ObiRope 3.2 Crane - Prevent Rope from passing through spool

[josemendez]

In ObiRope 3.2 Crane Example Scene.  If I increase the Load RigidBody Mass from 1 to 10.
Then the rope will eventually clip through pulley, with no user input.

I was unable to prevent this.  Experimenting with generating tethers, and increasing iterations in ObiSolver (Distance, Collision, Tether).

The one solution I could make work, was reload scene then:
- Increase the Load RigidBody Mass from 1 to 10.
- Increase the Crane.Pulley RigidBody Mass from 10 to 30.
- Increase the ObiSolver.Collision.Iterations from 10 to 20.


Is there a better solution?
Is there a ratio that must be maintained between rope loads and other RigidBody masses?

Possible solutions:

1.- Increase the amount of distance constraint iterations. These are what keep the rope from stretching under high loads.
2.- Create a rope with higher resolution. This reduces the gaps between particles.
3.- Increase the mass of the rope particles accordingly . This is useful if the mass ratio you're interested in maintaining is "load -vs- some other scene object", instead of "load -vs- rope".

Note that under high enough mass ratios the simulation won't be able to keep up no matter what you do. It will not explode (as Unity's PhysX does), instead will handle the situation as gracefully as possible.

No realtime general physics engine is capable of dealing with arbitrarily high mass ratios. There are particular algorithms that do (such as Featherstone), but they are limited to specific scenarios and have high performance requirements even in simple cases. This problem is usually circumvented in commercial games by establishing a maximum mass ratio between any two objects in the game, and sticking to it.

In engineering environments where you can't fake or cap mass ratios, this issue is dealt with by either increasing the amount of constraint iterations to a point where the simulation is no longer realtime, or a completely different approach is used (such as eulerian discretization instead of lagrangian, and direct solvers instead of iterative ones).