Experimental Comparison of Velocity Observers: A Scissored Pair Control Moment Gyroscope Case Study

We consider scissored pair gyroscopes as an auxiliary stabilization system for legged robots. A standard state-feedback control can stabilize the system if all states are available; thus, the velocity estimation becomes the key element for the stabilization. To this end, we implement and experimentally compare a model-free linear differentiator, a model-based full-state linear observer with time-varying gains, and a model-based homogeneous nonlinear differentiator. Moreover, we also show that the considered system cannot be partially linearized via a change of coordinates, and thus is not suitable for a recently reported class of nonlinear observers. The proposed designs are tested on an experimental scissored pair control moment gyroscope setup constructed for a walking robot stabilization.