Falling after almost completing a mission

ArduCopter Copter 4.0
,
1

Hello everyone,
I’m trying to identify the root of the problem that brought my quad down.
Copter specs:
680mm wheelbase
TMotor Air 40 ESC
TMotor 3508 380kv
Tarot 1555 Folding Props
5Ah 6S 20C Turnigy LiPo
AUW: ± 2100g

Checking at my log I’ve found a sudden voltage drop when in RTL, what could be the cause and how can I prevent from this to happen me again?
Any help is highly appreciated!
Thanks!
LOG DOWNLOAD

2

There was a loss of thrust on Motor 4. Motor 3 dropped to minimum to attemp stabilization and down it went. Motor, ESC or prop.

RCout
RCout3335×1046 215 KB

The voltage sagged because the current spiked.

Volt
Volt3376×1014 143 KB

3

Thanks for checking it out. So whenever you see only an RCOut channel to the max it’s probably due to a motor loss?

4

Yes, a thrust loss. Could be a broken prop, failed motor or ESC, a broken wire, cold solder joint…

5

Thanks a lot for your guidance!