22" hexacopter crash after take off

Today I made my second flight with success. PID values are default with initial parameters.
The drone weighed exactly 12.9kg and had 20" propellers installed. I noticed that the drone had slight problems with vibrations on the Z axis. In the VIBE window on the main panel, the Z axis vibration values ​​almost reached 30. I attach materials on google drive for analysis and videos. The flight lasted 24minutes witch 17% reserve in windy weather. I decided to start the flight in AltHold.

https://drive.google.com/drive/folders/1u2As_3C3GtAfVDmAe9IK9qFv-yX3iiIB?usp=sharing

I think larger propellers could be fitted, what is your opinion?

One thing I really like is the use of 3 legs for landing gear! So much better than 4 legs on uneven ground.

What I dont like is

BATT_FS_CRT_ACT,0
BATT_FS_LOW_ACT,0

In that flight you went right to the critical voltage - there was the Low battery failsafe warning message earlier, then you kept flying to critical voltage and landed, possibly unaware of the voltages (unsure).
If you miss those warnings the battery will be ruined, and the copter may crash too.
Because humans get easily distracted we have:

BATT_FS_CRT_ACT,1
BATT_FS_LOW_ACT,2 or 3

I would seriously consider setting the Fence too. This will prevent take off in ANY mode until there is a good 3D Fix and Home can be set.

The motor outputs are affected by a weight distribution problem, check the balance of the copter and see if you can even out the weight distribution better.
Motor outputs are quite good, in the correct range. Putting on bigger props may just cause greater electrical load and could even decrease flight time, you may be able to take a bigger payload for a short time though - you would have to work it out in ecalc.

Vibrations are not the worst, but right in the zone where you should definitely do something about it right now before it becomes and issue during a flight. I would advise investigating this before more flights.

You can set these:
ATC_THR_MIX_MAN,0.5
BATT_ARM_VOLT,44.30
PSC_ACCZ_I,0.7
PSC_ACCZ_P,0.35
INS_HNTCH_ENABLE,1 // set this then refresh params to see the rest
INS_HNTCH_MODE,1
INS_HNTCH_REF,0.25
INS_HNTCH_FREQ,45
INS_HNTCH_BW,23
INS_HNTCH_FM_RAT,0.7
INS_LOG_BAT_MASK,1
INS_LOG_BAT_OPT,4
and do another test flight to fine tune the frequency and bandwidth
then try Autotune on pitch and roll.

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Reaching the critical value in the voltage was intended, I wanted to check that the batteries connected in series will discharge in the same way. As it turned out, one of them is weaker (older), which turned out on the charger:

obraz
obraz

It seems to me that it is best to have one single 12s battery, because then the charger balances all cells at once.

Will try new settings, more flight reports coming soon!

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