We're bringing up a 3DR hex for use as an autonomous UAV. In a nutshell, the goal is to be able to tell it "Haul the camera out to location x, take video of the area, and RTL" with no human intervention.
We started with Arducopter 2.8.1. The first time we sent it off on an flight plan downloaded with Mission Planner, it performed flawlessly, until it returned to about 18 inches above the launch point. Then it suddenly slewed off in an apparently random direction, hit the ground at an angle, and cartwheeled.
We think that what happened is that, as the copter landed next to our two-story metal building, it lost sight of some satellites, and the GPS suddenly said "Oops, you need to be over there, not here", and crashed trying to get there.
I was hoping this might be fixed in 2.9.1, but I've discovered that a lot of people are complaining about unpleasant surprises during RTL. I also found out that the code has been dramatically restructured, so any fix I come up with for one version can't be ported to the other.
So I need to pick one.
I'd like to hear from people who've either used both for autonomous UAVs, or are familiar with the waypoint-navigating and other autonomous-relevant parts of Arducopter, about which would be the better choice for building a reliable system.
And, btw, the change we're looking at making is to start ignoring the GPS at some point during final descent, and rely on either inertial navigation or something like an optical flow sensor to maintain the horizontal positioning. That should protect us from unpleasant surprises when the sensor suddenly changes its mind about where we are.