Settings to make non-stretchy rope?

[josemendez]

Hi there!

Apart form the youtube videos, you have the official documentation:

http://obi.virtualmethodstudio.com/tutorials/

However we are aware that it might not be of much help when it comes to certain topics such as this one. (working on it!)

The general rule of thumb with constraints (all of them, not just distance constraints, but these are probably the most important for ropes) is that the more iterations you set in ObiSolver->Whatever Constraint parameters->iterations, the fastest they will reach the set stiffness.

Things to try:

• Set distance constraint iterations to 20-30 (the more particles in your rope, the higher you'll need to crank this up). 
  
• Use tethers (make sure that at least 1 particle in the rope is fixed, or no theters will be generated).
  

You say you have tried both, and still your rope isn´t rigid enough. If that's the case, try reducing its resolution and re-initializing it (so that the amount of particles in the rope is smaller). This will reduce the need for high distance constraint iterations. If the resulting rope mesh is too coarse once you reduce the amount of particles, you can increase the smoothness parameter. See:

http://obi.virtualmethodstudio.com/tutor...setup.html


[Start of physics rant]

Be aware that Obi is an iterative solver (like PhysX, or Bullet). This means it will only reach absolute, inconditional stiffness with an infinite amount of iterations. When faced with large mass ratios (i.e. extremely heavy crate hanging from extremely light rope), this will only get worse.

There's no general, high-performance algorithm to get stable and perfectly stiff rope/chains, afaik. They only one that gets close is ABA-Featherstone, but it has its own shortcomings: it cannot handle loops of any kind (closed ropes), and the cost of impulse-based collision resolution can be extremely high for long ropes (as each impulse affects all links in the rope, not just the one directly hit).

Another one that's popular is FTL (follow the leader) but unfortunately it's not really an accurate physical model, but more like a hack that resembles actual physics. Also cannot handle general ropes in its basic form, just the case where a rope has only one end attached.

[End of physics rant]