(29-03-2023, 09:45 AM)josemendez Wrote: 1.- Just in case: make sure all ropes are part of the same solver and the same updater, since they're involved in the same simulation. Otherwise they will behave independently, calculating and applying forces as if no other ropes were attached to the rigidbody.

2.- You're assuming the rope is kinematic and has no momentum, so it cannot stretch or compress due to inertia. I'd recommend to leave some room for the rope to expand/contract a bit, like so:

Code:

if (c2_len > c2_control_ip + room)
        {
            cursor_2.ChangeLength(rope_2.restLength - c2_control_ip * time_dt/10);
        }

        else if(c2_len < c2_control_ip - room)
        {
            cursor_2.ChangeLength(rope_2.restLength + c2_control_ip * time_dt/10);
        }

Otherwise if the rope stretches or compresses even a little bit, it will trigger a change in rest length.  This is similar to what the included sample ObiRopeReel script does:

Code:

// Update is called once per frame
void Update()
{
    // get current and rest lengths:
    float length = rope.CalculateLength();
    float restLength = rope.restLength;

    // calculate difference between current length and rest length:
    float diff = Mathf.Max(0, length - restLength);

    // if the rope has been stretched beyond the reel out threshold, increase its rest length:
    if (diff > outThreshold)
        restLength += diff * outSpeed;

    // if the rope is not stretched past the reel in threshold, decrease its rest length:
    if (diff < inThreshold)
        restLength -= diff * inSpeed;

    // set the new rest length:
    cursor.ChangeLength(restLength);
}

(29-03-2023, 12:44 PM)rohit_dhak Wrote: In Distance contraints I put stretching scale as 0.1, since with stretching scale = 1, the rope is sagging enormously.

(29-03-2023, 01:23 PM)josemendez Wrote: Setting the stretching scale to 0.1 will tell the rope to try and keep their length at 10% of their rest length. Should be left to 1 (100%) unless you're going for some special effect.

If your ropes are sagging, either:

- Use more substeps (10-15 is completely fine). This will ensure ropes reach their target rest length during simulation. The manual contains an in-depth explanation of how iterations and substeps affect simulation quality: http://obi.virtualmethodstudio.com/manual/6.3/convergence.html

- Decrease rope resolution. Less constraints will result in faster convergence and less spurious compliance (that is, less elastic ropes). A resolution of 0.6 means particles will slightly overlap each other, which means there's a lot of particles. Since your ropes are very long, that will require a rather high amount of substeps for the simulation to be accurate.

You can combine both: use lower-resolution ropes with more substeps.

Note you can use surface collisions in case your rope resolution needs to be low and gaps appear in-between particles.

kind regards,

(30-03-2023, 07:39 AM)rohit_dhak Wrote: I am giving the condition to get c2_len which is rope2.CalculateLength() set to the control input c2_control_ip
However when I logged the restLength, c2_len and c2_control_ip I saw that the c2_len is trying to set to restLength instead of c2_control_ip

Am I misunderstanding something?

(30-03-2023, 08:05 AM)josemendez Wrote: The actual -calculated- length of a rope always strives to be its rest length, so this is the intended result: in your case, c2_len will strive to be as close as possible to restLength.

Imagine you have a rope that's 5 meters long at rest (under no forces). Then you hang a heavy object from it, and the rope stretches to be 5.2 meters long. Its restLength is still 5, but CalculatedLength() would return 5.2.

If you now call cursor.ChangeLength(6), the rope's restLength is set to 6, but due to the force applied by the object hanging from it its CalculatedLength() might be 6.2 (or 6.5, 7, 8.2... depending on how many substeps are used and how compliant the rope is).

(30-03-2023, 08:31 AM)rohit_dhak Wrote: So If I got it right,

If the restLength = CalculateLength(), it means that the control input is applied properly, but with extra length in CalculateLength() due to stretching.
i.e. to say that the extra length is the sag length due to stretching?