Modular Prosthetic Hand

A lightweight prosthetic for partial hand amputees

February 2023

Designathon

Hosted by UBC Design League

Team:

• Horace Tang

• Kian Yazdanyar

In a 31-hour designathon, we were tasked to design a prosthetic hand for finger or partial hand amputees. It was meant to accomplish the following:

• Consist of at least 3 independently moving fingers

• Be easily worn/taken offf

• Total weight less than 300 grams

• Be able to support minimum weight of 9 kilograms

• Total cost less than $7500

We were not responsible for communication between the brain and prosthetic, and were told that a technology providing a seamless connection between the two exists.

Before diving into the problem, my team and I researched current solutions. Our goal was to make something versatile, so that it would work for a large range of finger/partial-hand amputees. After we decided on a general design, we moved on to specifics.

For the first 15 hours of the competition, we took several different looks at the specifics of the solution. We quickly realized how difficult it was to build a hand less than 300 grams, but capable of supporting 9 kilograms. Any motor that could directly support that weight already exceeded the 300 gram limit, not to mention using multiple for independent finger control. Gear ratios to get higher torque out of lighter weight motors would be far too big on any reasonable prosthetics, and would limit the modular design of our hand. After working all night to figure out a way around this wall, I decided on something that might work–solenoids.

Solenoids don’t have very high axial force, but they can withstand a large amount of force in the radial direction. My idea was to use lightweight, low torque servo motors to move fingers, but solenoids to lock the fingers in place for load-bearing. After completing stress calculations, we realized this was possible.

For the remaining designathon hours, we finalized the design of this modular prosthetic hand. A rigid support fits snuggly onto the palm of a partial-hand amputee. A power unit/control board mounts to this support. Based on the number of fingers wanted by the user, they can be plugged into the power unit in any of the 5 slots.

My team and I presented our project to other teams and two judges, where we explained the reasoning behind our design. While we did not win the designathon, we were happy with the problems we worked through and our final product. See attached for our project slides.