I have been playing with Drawing robots / Polargraphs for a few months now, first inspired by my friend Matt Venn’s Energy Monitor: http://www.mattvenn.net/2011/09/19/polargraph-energy-monitoring/
and later Sandy Noble’s Polargraph: http://www.polargraph.co.uk/
Like many projects, I have ended up making many revisions / versions of my drawbots. First, there was David, then Derek, then Doris, Delilah is the latest, and next up is Deirdre [can you spot a theme?].
There are many problems/issues/obstacles/characterful niggles that one comes across when building a drawing robot. I won’t list them here – take a look through the polargraph forums, or have a go at making your own to find out!
One challenge is the pen holder:
- must hold pen securely enough for drawing
- nice if can change pen easily
- needs to also hold servo to lift pen
- detachable from holding wires for transportability
- place to attach weight
Early experiments by Matthew and Sandy addressed some of these problems, but often included extra / hard to find parts, or more expensive parts, etc. Then Sandy (I think) came across Mr Drew’s pen holder (name of a drawbot by Darcy Whyte of mambohead.com ) and put it up on his own site.
There are pros and cons to different designs of pen holder / gondola – I was keen to address some of the cons of the holders I have been using and seeing how my own changes affected performance / usability.
Bigup Darcy and mambohead for sharing their Mr Drew pen holder! I can’t find the original file link, but Sandy has it up on his google code hosting (sketchup file) here:
I downloaded this file, converted it to dxf for my laser cutter and made one up. After getting a spring from an old printer in my junk store, I had a nice, easy-to-swap-your-pen, pen holder. Sweet!
After a bit of use I had a few thoughts of design improvements [in my eyes] and decided to make a few changes.
It is entirely possible/likely that I didn’t assemble the parts as intended (I used ~60% of the parts in the MrDrew file) but I had a working holder. From that base I tried:
- extend string hooks for easier stringing/de-stringing
- reduce number of components
- modify sprung arm to clear spacers
- modify pen holder to include servo holder
- extend weight attachment position
- widen pen space to allow larger pens to be held
- extended lever handles on sprung jaws
You can download my design here:
All files above are shared under a Creative Commons Attribution ShareAlike 3.0 Unported license – for more details see the Creative Commons website.
In addition to the laser cut parts (I used 3mm sheet stock), you will also need:
- 2x M3 40mm machine screws
- 2x M3 16mm machine screws
- 4x M3 nuts
- 10x M3 nylon washers (optional)
- 1x small spring
- 1x micro servo
- drawbot, pen, etc etc
Big nice to Matt Venn, Sandy Noble and the many other drawbot / polargraph people doing lovely things.
UPDATE - fatter pens
My first revised version could hold Sharpies but I got hold of some fatter markers that I wanted to try, so I did some more tweaks and have two other versions available – one that can take pens up to ~20mm in diameter and another that can take up to ~28mm diameter (pretty chunky markers).
Grab the files here: