I mounted my Tachyon XC on top of helmet using Nite Rider light helmnt mount system.
It has 2 fiber/nylon straps and foam on base. I bolted a Tachyon mount to the top of it and use the straps to tie thru the helmet vents. This holds tightly but I do not like helmet mount since I cannot insure the camera is pointing in right direction, and not till after filming and reviewing at home do I know if I had it right or not.
Also I find helmont mount does add considerable weight and feels awkard on head and neck.