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Cake day: March 15th, 2024

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  • The regular old FEM based models can be quite misleading and when I had the chance to dig into them some years ago, it made me vaguely anxious. Except that nobody trusts the existing CAE solvers, there’s always a process to verify that actually the structure does what you think it does.

    Aerodynamics, at least the coefficient of drag, is actually really good for this because you can’t cheat the air and it’s mostly obvious when you screw it up. Which isn’t true for flutter or the more structural details.

    So, yeah, there is that risk, that they’ll get high on their own supply. But thankfully the management already thinks that the current crop of CAE solvers are magical and so the credentialed professional engineers already know how to fight that battle for a lot of the structural details. (The long-suffering assembly line folk who are trying to assemble the airplane properly are, of course, a different matter and have had a lot less leverage)

    Although, I’d also propose that there’s a second risk, which is that the current validation process is oriented towards the ways with which the existing FEM models screw you up and it’s likely that when the large physics model screws you up, it won’t be the way FEM models do.


  • Yah, I have some vague experience in the space and, without getting into things covered by NDAs, I guess I can say…

    First, The popular media talks about the classic style of physics solvers as these magical black boxes but my experience is that they are sufficiently unreliable that I would never trust my life solely to the answers of a solver. They do provide very valuable feedback for refining a design without an endless hardware-rich cycle of destructive testing. Thus, I think that a large physics model is probably going to be the same sort of useful tool.

    Second, while the CAE engineers can be very very protective over the time they spend on the two week cycle the article talks about, it’s fucking drudge work and a waste of a good mind. At the same time, the article does not really talk about some of the nitty gritty details. Aerodynamics is a great place to start because there’s less setup but the coefficient of drag is only one problem that needs to be considered.

    Third, the good engineers can “see” things intuitively because things do operate with a pattern. Vorticies from protruding features… stress fractures from square holes in a beam… etc. This does feel like an area where spicy autocorrect can spicy autocorrect you to a useful answer.

    Finally, cycle time for real world engineers is just like the cycle time for software engineers. Nobody wants to go back to the world where programmers submitted a deck of cards and got the printout back a week later.

    The only real risk here is that somebody gets high on their own supply and decides that a large physics model is actually predictive and we don’t need the same set of actual physical tests that validate the models.


  • So the conundrum with the Voron world is that the Trident and 2.4 are basically as good as you are going to get for the constraints. You can add the Monolith gantry but that’s an involved mod. You can add a toolchanger or a filament changer, that’s another involved mod. And there’s a bunch of really great mods but each of them adds complexity to the build, makes the BOM larger, etc.

    The one thing with the Voron is that if you want the highest accels, you probably need to ditch the extrusions. But then you can’t make it as an open source printer because you’d need to do a lot to get a rigid metal frame and there would be minimum orders, etc.

    And, overall, if you look at Qidi, they’ve been making Klipper-based cube printers with active chamber heaters for quite a few years now, so the more recent Qidis are really just mods atop the ur-Qidi, kinda. So a lot of the new hotness, outside of a few Bambu things, exists as mods for the Voron. We’ll ignore that Prusa had problems delivering new printer designs for a while.

    Allegedly the INDX that looks actually pretty neat that’s going to be on the Prusa is also going to be available as a kit for the Voron.

    Neither of my Vorons are stock. The Trident came from Formbot so it already was a CAN-bus design with some Formbot tweaks. You definitely want a filament motion sensor, there’s a bunch of options there. I swapped to the DragonBurner toolhead, I’d probably try the A4T instead if both of them were full-sized printers. My Trident has the inverted electronics mod, that felt pretty handy. My 0.2 has the electronics compartment rearranged.