Help Rope pinned to two dynamic attachments has a gap when physics act upon it

[josemendez]

Hi! I'm new to Obi Rope and just wanted to say—it's a fantastic asset. I really appreciate the craftsmanship behind it.

I think I'm running into a user error and could use some help troubleshooting. I’ve attached three images below, in addition, here is a link to a video of the problem.

Each of the plugs in my setup are Obi Rigidbodies connected to the rope using dynamic attachments. I believe I’ve set up the constraints correctly for my use case, and I’ve experimented with different iteration and substep values.

I’ve also tested different mass settings—for example, setting the rope and rigidbodies both to 0.1, or the rope at 0.1 and the rigidbodies at 1.0, and vice versa—but the issue still occurs.

Hi!

How are you moving the rigidbodies around? Would it be possible for you to share any custom code related to this? gaps in pin constraints are often the result of either improper rigidbody movement or physics state interpolation issues. In can see in your screenshot that the solver has interpolation enabled, this will cause a 1-frame delay in simulation. If your rigidbodies aren't using interpolation as well, this may be the cause of the gap.

Here’s what I’m hoping to figure out:

If the gaps are unavoidable due to physics constraints, is there a way to reset the rope when it’s stretched beyond a certain threshold?

There should be little or no gap. See some of the sample scenes using dynamic attachments ("Crane" or "SpringRod" for instance). In any case, what exactly do you mean by "resetting" the rope when stretched beyond a threshold?

You can calculate the amount of strain in the rope like this:

Code:

float strain = rope.CalculateLength() / rope.restLength;

This is the quotient between the rope's current length - including any stretching - and the length it's supposed to have at rest. Strain will have a value of 1 when the rope is not stretched, >1 when stretched, and <1 when compressed. You can react to its value and take action if needed.

kind regards,