Howdy, Team Heck!
My name is Major, I'm a long time fan, first time writing, and I think I got a project that would be up your alley.
I make board games as a hobby, and I've found that prototyping card components is a pain. My options are to print out sheets of cards on card stock which is expensive and can be ruined if the double sided printing doesn't line up, or to purchase blank cards that can't be used in a printer because of their size.
I did some homework into how printers work and how to make my own only to find out that despite the almost universal disdain commercial printers receive, the DIY community for 2D printers is almost non-existent, but I did find some that were made from salvaged optical drives or laser cut wood parts and Arduinos.
My challenge for you is this:
Make a 2D Plotter that can be used to print images on blank playing cards using markers (or some other affordable/disposable method) to make rapid prototyping possible and look good. Bonus points if it can print in color.