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+--- Thread: Help Make rope more stiff (/thread-3825.html)
Make rope more stiff - 3DJames - 31-03-2023
I'm new to Obirope, so I'm just learning. I'm trying to make the rope stiffer, like a cable, but can't get it to work. I thought the Shape Matching Constraints would do it, but I don't see the options in the help file though. I just see Iterations and Relaxation. I tried adjusting these values but it didn't appear to do anything.
How can I make it so the rope is stiffer?
RE: Make rope more stiff - josemendez - 31-03-2023
(31-03-2023, 02:32 PM)3DJames Wrote: I'm new to Obirope, so I'm just learning. I'm trying to make the rope stiffer, like a cable, but can't get it to work. I thought the Shape Matching Constraints would do it, but I don't see the options in the help file though. I just see Iterations and Relaxation. I tried adjusting these values but it didn't appear to do anything.
How can I make it so the rope is stiffer?
Hi there!
Stiffer as in harder to bend, or harder to stretch? use bend constraints for the former, and distance constraints for the latter. Shape matching constraints are used exclusively for softbodies, as explained in the manual. They're not used by ropes at all.
Generally, you want to increase the amount of substeps in your ObiFixedUpdater used to allow for the simulation to reach higher stiffnesses (that is, lower compliances). Once you're happy with the overall behavior, you can tweak the amount of iterations used for specific constraint types. See the following page for an in-depth explanation of how the engine works internally and how substeps/iterations affect simulation quality: http://obi.virtualmethodstudio.com/manual/6.3/convergence.html
At the end of that page you'll also find a list of all available constraints and the actors using each one.
let me know if you need further help,
kind regards
RE: Make rope more stiff - 3DJames - 31-03-2023
(31-03-2023, 02:57 PM)josemendez Wrote: Hi there!
Stiffer as in harder to bend, or harder to stretch? use bend constraints for the former, and distance constraints for the latter. Shape matching constraints are used exclusively for softbodies, as explained in the manual. They're not used by ropes at all.
Generally, you want to increase the amount of substeps in your ObiFixedUpdater used to allow for the simulation to reach higher stiffnesses (that is, lower compliances). Once you're happy with the overall behavior, you can tweak the amount of iterations used for specific constraint types. See the following page for an in-depth explanation of how the engine works internally and how substeps/iterations affect simulation quality: http://obi.virtualmethodstudio.com/manual/6.3/convergence.html
At the end of that page you'll also find a list of all available constraints and the actors using each one.
let me know if you need further help,
kind regards
I may be doing this wrong, but I updated the substeps to 12 and saw no difference. I'm not sure if that's what I need. What I'm trying to do is make the rope look like the cable in this video. Where you can move the end and it will bend, but will mostly keep its shape.
https://youtu.be/cP0Hzyb4Pcg
RE: Make rope more stiff - josemendez - 31-03-2023
(31-03-2023, 03:56 PM)3DJames Wrote: I may be doing this wrong, but I updated the substeps to 12 and saw no difference. I'm not sure if that's what I need. What I'm trying to do is make the rope look like the cable in this video. Where you can move the end and it will bend, but will mostly keep its shape.
https://youtu.be/cP0Hzyb4Pcg
The behavior shown in the video has nothing to do with stiffness and it's unaffected by substeps, it's called plasticity:
The opposite of stiff is compliant: stiff materials are hard to deform, compliant materials are easy to deform.
The opposite of plastic is elastic: plastic materials keep their current shape when deformed, elastic materials return to its rest shape - regardless of how easy or difficult it was to deform them in the first place.
A spring is an example of an elastic object: there's both stiff springs -like the suspension on a car- and compliant springs like the ones in ballpoint pens. Both will return to their original shape when you stop deforming them.
Copper cable is an example of a plastic object: there's stiff cable that you'd have a hard time deforming with your bare hands, and compliant cable that's easy to deform. Once deformed, both will keep the shape they're deformed into.
Some materials transition from elastic to plastic behavior when deformation exceeds a threshold, this threshold is typically called the yield threshold. Think of a spring that you've stretched way too much, and it does no longer return to its rest state: part of the deformation becomes permanent.
You can set plasticity parameters on bend/twist constraints, which are used by rods instead of ropes. See:
http://obi.virtualmethodstudio.com/manual/6.3/ropesetup.html
http://obi.virtualmethodstudio.com/manual/6.3/bendtwistconstraints.html
kind regards,