I’m still waiting for motors, but in the mean time I have been busily printing cases and soldering polarshields.  An hour and a half now – now bad.

Here’s some new Polargraph motor brackets I’ve had made.  These have a couple of little improvements over the old designs that make them a little neater to install.  Cable management really:

But the other feature is that they can also be installed upside down, with the motor hanging rather than being lifted – this should make cables even tidier.  Harder to mount and unmount however.

Sorry for the continued wait folks, and thank you for your patience.

The Polargraph factory (my living room) is in full swing today.  I had a bit of downtime when my 3d printer decided to start acting the goat, but I stripped down the heated print bed and rebuilt it, and it’s going gangbusters again.  I’m printing in ABS.  It doesn’t look that nice, but it’ll be better at taking the heat that these more powerful stepper drivers can pump into the motors.

I’m hoping to have this first handful of PolargraphSD kits on their way to their owners during next week, and at that point I’ll take a little stock to figure out how much they really cost all-in.  The boards themselves are really cheap, but they use all SMT (surface mount) components and I know a lot of folk are wary of that – so will probably offer an assembled shield as part of an upgraded vitamins kit.  I’m getting the hang of it.  Don’t know what all the fuss was about!

Also, doing lots of drawings.  These micro-stepping step-stick drivers are wonderfully civilised, so quiet and gentle.  I miss the L293D’s singing a little though.

A few things came out of my initial tests:

1.  The board, fully populated, is prone to resetting while handling with fingers.  Now this, obviously is pretty disasterous and indicates something operating very close to its reset threshold.  I’m using a transistor in the XBee circuit so that the board can be reset by the XBee – this should allow remote programming / firmware upload, and I _would_ like to have it.  When I take this transistor out, then the board is robust, and doesn’t reset itself.  I will have a closer look at this and hope it is a matter of tweaking component values either side of the transistor.  If not, then I am going to dispense with the transistor entirely.  It has dual footprints, so either a SMT or through-hole part can be mounted, and if you’re happy with the risk, you can solder them in yourself. If it isn’t there, then everything will still work ok, but you’ll need to plug in with a wire to do upload firmware.

2) The voltage divider that handles the SPI interface to the SD card didn’t work.  Seriously.  I can see now that it’s obvious that it won’t work (5v input, 10K resistor between output, and 10K resistor to ground.  I guess the circuit was shooting for 3.3v output?).  I went back to check the source of the circuit to see what was different about that … turns out that doesn’t work either, and never has. Fixed by adding links instead of resistors in half of the divider.

3) Orientation.  The screen mounts onto the top of the board, and orientates the board so that all the cables come out the bottom.  While this looks very neat in a sketchbook, or when hanging up, it is a pain to work with loose .. because there’s no bottom-edge to put it down on.

4) Screen orientation.  The screen can mount directly to the board if the board has female headers attached.  This makes it really neat and handlable but perversely makes the problem above (wires coming out the bottom – oof) more of a stinker.  A solution is to put male pin headers on the board, and have the screen mounted on a short piece of ribbon cable so it can be orientated separately.  Thoughts about this are very welcome as the board can’t easily have both male and female headers, and there’s no going back once they’re soldered.

Currently looking at shipping these initial kits first thing next week.  Four days late, tsk, sorry about that everyone.

Progress is good!  Four or five days behind where I was hoping to be, but on balance, good.

Got my polarshield circuit boards through at the end of last week, and extremely relieved (and frankly shocked) that there are no horrible errors on it.  I did forget to order some parts that I need to test the XBee side of things, but those’ll come shortly.

Soldered up the first one without any problems – first time I’ve done anything significant with surface mount stuff.  Slow, but not the big challenge I feared it might be.  A few things that I’d do differently next time round came up but I’ll do a proper hardware review another day.

The real message is: It works!

Now, lets get this software into shape…

There’s a graffiti supplies shop in town, Spectrum Arts, run by this dude called Mark.  I approached him about putting a machine in his window – he’s got some covetable glass, and is a nice guy.

It’s been there for a while, but I’ve just got the kit to fit a big fat chalk pen in it.  I used this gondola that Stuart Childs designed which did the trick nicely.  Thanks to Stuart for this – very timely, and I think I got some great first results out of it too.  The slow speed of the vector drawing means that gravity can keep the tip supplied with ink.

Am hoping to formulate a sequence of drawings to go in the window, but would love to see something graffiti based, am thinking of a GML-aware system that can accept tags from all over the internet and mark them out on the glass.  For now, it’s just manually controlled, but it communicates using an XBee and has an SD card too, so that’s nice.

I always had a terrible fear of Eagle, the PCB design software.  It’s been written by and for engineers, which is great if you are one, but as a beginner to PCB layout and design it’s horrifically opaque and counter-intuitive.

But it’s gotta be done, so I soldiered on and successfully produced a suite of gerber files for a little breakout board that I need for the motors.

And I think it actually worked!  It’s off to the PCB makers anyway, so that’s exciting.  Actually it turned out to be – like most things – pretty easy when you know how.  I am positive I have done something wrong, and these will come back twice as big as expected, or with the text reversed or something.

This is a tiny board that will accept the 2mm pitch ELCO 8283 connectors that are on the end of my motors, and present a set of 2.54mm pitch pins which is a much more useful kind of connector to have.  Current plans are to use this 22AWG ribbon cable with these IDC connectors on the ends to produce the motor wires.

Didn’t really need a pic for that, but it’s so adorable I couldn’t resist it.  That shouldn’t be too onerous, and the mess and faff crimping the motor cables was always the main source of sore fingertips and misdirected rage for me in the past.   And they are a bonny colour too.

I plan to produce a variant of the motorshield that has 2.54mm pitch connectors instead of (as well as) the screw terminals currently on there, so I won’t need to make funky breakouts for the connectors on the motorshield end.  This is A Good Thing.  I’m gradually moving to a “designed” machine rather than a cobbled-together one.

I’m working on this Polargraph SD machine (basically the prototype for Polargraph SDs to come) for an artist who won’t be able to run “tethered”, so it was necessary to make a little doofer to control the machine.  It works!

This is just two buttons, and three little LEDs on a bit of stripboard, with a little 3D printed case.  The button signals and the LED sources are on pins A1, A2, A3, A4 and A5.  First click engages the motors and sets the position to preset value (i.e. the home point), and then you use the other button to select the command source to use, choosing between USB and SD card.  Then once that’s changed to SD card, and the start button pressed again, then it immediately starts reading its commands from a preset file on the card.

This is a little crude at the moment, and I think the code should be more-or-less rewritten to allow things like pausing and cancel / reset, but it’ll do the job. I don’t think a remote like this will be part of the standard Polargraph SD kit, but a couple of buttons might sneak in.

I’m thinking of the custom board being something like an add-on shield for a Mega / Sanguino, with motor drivers and an SD card reader built-in, but with passthrough headers to allow an offset shield to be added without getting in the way, and using an off-the-shelf LCD+buttons shield for hardware control.  Basically a mega motorshield.  I can’t really decide between a L293D/SN754410 (a la adafruit) setup or a A3988 (eggbot/pololu/stepstick) based design.  Any feelings either way?