This is the implementation of a variable structure velocity observer (a.k.a the Bin Observer in CRB) from the paper: B. Xian, M.S. de Queiroz, D.M. Dawson, and M.L. McIntyre, "A Discontinuous Output Feedback Controller and Velocity Observer for Nonlinear Mechanical Systems," Automatica, Vol. 40(4), pp. 695-700, April 2004.