Quadrupedal trotting with active compliance

We present a trotting controller for a torque controlled quadruped robot. Our approach uses active compliance to overcome difficulties that are crucial for the realisation of symmetric gaits, i.e. force equalization, disturbance rejection and impact absorption. We present a scheme for the compliant control of each leg that is based on a virtual spring abstraction. This active compliance scheme allows us to greatly vary the dynamical behaviour of the system on-the-fly, without altering the physical characteristics of the robot, by changing the parameters of the virtual springs. This way we are able to evaluate a wide range of trotting gaits with varying parametrizations. We report results of robust trotting in various speeds and push recovery in simulation, and continue with results of actively compliant trotting on the real quadruped robot. We further discuss difficulties and limitations with the implementation of such dynamic gait controllers on the real system.