I have used flexinol wire to control the movement of the fingers, as the wire provides dexterity, strength and flexibility. Furthermore this type of wire is affordable and easily available within any electronics, fishing or hobby store. The use of the wire to help provide motility helps reduce the overall cost of developing the prosthetic, maintaining within my goal of making the prototype affordable and durable.
In the image, I am attempting to connect the two ends of the flexinol wire to a servo motor.I had constructed the cardboard fingers our of a cardboard composite, which was internally corrugated ( to provide strength ), However I decided that by running the flexinol wire through the internal corrugation I would be able to effectively control the movement of the fingers. As a result I designed a finger that would enable me to internally run the wire from one end to another and these two ends were then attached to a servo motor. Initially these wires were attached to a wheel mounted on the motor, however I then realised that the ratio of string pulled for the downward motion of the finger to the upward motion of the finger was 4:1. Which effectively meant that more string needed to be pulled down for the inward motion of the finger as compared to the upward motion of the finger to return the finger to the original position. I solved this problem by mounting attachments called “horns” onto the servo motors, the horns allowed me to attach the flexinol wire at a ratio of 4:1, as shown in the images. This implementation effectively solved the problem that I was facing.