An attractive but little explored field of application of the shape memory technology is the area of rotary actuators, in particular for generating endless motion. This paper presents a miniature rotary motor based on shape memory alloy (SMA) wires and overrunning clutches which produces high output torque and unlimited rotation. The concept features a SMA wire tightly wound around a low-friction cylindrical drum to convert wire strains into large rotations within a compact package. The seesaw motion of the drum ensuing from repeated contraction-elongation cycles of the wire is converted into unidirectional motion of the output shaft by an overrunning clutch fitted between drum and shaft. Following a design process formerly developed by the authors, a six-stage prototype with size envelope of 48´22´30 mm is built and tested. Diverse supply strategies are implemented to optimize either the output torque or the speed regularity of the motor with the following results: maximum torque = 20 Nmm; specific torque = 6.31´10-4 Nmm/mm3; rotation per module = 15 deg/cycle; free continuous speed = 4.4 rpm.
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