Looking forward to the pcb’s! 🙂

And there’s a version of the firmware called polargraph_server_serialstepper_itead, and that is set to use serial stepper drivers (a la RAMPS), but it doesn’t have any extra mega-ability. To get it to work, what you’d need to do is change the pins it uses – It’s configured now to use ITead’s serial stepper shield, so there’s a section near the top where the pins are being defined that starts
// pin outs for the ITEAD motor driver shield
… [and then there’s 8 lines of pin definitions]

Replace that little block with

// pin outs for the RAMPS motor driver shield
const byte motoraStepPin = A0;
const byte motoraDirPin = A1;
const byte motoraEn = 38;

const byte motorbStepPin = A6;
const byte motorbDirPin = A7;
const byte motorbEn = A2;

and that sets it to use the X and Y motors on the RAMPS board. Now, RAMPS has the enable pin available, so that needs handling too (the ITead shield has the enable pin hardwired to ground so it can’t ever be disabled). It needs to be pulled low to enable the driver, so you’ll also need to add

pinMode(motoraEn, OUTPUT);
pinMode(motorbEn, OUTPUT);
digitalWrite(motoraEn, LOW);
digitalWrite(motorbEn, LOW);

to the void setup() procedure in the sketch.

This compiles ok for me, but I haven’t tested it for actual workingness on a bit of hardware – the actual pins I’m using on the polarshield are different again.

You can check out the source code from http://code.google.com/p/polargraph/source/browse/#svn%2Fembedded%2Fbranch%2Fpolargraph_server_serialstepper_itead

Good luck!

Thanks for the site and project in general,
Josh

Just posted some info on homing on my blog and also added a video

http://arckarts.wordpress.com

Bob

One solution to that is to use a more torquey motor so that it, itself, can carry and hold the weight of the gondola (just like you would with a thread+spools setup), and the spring-loaded takeup reels are just there to keep things tidy rather than to provide a counter-force.

The main reason to stop the dangle is to make landscape-orientation machines easier.

It would be nice and easy to have the trigger tripping on the vertical part of the cord run. You would need to tell it what the total length of the cord is, from gondola to trigger, but the trigger could just clip on. That’s a bit simpler than I was thinking, and removes the issue of having to find a trigger that can go partly around the sprocket.

I was planning on having a magnet a fixed distance away from the gondola (30cm or something), and the machine could use that to calibrate the gondola’s position in it’s own coordinates system.

Then there would be another magnet on the dangling end that would control the maximum extension. I reckon there’s some clever thing we can do to use it to measure the size of itself somehow too (the distance between the sprockets/sensors), but I need to draw it and scribble to figure that out.

A lot of this is to do with the idea of making it “automatic”, unattended. So it’s gilding the lily for most of us that run a machine that sits next to us so it’s easy to reset and rehome.

Have you decided to go with reels for collecting the beaded cord, or go back to counterweighted dangling cord for the default setup? I ask because it seems easiest to make the weights (or something attached to the cord above the weights) trip mechanical switches below the sprockets for homing. Yeah, that would move the home-point to bottom center. I seem to remember discussing this long ago, but I don’t remember your reason for not wanting to do it.