This prototype actuator was designed to provide 24 pounds of force and 3/8″ of stroke. There is a U-shaped Nitinol wire actuator on each side of the PCB (only one is currently installed), and they operate on a shared linkage. The SMA wire used here was 0.020″ diameter. The 3D printed ‘sled’ moves to the left when energized: compressing a spring that is pre-loaded to 12 pounds. If the load exceeds 12 pounds, the SMA wire can still contract by compressing the spring further. This protects the SMA wire from damage if the load exceeds the maximum design stress of the Nitinol wire.