Process Post

Zachary Ploude

In this studio, I wanted to create something that would allow people to run faster and more efficiently, while also being conveniently portable and unpowered. I came up with two ideas for how to do this, and worked on the first in the previous studio. In this studio, I worked on the second idea. This is a modified cast which uses leaf springs to capture energy when the wearer is about to push off the ground and release it for the push off. When running, there is a small amount of negative work for the ankle when the runner shifts forward past the foot, causing the ankle to unflex. Then there is a large amount of work for the ankle when it must flex to push the foot off the ground and propel the runner forwards. The leaf springs capture this negative work by resisting when the ankle unflexes, and push back when the ankle flexes. They are designed to only resist when the ankle unflexes past a 90 degree angle with the leg, and thus do not strain the wearer when they are standing.

The very first idea for this project was an attachment that allowed non-amputees to wear athletic prosthetics, as they are more efficient for running than human legs. Due to the price of these prosthetics, however, the idea was changed and split into two parts: an attachment for below the foot, and one for above. The attachment for below the foot mimicked an athletic prosthetic, providing a curved bottom and a spring to absorb energy when first hitting the ground. The other attachment would incorporate leaf springs to help the foot flex. At the time, the second idea was very undeveloped.

This project was faced with a few very large challenges. The first was creating a holder for the leaf spring on the bottom of the cast that would rotate. Originally, I planned to make it with wood, but found that the medium would not be strong enough, so I decided to 3D print. Once the pieces were 3D printed, however, attaching them to the bases securely proved to be a difficult task. After designing a way to attach them, I had to work with many small parts to actually do so. The entire process was very time consuming.

The second challenge I faced was attaching the leaf springs. I planned to drill holes in them and screw them in, but when the time came I found that our equipment was not powerful enough to drill through the tough steel. The dremel, however, could, so I used it to create notches for screws to go into.

The third challenge was making the leaf springs behave how I wanted the to. When I first put them in the cast, I found that they were so strong that they rotated the pieces they were attached to. After reinforcing the pieces with lock nuts, I found that depending on the amount of spring steel behind the holder, the leaf spring could either want to go up or down. Also, when in use, instead of bending, the leaf springs would be pushed back instead. Both of these problems were solved when I attached stoppers to the leaf springs that prevented them from going back through the holders after a certain point. After that, however, I found that the project was not as efficient as it could be because instead of bending with one's foot the leaf springs would shift forward in relation to the foot. To mitigate this, I attached some rubber to the bottom of the end of the leaf springs in order to increase friction.

The first iteration was the cast with the pieces that would hold the leaf spring attached. This would be changed according to how the first tests with the leaf springs went.

The second iteration has some improvements to the overall stability of the project to combat the strength of the leaf springs. All of the attachments to the cast were secured with multiple lock nuts. In addition, the top holders were changed to include 2 screw holes as the leaf springs needed to be attached with 2 screws.

The third iteration improved on the performance of the leaf springs and includes the stoppers and a piece on the end of the leaf springs that the foot pushes against.