SatCon is developing linear and rotary motors that rely on the peristaltic motion of a Terfenol-D element along a tight-fitting channel. Magnetostrictive inchworm motors offer extended or unlimited travel, as well as those attributes normally associated with magnetostrictive actuators: high force and torque densities, quick response, and fine resolution motion. Unlike Kiesewetter's cylindrical design, the Terfenol-D element is a rectangular slab placed between two tight-fitting plates that are spring-loaded to maintain proper contact in spite of wear. Also, the excitation coils do not enclose the Terfenol-D element, allowing extension of the concept to rotary motors. A model for inchworm performance has been developed, based on observations of a prototype linear inchworm motor. Speed is approximately the product of peak magnetostrictive strain and phase velocity of the magnetic field, but is reduced by the finite element of the contact zone between the Terfenol- D and the plates. As a result, speed drops with load, since magnetostrictive strain is reduced and the contact zone grows longer with increasing applied load. The speed was limited by the skin effect present in the Terfenol-D element. A second prototype employs composite Terfenol-D with its high resistivity, in order to permit operation at higher speeds. SatCon is also developing a rotary motor and making improvements to the design of linear motors.