embodiment actuation of the stepper motors 24 and 25 in the identical direction from the same initial position and for the identical displacement will vary only the inclination or pitch of the support platform 32 over a range of angles about the clevis pin 34 the nut members 26 and 27 translate horizontally from left to right as illustrated in fig3 to accomplish such motion as plantar flexion and dorsiflexion over a desired angular range the angular limits over which the dorsiflexion and plantar flexion occur are determined by the linear displacement limits of the nut members 26 and 27 which in turn are determined by the angular displacement of the stepper motors 24 and 25 the roll motion for inducing inversion and eversion is a function of the difference between the linear displacements of one nut member from the other nut member along the parallel axes along which they reciprocate to provide different roll angles as illustrated in fig5 and 6 consequently both inversion and eversion angles as well as dorsiflexion and plantar flexion angles may be controlled and smoothly varied to provide a gentle rolling pivoting movement by independently controlling selecting and varying the linear positions of the nut members 26 and 27 both of these motions may be simultaneously and smoothly blended by continuously displacing the nut members 26 and 27 along their respective lead screws 18 and 19 and simultaneously varying the difference between their displacements while a variety of actuators and particularly linear actuators may be utilized with.