IOU Theatre (Dean Clough Halifax) ran a workshop last week on making simplistic motorised drawing machines. Here's a video explaining the method: https://vimeo.com/154420315
About 21 mins in, there's a trial of everyone's machines on a very long roll of paper: It's a useful way of seeing the range of machines & results.
In case anyone wants to check it out further, I left my contraption at the hackerspace. Due to time pressures, instead of sawing, drilling & soldering as per the demo, I took a pragmatic approach to be sure of completing a working model - you can do a lot with gaffer tape . . .