Helping Hands: Modular Prosthetic Hands Designed For Global Accessibility

The Problem:

High performance prosthetics are currently a luxury rather than a standard. Because of extreme costs, millions of amputees around the world are left without functional support. This is especially true in underdeveloped countries where people lack the resources for modern medical technology. This is not just a technical gap but a global accessibility crisis.

The Origin of the Project:

I started a school passion project to see if I could bridge this gap. What began as a simple 3D printed prototype built for a few dollars has evolved through nearly four years of annual redesigns. My goal is to create a prosthetic hand that is more affordable and available than a smartphone.

(Figure 1)

The Human Impact:

Physical Development: For children, a prosthetic is a medical necessity. Growing bodies require even weight distribution. Without a limb, the lack of balance leads to spinal misalignment and chronic physical pain as they grow.

Psychological Affects: The inability to engage in everyday activities can cause mental health issues during critical developmental years.

Socio-Economic Challenges: For adults in developing regions, limb loss often results in the loss of their livelihood. Without functional prosthetics, it is difficult to find employment and support a family. My project aims to restore both physical function and economic independence.

Criteria

To ensure the prosthetic hand was effective for real-world use, I focused on four main goals. It had to be easily manufacturable, strong, affordable, and fully customizable for the user.

The Design Process

I used a modular approach to make the hand easy to assemble while maintaining all core functions. My workflow relied on OnShape for 3D modelling and Bambu Studio for slicing. I chose to use 3D printing because it allowed me to test new ideas quickly, keep costs low, and allow for full customizability. This technology is becoming more available globally as the price of 3D printers continues to decrease. By using this method, manufacturing can be localized directly where the patient is, rather than being separated from the end user. (Figure 2)

Iteration

Over the course of development, I went through 48 different versions. To get the measurements for the compliant mechanism, I created a linkage system in my CAD software to test different joint lengths. I did because I wanted to know the path the finger would take during flexion and extension. Then, over 20 versions, I created the compliant mechanism finger using those same measurements. (Figure 3)

Tools and Materials

Hardware: I used the Bambu Lab A1 mini 3D printer for its precision and speed.

Software: OnShape was my primary tool for computer-aided design.

Testing: Each iteration was evaluated based on how well it met my original criteria for strength and ease of assembly.

Overview

The hand is 3D printed in only 10 parts, which are connected with a custom Printed Circuit Board (PCB). The ESP32 is the "brain" that controls the hand. To actuate the fingers, I use servo motors that rotate a pulley that pulls on the finger's tendon. The thumb is actuated using a smaller servo that rotates the thumb around the hand. (Figure 4)

Fingers:

I developed a linkage-based finger system that utilizes compliant mechanisms. By using live hinges, the fingers gain motion through the flexibility of the material itself rather than using traditional pins or joints. This significantly lowers friction and eliminates the issue of parts rubbing against each other and wearing down over time. These fingers are designed to be printed in place, which reduces the number of separate parts needed for assembly. To improve grip, I added flexible outcroppings that act as compliant pads to wrap around objects for a more secure hold.

Thumb:

The thumb is a critical part of the hand and is powered by a dedicated servo motor. This motor turns a bracket that controls the thumb position. While it is limited to one direction of movement, this is enough to perform the most common grips used in daily life. The thumb also features the same flexible, compliant pads found on the fingers to ensure a reliable hold on different surfaces.

Electronics:

The entire hand is controlled by an ESP32 microcontroller. I designed a custom circuit board to connect all the components together in a small space. Using a custom board ensures that the electronics are reliable and fit perfectly inside the prosthetic.

Actuation:

I chose to use servo motors to move the fingers. These actuators pull a tendon that triggers the finger linkages to open or close. These components were selected because they are powerful, affordable, and they have positional feedback, which increases dexterity. They provide enough force to handle everyday tasks while keeping the overall cost of the prosthetic hand low.

Disclaimer:

For all images and data, I'm using the unfinished version of the new prosthetic hand I'm developing for CWSF. This is a different prosthetic hand than the one I brought to the regional science fair. The CWSF version is an evolved version of the regional science fair version, using many of the same technologies.

(Figure 5)

Design Conclusion

The success of this prosthetic hand proves that high performance does not have to be expensive. Through 48 iterations, I found that simplification is necessary to produce reliable designs. By moving to a linkage-based finger system and using compliant mechanisms, I reduced the number of moving parts while increasing the reliability. This demonstrates that even in the medical industry, there is still significant room for innovation.

Global Accessibility

My results show that local manufacturing is a viable solution. Since the design is modular and uses affordable 3D printing technology, it can be produced anywhere in the world. This removes the barriers of shipping. It brings the production of medical technology directly to the communities that need it most.

Impact

My project confirms that prosthetic hands can become as accessible and affordable as a smartphone. It shows a clear path toward a future where a person's physical capability is no longer determined by their financial status. I believe that this is a major step towards equitable healthcare.

Next Steps

Strength:

Have four independently controlled fingers on the hand

Print the prosthetic fingers with multiple different materials (Figure 6)

Usability:

Shrink the design so that everything is contained inside the hand instead of the hand and the forearm

Create a system for intuitive communication between the human and the prosthetic

Affordability:

Make the electronics contained on one singular board without using modules, which in production would decrease the cost by eliminating redundant suppliers

Create an online store where all parts are accessible for as little cost as possible, so that anyone can have access

I want to thank my parents for supporting me through the development of my project. Additionally, I'd like to thank my teachers who provided me with the opportunity to begin this project and the teachers who have been supporting me since. Also, I would like to thank the team that runs the Quinte Regional Science Technology Fair (QRSTF) for providing me with the chance to take my project to the national stage. Thank you!

Images:

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Inspiration:

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