Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Marble Fountain

willmorrison.net

Post reply on HN
Print view View original

91–97 of 97 posts

Re: Marble Fountain

#91

Post by there4 »

jjcob wrote: post #83
kazinator wrote: post #29

Designers of marble fountains who don't use computing to design the paths run into reliability issues: sometimes balls derailing out of their track. They have to observe the contraption, identify problems (balls getting jammed up or jumping out) and then guess at the root causes and make manual adjustments. That's the thing here: he has it running for hours presumably without any ball jumping out. Most of the tracks…

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 pr…

Another parameter - as a track designer you can manipulate the width of the track to change the ball speed. It raises and lowers the ball on the track, changing both the rolling diameter and the center of gravity. This can be used to make subtle changes to the ball speed before a turn.

Re: Marble Fountain

#93

Post by sixtyj »

bazzargh wrote: post #87
stavros wrote: post #52

Earlier quoted context omitted.

I think the physics are different, a ball is basically a car without a differential, so it's going to behave differently on the tracks. I'd imagine the ball is harder to simulate because of that.

One of the results for hilbert curve marble tracks, mentioned elsewhere in the thread, was a video showing how to make one in blender, which has a physics engine so it can simulate it pretty well. https://www.youtube.com/watch?v=8YeXyUNCnhM I'd imagine that the 3d-printable models could be imported into blender, so it's 'just' adding balls and motion to the lift.

You can simulate everything in these professional (and expensive) software.

https://ansyshelp.ansys.com/public/account/secured?returnurl...

But for hobby purposes I would suggest to contact some university, they have such software, and they could find simulation of balls motion at marble fountain interesting for research (and educational) purposes.

Re: Marble Fountain

#94

Post by timmg »

WillMorr wrote: post #62
bix6 wrote: post #40

Super cool! I would love to see a white / clear one with LEDs. Rainbow road :)

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 r…

Minor suggestion/request: would be great if you added a final STL file to the github repo of a working example. Might be easier for people to try if they can't get the python code running on Linux.

(I haven't tried yet. But I'd love to just send an STL to my printer to see how well it prints.)

Re: Marble Fountain

#95

Post by timmg »

WillMorr wrote: post #63
fogleman wrote: post #59

Earlier quoted context omitted.

What did you not like about the SolidPython2 / OpenSCAD approach? What would you want from a different "3D engine" for this?

Mostly speed, I'm mostly doing large boolean unions of primitives or chain hulls and OpenSCAD chugs pretty good at large numbers of operations. Don't get me wrong, they're great tools for what they're good at. I need to do more research before I start a port, SDFs seem like the best option but I'm not 100% confident. I am considering using your SDF library though (github.com/fogleman/sdf) but need do do some experime…

Not sure if this matters for you or not, but my understanding (with some experiments) is that the "slicers" implicitly do a union. As in: you could have an STL with a bunch of overlapping blobs and the 3d printer slicing code just checks isInside -- which is effectively a union.

At least that's what I found when I was generating STLs in code.

Re: Marble Fountain

#96

Post by rendall »

WillMorr wrote: post #35
kazinator wrote: post #29

Designers of marble fountains who don't use computing to design the paths run into reliability issues: sometimes balls derailing out of their track. They have to observe the contraption, identify problems (balls getting jammed up or jumping out) and then guess at the root causes and make manual adjustments. That's the thing here: he has it running for hours presumably without any ball jumping out. Most of the tracks…

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 largel…

Could (or do) you include a catch basin at the bottom to automatically return the odd errant lost ball to the queue?
Post reply on HN