I'm following this great tutorial https://www.youtube.com/watch?v=1gM8yEMFMjg to learn how to fill a mesh with a particle system but am having trouble replicating the simulation (at 6 min 50 sec if interested). I'm using Blender 2.8

To put it very simply, in my scene I have two meshes as follows

enter image description here

The larger mesh has Passive rigid body, displayed as wire, and with normals set to the inside

The smaller mesh inside has Active rigid body, with sphere collision shape

When I run the simulation, instead of the smaller mesh settling on the bottom of the larger mesh, it flys out into space ignoring its container completely. How can I get them to behave?

enter image description here

Here is a link to the file https://drive.google.com/file/d/19teuR5pLl0xqDDRli7tOwsv7u0lYx-Ij/view?usp=sharing

  • 2
    $\begingroup$ Change the sphere's collision type to "mesh". Default is convex hull, and with your normals backwards, this is not considered a convex shape by the rigid body sim. $\endgroup$
    – Nathan
    Jul 14, 2021 at 19:51

1 Answer 1


I'm no expert, but I'll see if I can help quickly. Is the outer mesh with normals pointed in the right idea? You might need to give it some thickness somehow, perhaps by using a solidify modifier on its surfaces. Or maybe the whole thing is trying to behave as a solid (even though you say the normals face inwards) ...if the tutorial got you here, then that sounds wrong. But just because it is being displayed as a wireframe doesn't mean it isn't a solid. (I don't think; I've been away from blender for a minute)

  • $\begingroup$ Thanks for responding, I added a screenshot showing the normals to my question and a link to the file. I tried the simulation with the outer mesh set to solid visibility and it was the same. Is there another way to ensure that a mesh is solid? $\endgroup$ Jan 4, 2020 at 12:12
  • $\begingroup$ Try throwing the outer sphere away, making a new sphere, and making another, smaller one. Then select the big one, add a "boolean" modifier to it, and use the eyedropper to select the smaller one. Hit apply. (This will cut a hole in the big one the size of the smaller one, because the boolean modifier defaults to "difference" - subtracting one shape from another.) Now you have your hollow sphere but you can't see inside. Make a big cube now, and use another boolean difference to chop off the top of your sphere. Now you can see inside your cup. Might be easier to chop top off first. $\endgroup$ Jan 4, 2020 at 12:25
  • $\begingroup$ One more step - you'll have to change the collision settings to "mesh" or an object won't be able to fall into the cup; it will sit on top (saving some computation time) $\endgroup$ Jan 4, 2020 at 12:36

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