Multiple UV maps -- One UV map always low res or missing

Question

For the life of me I can't figure out why this happens when I add a UV map.

Somehow, I managed to apply only a single image to my highest level UV map and the lower level UV map maintained the same resolution--allowing me to get the same resolution on both my UV maps and nicely import my mesh into another editor.

But I've not been able to duplicate this except on one mesh. What's going on?

Somehow I was able to set the mesh resolution without applying an image. This is exactly what I want because applying multiple images to multiple UV maps is creating issues for me.

Anyone know how I can set resolution on a UV map without applying an image? It's definitely working for me on one of my meshes, but I just don't know how. It's fine if they all have to be the same resolution

Here's a file with two proportional UV maps (which is fine). One of them doesn't even have an image applied to it, and yet it works...

https://docs.google.com/file/d/0B3jOsV51Z7CuRmFRb3JyOUFYVFU/edit

Which ends up looking like this with 2 textures applied

And then, what has been happening to me dozens of times, is this other version which ends up with 1 texture being very low res (or zoomed in somehow?) and the other texture displaying. Sometimes it seems to not detect there are 2 UV maps at all.

More info : I'm using FBX export and Unreal Engine 4.

Can anyone tell me what I've been doing wrong, and what I did right the one time? I'm pulling my hair out because I can't figure out why all of my UV maps come out terrible--except for one. What I'm doing seems extremely basic but FOR THE LIFE OF ME, I can't figure out what I've been doing wrong.

Edit : I was able to get a screengrab of a bad export.

Answer 1

I found the solution. It looks like the Unreal Engine only supports a single UV map for actual textures (you can still achieve multiple materials easily)

The reason my first example worked is because I was only actually using the 1 UV map and it had 2 materials inside of it and the other uv map was doing nothing.

I was going to delete this, but Blender and Unreal are pretty much attached at the hip at this point. They fund Blender and the FBX export just went into the main package, so I'm sure I won't be the only one assuming I can duplicate the 'blender way of doing things' with multiple true UV maps like in this video
Tip: Using Multiple UV Coordinates (archive)

Simply put, it looks like Unreal Engine 4 only looks at UV map 0 for textures.

Answer 2

Unreal engine 4 supports multiple UV's. I can Guarantee that. The problem is, blender's FBX exporter. When you add a UV map every different object in blender, FBX exporter overlaps them by looking the index of UV maps. In case of 2 objects having 1 UV each, exporter MERGES all UV's which are the FIRST UV of every object.

You can try it out by making multiple UV maps for each object. index zeros merged as 1 channel, index 1's merged as another UV channel and so on.