Greetings,
The following Blender model needs to be exported to Unreal - see first screenshot.
The 2 workspace files are available in the following zip:
https://new.dercetech.com/wp-content/uploads/2019/10/model_export_from_blender_one_or_many_uvs.zip
The second screenshot is the import result of option 1 (left, bad) vs option 2 (right, good)
I started with the “option 1”: having one UV Map per material.
Main steps:
- attempt to have no more than one material per mesh
- assign the same UV Map name to objects that use a similar material so that when joining the objects, meshes using the same material will have an identical UV Map.
- join the meshes
- for each material, add an UV Map input pointing to the right map.
- export fbx
- import in Unreal: bad result, only one material is rendered
Result: Only one material is rendered.
Option 2: having one UV Map for the entire model
Main stemps:
- same
- assign the same uv map name to all meshes
- join meshes
- no need to add input uv maps to materials
- export fbx
- import in Unreal: good result, every material is rendered
So I’m obviously tempted to think option 2 is good.
Is it really a good practice to have to assign the same name to all uv maps before joining the meshes in Blender? I’m too unexperienced to foresee the problems / limitations of this approach.
Moreover, secondary question: why is my “good import” so dark? It’s supposed to be worn by a character, so I understood it doesn’t need a “lightmap”. I’d be thankful you could fingerpoint at what I’ve done wrong 
NB regarding the workspaces linked above. There’s two of them, each have:
- a collection of separate meshes
- a collection containing the joined mesh based on the option 1 or option 2 technique
- both have some texture / material / cleanup / etc. python scripts I wrote to ease the renaming of UV Maps, meshes, etc.
Thanks a lot for your attention!