Contract A Rope (Vellum)

[Yannik]

Hey guys!

I want to create a simulation similar to this one, where the ropes contract and interact with a softbody: 

 

I'm well aware that he used c4d for his simulations but I would like to replicate it in Houdini, probably with the new vellum tools. But I can't seem to find a way to contract a vellum cloth sim, animating the rest length from 1 to 0 doesn't do the trick.

Any hints on how to achieve a result like that? I'm open to other solutions as well if vellum isn't the right choice for a sim like that. 

[BlackPariah]

I'd look into the stiffness / stretchiness of the vellum material. IE: start the sim with the material stretched out with low stiffness & then increase it to squeeze/contract whatever it's wrapped on?

I'm no expert by any means and I'm sure others will come up with better or more specific solutions

[6ril]

Hi,

there's the new vellum FIBER contraction, might just do the trick.

[coltonmil]

Perhaps adjusting Rest Length Scale under Stretch could achieve a similar thing. It defaults to 1 which keeps points at their input distances, if you drop it below 1 it should cause them to contract.

Edit: Doh, totally missed the last sentence!

Hmm, maybe stiffness is set too high for it to properly contract? Vellum is very sensitive to scene scale, so the values for stiffness often have to be wacky.

Edited May 21, 2019 by coltonmil
I'm bad at reading

[anim]

On 1/19/2019 at 1:40 PM, Yannik said:

animating the rest length from 1 to 0 doesn't do the trick.

animating restlength is the way to go, but you can't animate it in SOPs as that will not be reflected in DOPs

so you either animate Rest Length Scale using Vellum Constraint Property DOP or if it's not just curve (rope), but actual ribbon band like in the video then you can use Vellum Rest Blend DOP to blend towards shrunken version, that will update rest lengths accordingly and result in contracting