Help Zero-g

[josemendez]

Increasing the mass of the particles definitely causes the rope to become more twisty and wobbly. It spawns and wiggles and goes in a spiral around itself rather energetically even if there are no forces applied. This is not related to mass ratio.

I've put two identical ropes side to side, both with default settings. One of them with 2000 kg per particle, the other with 0.002 kg per particle. Both result in identical simulation, frame per frame.

See:


Obi's sequential solver is momentum conserving, both linear and angular, so there's absolutely no way increasing the mass of a rope would increase its energy. Make sure adjacent particles are not colliding with each other or with some object during simulation, as constraint fighting might cause unphysical effects.

If you can provide a sample scene that exhibits the behavior you describe, send it to support(at)virtualmethodstudio.com

[innovine]

Interesting, thanks for taking the time to look into that.
I notice two immediate differences. I've set the solver gravity to zero, and I have a rigidbody on each end, with the last particle having a pin constraint to the rigidbody. 

I don't get the opportunity to work on this every day, but the next time I get the chance I'll try an isolated scene, and if it still behaves the same, send it to you. Thanks

[josemendez]

Interesting, thanks for taking the time to look into that.
I notice two immediate differences. I've set the solver gravity to zero, and I have a rigidbody on each end, with the last particle having a pin constraint to the rigidbody. 

I don't get the opportunity to work on this every day, but the next time I get the chance I'll try an isolated scene, and if it still behaves the same, send it to you. Thanks

Make sure the last particle (the one that's pinned to the rigidbody) isn't intersecting the rigid body in its rest state.

If it is, that's the source of your problem, as the collision constraints are trying to keep the particle out of the rigidbody, but the pin constraint is pushing the particle back into the rigidbody. This is what is known as "constraint fighting", it can create an energy feedback loop that keeps your rope twisting in an attempt to free itself from the collision against the rigidbody. In that case simply set that last particle "phase" value the same as the rigidbody. Bodies/particles in the same phase do not collide with each other.