ok im stuck here. trying to scatter some stones in my sand simulation.

i created the stones and imported them as obj. circa 300 stones. using the fractured object shelf tool, i drop them onto my sand.

with the sand disabled, i can get them to react relatively well to the ground plane using either the bullet or rbd solvers, although if i choose concave for the collision shape, they tend to fall through the floor geometry with bullet.

anyway, i wish to use the rbd solver, as i need to use a decent volumetric collision object with my main “collider” in the scene, as polygon based collisions seem to cause sand explosions.

i have no idea wether you can use grain solver, bullet solver and rbd solver in the same dopnet and have them all play along.. i do know i need my ground plane to be on the same rbd solver as my stones or they fall through the floor.

ive not tried adding my main “collider” to the mix yet.. but i do know it only seems to work with the rbd solver.

anyway my main problem is as follows:


when i use the RBD solver, the moment the falling stones touch the grains, they fly off at high speed. they are falling from a very small height.

if i use the bullet solver, i dont get rocket stones, but i do get odd effects with stones refusing to come to rest in the sand.. suddenly moving after a few frames, or rotating randomly, even though the grains are settled and unmoving.

ive tried cranking up the substeps and iterations on the bullet solver and min and max on rbd, and ive tried different collision types.

how to get this to work?

if anyone is interested i can package up a file.

+1
I am facing the same issue.

There is an option with the bullet solver for objects to go to “sleep” below a certain threshold in regards to velocity and time, might be worth giving that a go to see if you can get the objects to settle better.

I got issues with bullet or rbd interacting with grains too.
When I shoot a sphere onto a granular sheet the sphere just goes through the grains not experiencing any slowdown.

Dropping a sphere onto a pile of wet sand the sphere bounces back higher as it's initial position … so it is gaining energy … reducing bounce is ignored .. at least the result looks the same.

Some help would be nice.

Cheers

Hi, did anybody already figure out how to prevent the rigid objects from falling through the grains?
I'd love them to have the same weight as the grains.

I would also like to know how to incorporate an RBD/Bullet solver with a grains solver. For instance, how would you rig up a simulation where a metal object is dropped into the sand, which would initially go somewhat into the sand and then over time would settle into the sand, but at a certain point the sand would fully displace the object and it would come to a stop? In the meantime, I use the RBD grains, but these have to be relatively large/few or it becomes too time-intensive to compute.