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Initially, the task was looking pretty simple: Make a wooden sign tied with 2 ropes showily appearing on the screen and swinging on those noose knots. After 3 sec one of the knots come untied and sign is falling down with the other rope.

I tried easy ways: Tried to animate some classic ropes based on curves, tried both cloth physics and rigid body physics. In the outcome, it turned out that once i start to tie the simplest knot (i'm not even talking here about that sophisticated noose knot i initially wanted to make), the rope just intersects itself and straightens.

I tried harder, read some manuals and questions concerning that issue with self-intersection, adjusted physics, gave it a gigantic amount of render substeps, but finally i got that it is impossible to tie knots with blender classic physics because there is no way to completely avoid self-intersection in this program.

enter image description here

My words were proven by some forum post where was a guy with typically the same problem, and the answer was like "it is impossible to do it in Blender. The only way you can try is by using Molecular Script (pyroevil.com/category/scripts-addons/molecular-script/)". I watched the preview with ropes and it impressed me. I downloaded the script and spent about 1 week in trying to tie a knot using this plugin.

Result: I finally made a simple animated knot, but: 1 - When i try to perform the same with my noose knot, it likely has the same problem with intersection (i didn't try, however, with 100 substeps). 2 - The rope interacts with a sign, however, a rigid body sign does not care about the rope, on which, in theory, it should hang on.

I tried CubeSurfer plugin (pyroevil.com/category/scripts-addons/cubesurfer/) which allows to create a mesh based on Molecular Script's particle system. I fought that would allow me to make that object a rigid body and let the sign and rope interact with each other. However, the IsoSurface was only mimicking its particle system, ignoring gravitation and other rigid bodies. A sign was reacting on IsoSurface, a particle system was reacting on sign, IsoSurface was reacting on particle system, but together, it all did not work actually.

I'm tired, i've spent about a month on this stuff, and i'm pretty sure there must be much easier way to achieve my goal. Generally, SOS. I need some help, guys. The only way i can see here (except using proprietary software) is to animate all the rope and sign animation manually, by hands, but it sounds awful and non-professional.

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  • $\begingroup$ Welcome to Blender.SE! What you are trying to achieve would be pretty hard for every software. Simulations always takes a good amount of time in finding the right parameters, I would personally give one more try Cloth simulations: youtube.com/watch?v=0rn2M8CMpKA. Could you tell a bit more about your scene setup? $\endgroup$ – Carlo Feb 2 at 8:51
  • $\begingroup$ Given all of the amazing things I've seen Blender do I'd be hesitant to write it off as impossible (though surely not simple). My wee bit of advice is to "think outside the (physics) box"; nothing says it actually has to be rope+rope or rope+ring blocking passage of one another. What if there were some other "contstraint" (I'm using that word generally, not necessarily the literal Blender thing) between two other objects and they in turn were locked to the rope/ring? As long as those two other things were hidden it would be just fine, right? Not much help, I know. Keep researching tho! $\endgroup$ – B Layer Mar 1 at 5:39
  • $\begingroup$ ...beyond that, if you've reached the end of your rope (heh) surely take a look other offerings. There are a lot of open source physics simulation packages. There are also, I believe, one or two of the commercial packages that have very good sim and single seat licenses or short-term subscriptions that are pretty inexpensive (possibly...I don't know your situation) or even, in the case of Houdini, apparently free...? $\endgroup$ – B Layer Mar 1 at 6:14

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