I am relatively new to this, but I have been flying my 550 Hexacopter for several weeks now. I initially loaded APM 3.3.3, and have had no major issues except one.
I noticed many comments about earlier versions of APM whereby While in Loiter or RTL mode, the drone does not always sense when landed and the motors do not cut off causing all sorts of problems.
I am still experiencing this regularly on 3.3.3 It came to a head on Friday past, when I was in Loiter mode. I had a nice controlled landing on my patio. I realised right away the drone had not sensed the landing. The blades began to speed up even though I had the controls clenched into the disarm position. The drone then flipped, even then it wouldnt disarm. Bits of blade and plastic were flying off. I grabbed a landing leg and the craft went nuts as the ESCs began fighting the variances in position from me trying to move the drone. I had to grab at the power lead from he battery and yank it off, cutting my thumb badly from carbon blades.
This problem is definitely not sorted. I have not experienced this in any other mode, and I am using Loiter mainly while learning to fly as it is a lot more forgiving.
My second query concerns the latest 3.4.1 update. I am quite happy staying with 3.3.3 but I had to update to 3.4.1 to run Craft and Theorys flightdeck telemetry setup. On doing so, I noticed a massive difference in how the throttle responded on takeoff via Loiter mode? In 3.3.3, the throttle was very predictable and smooth when building revs for lift off. On 3.4.1, this has been replaced by a surge of power at about 15% throttle and a less predictable delivery which I don't like. Its more like Stability mode on 3.3.3
Is it usual for updates to affect throttle response for existing flight modes? To ensure I wasn't doing anything wrong, I downgraded again to 3.3.3 and my smooth throttle response on Loiter came back. Reloaded 3.4.1 and uneven surge at low throttle on take off was back.
Yes, 3.4.1 has auto throttle mid enabled on it so yes it does spin up differently but should be fine.
When using loiter you should be in the clear as this mode relies on a good GPS signal to work correctly. You said you landed on your deck so it's possible the GPS lost its position and started to take off in the direction it was told too.
Also holding it in the disarmed position will not disarm the unit but make it yaw in that direction causing more problems.
It must know it has landed before this operation will work.
A log of the flight will tell all.
I really don't think this was a GPS issue unfortunately. I have a large clear 1 acre paddock at the back of my house, I have a consistent 8-10 sat lock. This issue when the motors refuse to spin down on landing has happened about 4 times out there, and 3 of these were out in the open not near the house.
It also happened a week ago on a disused airfield with acres of open space. If it happens again (although I have not tried it in 3.4.1 yet), what do you suggest I do to stop it? With the disarm command not working how can I get the blades to stop spinning. I had thought of programming an emergency stop switch but I am afraid of hitting it accidentally during flight.
Also, Can I "disable" Auto throttle mid enabled" in 3.4.1? I much prefer the predictable throttle curve for Loiter in 3.3.3
While I might not use the copter in the same way you do I often use the land command set on one of my switches when I want it to land. Otherwise I use Stabilize mode when I want to land and that seems to work for me.
I have not done a lot of landing in Loiter as I most of the time use Position Hold. I do believe there is an issue with 3.3.3 with properly detecting that it has landed which looks like your issue. I did think that it was corrected but maybe not.
In any case providing a flight controller log of a failed landing would be helpful in determining what maybe going on here.
I have a 550 Hex as well running 3.3.3, and recently upgraded to 3.4.1 for the exact same reason (running Craft and Theory FlightDeck). I have not experienced the "crazy" behavior when landing in Loiter mode, but more times than not when landing on grass it would tip over and then shortly after that disarm due to sensing a crash.
I now make it a point to switch over to Stabilize mode and land in that. I've gotten pretty good at getting it into a nice stable hover about 6 inches off the ground and then "drop" it by quickly dropping the throttle to 0. That's a low enough height that it doesn't bounce and also ensures that the props immediately come to a complete stop.
After yet another crash landing breaking an arm, my frame had taken enough. It was more hot glue than carbon fibre by that stage! :-)
SO, stripped it down, refitted all the parts to a new Hex frame and re flashed with 3.4.1. I ran auto trim and Autotune and I am getting very stable flight. Also no issues so far after about 8 landings in Loiter and Alt Hold. Hopefully thats sorted.
Also, re my earlier questing about the difference in throttle response in Loiter mode between version 3.3.3 and 3.4.1. Is it possible to uncheck "auto throttle mid enabled", or bring it as close to the response on 3.3.3 as possible? I just preferred it that way. I cannot get my head around the "dead" space in mid throttle positions on some flight modes, or indeed the delayed throttle responses seen while throttling up or down. It doesnt seem intuitive to me. Moving the throttle stick and nothing happening, then sudden surges (or upsurges) of power at the extremes is hard to get used to.