I finally started laser cutting the plastic pieces for the chassis.
I happened to have some orange 3mm acrylic and thought it would make a nice accent color.
Unlike the standard shell, mine is cut in three pieces and glued together. I had some worries that this wouldn't be very strong but it turns out that the glued joint is extremely tough. With acrylic, we're basically welding the pieces together. The solvent cement softens the plastic and the fused joint is incredibly tough. Even so, I reinforced it with a couple pieces I'd cut to calibrate the laser. These are just glued in underneath to add some thickness to the glued surface. I don't know how durable it will be over time, especially flexing it from time to time to assemble, but so far, so good.
I have all the little bits for the electronics chassis modeled now. I think all these parts will be cuttable for me. I still have to model the endcaps for the tube and some minor cleanup. Then it should be ready to cut.
In the full assembly picture below, I don't know why the edge of the tube is showing through the wall of the shell. It isn't penetrating and the shell isn't set to transparent but FreeCAD's rendering is goofy.
The project is open but the design files are all done in Autocad Inventor. I wanted to see if FreeCAD could model everything, so I started redesigning the files as fully constrained sketches.
This means the the critical dimensions of the various parts can be changed and everything else will adjust correctly. If you want to change the thickness of the acrylic used, it's relative straightforward to adjust the dimensions.
So far, I've done the major frame pieces.
One other change I'm making with my design is the shell. The stock OpenROV has a large shell that is made from a single piece of acrylic. It has two 90 degree bends to wrap around the sides. This is a problem for me for a couple reasons. First, FreeCAD can't model the bends yet.
More importantly, the piece is too large to cut on my laser cutter and requires a hot wire bender which I'd have to build or buy.
My variation cuts the shell into three parts that are glued together. It's not quite as attractive as the stock design, but easier to build and will fit in the build envelope of a smaller laser. I'm publishing my files on github. My next bit of work will be to model the parts inside the tube.
Anyone who knows me knows that I totally dig submarines and sub movies. Whether it's a great one like Crimson Tide or a total pooch like Down Periscope, I gotta watch it. Submarines are the ultimate toy and the closest thing to real spaceships we're likely to see for a long time. When I first stumbled across the OpenROV project, I was hooked at once
Obviously an ROV isn't the same as a submarine, but it offers many of the same benefits and even a few advantages -- like the ability to actually see while remaining well above crush depth. In the past, ROVs have been expensive so the design and testing cycle is long and they're reserved for high-value missions.
The OpenROV project is very young and they're still getting their legs under them but it has some really cool things going for it. It's designed to be inexpensive, flexible, and require few specialized tools. The physical structure is almost all laser-cut acrylic. The bottom side electronics are meant to be open hardware like a Beagle board or Raspberry Pi. That means the ROV can be cheap enough that innovations and improvements can be tried out quickly even if they risk the ROV. It doesn't have anywhere near the depth capability of a 'real' ROV but at theoretical depth of 100 meters it could reach most of the continental shelf. That's a lot of room to play. My goals are a bit more conservative. A 5 acre pond in my Missouri back yard that I'm certain is, like McElligot's Pool, connected to the deep ocean. There's no telling what I'll find down there.
OpenROV recently started a Github repo to host hardware design files and software. They seem to be working in Autodesk Inventor which is, unfortunately, a closed format. A friend converted the files to both STEP and IGES for me and I was easily able to import them into FreeCAD. From there I was able to assemble it in the computer to produce this:
I've forked the OpenROV repo and added my converted files and FreeCAD file. FreeCAD doesn't support any bending of solids which is necessary to model the outside shell. The friend who converted the files made both a folded and unfolded version of the shell for me.