arckarts

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It’s been a while since I posted on the blog but I have been busy. I’ve always been interested in the juxtaposition of art and technology stemming from my engineering and photography backgrounds.

I started researching drawing machines and was inspired by Marginally Clevers machine http://www.marginallyclever.com/ and also the Polargraph http://www.polargraph.co.uk/.

I’ve done most of my work with the Polargraph software as I like the interface however Marginally Clevers is also very good!

I made my first drawbot using an old white board and some parts I made up on my Thing-O-Matic with a couple of steppers from eBay and was very pleasantly surprised by the results. I showed this at our local art association (plug plug please visit www.bvaa.org)  and everyone was blown away by the possibilities.

So, I started on the MkII version.

• Bought a 2x4ft piece of 5/8″ particle board from the local home centre as it is nice and flat and reasonably stable
• Printed up some stepper holders from Thingiverse  http://www.thingiverse.com/thing:16725
• Added some leds across each phase of the motor as eye candy
• Ditto the  pen holder http://www.thingiverse.com/thing:19426
• Glued it to a transparent CD that you get in the bulk packs
• Added a pico stepper to raise the pen
• Use 50lb Omniflex braid fishing line for the cord (note: i don’t use a suspension system like the others, I just wind the cord around the spool)
• I use two circular hooks to direct the line and fix the x dimension

This worked pretty well and I’ve been tinkering with it for a while.

Then decided to add a homing routine which took quite a while to get working to my satisfaction. ( I will post the code somewhere for y’all, not quite sure where yet!).

Several issues

• As I’m not using a suspension system the cord would unwind, get tangled up and often reverse direction
• Sensing the home location proved a challenge using microswitches

So, in the best KISS principles I added some copper foil to the edge of CD gondola portion and connected this to OV which was available in the servo feed. Then hooked up a couple of LED’s tied to 5V via a 1K to the circular eye hooks and used two of the spare analogue inputs on the Arduino to sense if the gondola had hit the relevant home location, which would also light the led.  This worked!!

To get the software working reliably I had to play with the algorithm, here’s the general idea in pseudo code

• De-energise right stepper
• Rewind left stepper until contact made
• De-energise left stepper
• Rewind right stepper until contact made
• //now we know how many steps from L to R
• Move right motor away from home
• Rewind left and wind right, move to left home
• Verify at left home
• Use machine dimensions from Arduino sketch to move to centre location first left, then right
• //complete

To make it easy to use I added the homeRoutine() call into the HOME command (C06) issued by the PolarGraph controller and it works great!

I must say that I greatly appreciate all of the work done on the previous Drawbots and there designers !! Couldn’t have got it working without you!

I’ll add some more details and photo’s, please let me know if you like this or need anything from me