grains deciding to go wherever they want, with the behaviour they choose!

[kerguestenen]

Hi everyone,

I've search here for an answer, but with no luck, so here is my problem.
(And thanks for anyone reading and yet more for anyone that could help me!)

In the attached video, you can see that some packs of grains choosed to not behave as the others...
Some pack are going up ignoring gravity, and some others, worst, seems to be thinking "oh, let's stop going that way and let's go straight in another random direction"...

Of course i'm just discovering grains, but after one week trying all kind of setups/parameters values, i'm really lost!

This test was done by the shelf, with "wet sand", and i've only changed a few parameters:
- min/max substeps in pop solver to 20 (and just 1 for the main popnetwork substeps).
- constraint iterations to 60 in the pop grains (my grains are stacked in about 50 layers).
- scale kinematic set to 1
- clumping weight: 2
- clumping stifness: 20
- use openCL: on
- my monster and ground are bullet colliders set to concave and no bounce.
The rest are default.

Does anyone by any chance have any kind of idea?
Thanks a lot for your time, and really, sorry if that was asked before, but i really didn't find it...

grains.mov