  An omnidirectional closed-loop gait based on the direct feedback of
orientation deviation estimates is presented in this paper. At the core of the
gait is an open-loop central pattern generator. The orientation feedback is
derived from a 3D nonlinear attitude estimator, and split into the relevant
angular deviations in the sagittal and lateral planes using the concept of
fused angles. These angular deviations from expected are used by a number of
independent feedback mechanisms, including one that controls timing, to perform
stabilising corrective actions. The tuning of the feedback mechanisms is
discussed, including an LQR-based approach for tuning the transient sagittal
response. The actuator control scheme and robot pose representations in use are
also addressed. Experimental results on an igus Humanoid Open Platform
demonstrate the core concept of this paper, that if the sensor management and
feedback chains are carefully constructed, comparatively simple model-free and
robot-agnostic feedback mechanisms can successfully stabilise a generic bipedal
gait.
