The world’s cheapest, simplest possible pen-plotter.

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

BrachioGraph plots cheerful, low-fi drawings, and can produce robotic sketches using a variety of drawing implements.

A BrachioGraph can be built for about €15 in an hour or so, using a Raspberry Pi computer, hobby servo motors and household items. The BrachioGraph library is published on GitHub and includes simple Python code to drive the plotter and vectorise bit-map images.



Start here: build the machine, install the software, make your first drawings

How-to guides

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


Guide to key classes and functions


Understanding the mathematics, choosing hardware

From bitmap to plot via vectorisation#

'Anselmo' 'Prague'

The BrachioGraph community#

BrachioGraph benefits from contributions from the open-source community, and independently-created community resources. These include videos,, a web version of the linedraw software used to vectorise images and 3D printed plotter components.

About the documentation#

This documentation uses the Diátaxis documentation structure