  We present experimental results using a passive whole-body control approach
for quadruped robots that achieves dynamic locomotion while compliantly
balancing the robot's trunk. We formulate the motion tracking as a Quadratic
Program (QP) that takes into account the full robot rigid body dynamics, the
actuation limits, the joint limits and the contact interaction. We analyze the
controller's robustness against inaccurate friction coefficient estimates and
unstable footholds, as well as its capability to redistribute the load as a
consequence of enforcing actuation limits. Additionally, we present practical
implementation details gained from the experience with the real platform.
Extensive experimental trials on the 90 kg Hydraulically actuated Quadruped
(HyQ) robot validate the capabilities of this controller under various terrain
conditions and gaits. The proposed approach is superior for accurate execution
of highly dynamic motions with respect to the current state of the art.
