Do the default Roblox spheres have perfect collisions that can’t be replicated with a mesh? I wanted to be able to change the shape of the sphere to something else with ease, and though just changing a mesh ID would be a good idea. But after some testing, I have found that even if you export and re-import the default sphere, the collisions are not the same.
i would be inclined to say that doing this isn’t a good idea - the collision models that the engine generates for user-generated meshes are not (and are not intended to be) polygon-perfect.
that being said, my partner has a low-poly sphere with good collisions when CollisionFidelity is set to Hullhere. This may be possible to do with other sphere meshes; I’m not quite sure. I have a hunch that it should, because a sphere should be 100% convex… at any rate, I know that it seems to be acceptable with this one
Try to separate the sphere into 2 parts and import it that way. Make sure Collision Fidelity is set to Default. They recently updated the collision fidelity calculations and you should not have any problems.