Best way to do hollow collisions?

What I am trying to do is import a static mesh (which will only be used for collisions) that is hollow (like a pipe, or an indoor enclosed arena like what you see in the game Rocket League), and make it work for online gameplay, but I just can’t figure it out.

I have attempted to do the following:

  • Simply import a mesh with inverse normals. The result is that it has a fairly nice collision mesh, but it doesn’t match the mesh’s details and cuts out very important details.
  • Import the same mesh but turn off “Only One UCX Per Hull”. This results in collisions similar to what I am going for, but they do not seem to be the most stable (the physics can sometimes randomly hit very high velocities or hit a bump that doesn’t seem to be there). Additionally, some extra collision meshes seem to fly outwards from the mesh, meaning that you cannot go around the mesh.
  • Import the mesh but within a container in hopes of stabilizing the collisions. The only noticeable effect is the container has near perfect collisions, but it was just a simple box.

I feel that knowing how to have multiple UCX meshes in one file would probably help, but no matter how much I search I cannot find documentation or a good tutorial on how to do this.

I am using Blender 2.75.


It does not matter what kind of 3D software you use. You need remember some basic rules.

  1. Collision mesh can be only closed mesh - sphere, box, cylinder, cone. But tube or similar not acceptable.

  2. For complex meshes, you can use group of collision meshes.

  3. Collision meshes should be in scene Root and do not grouped and not parented.

This video for 3DS MAX, but rules is valid for all 3d programs: Unreal 4 Creating Custom Collision (for concave surfaces) - YouTube

I noticed that if you name blender objects as UCX_object_001,UCX_object_002… they were all imported

in unreal when you open the mesh, you can display simple collisions, your collision objects will be there

Leaving this here in case it helps anyone. I needed to create a hollow “pipe” collision for an object that the player can go inside of and all around that can also simulate physics.

I used the UCX_prefix method but could not get the hollow bit to reflect my collision shape and it just created a solid cylinder with no hollow “void” cylinder.

I then tested by splitting into 4 individual quadrant shapes to make up a combined collision but it shortcut the interior faces and created a face (represented by magenta lines) that resulted in a square and inaccurate hollow area.

Lastly, the solution I arrived at was to create a simple trapezoidal extrusion that had no “concave” geometry (since convex decomposition is what we are working with here… finally realized it is taking the outer/convex bounds of the UCX shapes and ignores concavity) and then used a polar array to duplicate this simple shape fully around the “ring” (tape roll).

This resulted in a custom collision with good accuracy that my player could move around, on, and through.

Maybe this will help someone trying to simulate a fairly simple hollow form or pipe with physics.


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