Kyle Cothern

Founder Flotilla |
Former SpaceX, Vast |

Emily the world is grey without you. May we meet again after this life. Fair winds and following seas.

[Kyle Cothern @risknc]

Someone very important to me left the world today.

I will never recover from this.

Hug your friends, tell them you love them.

[Kyle Cothern @risknc]

@lgwalker2010 It's some test hardware to develop control algorithms against.

[Kyle Cothern @risknc]

Control rods stuck. 😬

[Kyle Cothern @risknc]

@joshu

[Kyle Cothern @risknc]

@joshu ?

[Kyle Cothern @risknc]

@joshu #butwhy

[Kyle Cothern @risknc]

@joshu you invented tagging?

[Kyle Cothern @risknc]

Trick question: It was Roadster.

[Eric Berger @SciGuySpace]

Which flies first:

[Aaron Burnett @aaronburnett]

thanks to AI, now we know what starship's pez dispenser would sound like if space wasn't a vacuum.

[Kyle Cothern @risknc]

@blind_via just a bunch of self propelled modular transporters and a fixture.

The crawler transporter was built by Marion power shovel in the 60s. it's way, way bigger cause it carries the launch tower as well.

the built in cranes / chopsticks on the starship tower handle integration.

[Kyle Cothern @risknc]

Somehow they could only fit 1 ohm in this resistor

[Kyle Cothern @risknc]

@12atatosk @rednecknerd123 Yeah. Still happens a lot in engineering companies tho. Like that time SpaceX did their own Ethernet standard.

Most people are bad at doing trades.

[Kyle Cothern @risknc]

You can qual just about anything with enough effort.

it's worth flagging that FDM parts have way more issues than isotropic materials with certs.

but with QA, statistics and test equipment you can qual printed plastic parts for sure.

do you want to?

[em m0shouris @emm0sh]

FDM parts of any material are an inappropriate (and i would argue unsafe) choice for any loaded application where they’re critical (supporting humans, a part of a critical safety mechanism, etc.)

this goes beyond anisotropy (which is a challenge, but solvable). you could in theory use non-linear FEA to model the behavior of the part, but it takes a herculean effort and still doesn’t provide the whole point of FEA in the first place for safety critical parts — the predicted failure mode at a specific loading

this isn’t because these parts are hard to model, instead, it’s because FDM is inherently flawed. there are no guaranteed mechanical properties. vendors will list toy values on their websites, but they do not reflect the “real” values and are misleading. real means as built

every car, plane and multi-story commercial building utilizes an important property of materials that manufacturers have gifted to engineers over the centuries, and that’s reliable mechanical properties

aluminum, steel and most metals have a yield or ultimate value by which engineers design to, enabling us to predict when and how parts will fail. FDM does not, and it isn’t the material’s fault, it’s the process’s fault

when i analyze a part, it produces values by which i can meter against mechanical properties of the material. the main problem with FDM is that it does not. the process itself invalidates the underlying mechanical properties

the produced part does not have bulk material properties of the constituent material due to the geometry of the “lay up” of the filament that produces the part. this means an accurate analysis would not be on the “as modeled part”, it would have to be on the “as manufactured” model of the part, or the “sliced” model of the part

and even if you did this: it would still be for moot because the shear resistance of each layer produced is dependent on the orientation and settings of the print and the environment in which it was printed. the properties can vary wildly between prints

i won’t even get into cold flow which is exacerbated by this lamination issue. i still think FDM is great in the limited cases of onesie-twosie fixtures and tooling

here’s a solution: sheet metal is cheap. use a sheet metal substrate to build up the load bearing structure of your parts. they become safe with proper analysis and can also get rid of the temperature independent cold flow problems that hamstring most FDM parts

[Kyle Cothern @risknc]

@rednecknerd123 Usually there's way more than just one environment or load case too

[Kyle Cothern @risknc]

@rednecknerd123 The only thing I'm aware of that that uses 10 factor of safety is civil infrastructure.

There are all sorts of rules of thumbs on what margins to carry, it's very industry and application specific.

[Kyle Cothern @risknc]

@HalenMattison maybe Elon just doesn't like Delian?

[Kyle Cothern @risknc]

@JasBilyeu the leader lines on all the dimensions don't have the appropriate gap to the model. you probably should've done a section view instead of the front view and turn off hidden lines.

[Kyle Cothern @risknc]

@andrewmccalip humans can find time to make anything an engineering problem.

[Kyle Cothern @risknc]

@andrewmccalip I've worked across from an engineer that spent an inordinate amount of time designing a soft goods apple box to send apples to astronauts on ISS. it was basically a big rectangular prism with foam in it that had cylindrical holes for each apple.

[Kyle Cothern @risknc]

the goal was to fit check and form tests for parts before injection mold.

for decorative stuff, low risk designs, fixtures, it's awesome.

kitbashing one mfg process because it's all you've got or know is pretty common, but pins off a lathe are always going to beat a mill.