X700 Cube 2.1 mayday mayday

After many years, yesterday was the first time i saw a build coming down from 120m height.
From my research so far it all comes down to a faulty power plug and a complete power failure.
This build has been flown a number of time and after each one, it has been taken care with lots of love, but it seems that it only take a 10usd power plug for all to fail.
Yes i can see the logs and slightly elevated vibrations but no clipping and also for some strange reason a first-time imu mismatch, but as you can see flying at 120m, power simply shuts down.
Fiscal evidence seem to show that the main battery plug is loose and i down think it happened at the moment of impact. (found traces of lots of arching and saw that power dropped from 23 to 13 in
Luckily the damage so far and after complete disassembly seems to be minor since it landed (yes almost landed) on top of high wheat plants. At the moment i heard the propeller stop having power and saw my altitude being lost, the quad stayed level until it hit the wheat. (perfect balance and 10m/s flight speed?)
Cube will be set aside for inspection and maybe be tested on a future build, but for now all components are being inspected one by one and logs are being reviewed to find the cause.
Any comments will be highly appreciated. https://plot.dron.ee/QvQd

Just a couple things I noticed:

  • your servo rail has no power. Not necessarily a bad thing depending on your setup, but a bit unusual.
  • You have main power 1 and 2 plugged in as well as USB power, but the board voltage is only ~4.8V. The danger zone is <4.7V. The power selection module chooses the source with the highest voltage, so this means all of your sources are <4.8V, which is a bit low. Also, the board voltage trends downward over time - a high quality BEC should have a stable output regardless of input voltage.

Neither of these things caused the crash, but may be worth noting.

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First of all i would like to thank you on your comments.

  • Servo Rail does not have any power because i only use one servo for auto tilt on my front-face FPV camera and since all ground around has been measured as common and without any loop, i power the servo direct from a BEC.

  • I have power on both sides of the Cube as a precaution and power 1 is the original Cube brick with measured (also today) 5.3V and power 2 is a BEC with 4.99V (again measured today) , both with an empty battery and under hover load, so the numbers you are giving me that i did not notice seem strange. It seems that on POWR/Vcc it shows power 2 and not power 1. Also based on manual minimum voltage range, in theory, is 4.1V

  • USB power…i have no USB power connected, maybe what you see was the USB cable connection prior to flight? Can you tell me on which parameter you saw the USB power? Because today i noticed that while i can connect any Cube on my PC and i can connect on this one through telemetry, when i connect this on pc via cable it show a bad driver and it had done so in the past once or twice.

*****Edit: nothing is being powered by the Cube, only the cube it self (and RC receiver). All temetry modules, Rpi (Connected on Tel2), servo, camera, cam trigger and anything else are powered from separate power sources that are connected on the same PDB.

This appears in POWR.Flags. The flags are a bitmask that describe the power supply status. For a Cube, it’s:

    1 - Power1 input valid
    2 - Power2 input valid
    4 - USB power input valid
    8 - Telem1 power overcurrent
    16 - Peripheral power overcurrent
    32 - Power status has changed since last boot

Your POWR.Flags is 7, which is 1 + 2 + 4, so it seems to think that you have USB power connected. Do you have anything plugged into the buzzer/USB connector? That connector is the same as the micro USB port on the side.

Since prior to my flight i had the USB connected in order to download a certain log, it might appear because i connected it for only a couple of minutes.
In any other case, the USB had no plug connected.

I have take this Cube out in order to further inspect any potential cube issue and i will test same flight in same area.

Once again thank you for your input.