Strange collision meshes

Hello there!

I’m having a slight problem importing UCX_ collision meshes. For some reason they don’t seem to work on every mesh. First of let me explain the problem with a little more detail:

I have a map existing of 84 floating islands, each island is exported with it’s own number. For example Island01, Island02, and so on. Every .fbx file exists of 1 island and 1 UCX_ copy of the island without details like grass. Since the islands are low-poly models I figured it could be used as a convex hulls as well. However this doesn’t seem to work for every island. Island03 has a perfect collision while Island01 and Island02 don’t have a collision at all when imported in UE4.


First I thought it might be the import setting in UE4 or the export settings in 3DS Max, but I didn’t find anything wrong. The Islands were exported and imported the same way after all. I also tried optimizing the UCX collision mesh in 3DS Max to lower the polycount but it didn’t seem to matter since it didn’t read the collision mesh at all in UE4.

It’s important that the collision mesh is UCX, since USP and UBX are not accurate enough. Building a collision mesh in UE4 can take a long time, and might not be as accurate as well, let alone building a collision mesh for 84 islands.

Any ideas what might cause this problem?

Thanks in advance!


well if I had to say your UCX collisions probably don’t work because they are not convex(by that I mean they look like they have both convex and concave angles and so are not really convex) the diagram in the collision section of the static mesh pipeline documentation shows the difference best, you could use per poly collision so you don’t need to manually create collision meshes but that can be expensive on performance or you could try the automatic collision generation options, if you make the collision meshes manually in your 3D app then you’re probably going to need multiple convex hulls for each mesh, just duplicating the mesh to use as a collision mesh doesn’t usually work very well(if at all) in most cases especially when the meshes/models are quite oddly shaped like your islands.

hope that helps:)

You just confirmed my fear haha :slight_smile: I was a little confused about why Island02 didn’t work and Island03 did. Guess it’s gonna be a little more work after all.

I’ll try a few solutions and post the results. Thanks!