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+--- Thread: Help Obi Rope Pin constraint (/thread-2803.html)
Obi Rope Pin constraint - giuseppe.b - 12-03-2021
Good morning,
I am using the latest version of Obi and I am having problems to attach object to an Obi Rope. The effect that I want to obtain is that the object hangs from the rope without falling on the floor. I have read the user manual so I used an Obi Particle Attachment with target on the object that I want to link to the Rope and I used the dynamic type.
If I grab the object, the rope will follow it, and I am satisfied with this effect. But when the object is released I'd like the rope to keep the object "suspended in the air", like a true rope would do. Even if I have changed the stretching scale and stretch compliance the rope is still too stretchy and will stretch until the object falls on the floor.
I have also tried to change some parameters in the Obi Solver, such as the iterations of the distance constraint and I also changed the number of substeps in the Obi Fixed Updater in order to add particles to my rope and make it more stiff, but nothing seems to work.
What should I do to keep the length of my rope fixed and make it stiffer as it's necessary to hold the objects without stretching too much?
Thank you for your support,
Giuseppe.
RE: Obi Rope Pin constraint - josemendez - 12-03-2021
Hi Giuseppe,
Quote:Even if I have changed the stretching scale and stretch compliance the rope is still too much stretchy and will stretch until the object falls on the floor.
For a stiff-as-possible rope, stretching scale should be 1 (100%), and stretching compliance (compliance = elasticity) should be 0.
Quote:I also changed the number of substeps in the Obi Fixed Updater in order to add particles to my rope and make it more stiff, but nothing seems to work.
Changing the number of substeps does not affect the number of particles in the rope, but the precision of the simulation. More substeps will yield stiffer rope. Also, make sure the SOR factor for distance constraints is 1 (100%). This controls the weight of the constraints in the simulation, so if the value is lower than 1 distance constraints won't be fully enforced resulting in stretchy rope.
Adding particles to the rope won't make it more stiff, but the opposite. If anything, you should reduce rope resolution.
The mass ratio between the rope and the rigidbody also greatly affects the convergence of the simulation (and as a result, the stiffness of the rope). If the rigidbody is much heavier than the rope, the rope will have a hard time supporting it. This behavior is common to all physics engines, not just Obi. If the rigidbody is very heavy, reduce its mass or increase the rope's mass.
You can see the "Crane" or "FreightLift" sample scenes for examples of rigidbodies hanging from ropes.
Let me know how it goes!