At the start of a project it is always useful to write down our mission objectives to ensure we stay on target and not lose sight of what we set out to accomplish. For future Sawppy evolution I have written a list of what I want to improve, and what I am/am not willing to compromise for those improvements. For the most part they look pretty good, but unfortunately I’m left with a set of conflicting requirements.
The first is my desire to make Sawppy easier to modify and experiment. This was actually a Sawppy goal from the start, and I thought leaving the aluminum extrusion beams unmodified would be the best way to do so. Unfortunately that meant using a lot of little fasteners to hold 3D printed parts onto those beams, and the sheer number of fasteners discouraged modification and experimentation as every project became a tedious slog of undoing and redoing fasteners. For the next revision I want to follow the precedent set by 3D printer chassis using these 20mm extrusion beams: drill holes through the middle of the channel to accommodate fasteners that can be larger and therefore we would need fewer of them. Drilling holes are an irreversible modification, but I hoped it would be worth the tradeoff. Unfortunately, drilling these holes accurately are difficult to do by hand and are best done with larger shop tools like a drill press and a vise holding the beam. Adding this requirement would exclude aspiring rover builders without ready access to such tools.
Another problem is that reducing fastener count can only go so far to make Sawppy simpler. Because these rocker-bogie suspension components are larger than the print volume of common 3D printers, these aluminum extrusion beams are required for structure. Building with beams impose a lower limit on parts count: every suspension subassembly would have the beam, the 3D printed connectors on either end, and fasteners to hold them together. The only way to be even simpler would be to eliminate the aluminum beam so we can 3D print Sawppy structures in single pieces, but that means shrinking everything down to the volume of a typical 3D printer. (Which I’m defining as something with print volume of at least 200mm x 200mm x 200mm.)
Shrinking the rover to be printable instead of relying on extrusion beams for structure would drastically reduce parts count, and allow people without access to tools like a drill press to participate in rover building. Such a smaller simpler rover should also be easy to build, with much simpler instructions for construction. Closer to what people expected from a commercial product. But a smaller rover would mean giving up a lot of capability on the high end, including flexibility for adaptation to experiments.
Seeing how a single design would not be able to accommodate the entire spectrum of rover builders, I’m splitting Sawppy into two variants: I’ll revise Sawppy at the current size (or possibly grow a bit larger) for the original audience of tinkerers and experienced robot builders. To accommodate those that would be left behind by the elevated prerequisites of such a design, I’ll also design a smaller variant that is easier and friendlier for beginners to pick up and build.
2 thoughts on “Conflicting Requirements Call For Sawppy Variants”
The smaller variant idea is great especially for doing faster design iteration on software and AI. Having a managed compatibility path with the larger version of SAWPPY would be really cool.
I noticed smaller Rocker Bogie design with 3d printed integrated support beams being publicly maintained by an ESA team.https://github.com/esa-prl/ExoMy/wiki/Bogie-Assembly
ExoMy is really cool! I’m planning to build one of my own to add to my rover fleet.
But as the link you posted explained, ExoMy uses a triple-bogie suspension design and not rocker-bogie of JPL rovers, with different upsides and downsides.
I wrote more about ExoMy here: https://newscrewdriver.com/2020/12/15/quick-look-esa-exomy-rover/