TriCopter central board (RC explorer)

TriCopter central plate

This is a modified design based on jphilips boards (the postion of bolts is same; shape very slightly differs).

Main differences:
-The plate is universal e.g. same board for top and bottom
-No recesses for bolts and nuts on "print bottom" side. Makes print easier and cleaner
-Added nut holder for KK2 at the inner side
-Bigger arm retainers (cut their edges by knife to tune hold/fold force)