Big octa very strange behavior

I need help to explain strange copter’s behavior.
While hovering in Loiter mode on 75m in air telemetry has lost, at the same time data logging is stopped and copter began to fall flat on his side.
I do full throttle on RC. On about 50m copter has reacted, leveled and began to slow down the fall. But it did not have time to full stop and landed (hard).
On log-file power not very clean and there is an assumption that there was a power drop below the critical value.

  1. Is it possible that the controller rebooted in the air and after continued to fly? I do not re-Arm it.
  2. Do you remember any cases when controller partially freezes (stops datalogging and telemetry output) but can react on RC sticks?
  3. Can you guess another possible scenario for this behavior?
    Copter: Big Octa, firmware 3.4.6, props 18", 6S LiPo

Can you post the log file for this flight?

Of course

It looks like there’s something not right with your wiring or the battery is bad.

The ripple on your 5V supply correlates directly with huge voltage sag from your flight battery.

At one point, the battery voltage drops to 14v which very unusual for a 6S setup. While the log only records ripple on VCC of about 0.15v, it’s possible that at the point the logging stopped this was much greater causing a brownout.

I would check all your solder joints and bullet connectors, and check the internal resistance of your battery if you have a charger that can measure it.

Unrelated, depending on just how big your ‘big octa’ is, there are some settings you should consider changing for more stable flight (specifically ATC_THR_MIX_MAX, ATC_RAT_RLL_FILT and ATC_RAT_PIT_FILT see for more info)

Justin, many thanks for your time and answer.
Yes, I know about my power problem. I complete agree - a crash is consequence of bad power.
But a main question - how my Pix can freeze (lost telemetry, stop logging and beginning of fall) and after that partially reestablish control? Is it possible?
BTW: how low VCC can drop without influence on work? I thought 5.2V is ok, it is not so?

A brownout can cause very strange problems. There are many different components on the flight controller, and all have different operating voltage / ripple tolerances.

It is possible for the CPU to continue running, but other components e.g. sensors to malfunction in this case.

The Pixhawk can accept between 4.1v and 5.7v, but has low tolerance to votage ripple (max 0.15v)

There is some info here:

Also, there is confirmation this is possible in the arduplane release-notes.txt (different software but same hardware)

'One of the most common causes of issues with autopilots is power
handling, with poor power supplies leading to brownouts or sensor

If you are still concerened after you have fixed your power problem, you may want to use a higher quality power module (e.g. Mauch) and also add a 5V BEC to the servo rail.

I understood. Thank you very match.