Tristan, are you sure?
what you say sounds perfectly reasonable... but if he chooses a non-commercial license for a technical drawing and they use that drawing to create something....
Oh I see. the drawing itself is protected but not the concept that the drawing depicts!
but they used that drawing in a commercial way! the omni-wheel may be considered to be a derivative work of the initial drawing! (?)
this license may apply: (human readable format!)
http://creativecommons.org/licenses/by-nc-nd/3.0/us/
tricky!!
-Leav
p.s. I hate when things get all lawyered up.