Why does applying rigid-body to a cell-fractured mesh cause it to explode despite collision shape set to Mesh instead of convex hull?

Question

I have seen numerous threads on this topic which all have similar attribute as my issue but are not the exact same.

Here is what I did:

1. Select a cube and cell fracture it
2. Remove the original cube
3. Apply rigid body active on the fractured cubes
4. Animation proceeds as normal, meshes fall down as expected
5. When collision shape is set to Mesh, instead of Convex Hull as in 4), the fractured cubes explode in every direction

Can someone explain the logic behind this? Isn't Mesh more accurate of a setting than Convex Hull? Convex Hull if i remember correctly, uses a bounding box that only somewhat follows the shape of the mesh it is applied on

I recall reading the explosions happen when the rigid body meshes intersect each other. This is confusing however. Logically, wouldn't convex hull setting have more intersections than Mesh? Mesh would be more accurate and have less intersections, yet it is only Convex Hull that doesn't explode while Mesh does

I've tried everything. Applying scale, setting the centers of all the fractured meshes to their volume again yet nothing seems to work. Why isnt this working with Mesh and how do I get it to work with Mesh?

Link to the file : https://drive.google.com/file/d/1oUC7tagOsGEZtKJIo11IjR4yJwtTQAlF/view?usp=sharing

Answer 1

Convex hull is not bounding box, but rather “bounding plastic wrap” as it were, and actually produces better results than mesh shape collision most of the time. For mesh shape Collision, Blender apparently has to do some special set up to detect concave areas, and a margin is necessarily put in place around the body. For a convex hull, however, the collision can be right on the surface. Since cell fracture does not produce concave mesh (I think), Convex hull is probably your best option here.