Re: GPS
It seems to be coming down to; not getting far enough away from you to establish actual GPS coordinates, 40-50 feet above and out the same distance, magnetic interference, (any cell phone towers near you), or switchs not in the correct position. The other option may be that you are losing a satalite lock after take off. What are the wind conditions during the flight? If GPS lock is established, the quad will attempt to maintain a horizontal hold in about a 4-10 foot radius. Otherwise, there may be a larger horizontal shift. If GPS lock is established and the winds are strong, the quad will return to the position before the winds moved it.