Summary

One-piece printable drawbot/polargraph gondola intended to replace the CD-based, pop-riveted lash-up I had been using up to now. Contains mounting points for a bulldog clip (fix into place with two M3 bolts), micro servo for pen lift and M10x75 bolt & 3 nuts for weighting. Beaded cord will fix through the pen holder with no additional fixings.

Printed at the Bristol Hackspace on a RepRap Mendel.

Instructions

Print the gondola - warning: overhangs! You may find that the first few layers of the edge don't adhere very well near the bottom, this wasn't serious on my print and just required a bit of sanding

Drill two holes in the back of a bulldog clip - the drill bit will certainly wander unless you centre punch it. Once the holes are drilled mark the required holes on the bracket and drill through the plastic, I didn't include holes in the bracket because I found it hard to drill the bulldog clip accurately. I used M3 bolts to fasten the bulldog clip in place, this takes up a bit of space inside the bulldog clip but helps to centre the pen.

Drill out the pilot holes for the servo mounting to the size you need, then fix the servo screws.

Thread the beaded cord through the holes in the bracket under the bulldog clip, the arrangement is shown in the picture of the assembled part but you generally need to have the cord come out of the upper hole, pass through inside the bracket between the holes, out of the lower one again and underneath before being mirrored on the other side.

NOTES: the hole for the pen lift arm of the servo isn't quite in the right place on my version, I'll alter it on the next iteration but it seems to work and could easily be filed down if it binds too much. The overhang around the edge is a pain to print, I'll probably alter it for the next one. It's hard to access the pilot holes for the servo mount when drilling them out, I might move one of them to the other side or change to a different mount principle. The base plate is probably strong enough but it feels a bit thin, I might bump the thickness up a bit. As it stands it is functional but not very 'polished'.

NOTES (after first use): the bulldog clip can interfere with the cord, this can cause quite a lot of lack of precision so I found it best to thread the cord through the centre of the clip arms. The servo position seems to work well, I get clean lifts with no odd movements at the start or end of lines. The width of the support (around 15mm between the ends of the cord) needs to be considered in any driver code, as does the height of the pen above the cord attachment (also around 15mm). Overall: works well, still needs a few changes.

Drawbot/Polargraph Gondola