Egad. "Moho" is a real word

[Erom]

I concur with nivek. I always imagined the metal makers to be fusion engines, not relativistic engines. Same with the tree- nanotech is still bigger than atomic, so I assume sucking in a tree doesn't give you a mass-energy conversion, it gives you a lot of light organic molecules which the com bot can't magically turn into metal, so it "burns" them and gets the energy instead.

Though it is worth considering... the metal makers can fuse lighter elements into heavier ones... why can't the com bots?

Unit idea! Something that, when reclaiming an energy source, instead of providing energy, consumes an energy spike like a weapon firing and provides metal instead. Call it a Metal Maker K-Bot or something.