Thanks! We're always testing our assumptions to keep the complexity out. Actually our original build was a Watercolor Bot (http://watercolorbot.com/). Although it managed to do a few pick and place operations, ultimately (and as predicted by everyone) it had way too much backlash.

Regarding y-axis I hear you. I've got an old Mendel of my own sitting around gathering dust. The issue is really that a pick and place for moving y beds would have to be a very different design.

It would be cool if someone took our work and made a fork that focused on Mendel-type printer compatibility but the focus of the RetroPopulator project for now is on getting the pick and place functionality working.

Regarding a secondary control board, I do wonder if ultimately we may end up adding one for some super-high-end version of the design (maybe even going as far as to design a full-fledged p+p-specific Populator cartesian bot at some distant point in the future). It's certainly a possibility.

The second board would mean a significant software change. I'd need to write a Tegh* driver that can control two arduinos. And we'd need some way to sync their movements.. that would be difficult since GCodes are buffered on RepRap firmwares so you don't get any notification of the completion of a movement. Then again, we might even just be able to use timing to sync them. It doesn't need to be super precise if it's just a part rotation during travel. Weird. Definitely possible though..

Thanks for the idea and taking the time to check out the project!

*Tegh: my Wifi RepRap control software, it's a cross between Pronsole and OctoPrint.. I've got a lot of documenting to do on the software side :)