First steps for Super Mega Microbot

**tician** · 2 Weeks Ago

http://www.etotheipiplusone.net/?p=4688

Onyx is plenty strong enough for full-combat beetleweight robots, so will likely be good enough for MechWarfare as long as you use proper wall thicknesses and infill settings and maybe add fiber if it's really needed. Would even work for the gearboxes if the teeth are large enough. Which reminds me that I still need to get my compound epicyclic gearbox printed - got put on hold a few months ago because of funding issues and my BuildOne is still likely several months away from delivery.

**jpieper** · 2 Weeks Ago

Yeah, I'm not worried about anything getting fractured by BBs with any of the materials, even shapeways nylon. I used Onyx for the legs because they were bearing load over a long lever arm. With at least the setup I have now, they are less rigid than I would like in the lateral dimension. I don't think I want to make them wide enough to achieve the same rigidity in both axes and ridges or webbing aren't really an option because of the link geometry.

**tician** · 2 Weeks Ago

Is the lack of rigidity a bad thing, given you have been making this thing jump about? Elastic elements are a very big deal when dealing with non-trivial masses/velocities and less than smooth motion no matter how nice you think your sensors and control algorithm are. A bit of flex or springiness is better than breaking teeth, snapping bolts, or deforming bearing surfaces.

Is the bigger issue not "bolting a leg to the face of a gearbox" instead of supporting it on both sides with bearings to prevent it ripping out the output stage of the gearbox?

**jpieper** · 2 Weeks Ago

In this case the gearbox is actually supported by two separate bearings internally on either side of a planet carrier, so it is plenty rigid and robust to torsional loads. However, the Onyx printed leg when fully extended can deform by +- 4cm laterally even when rigidly mounted on the top. My goal is not to make a series elastic actuator, but instead to have something that is accurately controllable with a high bandwidth while still being highly backdrivable.

And yes, my mostly non-existent sensors and control algorithms are very nice thank you very much!

**jwatte** · 2 Weeks Ago

Do you find a big difference between the "Onyx" black nylon versus Shapeways "Strong Flexible" in black? They're both nylon ...

Also, for SMMB I might be able to make some parts in aluminum for cost of materials + tooling, as long as they can be done in 2.5D + flipping and rush speed wasn't important. Send me an email if there's something particular that would be useful for.

**jpieper** · 2 Weeks Ago

Originally Posted by jwatte

Do you find a big difference between the "Onyx" black nylon versus Shapeways "Strong Flexible" in black? They're both nylon ...

They claim it is significantly stronger and stiffer than straight nylon. https://support.markforged.com/hc/en...209934486-Onyx

Subjectively they certainly feel much stiffer than what I would expected from a normal strong and flexible print.

Guess I should get those parts done at Shapeways too and compare.