Hi, Take a close look at the RC timer F1000 Cinestar knock-off... The central bottom plate has centered notches that engage equivalent "pins" set on the booms. another "pin-brace" is used to keep the motor mount in flush alignment with the XY plane. The FamousHobby GPS thingy would do the trick, but the RCT solution is better thought out. Cheers http://rctimer.com/index.php?gOo=goods_details.dwt&goodsid=860&productname=
That came up on another post Gil. Not a bad idea if you take your arms on and off but really the alignment of the arms is pretty quick after you have been doing this for awhile. It's really about the motor/prop alignment.