  We present a framework for dynamic quadrupedal locomotion over challenging
terrain, where the choice of appropriate footholds is crucial for the success
of the behaviour. We build a model of the environment on-line and on-board
using an efficient occupancy grid representation. We use Any-time-Repairing A*
(ARA*) to search over a tree of possible actions, choose a rough body path and
select the locally-best footholds accordingly. We run a n-step lookahead
optimization of the body trajectory using a dynamic stability metric, the Zero
Moment Point (ZMP), that generates natural dynamic whole-body motions. A
combination of floating-base inverse dynamics and virtual model control
accurately executes the desired motions on an actively compliant system.
Experimental trials show that this framework allows us to traverse terrains at
nearly 6 times the speed of our previous work, evaluated over the same set of
trials.
