college of engineering white

Project 3a: Prosthetics for percussion


This initiative has been developed to address the distinct requirements of a young woman traversing her middle school journey while confronting the obstacles presented by bilateral amputation. With extreme attention to detail, our primary goal is to create a prosthetic arm, precisely engineered to enable her participation in percussion activities with a seamless blend of refinement and skill. Through this endeavor, our aim extends beyond mere functionality; we aspire to instill within her a profound sense of empowerment, fostering the confidence and grace necessary to fully embrace her passion for percussion.

Back Row: Micah Page, Zac Fisher, Elijah Sayer, Michael Cantrell Front Row: Branson Blaylock, Addie Johnson, Luis Flores-Moreno, Zakary Henson, Andre Braden Not Pictured: Andrew Sobol

Problem Statement

The client we have been paired with is a middle school girl who is a bilateral amputee. She is in a band class and wants to fully participate in percussion. Our challenge is to create a prosthetic arm that has an attachment for a drumstick, is comfortable, and durable.

Design Specifications

For this design the individual who we were paired with had a specific set of requests to be met. Initially, we intended to create an elaborate design that could do it all. Upon more meetings with the individual, we quickly noticed that she wanted a simplistic solution to the troubles presented to her. To do this we measured her arm. Upon showing her the first print of the design she mentioned to us that she wanted the prosthesis to be shorter. With our updated design we are going to be cutting off around 2 inches from the front to meet her demands.

Background Research

As of recent, prosthetic arms have been evolving to account for recent technological advancements. However, with this project being conducted by amateur engineers, researching this topic consisted of looking at materials for the arm and simplistic ways to effectively accomplish our lofty goals. To start with materials Branson was able to find some skin-safe TPU to print with that is commonly used in applications such as ours. Following that, he also found some durable yet flexible TPU that we are going to use for the outer shell. The debate in our designs comes down to how we want to fasten the prosthesis to the patient’s arm. Setting this aside, we plan on using a similar “hand” design as used in the hero arm with an easy and detachable section that would hold the percussion sticks.

Concept Design 1

The rough idea for the sleeve is to have a function that tightens as a nob is twisted as seen in the sketched picture below. This should also be made of a flexible printing material that is more skin-safe.

Concept Design 2

The main inspiration comes from a “Hero Arm” design seen below. The idea would be to securely hold the drumsticks, look aesthetically pleasing, and remain comfortable/safe throughout any performance/practice.

Concept Design 3

The idea for the main device/mechanism is to provide a secure way to hold multiple styles of drumsticks and fit comfortably on the arm of the client. Since both arms are developed differently (one arm not having the elbow joint), two different assemblies are required. Both versions are displayed in the image provided along with a potential idea for the stick-clamp.


Selected Concept Design

The selected design is a combination of concept designs 1 and 2. Our decision to go with this design was determined in a meeting with the client in which she stated that she wanted both a nob tightener and a small simple arm. Through the combination of both of these ideas, I feel we will provide her with the best product that will be perfectly suited to her needs.

Decision Matrix

Overview of Selected Design

Our selected design consists of a TPU outer shell accompanied by a neoprene sleeve on the inside to keep the individual comfortable. To tighten the apparatus we will also have a boa fit tension system to secure it to her arm.

Describe Design Details

The outer TPU design is made from Ninjatek 95A which has hexagonal perforations for ventilation and additional flexibility. The neoprene sleeve is a medical-grade sleeve that was engineered specifically for prosthetics. The benefit of utilizing this is it adds comfort to the user of the prosthetic and ensures it stays adhered to the individual after fastening. The last major detail in the design is the boa-tightening device. This device has many benefits in this circumstance. First, the client can tighten the boa with ease. Secondly, the boa can efficiently distribute the tightening pressure across the prosthetic. Last, the boa is durable and able to withstand the impacts of percussion use.

Engineering Analysis 1

One thing that we had to consider is the thermal properties of the material that we selected for the arm. Among such considerations was the ductile to brittle temperature transition, also known as glass transition, for the TPU. To find out if this would be a problem, we searched for the company’s technical specs for our selected material. We found this temperature transition to be   -11 degrees Fahrenheit. This is lower than any temperature she would ever be playing drums at so we proceeded as planned.

Engineering Analysis 2

One of the things we wanted to analyze was the elastic region of the stress-strain curve for our selected material. Again, we looked at the technical specs for our materials and created a stress-strain curve from that information. This curve shows how strong the material is while remaining flexible. The yield strength for this material is far more than it will ever have to endure so the client will be able to use this arm for years to come.

Engineering Analysis 3

Shore hardness, particularly 95A, refers to measuring the material’s resistance to indentation using a durometer. The specific rating indicates a moderately hard but still flexible for her prosthetics. The most common 95A applications are caster wheels and industrial seats for damping. This was an important factor when choosing the material for this project since PLA, ABS, and PETG are hard but not flexible for comfort. Although TPU 75A was too soft, and malleable and wouldn’t be durable enough to withstand drumming purposes.

CAD Drawings

Bill of Materials

Document Fabrication Process

To create the prosthetic for our client, we used an iterative design process. To begin, we took measurements of the client’s arm and made our CAD model as iteration 1. Because the prosthetic is 3D printed. We were able to make replicas and changes with ease and at an extremely low cost. We printed each arm on a personally owned Bambu Lab P1P printer using a TPU filament which is traditionally used for prosthesis. The general process for our iteration was: modify, test fitment, receive feedback, repeat. With the quick attachment and detach system. We again modeled and tested a few different designs and settled on a final design that the client was happy with.

Testing Results

The testing results for the prosthetic were largely successful. The prosthetic as well as the attachments were put through extensive impact loading, bending and torsional stressing. The arm itself withstood all testing it was subjected to with no failure occurring. The attachment system withstood all axial and impact stresses. It was also able to withstand being twisted five hundred forty degrees before failure occurred. These results support the durability and longevity of the product for the client.

Completed Design Photos

Instructions for Safe Use

There are not many risk factors associated with the designed prosthetic. None of them pose any significant danger. The first is skin irritation. Should the client use the prosthetic without the use of a sleeve some skin irritation may occur. The second is slight loss in blood flow due to over-tensioning the tension system. The client will easily be able to tell whether the arm is over-tensioned based on the comfort of the fitment. The final is only a risk should a failure in the arm occur. This is extremely unlikely. However, should a failure occur, a slightly sharp point may cause superficial scratching. Again, this again poses no substantial risk to the client.

Project Summary/Reflection

Our objective was to create a prosthetic arm to help a middle school girl participate in band class, specifically in percussion. Our solution was to 3-D print an arm with attachments that holds drumsticks. We were able to successfully create two arms, one for the right and left. Each arm is made with TUP filament that is durable and comfortable, a fastener to keep it secure, and detachable holders for various percussion sticks. We learned a lot about collaboration, teamwork, problem solving, and time management while working on this project. It also broadened our perspective on people living with physical impairments and how they are able to overcome their disabilities. Overall, this project was very successful.


2024 Spring