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 in an hour or so without any special skills. The total cost of all components can be as low as €15 or so. Apart from a Raspberry Pi computer and some hobby servo motors, the plotter can be built with everyday household items such as a clothes-peg. The software in the BrachioGraph library includes code to drive the hardware and vectorise bit-map images.

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.

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