What do you do with a blank 50 foot wall? (Patreon)

Unlike my previous shop which was packed to the brim with project scars and the skeletons of projects past, the new shop feels cold, sterile, and just plain boring. The new shop has some huge blank walls and I decided they were a canvas just begging to be painted. Ideally by a robot. How cool would it be to have the windows XP background in full 50 foot glory?

I've been working on the design and fabrication of a robot that could do this for the past several weeks. I'm nearing the end and as I type this the robot is diligently r̶u̶i̶n̶i̶n̶g̶  painting the wall. 

When I started to really get into the nuts and bolts of this project it turned out to be more of a challenge than I anticipated. Let me walk you through a few of the bigger issues I've been working on.

1. Painting arbitrary colors

This was the crux of the project and has dictated the design of pretty much everything. Ideally I would have a robot that could mix up any arbitrary paint color then apply it to the wall. Unfortunately this is completely infeasible. Imagine if I need to paint a single square inch with a specific green color. Due to practical accuracy considerations, the robot would have to mix up much more green than I would need, apply it, then somehow dispose of that green paint and clean itself for the next color. Extremely wasteful and difficult.

Fortunately for me this problem is faced by practically all machine generated color printing. There's a really good solution that only requires four colors to approximately generate any color. The process is called halftoning and all I have to do is apply hundreds of thousands of variably sized dots to the wall. This certainly feels like exchanging a hard problem for a hard problem. But at least the new hard problem feels solvable...

2. Reliable paint delivery for days

It's one thing to say "yeah I'll apply a million dots to the wall," it's quite another to actually do it. If like me you do it one dot at a time it will take upwards of a week to do. Making a (prototype) robot that can run reliably for this amount of time is a challenge. The software can crap out in endless ways and when you put that many cycles on a mechanical system it tends to fall apart. In the process of making this I've had a fair share of those issues, but the real doozy has been the paint delivery system. 

Somehow you need a system that can make controllably sized dots day in and day out. This is a problem that I considered the best approach for at length. Bingo dabbers, brushes, sprayers, self inking stamps, giant ballpoint pens, and many other applicators. I couldn't find a system that felt great on paper, but all things considered I felt that a paint spray gun had the best odds of holding up and being controllable. So this is what I designed and built the system around. 

So far the sprayer has worked out pretty well, though I'd estimate that 85% of integration hell has centered around paint application related issues...

3. Moving the robot anywhere on the wall. AKA Gigantic 50 foot wide gantry

The paint sprayer can make a dot, but to paint the whole wall I have to be able to move it anywhere on the wall (obviously). I also have to be able to precisely control how far the sprayer is from the wall since this has a major impact on the size and density of what it paints. Also, since I have to paint so many dots and I'd like it to finish this century, I need a system that can move around super fast. I considered an arrangement like a Maslow style CNC router  but practical considerations with speed and running over the paint led me away from it.

I ultimately settled on a very strange but neat arrangement that I've always wanted to build. I have a very big slow gantry that moves around a small fast gantry. 

This gives me the best of both worlds. I can move the robot anywhere on a very large area with the super heavy, slow, cheap gantry and then use the small gantry that is light and fast to apply a ton of spots quickly. There's some neat details that allow me to make this accurate, but I'll save those for the video. 

You may be wondering why I wouldn't put a small gantry on a maslow style cable system. This certainly would have been easier, but there were some fundamental issues related to balance and reachable wall area. 

In any case I'm in the late stages of tuning and laying down a bunch of paint on the wall. During this process I've printed a series of increasingly less bad portraits of wifemadehere....

 I should be making the video with all the juicy details in the coming week and a half or so. I think the results are going to be pretty cool and will hopefully be a big step towards making the shop feel awesome. 

Let me know if you have any questions and as always thank you so much for supporting these projects!

- Shane