The Boeing Company
Cooperative shape memory alloy torque tubes for continuous-action turning motor

Abstract:

An engine turning "clock work" motor including two shape memory alloy (SMA) torque tube actuators, ratcheting mechanisms, and gearing. The gearing communicates the SMA torque tube actuators with a common gear that applies torque to a shaft, so that while one torque tube is heated and applying torque, the other torque tube is relaxed (using a cooling mechanism). The ratchet prevents the relaxing torque tube from applying torque in the incorrect direction.