I have a question regarding both Blender and Unity 3d. It seems when importing models from Blender in Unity, that the Unity engine does not import the whole model and leaves parts of it out, so there is like big gaping holes in the mesh. I posted on the Unity 3d tech support forum about this and someone said it is probably because all of the normal are not facing the same way. Is there an easy way to get all of the normal facing the same way without having to adjust each one? I have tried using “Recalculate” but it does not fix it. There are still some showing up dark and others light.
Before calculating normals you need to remove other faults such as faces inside your mesh, non manifold edges (check Select menu to show them) and double vertices (select all vertices and W / remove doubles).
In the properties panel (N) in edit mode you can turn on the face normal display. You can manually flip selected normals with W / Flip Normals
Is there anyway to tile an image without subdividing a face with Ctrl E and creating many polygons and vertices? I thought that was what the UV grid was for.
Hello, after fixing non-manifold issues I select all vertices (A) and select normals menu -> recalculate outside. Remember when using Select -> Non-Manifold it seems best to begin with no vertices selected and make sure you are in Vertex or Edge Select Mode; it won’t work in Face Select mode, I think, so you may miss something.
I had a little rant a while back about the process of snapping a vertex to an edge and how it doesnt connect (it just sits unconnected), leaving many unsuspecting people with non-manifold meshes. In Unity3D this will also equate to holes in your model regardless of Normals.
So remember, if you snap a vertex to an edge you must create a vertex on that edge also and slide it to where you want to connect the vertex and importantly, as Mr Marklew says, Remove Doubles in the Vertex menu. [ I use automerge 
]
Hope this helps.
OFC, I am also quite new when it comes to all this so if anyone does know a faster way of connecting a vertex to an edge, please fill me in!
Oh yeah, the UV grid is simply the polygons of your 3D model laid out into 2D space. It’s U and V, to use coordinates that are not X and Y, to avoid confusion. In the UV grid you can move the polygons around as you please and it wont affect the model except to display whatever the polygon has landed on when slapped over a picture (texture) in the UV editor. Resizing the polygons in the UV grid has no effect on the actual model except for altering the ‘resolution’ of what is displayed in that polygon. i.e a small UV polygon will contain a lot less of the actual image than a larger one. Use this to vary the amount of detail you want to be shown in different parts of your model and help with space efficiency when you are drawing your texture.
If you don’t already know this, you can Export your UV map in the UV editor. Stick it in to Gimp or something, (duplicate the layer then lock the base layer if you want) and simply draw whatever you want in the polygons. Export your new textured UV and slap it back in to Blender… and watch your model come to life. Of course, if you are using Unity3D don’t bother with that step; just ‘CrazyBump’ it and import it straight in to your Unity project. Then, use the built in shaders to add the textures to the material that exported with the model from Blender.
Kind Regards!