[sleepybrett]

there are several versions of this basic robotic design available for purchase both diyish and fully fledged products (neither one I'm about to list is spray paint based though, but in the case of the diy version, it could be hacked in with a redesign of the 'shuttle')

Sandy Noble's Polargraph (diy and very hackable) : http://www.polargraph.co.uk/

the Scribit (buttoned up product with multiple pen support) : https://scribit.design/

This looks like the exact same system but because of the pendulum effect when you "turn a corner" these guys wen't with just running it up and down in vertical lines and only moving a bit to the side when the line is done.