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.

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 abd includes simple Python code to drive the plotter and vectorise bit-map images.

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



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

How-to guides

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


Understanding the mathematics, choosing hardware.


Guide to key classes and functions

From bitmap to plot via vectorisation

'Anselmo' 'Prague'

The BrachioGraph community

BrachioGraphs 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