Prosthetic Hand Project

Designed a low cost prosthetic hand
Highschool Engineering Independent Study Project

Hand Design

InMoov is an open source project from French designer Gael Langevin that provides detailed instructions, 3D printing files, wiring schematics, and code at no cost. The base design started with this project's design.

Concept of Action

The prosthetic works by replacing tendons with two strings that are pulled by servo motors in the forearm. The string on the top side is responsible for pulling the finger into the palm, while the bottom is used to bring the finger back to the resting position.

The placement of the strings is shown in the photo on the left, where the exposed top string in the thumb is further illustrated using the white dashed line.

When the line is fully threaded through the finger, it must be tied off and covered with the fingertip piece, these are shown as the circles labeled 1 and 2.

The lines are threaded through the wrist tunnels into the tensioning system.

The tensioning system consists of .5 mm springs with silicone tubing to prevent damage to the tendon strings.

The tendons are threaded to the servo caps, the physiological inputs and the code then determines if the servos turn clockwise or counter clockwise. This results in a finger closing or relaxing.

Electronics & Code

The electronics of this project were kept simple. An Arduino Uno, PWM/servo driver, and a Myoware sensor. The five servos and Myosensor was wired to the PWM using jumper cables. New electrodes were used for each use of the test runs of the electronics.

The code was adapted from Carlos Alquezar, the code intakes the analog data given from the Myoware Muscle Sensor and assigns it a value between 0 and 800. If the mean of the incoming 10 variables is higher than the threshold value, the servos would turn to their closed position.

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Skills Advanced

  • Mechanical design

  • Wiring

  • Coding

  • 3D modeling

  • Engineering Design Process

  • Project management