  Planning whole-body motions while taking into account the terrain conditions
is a challenging problem for legged robots since the terrain model might
produce many local minima. Our coupled planning method uses stochastic and
derivatives-free search to plan both foothold locations and horizontal motions
due to the local minima produced by the terrain model. It jointly optimizes
body motion, step duration and foothold selection, and it models the terrain as
a cost-map. Due to the novel attitude planning method, the horizontal motion
plans can be applied to various terrain conditions. The attitude planner
ensures the robot stability by imposing limits to the angular acceleration. Our
whole-body controller tracks compliantly trunk motions while avoiding slippage,
as well as kinematic and torque limits. Despite the use of a simplified model,
which is restricted to flat terrain, our approach shows remarkable capability
to deal with a wide range of non-coplanar terrains. The results are validated
by experimental trials and comparative evaluations in a series of terrains of
progressively increasing complexity.
