My drone crashed in RTL mode

I had a little test yesterday and set to RTL mode during the flight.
But while the drone was flying back home, it suddenly crashed with alt 150 m.
I had check the log and found that the vibe is too big, but I don’t know if big vibe is the reason.

Firmware copter 3.5.4
here is log;

Your Z vibrations could be a bit better, but RTL mode seemed to be working fine. The cause of the crash appears to be a failure on motor 4:

The 'copter performed an uncommanded pitch up and roll right. To correct this, the flight controller asks for more effort from motor 4 while throttling down motor 3. It seems motor 4 was unable to respond, as the copter began tumbling over the back right corner.

Crashing from 150 meters might make it difficult to tell what happened, but check for damage, loose connections, or bad solder on motor 4 and its ESC. Motor/ESC overheat is a possibility as well.

@Anubis Thanks so much. Our motor/ESC is over-capacity, never just a bit warm, and also its in winter here. But I will check the motor 4 carefully.

@Anubis Also I don’t think RCOU.C4 is the PWM of motor 4?

It is, unless you have a non-standard setup. It may be worth noting that motor 4 was working very hard throughout the flight, at ~1700 PWM the whole time:

It looks like it was pretty windy, as the motor loads change significantly when the drone turns. Motor 4 has the highest PWM the whole time, though. Sometimes this can mean that the motor bearing is worn out, or there is some other source of resistance. However, because motor 3 is also high, this may be a result of a misalignment in your motor arms (twisting), causing the drone to naturally want to yaw left, so both CCW motors have to work harder to counter that torque.

@Anubis Ive confirmed, RCOU.C4 is not the pwm of motor 4, its output pwm of yaw control.

How did you confirm that? RCOU C4 is the PWM motor output of Main Out channel 4. There is no single “output of yaw control”. That is derived from output on all motors. I think you are confusing this with Yaw, or Rudder, input.

Yes, as @dkemxr and @Anubis have pointed out, you are flying a quad, therefore your outputs 1 to 4 are your motor PWM outputs.
Graphing those tells you how hard your motors are working during the flight.

You either were flying in heavy wind or your quad is out of balance or has misaligned motors or combinations of all three.
As Rick pointed out M4 was working flat out the whole flight until it failed.

Very big discrepancy between motor outputs with M1 hardly working at all.

Then M4 fails and the flight controller is giving it max output to try and save things.

Motor 4 failed, cut and dried.

If I get a 8 motor copter, then c1-c8 is pwms of 8 motors?

@mboland How can I confirm this c1-c4 output pwm in the codes? I cant find it.

Really.Channels 1-4 are motor outputs.From your log.Servo 1-4 corresponds to motor PWM out 1-4 (in the code as 33-36)

PARM, 273053034, SERVO1_MIN, 1102
PARM, 273053105, SERVO1_MAX, 1927
PARM, 273053176, SERVO1_TRIM, 1514
PARM, 273053271, SERVO1_REVERSED, 0
PARM, 273053544, SERVO1_FUNCTION, 33
PARM, 273053620, SERVO2_MIN, 1102
PARM, 273053696, SERVO2_MAX, 1927
PARM, 273053774, SERVO2_TRIM, 1517
PARM, 273053877, SERVO2_REVERSED, 0
PARM, 273054129, SERVO2_FUNCTION, 34
PARM, 273054211, SERVO3_MIN, 1102
PARM, 273054293, SERVO3_MAX, 1927
PARM, 273054419, SERVO3_TRIM, 1105
PARM, 273054665, SERVO3_REVERSED, 0
PARM, 273054777, SERVO3_FUNCTION, 35
PARM, 273054864, SERVO4_MIN, 1102
PARM, 273054955, SERVO4_MAX, 1927
PARM, 273055191, SERVO4_TRIM, 1514
PARM, 273055310, SERVO4_REVERSED, 0
PARM, 273055473, SERVO4_FUNCTION, 36

Near the bottom of this wiki page for motor connections.

Really.RCOUT 1-4 are motors. RCIN 4 is yaw.

12S power supply,so big props ? Got any bullet connectors in line ? Specs of the motors and ESCs ?

@Jagger Thanks! Yes 12s battery, T-Motor u10 plus, ESC from hobbywing

Well T-Motor are exceptional bits of kit.Hobbywing are good too.But there was a motor shut down in mid air for some reason.I have had problems with bullet connectors before now which is why I asked if you use them.I do not have experience of 12S systems though.It’s unlikely to be a T-Motor fail but it can happen.Ditto with the Hobbywings.

The fact that one motor was elevated output throughout before maxing out would lead me to check the motor mounting is perfectly level as mentioned along with all wiring.It’s certainly a hardware fault somewhere along the line.

@Jagger Yes, All expensive. Copter had a little crash (turn over on the ground)before, I think this may be the reason!

My 2c worth, the ESC for motor 4 may have overheated and lowered it’s output so as not to damage itself, especially at 12S voltages? It would’ve cooled down after the crash, show minimal signs of overheat and won’t show up again as a problem unless in the same set of circumstances.

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To all good guys, Ive checked all the motors and yes ESC 4 has problem with its power wires. It was sliced by motor holder.