Polargraph at the Edinburgh Science Festival

So I’ve finally been able to step away from the new installation that I’ve been building to be presented as part of the Edinburgh Science Festival, in the Grand Gallery in the National Museum of Scotland. It’s pretty swish.

Polargraph at Edinburgh Science Festival

A little PC inside uses a webcam to detect faces in the crowd, and the faces that stay still are snapped, cropped, converted to line art and then drawn out on one of the two drawing machines either side.

The machines themselves are a new prototype breed of Polargraph, with Teensy 3s at their hearts, and Easy Drivers doing the moving. The guts of them are laid out as on an dissection table.

Polargraph at Edinburgh Science Festival

The drive chain consists of a stepper motor and an optical encoder, coupled by the beaded cord. The encoder keeps track of the true position of the cord, and so these machines are wonderfully robust. They can hop and skip, get pulled around and abused and they do not lose position.

PolargraphPro transmission

Small magnets sewn onto the cord, and reed switches above the encoder wheel make self-homing trivial.

PolargraphPro homing mechanism

The pen lift is half a lolly stick, hot-glued onto a servo motor, blu-tacked onto the gondola.

Polargraph at Edinburgh Science Festival

The controller is a Python Flask web app, publishing its interface as a web page. It is very simple at the moment, but is pretty extensible. Part of the app is a core class that encapsulates the communications, queueing and commands. Writing this in Python rather than Processing / Java has been a resoundingly positive experience (less so actually installing Python and it’s libraries on Windows – but you win some, you lose some).


The firmware is a stripped-back version of the standard Polargraph firmware, using a couple of nice Teensy features – namely the IntervalTimer library to deal with serial concurrent serial comms.

The Making It exhibition runs from the 5th to the 20th of April, in the Grand Gallery of the National Museum of Scotland. It is presented by the Edinburgh International Science Festival. You should go and see it!



5 thoughts on “Polargraph at the Edinburgh Science Festival

  1. That looks really cool! How long between snapping a pic to a finished face drawing?

    I see it dispenses hot and cold beverages, too. Amazing! ;-)

    • Ha no the drinks are what you need to put in to make it run. The blood is in the insulated cup and the sweat and tears are in the bottle.

      Image acquisition takes a second, conversion to vectors takes a minute or two and a drawing takes about 10 minutes, but it gets through plenty because there’s two of em running at a time.

        • I haven’t, but the science communicators (staff on hand) are really great, and getting good at working the exhibit, so I really should go and get some clips. It doesn’t have an awful lot of immediacy as an interactive thing – a bit of hurry-up-and-wait, which is a bit of a shame, but it is interesting while it draws.

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