Legged robots on rough terrain: experiments in adjusting step length

To travel on rough terrain, a legged system must use the available footholds, even when they are isolated or hidden by obstacles. This thesis addresses the task of adjusting the length of each step to place the feet on available footholds, in the context of a dynamic biped robot that actively balances itself as it runs. In order for the biped to use specific footholds, the control system must simultaneously satisfy the constraints for stability and the constraints dictated by the geometry of the terrain. I explored three methods for controlling step length each of which adjusted a different parameter of the running cycle. The parameters were forward running speed, running height, and duration of ground contact. All three control methods were successful in manipulating step length, but the forward speed method provided accurate control of step length (average absolute error 0.07 m) and the widest range of step lengths (from 0.1 m to 1.1 m). In laboratory demonstrations the biped used step length adjustment to place its feet on targets, leap over obstacles, and run up and Clown a short flight of stairs.