The position of the wobbling disk (body-fixed coordinate system di ) with respect to the inertial coordinate system ni is described by the three Cardan angles q1, q2, q3. The brake pads are allowed to move in the n2 2n3 plane only. Their displacements (relative to the equilibrium configuration) are given by q4 and q5, respectively (cf. Fig. 2). The relative twist angle of the visco-elastic coupling, measured from the equilibrium configuration, is denoted by qH.