-89 degree ATT.RollDes : Flip @ start with U11/27" Props / Hexacopter 3.5.0 RC4

Hey guys

I need your help - maybe we’ve found a bug in the software.
I had great results with autotune @ 10 Hz at several flight before the weak crash happened . After that i bring up the AltHold Rate because the copter fall 1-2m after I am braking down the Hexa. But I think too much .

Before I started to the flight with the Alt Hold P value (1,000 to 1,035) I switched the Sport flight mode back to AltHold flight mode but the log didnt show that. I displays still the Sport Mode.

At the start the Hexa (wasn’t in the air too) it made a flip to the left and all 27" props are dead now ;-( and a view foldable mechanism too…

The log say ATT.RollDes value -89 right before and at the start up procedures !!!

Here is the log:

And few pictures from the log and the bird are attached.
Thanks for your help, Fabian.

Any more information: Sometimes I do the ARMING with DJI Arming Stick position.

Ufffff…sorry to hear that…I dont understand what happened but maybe can give you few ideas…
First:you know what Philip Rowse repeat again and again;always use latest beta!
Latest beta is 3.5 rc6,you are on rc4 and there was a lot of changes between rc4 and rc5,take a look by yourself

I don’t know if it’s connected but where did you get idea to manually change AltHold P…
About AltHold problem Wiki only say this;" increasing the INAV_TC_Z parameter to 7 (default is 5) reduces the effect but increases other problems…"
Second strange decision is to fly such a big and expensive craft in pretty much unknown Sport mode.…i say unknown because is very difficult to find what does that mode exactly do…here is few links i manage to find:
http://ardupilot.org/copter/docs/sport-mode.html (this does not tell me nothing because i do not understand)
http://3drpilots.com/threads/sport-mode-explain-some-things-for-me.7873/ (here someone mentioned similar problems)
https://github.com/ArduPilot/ardupilot/issues/1064 (developers discuss problems in that mode)

From your logs(and i am no expert in them at all) it is clear that after you landed after Autotune(did you Disarm and save parameters?) you start to fly in Stabilize and switch to Sport mode(now you can claim you did not but logs don’t lie)…how do you have your Mode switch setting?Does your 3 position switch have Stab-AltHold-PosHold…
Where do you have switch for Sport mode(did you check in MissionPlaner Radio calibration if one switch does not trigger another mode too?)
Also,can you please explain what do you mean;“At the start the Hexa (wasn’t in the air too) it made a flip to the left and all 27” props are dead now ;-( and a view foldable mechanism too…" Did you have a crash and brake props or did you do that from simple tip off at beginning of flight(how can damage be so severe just from tip-off??)
ATT.RollDes value -89 must be in connection with Sport mode…
RcIn and RcOut is also suspicious at the end on Channel 4…
And again,i am no expert but just try to give you some ideas…

Hey Emin Bu thanks for your Answer.

But it doesn’t help me…

Why I should not flying in Sport Mode? The hexa flown great in this mode. And you have to be a good pilot in Sport Mode and then it’s great!

No I choose only a 3 position switch for flight modes. In the flight before the crash I tried the Sport Mode in the middle switch position. After that flight (right before the crash) I switched back the Sport Mode into AltHold Mode and yes you are right - the diagram didn’t show that change of flight mode in the middle switch position!
On the diagram it is still in Sport Mode at the crash/flip.

The Hexa does a completely 180 degree flip on its back. I could not do anything.

-89 degree ATT.RollDes in Sport Mode may not be possible! Max degrees in Sport Mode are + - 45 degree! But who can say something to this bug ?!

Thanks, Emin Bu.

I’ve had a quick look at the logs and there are a couple of suspicious things that I need to investigate further:

  • it looks like channel 5 is changing but the flight mode hasn’t changed.
  • the attitude targets look like they may be updating while the vehicle is on the ground.

I’m sure there’s a reasonable explanation for the first item. The second could be a bug in the sport mode’s code.

Anyway, i’ll investigate further and reply here.

I have flown for at least three times in Sport mode recently for a total flight time of 30 minutes with my Hexa and 16" props and did not have notice problems, same for Hybrid mode.
I use 3.5.rc4

Hey rmackay9,

Thanks for checking my log.

Yes perfect. How I said I changed the flight mode for the Flight mode switch (same switch position on my transmitter) back from Sport to AltHold in MissionPlanner but the log didn`t show that change.

Okay attitude target had updating on the ground. Can this explain a flip?

I hope we found a bug - solve it - and I can go back to fly with my little monster.

Looking forward to your next findings in my log!

Thank you!

@lucamax I had flown the sport mode before with no problem at all! Thanks!

For the first issue related to the flight mode apparently not changing when the ch5 flight mode is changed - I think the FLTMODEx parameters were set so that FlightMode 4 (ch5 input pwm between 1590 and 1620) was sport mode instead of AltHold. I can’t be 100% sure but it seems the FLTMODEx parameters must have been changed after startup because at start-up Sport mode was not possible from the ch5 switch (only Stabilize, AltHold, PosHold were setup).

Remember that, as a user, if you change the FLTMODEx parameter value (maybe using the MP’s Flight Mode setup page), you must then move the switch on the transmitter to another mode and back again. I.e. simply changing the FLTMODE4 parameter will not change the currently active flight mode.

Re the flip on take-off - the problem comes from the pitch stick being off center between when the interlock switch was moved and take-off. During this period, even though the vehicle is landed we do update the target attitude. So what happened is the target attitude went inverted and then when the throttle was raised the vehicle immediately flipped over.
I’ve made a patch to fix this, it just needs to be peer reviewed and if all goes well we will release it with -rc6.

I don’t think this issue is new to AC3.5 although I’m not sure that makes anybody feel any better.

Sorry for the troubles but thanks for the report!

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