Based on Sandy Noble's Polargraph: http://polargraph.co.uk
This is the first pass at a printable gondola for a Polargraph. It works, but it could use some tweaks.
Anyone looking to improve it: the lower section arms are a little thin, and the spot for the captive nut isn't exactly sized right. I'd also beef up the upper chain mounts, as there's not much plastic outside the hole.
The motor brackets and pulleys I'm using can be found here: http://www.thingiverse.com/thing:12403
Lots more photos of the whole process here:
Print it out, no assembly required. Uses an M3 bolt to adjust the grip on the pen, and another to mount some kind of weight on it. You could use washers, I used quarters with holes drilled in them.