This weekend I built a polargraph from random junk around NYCR. It’s amazing how much stuff we have available for projects, if you just take the time to dig through our thingsgiving bins. This one used NEMA17 stepper motors and pulleys, a surplus tinyg board and a dry-erase marker suspended from thread found in the fabric bin.
Originally the servo was going to lift the pen, but I ran out of time to integrate the servo with the tinyg system, so it just drags the pen between elements. The pen’s angle isn’t controlled, so sometimes it “gouges” the whiteboard and skips around. Hackish source code to generate the gcode and more details are at trmm.net/Polargraph.