Spring 2017 Prosthetic Arm: Gear Test

The Robot Company | CEO Professor Gary Hill

Blog Post Created by Project Manager | Bianca Esquivel

Project Test Executed by Manufacturing and Design Engineer | Cedric Yannick Mbetga

Preliminary Information

Test Objective

Purpose: The rotation of the wrist is controlled by the servo, MG996R, which will be located in the lower arm. The 90 degree turn (L2-2-1 requirement) of the wrist is met by applying the appropriate gear ration of 17/11= 1.55.

Two gears are designed:

  • Driven gear with 17 teeth
  • Driver gear with 11 teeth

To avoid the prosthetic hand wire bundle hanging out from the connection of the hand and the arm, a hole is drawn through the driven gear such that the wire bundle can be placed through it and so the wires are able to reach the PCB in the arm.

Aim: Verify that the the two designed and printed gears will rotate accordingly to the gear ratio and make the 90 degree turn. .



3D Printer

3mm Blue PLA

Test Set Up


The gears have been printed out and they are able to be used together to be controlled by the servo.



The gears of the design to rotate the wrist a full 90 degrees are able to work to fulfill the requirements listed above.