Abstract: An electrically-powered expansion/contraction apparatus is disclosed. The apparatus preferably contracts and expands due to magnetic interaction within a plurality of motor units (20) or (21). Each motor unit (20) or (21) is in turn made up of a pair of interlinked subunits (22), (24). The subunits (22), (24) include inner elements (22) and outer elements (24) which contract when unlike magnetic poles are juxtaposed and expand when opposite poles are proximate to one another. A control circuit (44) for each subunit (22), (24) selectively prevents current flow or directs it in one of two directions to appropriately empower electromagnets (26) on the inner elements (22). Outer elements (24) can either include permanent magnets (40) or electromagnets (27). Mechanical stop means are provided by the nature of the interlinked design to give the motor unit (20) or (21) an "all-or-none" behavior akin to that of natural muscle.