Softbodies intersecting easily

[josemendez]

You're right that gravity is quite high, about -30 in total (-9.81 for the solver and another -20 externally). CCD is already 1 though. I've attached my solver settings, it's possible they've diverged with sensible values over time.

That's a huge acceleration, more than 3 times Earth's gravity. CCD will help for high velocities as it expands the collision bounds in the direction of the velocity, but for large changes in velocity between frames (that is, large accelerations) you'll likely need to increase the collision margin for the collision detection system to get ahead and consider contact pairs that would otherwise be missed as gravity increases velocity mid-simulation (during substeps).

I'm unclear why tunnelling can happen so easily at such low speeds (force is quite high but not overly so). Is there anything else I can do to prevent it? Larger particles, more iterations etc...?

Tunneling doesn't necessarily happen at high speeds: the smaller the objects involved, the lower the velocity threshold that triggers tunneling. We have an older video on tunneling here that explains it in detail:



Since particles are very small objects, using traditional static collision detection would cause tunneling even at very low speeds. That's why Obi uses speculative contacts, which is a very aggressive form of CCD - not failproof but more robust than sweep-based systems.

Things I'd try in your case, from cheaper to more expensive:

- Increase platform mass (even if it's already heavier than the ball, the larger the mass ratio in favor of the platform the more resilient it will be to clipping).
- Increase particle radius.
- Increase the solver's collision margin.
- Use a smaller fixed timestep (you can find this setting in Unity's Time settings).

let me know if you need further help,

kind regards