Reachability Aware Capture Regions with Time Adjustment and Cross-Over for Step Recovery

For humanoid robots to live up to their potential utility, they must be able to robustly recover from instabilities. In this work, we propose a number of balance enhancements to enable the robot to both achieve specific, desired footholds in the world and adjusting the step positions and times as necessary while leveraging ankle and hip. This includes improving the calculation of capture regions for bipedal locomotion to better consider how step constraints affect the ability to recover. We then explore a new strategy for performing cross-over steps to maintain stability, which greatly enhances the variety of tracking error from which the robot may recover. Our last contribution is a strategy for time adaptation during the transfer phase for recovery. We then present these results on our hu-manoid robot, Nadia, in both simulation and hardware, showing the robot walking over rough terrain, recovering from external disturbances, and taking cross-over steps to maintain balance. Video online at https://youtu.be/0uU7uwm9blA.