A hand that copies mine

I built this robot hand in February and March 2026, mostly at home. It copies whatever my own hand does in front of a webcam, finger by finger.

How it works

A Python script reads the webcam with OpenCV, and MediaPipe finds 21 points on my hand. For each finger the script turns the distance between fingertip and knuckle into a bend value from 0 (straight) to 1 (bent). The values are smoothed against jitter, converted into five servo angles and sent over USB to an Arduino Uno.

The Arduino sets each micro servo to its angle. Each servo pulls a string tendon that runs to a fingertip, so the finger curls when the servo turns. The screen shows the tracked skeleton and the angles sent.

From cardboard to 3D print

The first version was cardboard: a cut-out hand with five micro servos on the palm. Once the Arduino drove all five, I split the fingers into taped segments the next evening and ran tendons from the fingertips to the servo arms. That same evening the hand followed my movements.

One fix was needed: the newest MediaPipe release dropped the hand-tracking module my script used, so it crashed on startup. A separate Python environment with an older version solved it.

For the second version I 3D printed a hand with hinged finger joints and a forearm that holds the servos. Each servo turns a spool that winds up its tendon. The servos run on a computer power supply through a breakout board, because together they draw more current than USB can deliver.

What I learned

Cardboard let me test the whole chain, from camera to fingertip, in two evenings. Keeping tracking, communication and mechanics separate also made problems easy to find: the angles on screen showed right away whether an issue was in the code or in the hand.