BrachioGraph - the cheapest, simplest possible pen-plotter

BrachioGraph - arm-writer - is an easy-to-build pen-plotter, driven by a library of simple Python applications.

The hardware

The plotter is made of:

  • two sticks
  • a pen or pencil
  • a clothes-peg
  • 3 servo motors
  • a Raspberry Pi, to drive the servos and run the custom code
  • glue

Total cost: ~€14

The software

The software in the BrachioGraph library includes code to drive the hardware and vectorise bit-map images.

From bitmap to plot via vectorisation

'Anselmo' 'Prague'


Get started

Build the machine, install the software, make basic tests

How-to guides

Improve the calibration, process images, visualise plotter behaviour, alternative designs


Understanding the mathematics, choosing hardware.


Guide to key classes and functions