A little mechanical concept sample...

 Some mechanical design concepts I did a good while back that shows a bit of how I typically approach hard surface designs when needing to call out specific details for 3d modeling for game development. Depending on the complexity of the design and time constraints, I try to spell out as much as I can in "turn-arounds" and "call-outs" and if time permits I'll even dive into some 3d modeling myself to further realize the design and also allow for art direction to consider the design in context of a 3d environment (in most cases for me, in game engine).