Invisible Mesh when i imported from blender to unity

Im trying to import a 3D robot that i created to unity but im having problems with some parts.

This is how it looks in blender:


I exported it to fbx and then imported in unity and this is how it looks:



As you can see mesh it's only visible at the border of object. This only happend with the shoulders. Materials are in opaque mode.
If i upload to mixamo to make animations it getting worse and this thing happen to a feet and a leg too.

Is there any solution for this? Thanks for you help.

 

I solved it. In blender you have to go Edit mode, select all faces, then Mesh -> Normals -> Recalculate Normals.

With this if you export it to fbx and upload to mixamo it will continue generate problemas, so you have to export it to .obj and zip it with the .mtl file, then upload and all will work perfectly.

 

Thanks for this info. It will come in handy.