UCLA

This work focuses on how to implement modern online-reactive control strategies developed for robots with backdrivable actuators on robots with conventional high gear ratio, position controlled motors. The vast majority of robots today have motors like this. Robots with torque-controlled proprioceptive actuators which are backdrivable and have high torque density are currently being developed. However, there are still many situations in which robots with more traditional position-controlled, high gear-ratio actuators are more appropriate. For example, since actuator weight scales exponentially with size while torque scales linearly, it is still cost-prohibitive to use torque control for robots that are large and or very tall. In addition, backdrivable actuators typically require low latency communication to function and consume much more current than high gear ratio actuators because they are dampening motion during operation. Both restrictions can make these motors prohibitively difficult to use and expensive to obtain. For these reasons, research on robots with non-backdrivable actuators is still valuable. Many of the basic assumptions made for control systems are violated when using these actuators; with the intent to develop robots capable of dynamic, robust locomotion, we will attempt to categorize these obstacles, record the attempts to overcome them, explain why or why not the interventions were successful and finally, recommend paths of inquiry for future work. Contributions from this thesis project include creation of a bipedal robotic platform for locomotion experiments, multiple gait generators for bipedal robots with non-backdrivable actuators which were tested on physical hardware, investigation of methods to compensate for non-backdrivability during locomotion and several principles for designing control systems for dynamic, stable locomotion. Supplemental media included: - dcm-disturbance-rejection-sim.mp4 - dcm-omnidirectional-walking-sim.mp4 - model-free-omnidirectional.mp4 - parametric-lip-gait-robocup.mp4 - parametric-lip-omnidirectional-walking-sim.mp4 - pebl-spline-based-traj-opt.mp4 - sinusoidal-walk.mp4 - time-optimal-mpc.mp4 - walking-in-simulation.mp4