Suspending Long Rope

[Skotty]

One last noob question.  What is the right way to do a long suspended rope (like a power line as an example)?  I played with various stretching parameters, mass scale, and one or two other things, but the rope would always drag all the way to the ground (even with stretching scale at 0.001 and stretch compliance at 0).  The one thing that worked was to reduce gravity in the solver.  I can make that work, but is it the right solution?

I only need a couple of such ropes.  And I could (and may yet) switch those to just static meshes since these particular ones don't really need to move.  But I'd still like to know is there are other parameters I should be adjusting for a long suspended rope.

Thanks,

Skotty

[josemendez]

One last noob question.  What is the right way to do a long suspended rope (like a power line as an example)?  I played with various stretching parameters, mass scale, and one or two other things, but the rope would always drag all the way to the ground (even with stretching scale at 0.001 and stretch compliance at 0).  The one thing that worked was to reduce gravity in the solver.  I can make that work, but is it the right solution?

Long chains of constraints cause the solver to converge slowly (that is, takes more work for it to reach an accurate solution, and any remaining error manifests as overly stretchy/elastic ropes). So if you have a very long rope but still a fixed "budget" for solving, the work the solver is able to do within that budget won't be enough to reach a completely stiff state. The solution is to either reduce the amount of work or increase the budget for solving it.

These are the settings you can tweak (in order of preference) to get less saggy long ropes:

- Reduce rope's blueprint resolution -> less constraints per length unit, taut rope with less work.
- Increase the amount of substeps in ObiSolver -> chops up time into smaller discrete pieces, less constraint error, taut rope. (more substeps = costlier simulation)
- Increase the amount of distance constraint iterations in ObiSolver->more time spent enforcing constraints, less constraint error, taut rope. (more iterations = costlier simulation)

The manual has a very in-depth explanation of how the engine works internally and how substeps/iterations affect results, this can help improve your understanding.

kind regards,

[Skotty]

Long chains of constraints cause the solver to converge slowly (that is, takes more work for it to reach an accurate solution, and any remaining error manifests as overly stretchy/elastic ropes). So if you have a very long rope but still a fixed "budget" for solving, the work the solver is able to do within that budget won't be enough to reach a completely stiff state. The solution is to either reduce the amount of work or increase the budget for solving it.

These are the settings you can tweak (in order of preference) to get less saggy long ropes:

- Reduce rope's blueprint resolution -> less constraints per length unit, taut rope with less work.
- Increase the amount of substeps in ObiSolver -> chops up time into smaller discrete pieces, less constraint error, taut rope. (more substeps = costlier simulation)
- Increase the amount of distance constraint iterations in ObiSolver->more time spent enforcing constraints, less constraint error, taut rope. (more iterations = costlier simulation)

The manual has a very in-depth explanation of how the engine works internally and how substeps/iterations affect results, this can help improve your understanding.

kind regards,

Thank you.  Reducing blueprint resolution definitely seems like the right solution in this scenario.  That particular rope scenario no collisions need to be handled so there is no reason not to reduce the blueprint resolution.

[josemendez]

You're welcome! as a side note: when reducing blueprint resolution, the visuals of the rope will also reduce their resolution, resulting in coarser/less detailed meshes.

You can upres/smooth the mesh used to render the rope by increasing the ObiPathSmoother component's "smoothing" parameter. This allows you to decouple the rope's physical resolution from its visual resolution.