Almost Crash when starting Mission


I had started this topic on Gitter yesterday, but it turned out that it was not appropriate for a chat.

I just had my first flights after switching from arducopter. I’d call it a success. I lost one prop only
but once, I almost crashed badly. That was when starting a mission inflight. strong oszillations started, and continued even after switching off the mission again.
Could that be related to to high PID gains? I do have the impression, that my gains could be a bit too high, even in manual flight. But I was not at all able to create these strong oszillations (the one when switching to mission) in manual flight -by far. The oszillations in manual flight are very subtle, if at all. I wouldn’t even call them oszillations, only small over-shoot.

@kd0aij and @LorenzMeier supported, and asked me to upload the logs. Unfortunately, I am not able to download any Logs. None are visible under the Log-Download App.

Also under Onboard-Files -> fs/microsd/ I cannot see the flight logs. A folder logs exists, but that cannot be browsed.

Now, I think we cannot get futher without logs. I cannot access the sd-card easily, but if there is a high probablity, that logs are accessible directly on the SD-Card, I’d dismantle the copter for getting the card out.

So, questions:

  1. is it likely?
  2. Is there a way that I can check why no logs are written/ensure that logs are written in future?
  3. Is there a way to make sure that less pitch/yaw/bank autority is given in the auto-modes?
  4. Any other suggestions to try to fly a mission again, but reducing the risk? It was really close to a crash.



update: I did fly again with lower PID gains.
I first verified Stabilize handling qualities, then went to position hold --> all good.
Then I started a mission --> also ok. But I was quite nervous…
So, I think it was related to too high gains. I used the ones from 3DR DIY Quad.

I am not yet happy with the PID gains though. When switching from Stabilize to Acro I almost lost the Copter again. I am struggling adopting the gains though without
a) Logs
b) being able to tune the parameters in flight via remote (“CH6 tuning in Arducopter”)

Regarding a):
In QGC I see '[Blackbox] failed: 12_50_40.px4log
How can I debug this?
It comes from and is apparently caused by the flight controller not being able to create the file.

Regarding b):
Any way to do the CH6 tuning equivalent in PX4?

I am a bit hesitant to have the copter in my handy while tuning the PID as suggested in the Userguide.


I agree with you on PID tuning; I have never been tempted, in 4 years of working with multicopters, to hold one in my hand while trying to tune PID gains. There is a mechanism in PX4/Firmware to tune gains via RC, but it is not well supported by QGC, and I find it too awkward and error-prone for practical use.
Have you tried reformatting your SD card?

Hi Mark,

I did see under
Parameters -> MC_Roll_P --> Advanced the possibility to link the parameter to an RC channel. I did try this, but it did not seem to change the flight behavior.
I think I need to solve the logging first.

Formatting the SD: Is this possible without physically accessing it? I.e. via Telemetry?


Not that I know of. It’s best to run this formatting utility:

What happens when you read the SD directly from your computer?

Hello Mark, hello Sanderux,

I have no physical access to the SD-Card. If there is no other way, I can dismantle the copter. But I’d do that as a last resort only. How confident are you, that this would solve the issue and is there no way to format via USB?



I dismanteled the copter now.
In fact, the SD-Card was corrupt. I am using a new one now