College - Author 1

College of Engineering

Department - Author 1

Biomedical Engineering Department

Degree Name - Author 1

BS in Biomedical Engineering



Primary Advisor

Karla Carichner


This critical design report describes the product development of a prosthesis for use on sand. Quality of Life Plus (QL+), a national non-profit organization aimed to develop prostheses for veterans and people with disabilities, introduced this project and its accompanying challenger, Sgt. Brady, to Cal Poly’s Interdisciplinary Senior Project class in September 2018. After consulting with Sgt. Brady and QL+ and performing extensive research, the Sand Foot team defined customer requirements and engineering specifications to meet these requirements. Comfortability, durability, and sandproof were key customer requirements. Several conceptual models were brainstormed and a final design was selected based on the best design concepts of all considered models. The first prototype was composed of aluminum, carbon fiber, and polyurethane rubber -- all waterproof, sandproof, and non-corrosive materials -- and includes a curved toe design and rubber block used to mimic a flexing ankle and thus improve comfortability and functionality and several drains to waterproof and sandproof the prosthesis. Manufacturing occurred on the Cal Poly campus utilizing the Mustang 60 machine shop, the Cal Poly Composites Lab, and the QL+ lab. Funds were available to outsource parts if needed. The Sand Foot team manufactured the first prototype and sent it to Sgt. Brady for product testing and feedback. Unfortunately, the carbon fiber sole broke in transit to Sgt. Brady, and a thorough investigation determined the break was caused by impact. Poor manufacturing practices and unfamiliar materials resulted in a brittle sole. The team quickly pivoted and redesigned the sole using aluminum tubes, aluminum fittings, and canvas. The new design featured a curved toe and fit with the intended flexing ankle mechanism. A local amputee tested the final design. The amputee positively comments on the prosthesis’ functionality and comfort, while weight, shape, and sand proofness were concerns. The feedback was helpful for the team as well as engineers and student who wish to adapt the design and improve others’ quality of life.