Autotune crash

My attempt at autotuning resulted in a crash this morning.

I fiew the quadcopter previously with a 2S battery. It was quite stable but underpowered.

After upgrading to a 3S battery I set the PIDs to what I believe is the default values:

Stabilize P: 4.5

Rate P: 0.15

Rate I: 0.1

Rate D: 0.004

Taking off and switching to Alt Hold went smooth. I then switched to Autotune and nothing happened. I believe this is because I had the throttle still a tad above hover. Closing the throttle down slightly to get it in the hover range started autotuning and on the first or second autotune roll it started oscillating ending in a crash. I was way too slow to recover it.

The way I read the log file, theses values were used for autotune:

Stab P: 4

Rate P: 0.2

Rate D: 0.005

Dataflash log attached. No CoG issues. Props and motors tuned recently, so low vibrations.


My primary question is:

What caused this crash?

My theory is that the motors may now even be slightly overpowered and I guess that an average PID settings may caused it to respond too violently. But I would appreciate if anyone else can confirm that from the log or share their own experiences.

Secondary question:

Is there a way to tell autotune to cool things down a bit and use a range of lower PID values?

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    • Oh dear god, the trollbot has found us..

    • +1000

      the moderators should divert all his comment to his own page...

    • Hey, Darius is an awesome guy, he told me so himself ;)

    • Got it...

  • Jack:

    I got a reply in e-mail that mentioned split collar prop adapters, but I see you have deleted it.

    Just for general consumption, if you are using split collar (AKA collet) adapters, put a drop or two of RED thread locker into the adapter and then push it all the way down onto the motor shaft.  

    When you tighten the prop nut down, the thread locker will keep the collet on the motor shaft.

    And, FWIW, those collets are seldom if ever bored true...

    And to dampen vibrations, I use these:  Damping Mount

    I do have a question:  Why are you running Auto Tune in the first place?  The reason I ask is because I have an X-525 with an APM and a Tarot 680 Pro hex with a Pixhawk, and I have not run Auto Tune on either system.

    • Jack:

      I started out with my Pixhawk mounted on Black 3M double sided foam pads.  Vibrations were acceptable, but Loiter was not, hovering seemed uneven, and my flight times were not meeting my expectations.

      When I replaced the 3M pads with the damping mount, vibration amplitudes dropped significantly.

      Also, with the 3M pads, the plot of hover current had a high frequency component that was eliminated when I installed the damper.  As a result of using the damper mount and reducing vibrations reaching the Pixhawk, hover was more stable, loiter was more locked in, hover current was much more even, the motors were running at a more constant RPM, as a whole the aircraft made less audible noise, and my flight time actually increased....

      With respect to the prop collet issue, I ran into this problem with my X-525 quad.  I got it as an ARF kit with the ubiquitous 2212 1000Kv motors and collet prop adapters.

      The aircraft flew fine for a while. 

      I dumped it a couple of times due to pilot error, and after one incident I noticed that one prop was sitting higher than the other three...  Then I noticed the collet was not holding...

      With the motor shaft being polished steel, there was no way to scuff or knurl it, so I grabbed some red thread locker...  And it worked.

      I literally flew that quad until the motors started to fail and I never had a prop come off.  It was my test bed for a camera and gimbal, and I used it to learn about  APM as a precursor to building a hex with a Pixhawk.  I did have a prop break in a hover once.  I was letting my grandson wear my goggles to ride along while I was testing my FPV gear,  I'd been doing some yankin' and bankin' and then I stopped and put the quad into a hover.  2 seconds later the right front prop failed at the hub and the quad "landed".  Rhylee thought it was hilarious....

      If you do the red Locktite thing and you need to remove a collet, just heat the conical end with a Bic lighter or hot air..  My SMD rework hand piece works fine for this...

      Fly Safe.


    • Thanks Cliff,

      Sounds like good advice. I will add both ideas to my improvement list.

      Here are some images that shows my current setup and the damaged components. If anyone has any suggestions on improvements, please shout out.

      Since the general opinion was that there is something fundamentally wrong with the setup, I will check the setup again. This is my current plan:

      1. Repair / replace the broken components to get it to the previous flight's condition.

      2. Test it on the test bench again to validate that everything is working again as it used to and to get a baseline for improvements.

      3. Verify all components of the power setup:

         Check ESC configurations and calibrations.

         Use threadlocker on the propeller collets.

         Dynamic balancing of the props / motors.

         Maybe some kind of motor test to confirm each individual motor / ESC combination performs well over different throttle settings for a couple of minutes.

      4. Replace the current pixhawk tape attachment with damping mount.

      5. Perform manual tuning on the test bench.

      6. Perform auto tune while on the test bench.

      7. If all performs well up to this point, I will risk another free flight autotune again.



    • Hi Jack, that's not a genuine flamewheel is it? I remember reading from a few people that the cheaper clone variants of these arms flex a lot, which is known to upset autotune (well flying in general, but particularly autotune). The original flamewheel arms are pretty solid and don't move much.

    • I think that's it!

      You're right. It's a flamewheel clone. I just tested it by hand. It's quite stiff for lateral movements, less stiff when bended up or down and not stiff at all when twisting. That would explain why pitch and roll oscillations are coupled.

      Can anyone recommend a good 450 frame? It would be great if it can solve some of these problems:

      1. Obviously the main problem is frame rigidness.

      2. Would be great if cables could be managed inside some kind of tube - both motor cables and the network of cables connecting to the pixhaw.

      3. Vibration mount for the pixhawk. (Or space available to mount own vibration mount).

      4. Solid mounting options for battery.

      5. Enough space / mounting points for GPS pole, receiver, telemetry radio, arming button, buzzer, etc.

      Any suggestions?

    • The dji flamewheel is excellent and cheap, and spares are plentiful.  It's an excellent option.  If you want good rigidity then you can't beat carbon-fibre.  I now run the tarot 650sport which is a bit bigger but you can do an awful lot more with it and the carbon-fibre arms are rock solid.  I run afro slim ESCs inside the arms.  It has dedicated battery plates for hanging on the rails and you can get gps plate for the rails and there's plenty of room for various components.  And it has a nice canopy/hat to hide it all :)

      I mount the pixhawk on one of those two-plate mounts with rubber grommet things with great results. 

This reply was deleted.