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Way point flying the APM 2.6 on DJI equipment

So I've got the APM 2.6 from DIY Drones on DJI 450 equipment.
After some pain I have it up and flying (although I probably need to do a better mount of the board).

I'm looking for some feedback from anyone who has done way point flying on the APM equipment. I'll describe my last flight :

So things are progressing nicely. It's not "Naza stable" but it's certainly flyable. I observed some odd waypoint flying characteristics that I thought you all could advice on.

So I set a way point course with about 3 way points. Close enough that I could keep an eye on it, but far enough away I'm not able to discern orientation (short of it moving across my field of view).

After achieving GPS lock, I lifted off and hit the AUTO switch. Off it flew away from me. It reached the first waypoint. It was far enough away that I couldn't determine what exactly it was doing but it stayed in that general area for a bit before turning and flying to the next (across my line of sight).

With this horizontal track I got a good look at what it was doing. It would fly at an increasingly fast speed/pitch. You could hear the props loudly chopping through the air just before it would right it self with a quick gain of altitude due to the sudden pitch correction, wobble back, stabilize, then try again by tilting "forward" and continue to fly towards the way point. It would repeat this every 3-4 seconds until it got to the way point.

At the way point there may be some oscillation - hard to tell as it's far enough away and visually I couldn't determine if it had reached the way point or doing another one of those stabilization correction things I described above.

By the time it looking like it had reached the last way paint before it should turn and fly back to me (RTL) it started doing another corrective stabilization thing but it was dropping a lot of altitude and getting to a point low enough that some trees closer to me would block visuals, that I flipped the mode back to STAB and hit the throttle to watch it sky rocket up and right itself.

I then flipped the switch into RTL mode and watched it make it's way back to me. Once it was close I took control and landed it.

I wasn't going to try way point navigation again on this configuration but I wanted to test more RTL and stabilization stuff. I'd take it quite a ways up and kill the throttle. It would of course start slowly tumbling out of the sky, rolling unto it's back. I'd hit the throttle and in a loud whirl of the props it would right itself. Very impressive. I did this several times.

Another test I just flew it off in the distance and this hit RTL. It didn't look like it was flying back to me - more like across my field of view - I was getting nervous as it was getting towards some houses so instead of giving it a few more seconds to figure itself out I took control and brought it back. Since it seemed to worked fine after the way point this might have been me having a hard time determining the orientation and not it having a hard time finding it's way.

While doing some simple hover/control tests up high, it all of a sudden tumbled out of the sky. It wasn't a gentle tumble like if I just killed the throttle, it started " flipping out". Crash landed in the grass. Luckily it was very tall grass and there was no visible damage. WHEW!

I did however notice the BEC (that just powered the board and not the props) had one lead come unsoldered from the power lines. This could easily have happened post crash but I don't know. I would have thought it would have just caused the motors to quit resulting in a gentle tumble rather than this violent one - but who knows. I am actually less concerned with this for the moment since it very well could have been a poor solder joint on my part.

So I plan to get it up in the air - but I was hoping someone could advise on the flight characteristics I described. One setting I had changed before this flight was lowering the way point flight speed from 5 to 4. Perhaps all I have to do is drop this some more? Or is there another setting I can tweak to make simple forward flight more stable - stable to the point where it won't zero the pitch suddenly (causing oscillations)?