It's actually much weirder than that: banking changes the axis of rotation and thus kills the rotational inertia. The tracks bank super aggressively in order to prevent the ball from accelerating too much and hopping the track. This is part of why the descent is so smooth and all the balls move at more or less the same speed.

Also to be fair the final system does lose a ball every 30ish minutes. The tuning was largely me staring at the run or taking a video trying to catch where they get lost. Instead of hand tuning I would just update the generator and print another one. I'm considering closing the loop with a camera but that would be a whole new project.

You are missing inertia!

The state of each ball can be described by 9 parameters: the current location of the center of mass (x,y,z), the current linear velocity (vx, vy, xz) and the angular velocity on 3 axes.

I don't think the forces acting on the rails need to be similar -- they just need to be such that the acceleration of the ball is always parallel to the track. Unfortunately the equation of motion will look pretty ugly and optimizing the system will be quite a challenge.

And finally, the system has to be stable, ie. small perturbations should be cancelled rather than grow - if a ball gets a little too fast there should be something like a bend that slows it down, but that bend should at the same time not slow down a ball that is already too slow...

Not to dimish the achievement, but TFA is pretty clear about the limitations of the piece:

> I was able to get it working consistently, although it did lose 2-3 balls an hour and could only run for a few hours without the motor overheating.

IMO that's more impressive to hear than if he hadn't mentioned it at all. (I would have assumed more marbles getting lost.)

> That's the thing here: he has it running for hours presumably without any ball jumping out.

You can see a ball on the ground at the end of the video :-)

Just nitpicking, but there is at least one ball next to his contraption in his video :-)

Doesn't make the whole thing less remarkable.

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My naïve guess would be that you can't change the route of the ball without asymmetrical track pressure.

I actually attempted this, the idea of a python script that converts a midi track into a marble run is just too good to not try. I printed a large drum with different track structures inside so I could test various "slopes" by changing the speed and it just doesn't work, the balls bounce around too much to get an audible pitch. A less rigid material or a larger bearing would likely work better but I decided to focus on getting the normal version working well.

There's a Tom Scott music about a musical road in California: https://www.youtube.com/watch?v=Ef93WmlEho0

That's pretty much it! It's the simplest method of supports I could come up with that allows for robust keepout zones. I did have a bunch of issues at first with supports blocking the path but with a little tuning it became surprisingly consistent. I doubt I'm the first to come up with it but I have not seen any similar systems.

Thank you! The emergent forms are much more interesting than they have any right to be for such a simple system.

A good use case for 3D printers is random, small, custom household items that greatly increase my quality of life, much more than it is a unique sculpture.

Mesmerizing is the right word. "I can watch them for hours" was the key bit for me - I have always been fascinated how humans can stare at a random visual generator for forever, if it's the right one.

I think there is an instinct built deep in our lizard brain somewhere for this. Humans will happily stare at a fire, or an ocean, or a wave in a river, or (sometimes, especially children) a TV screen - and all I have worked out why is because it is constantly changing in an unpredictable way.

This marble run shouldn't even be unpredictable - clearly the paths are fixed and the cadence of balls is regular - but somehow it is still mesmerizing.

Be sure to turn on sound for maximum mesmerization.

I've actually done clear prints with LEDs installed. The bottom is much brighter than the top and it just look kinda tacky. I briefly hollowed out the supports and tried running fiber optics but it didn't help much.

I'm realizing now that I tried a lot of weird shit during this project that just did not work at all or make it into the final product, I should do another video just of all my failed abomination marble runs.

White/clear is just a matter of picking filament, I'm not sure LEDs would be easy to incorporate into the build

Are procedurally generated rollercoasters a thing?

There are serious efforts and working prototypes of printing houses. This works surprisingly well, allows construction in days instead of months, and shows a lot of promise. It’s a great rabbit hole to fall into!

Blame! is a manga where in the future humans have robots that build, and are controlled by people with Net Terminal Genes. Something happens and those humans die leaving the robots building non-stop procedurally for eons. By the time our protagonist moves about in the world, its said the Megastructure reaches from Earth all the way to Jupiter.

Also, the movie Fracture features these cool marble machines. https://www.youtube.com/watch?v=Y-v6E9H6nh0

Back when movies were made with unique good scripts and not marvel slop.

Small world, I opted for a Gosper curve myself, but when it got too big, cut out specific pieces and connected those.

It gives everything a uniform look while allowing to fill the space in a different way.

That sounds super interesting, do you have a link?

That guy who makes marble music recently worked out a ball funnel that uses inserts in a different material to eat most of the noise. But in that case it’s also eating momentum as well so I’m not sure how that would work for this design. Maybe some bushings in the supports to reduce harmonics.

A pun? I don't get it, could you explain?

It says that the banking is intentionally excessive.

Looks like fiber infused filament.

It's specifically using SolidPython2 to generate the models. I originally wanted to do a quick code cleanup and have the specific math be much clearer but by the time it was working that was an absolutely massive undertaking. If I touch the code again I'm probably going to refactor the entire codebase and use a different 3D engine.

I bet this would look baller with green rails and brown supports. Also might help with losing the balls visually as they get to the bottom. The visual noise makes them harder to track.