function of this parameter, as well as body-pitch angle, ground slope, and body mass. When these parameters were optimized, the robot consistently achieved a speed of six body lengths per second, even when pulling a large load in the form of a trailer cart.