  In this paper we present advancements in control and trajectory generation
for agile behavior in bipedal robots. We demonstrate that Whole-Body
Operational Space Control (WBOSC), developed a few years ago, is well suited
for achieving two types of agile behaviors, namely, balancing on a high pitch
split terrain and achieving undirected walking on flat terrain. The work
presented here is the first implementation of WBOSC on a biped robot, and more
specifically a biped robot with series elastic actuators. We present and
analyze a new algorithm that dynamically balances point foot robots by choosing
footstep placements. Dealing with the naturally unstable dynamics of these type
of systems is a difficult problem that requires both the controller and the
trajectory generation algorithm to operate quickly and efficiently. We put
forth a comprehensive development and integration effort: the design and
construction of the biped system and experimental infrastructure, a
customization of WBOSC for the agile behaviors, and new trajectory generation
algorithms. Using this custom built controller, we conduct, for first time, an
experiment in which a biped robot balances in a high pitch split terrain,
demonstrating our ability to precisely regulate internal forces using force
sensing feedback techniques. Finally, we demonstrate the stabilizing
capabilities of our online trajectory generation algorithm in the physics-based
simulator and through physical experiments with a planarized locomotion setup.
