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A project log for Affordable bionic prosthesis

This project aims to create an affordable lower limb prosthesis for above knee amputees using hobby grade components.

Maximiliano PalayMaximiliano Palay 06/27/2022 at 16:450 Comments

To avoid compromising the safety of anyone external to the project, I performed the tests myself using a splint. The splint was made out of aluminum extrusion and 3D printed PLA+, using the same nylon stars as the data capturing device. This enabled rapid testing and iterations over the control mechanism, which was -at first- useless. On paper and on the bench tests, the control scheme worked quite nicely. When the prosthesis was loaded with weight, it didn't work, basically.

Let me share a few thoughts that appeared with the tests:

This might seem trivial to some. But experiencing these things made me realize actually how hard it is to use a prosthesis.

After several tests and trips, I observed that when I stepped over the prosthesis, the thing gave in too much. It flexed the knee, producing a sensation of instability. But the neural network was performing ok, it's just that the training data shows that -presumably- at impact, the knee flexes quite a bit. Probably to dampen the strike on the ground. The data was then filtered to remove high frequency components, these "impact flexes", and the model was retrained. This helped very much with the problem.

Although the first tests looked quite terrible, they evolved into something much smoother. I had to learn to trust the device and produce full steps. The final tests are shown in the following video.

On this video, some gait deformations can be seen as a result of the prosthesis being too tall for myself. The prosthesis size can't be shortened on the current design. The prosthesis behaves correctly in swing and stance phases, extending and retracting as needed, resembling a biological limb.

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