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.
An interesting link found among my daily reading