I'm well into making significant changes to my Ai Freedom II, which is essentially a rebodied Syma X8-series quad. Being an Air Force vet, I use similar classifications for evolutionary changes. 'A' model being the original configuration from the manufacturer. 'B' model is where I swapped the original 3.7v 550 mAh throttle controller, and 7.4v 1800 mAh lipo batteries, gor 1200 mAh, and 2500 mAh versions respectively. 'C' model is the current "tall tail" modification. Where both the controller and the drone are being retrofitted with 2.4 GHz wifi antennae. The controller is already completed, and the drone will get one next. I'm using a 2 dbi antenna on both, but have a couple 6 dbi, that I will try to see how well they work out.