Merge objects together I have downloaded a model of a quadrotor. It is comprised of a zillion different parts. Is there a way to wrap it with a mesh or something and get the outside of it. Kind of like a mold that just leaves you with a thin layer.

Yea, I know this sounds crazy but it would be extremely delightful if someone knew this. I need to feed it as a mesh to Unity3d So I can make a collider for this complicated shape. I really need it to be the exact shape of the quadrotor, just because I am going to need to do this with other shapes. 

Maybe there some sort of merge tool?
It's okay to be composed of a zillion different parts.  Really.

There are a couple of options for dealing with all those parts.  The best is to create an armature for the whole quad, and then parent all those parts to it.  Or you could create an empty and parent all those parts to it.  Or, you could just join all the parts into a single mesh, that works too.  In case you're wondering, just select one object, shift select another, and ctrl-j.

Now, can you merge them into a single mesh?  Yes.  Even though you shouldn't.  You can do this via a boolean modifier on union mode.

Will this screw up how your models look?  Yes, probably.  It will likely require that you retopo the mesh.  That's one of the reasons you shouldn't.

Now, how should you handle this in Unity?  You shouldn't use mesh colliders.  Especially not concave mesh colliders.  Seriously.  They are easy, but they have problems.  You should use primitives-- capsules, spheres, cubes-- that represent your mesh instead.  It is far better to use one hundred primitives than it is to use a single mesh collider.