Pen Drawing Robot (Mindstorms NXT)

Back when the Mindstorms NXT was the latest and greatest Lego robot, I created the following model for a pen drawing robot. I haven't had the time to revise it for the EV3, which would require a fair amount of work. This is in part because the EV3 has a third motor with a very different footprint than the other two motors. It would be interesting to work on that, but in the meantime, here is a model that anyone should feel free to employ or modify.