A method for reciprocally transporting a workpiece on a scan arm through an ion beam is provided, wherein the scan arm is operably coupled to a motor comprising a rotor and stator that are individually rotatable about a first axis. An electromagnetic force applied between the rotor and stator rotates the rotor about the first axis and translates the workpiece through the ion beam along a first scan path. A position of the workpiece is sensed and the electromagnetic force between the rotor and stator is controlled in order to reverse the direction of motion of the workpiece along the first scan path, and wherein the control is based, at least in part, on the sensed position of the workpiece. The stator further rotates about the first axis in reaction to the rotation of the rotor, particularly in the reversal of direction of motion of the workpiece, thus acting as a reaction mass to the rotation of one or more of the rotor, scan arm, and workpiece.