Arducopter 4.0 : suddenly drop and crash. (Potential Thrust Lost (1) Warning)

Allright guys, My Agriculture quad just fell off today, and I don’t know what caused it. this is the second flight for this day, and maybe around 80th flight from total flight and I don’t have any flight attitude issues before.
I need help from an expert to check my log.

I’m using Arris E410 with 8320 120kv motors and 30" propellers.
for flight controller, I’m using The Cube.

your copter was under-powered

also you have a voltage drop before crash (it could be normal while crashing but checkout your battery health)

and the main problem should be motor unbalance or twisted arms

there is a big difference between motor 4 and 3 it seems that one of these arms are twisted

Thank you for your help @hosein_gh .

for first problem,
i thought it is normal for Agriculture drone to have 50-60% throttle for hovering with full payload.
this crash happened when the payload is about 60% of it is capacity.
But i will talk to the Arris Hobby, as they recommend the motor and propeller for this setup.

i will check the battery more further. by checking its hovering flight time and compare it to other batteries.

yes, i never balanced the prop before, i will do it.

but can i ask for your help to analyze my last successfull flight before this, especially to check the RCOut for each motor ?
i want to know, whether these problems occur in my other flight or not.
Log :

Thank you so much for your help

i’m not talking about propeller balance my mean was physically balance and twisted arms or motors

but in this log everything was better i think your copter was underpowered by adding 10% more payload

could you please send full specification of your copter ?.

also note that for a good and stable flight you need to keep on 2:1 thrust to weight ratio

This is a pretty straight forward case of thrust loss on Motor 4 with a corresponding drop in throttle command on Motor 3 (opposite arm). Check prop, ESC or Motor on 4. I don’t think it’s underpowered if it was carrying a 60% load particularly if you have made 80 successful flight.

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it is a quad copter with 8320 120 kv size motor and 30" folding propellers.
i bought this copter from Arris Hobby, link :

by the way, how to make this graph ? i tried using mission planner, but i doesnt give a same graph as yours.

Thank you for your input,

I’ll check it,
this crash make my propeller on motor 4 is broken,
i will check the ESC and Motor once i back to my workshop.

Thank you dave.

Those graphs are made using
APM Planner.