Obi Official Forum

Hello,

I am a new Obi Cloth user. I am trying to simulate a tennis net.

If a ball flies into the net, I need Obi Cloth to stop the ball.

However, because of the speed that the ball flies at, it is able to push the cloth particles aside and pierce through the net. Here is a slow-motion video of what I just described: https://drive.google.com/file/d/1eE42ExB...sp=sharing

Is there any "stiffness" setting that limits the maximum distance between particles? Or is there any way to prevent fast objects from piercing a cloth?

I have tried increasing the number of substeps on the Obi solver--which does fix the issue--but because my tennis net is rather large (between 3,000 - 4,000 particles), the performance is terrible. I am worried that if I use a proxy mesh, the reduced number of particles makes it easier for objects to pierce the cloth.

Any help would be appreciated.
Thanks! 

Hi!

(31-08-2023, 07:39 PM)slowheii Wrote: [ -> ]Is there any "stiffness" setting that limits the maximum distance between particles?

There is, it's called stretch compliance and set to zero (= infinite stiffness) by default. The solver will try to reach the specified compliance within the substeps/iterations budget you've set, but it might not be able to if the amount of constraints is too high. In this regard, Obi works just like all other existing physics engines.

The manual contains a very in-depth explanation of how the engine works internally and how substeps/iterations affect the results:
http://obi.virtualmethodstudio.com/manua...gence.html

(31-08-2023, 07:39 PM)slowheii Wrote: [ -> ]Or is there any way to prevent fast objects from piercing a cloth?

CCD (continuous collision detection) is enabled by default in Obi. If the ball is piercing the cloth it can be due to one of two things:

- The ball has much greater mass than the net. Try increasing particle mass (you can do this in the blueprint editor) so that it is comparable to the ball's. This will give the net a chance to stop heavier objects.

- The ball is slipping trough gaps in between particles. You can either increase particle radius (again, in the blueprint editor) or use surface collisions. This will also allow you to reduce the resolution of the net mesh, leading to cheaper simulation.

kind regards,

Thank you for the very detailed response!

Increasing the mass of my particles works really well!

I'm really impressed. The net can now handle really fast ball speeds, it stretches in a realistic way, and it brings the ball to a halt rather than shooting it back like a trampoline.

Thank you.