Pi Wars T-44: Body work redux
From the start of the project I knew the robot's shell was going to be tricky, but vital for the finished look. I started with this low-detail model of a Reliant Regal, which I turned into a hollow shell that I could print, and in a surprising fit of foresight I planned the entire internal layout of the robot around the size of the shell. This involved a fair amount of CAD work measuring all my components and recreating them in Sketchup so I could push them around inside the shell model.
Of course, once I've got a CAD model showing cutaways of the inside of my classic car build, it would be a shame not to do one of these...
The shell itself was printed in eight parts, because the overall length is bigger than the 200x200mm bed of my 3d printer and I didn't want to make acres of support material, but this meant gluing the printed parts together. I learned fairly early on that my machining teacher's favourite phrase, "Hot glue is not a structural member" was entirely true in this case. Superglue was out too as the mating surfaces weren't flat enough due to the layer lines, so most of the shell is held together with two part epoxy.
After I'd got the entire shell glued together, I had to start modifying it to fit all the various parts of the robot which stick outside or need some kind of access. The motors fit into cutouts on the rear panels, the IR distance sensors used for navigation each have cutouts in the wings/grille, I made a small square cutout for the OLD screen behind a door, and the battery leads stick out through the rear window.
Spot the modifications
I also didn't want anything rigidly attached to the shell, so I could take it completely off without affecting the robot's ability to do the challenges (both for easy maintenance, and in case at some point it gets broken and I have to compete without it). From previous experience I knew the shell has to be solidly attached, but also easy to take off for maintenance in the short breaks between challenges. To achieve this I went with two 3d printed brackets under the floor pan near the front wheel, and two bolt holes through the sides into the "mezzanine" frame which holds the power electronics. The brackets at the front have captive nuts in hexagonal holes, because I love a captive nut and it seemed like the easiest way to get a threaded attachment point underneath a flat acrylic surface.
The shell, while mostly mechanically complete, will most likely need one or two additional holes for voltage monitoring and attaching flashy flashy lights and challenge-specific attachments, but for the moment it's adequate - now I have to drive it into a lot of walls and see what breaks - if anything is going to break I'd like to know about it now rather than on competition day!