This is a modification of a ball chain pulley, and a part to attach rolls of pennies (or other weights) to a ball chain for use as part of a Polargraph drawbot: polargraph.co.uk/
The Ball-Chain Pulley wheels are modified from "Parametric Ball Pulley" by zignig (http://www.thingiverse.com/thing:1322) to fit some old stepper motors I had and the chain I am using, and be able to mount then from the back of the board.
The small, quick-printing, and versatile second part is made to attach weights (I use rolls of pennies) to a ball chain using zip ties. It is parametric, so you can measure your ball-chain and zip ties. This is a simple replacement for "Weight for swinging pendulum" by Bre (http://www.thingiverse.com/thing:17016)
Print out ball chain pulley, attach with a captive nut (optional) and a screw to your stepper motor axle.
For the weight attachments, print it out (the orientation of the file works best on my Makergear Mosaic). You can thread zip ties through the rectangular holes, and zip them around a roll of pennies or other weight. Then pull the ball chain through the hole, and lock it in by pulling down.