Sawppy Issue: Misumi Aluminum Extrusions

Sawppy has hundreds of fasteners to hold 3D-printed parts on aluminum extrusion beams. Managing all those fasteners has turned out to be a chore and it is something I want to improve in a future revision. While I’m reconsidering those fasteners, the extrusion beams are worth a bit of thought as well.

I designed Sawppy around extrusion beams with a 15mm square profile, chosen because it felt like roughly the right size to stay proportional to the real Mars rovers. Designing in metric was an intentional choice to make it friendlier worldwide. This was in response to chatter on the JPL Open Source Rover forums, where its non-metric parts caused headaches for builders outside of the United States.

The aluminum beams in my own Sawppy was purchased from Misumi USA. I chose their 15mm HFS3 series because the slots were cut in a way that permitted the option to use commodity M3 nuts instead of their specialty HFS3 nuts. Another reason for choosing Misumi was that they are a global company with distributors around the world, making HFS3 available worldwide.

After I published Sawppy instructions online, I started receiving feedback from builders outside of the United States and learned of a catch: while Misumi USA is happy to sell to anyone with a credit card, other Misumi distributors around the world are not so hobbyist friendly. Misumi Europe, for example, deals only with businesses and is not interested in earning income from hobbyists.

Fortunately resourceful hackers in Europe quickly found that the MakerBeam XL is a direct substitute and there are hobbyist-friendly distributors in Europe. It is more expensive, but at least it is available, and several European Sawppy rovers were built with it.

Aussie Sawppy, on the other hand, had none of those options domestically. So 15mm extrusions were ordered from China. That rover had to wait a long time for parts to arrive, but at least it is an option. There are a few countries where prohibitive import duties make even that impractical. I’ve heard from two aspiring rover builders in Argentina who will try to build a Sawppy using rectangular profile metal tubes.

I think aluminum extrusion beams are still the way to go for a Sawppy-sized project. And thanks to the availability of MakerBeam XL and AliExpress, staying with existing 15mm profile is still a good option. However, I am contemplating a move up to 20mm square profile. They’ll make the rover look a little bulkier, but 20mm is far more common worldwide than 15mm. If nothing else, 20mm extrusion beams are popular in maker circles due to a large number of popular 3D printers built with them like the Creality Ender 3. If I move up to 20mm there is a long term possibility for a rover built from chassis beams of retired 3D printers. Based on feedback I’ve received, moving away from 15mm extrusion beams and serial bus servos for Sawppy V2 would help mitigate two of the biggest problems with worldwide availability of Sawppy parts.

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