Myoelectric Prosthetic Arm

Designing the finger

The team set out to build an affordable prosthetic arm controlled by electromyography (EMG). My mechanical work focused on closing a three-joint finger with a tendon routed through grooves at the joints.

I modeled the joint range of motion and tendon displacement and checked clearances through the motion. The design included a separate return tendon for opening the finger. The grip test used the closing tendon alone.

Sizing the servo

I estimated the tendon force from the finger geometry and used a hand scale to pull the prototype’s tendon until the finger reached the grip I was targeting. The scale measured tendon tension. I used the average measured tension and the servo spool radius to estimate the torque at the spool.

The resulting servo torque requirement was approximately 12 kgf·cm (1.18 N·m). The grip endpoint was based on feel, so this value served as a component-sizing estimate. A calibrated fingertip force test would be needed to quantify grip strength.

Prototype and documentation

The mechanical prototype weighed 390 g before electronics. I documented the hand and forearm assembly, the electronics layout inside the housing, and the geometry of the middle finger. I also co-authored the team’s technical report.