Abstract: A prismatic actuator for imparting a hopping motion to a supported load such as a leg of robot. The apparatus includes a direct drive motor, such as a voice coil, operable to provide translational motion. The apparatus includes a spring element and a prismatic guide assembly. The guide assembly is configured to support the direct drive motor to constrain the translational motion to be along a drive axis and support the spring element to constrain compression and expansion of the spring element along a longitudinal axis parallel to the drive axis. The apparatus includes a controller that: (1) first controls the direct drive motor to compress the spring element during a first time period beginning when the apparatus initially contacts a surface; and (2) second controls the direct drive motor to expand the spring element when the apparatus has zero velocity while contacting the surface.