With help of Onshape in-context modeling, I started creating a chassis for Phoebe to support an arrangement that fit every component compactly like a 3D puzzle.
It was immediately obvious that I would not be able to print the entire chassis in one piece, as the footprint is greater than my 3D printer’s 200mm x 200mm print area. As I typically design parts to be printed without supports, I started with an approach that would split the chassis into top/bottom pieces. The top deck would support Phoebe’s caster wheel and Neato LIDAR. The bottom deck would support all the electronics. Then the battery compartment and motors would be bolted in between the top and bottom decks.
Here’s one of the drafts of the low deck, with a representative sample motor, battery, and Pi. I was not terribly confident about placement of the electronics. I could model the individual parts in CAD but there will be a lot of wires going between them. Wires take up space, and they are flexible with spring that push against each other, making them difficult to model accurately in CAD.
I looked at the electronics tray here and foresaw printing several iterations as I worked through wiring challenges. The bottom deck also includes part of the battery tray and motor mounts. Since these two things aren’t expected to change, printing each iteration would waste a lot of time going over the same thing. This was the first strike against a top/bottom split.
The second strike is physical strength: since top deck would house the caster wheel sticking out the back, it has leverage to put a lot of stress on however the top and bottom decks will be joined together. No matter if I used glue, or bolts, or something else. Foreseeing the structural loads, I decided it made more sense to have a single strong backbone connecting both motorized wheels and caster wheel.
This will require printing with supports, but the resulting strength should be worth the effort, and it isn’t likely to change as I evolve through the electronics. So I abandoned the top/bottom split and changed to a front-back split, with the strong single piece supporting all mechanical parts in the back.
(Cross-posted to Hackaday.io)