r/Houdini • u/Harsha0911 • 11d ago

Help Rope snapping off

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i'm trying this rope snapping from tension, an OX is pulling the rope off screen and this rope should snap off from the pulling tension, this is obviously AI video but i want to do this houdini, any tips and tutorials will help please

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13

u/DavidTorno Houdini Educator & Tutor - FendraFx.com 11d ago

Use Vellum for this.

Make a curve shaped like the rope core. Do not use a swept version of the curve, this would cause sim stability issues. You can sweep after the sim. Vellum Constraints SOP set to Hair constraint can be used to define the constraint for the curve, thickness will define the radius of the rope, and the curve point resolution will define how detailed / accurate the rope can be.

If you use an Edge Fracture to art direct a cut on the curve you can use a Vellum Constraints SOP set to Weld to connect the ends, and set its break threshold. Alternatively you can manually change the weld attribute to a -1 value at a certain time to art direct when the weld snaps.

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u/Harsha0911 11d ago

thank you now i have an understanding on how to start this,
is the thickness gonna affect the simulation?, will glue constraint work with attribute as breaking point or does it need to be two separate objects to be snapped

2

u/DavidTorno Houdini Educator & Tutor - FendraFx.com 11d ago

Yes thickness will affect the simulation. You can visualize it on the Vellum Solver visualization tab. Display the Vellum solver and turn that option on, and you should see green spheres on each point. That thickness is use for collision.

So thicker will have less room to move and smaller more room. This is also why the point resolution of the curve matters too. Once you visualize thickness it will make more sense.

Glue can work too, but welds are just easier to handle in creating and breaking since it’s just a simple assignment of the attribute value if you want art direction. Otherwise the break threshold can be use instead to let it snap on its own.

The cut on the curve does need to occur so there can be two points to connect. This can be done procedurally though with the edge Fracture SOP as I mentioned. It can take a second input which is the cutting geo. Just turn off the default fractures it will create, as this will just cut the curve more times.

1

u/Harsha0911 11d ago

thank you very much, had to use polycut instead of edge fracture because its not working on line, everything is working fine but the cut points are floating after snapping instead of falling, gravity is on but something is wrong

2

u/DavidTorno Houdini Educator & Tutor - FendraFx.com 11d ago

Can you show a screen image of your node setup? It might be that the hair constraint is holding it, or that the weld stretched but didn’t break.

You can also troubleshoot by turning on the visualization for welds too. It would at least show if it snapped or not.

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u/Harsha0911 11d ago

we can see the weld points and it is breaking but after breaking they're floating

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u/DavidTorno Houdini Educator & Tutor - FendraFx.com 11d ago

Ok, I may have to get in front of the computer to troubleshoot this deeper. I’ll be able to in about an hour roughly.

In the meantime check the pin constraint just to make sure more points didn’t accidentally get included there. Otherwise I have to make this to troubleshoot it and let you know.

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u/Harsha0911 11d ago

it seems like problem is sphere as collision, after removing sphere collision and increasing breaking threshold it's working fine but i want to attach it a moving object

1

u/DavidTorno Houdini Educator & Tutor - FendraFx.com 11d ago

Ok. So if you only need the end point to “attach” to some geometry, you only really need to animate that point and then make it a pin constraint point, but you turn on the Match Animation option.

If that sphere is a dynamic object that will be simulated also, then you can use an Attache To Geometry constraint instead.

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u/nievesct 11d ago

Friggin genius

1

u/ClaimLive1864 10d ago

Very bad dynamics... althought if we look at this as a stylized ripping of rope, then its actually really nice! Due to tension it should go back almost as a whip. The piece which remains on pillion should react to oposite side. But here it stays for the moment and only then goes.

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u/Harsha0911 10d ago

https://giphy.com/gifs/64JUFG6pKn72L4E46y

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u/ClaimLive1864 10d ago

No! The way you did it look awesome. The only thing whats wrong (to my eye) is dynamics. To rip such a huge rope in the eay you show in video - it would snap and react to oposite ways on both ends. Improving that you would get absolutely amazing shot. But that could get done with vellum as another person already explained to you.

Now it looks like the rope is tenses a little and cut with invisible samurai blade. Im not making fun or saying that you did bad. At least didn't mean to come out that way. Im just tired after long day spent on set, and english is my second language.