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Endurance test ended with crash with Copter 3.6.9

(RsX) #1

Hi all
i have a 3DR pixhawk and i had a crash with my quadcopter after upgrading to 3.6.9
before this day i had a similar crash on an older version, maybe 3.7.x and i thought it was a faulty esc
after this i changed the GPS with a NEO M8N, the 4x DJI 30A ESC with hobbywing 4 in 1 and the batteries with a pack 10400mAh 3S LiHv (2x 5200mAh)
i did a couple of flights before the crash and run the autotune successfully and a couple of missions with spline waypoints and take off/landing: all perfect :grinning:
at this point i decided to test how long the quad could fly and fully charged the lipos and put the quad in loiter
i have to admit i soldered the current sensor the other way around, so i had no current measurement and i just monitored the voltage that was very stable during discharging
after 43 minutes the quad had still 10.75V and started doing some twitch every once in a while
at 44 minutes the quadcopter entered in an uncontrolled wobble and went down flipping into the ground
the battery had another 10% capacity
i know i overdischarged it, i was set on coming down at 3.5V per cell, which now i know it is too low :sweat:
nevertheless i still had another 10% and the voltage was not dipping
i reviewed the logs and i’m not sure what is the problem
there are many errors but they appeared either after the crash or way before the crash (40 minutes earlier)

this is the log https://plot.dron.ee/tWIg

what could be the problem?
thank you :slightly_smiling_face:

(Andras Schaffer) #2

Looks like a motor/esc failure of motor connected to RC12, same motor twitched a couple of times before the crash.

(RsX) #3

Hi Eos
both motor no 2 (RC10) and motor no 4 (RC12) seems that have twitched more than a couple of times
i don’t think that a double esc/motor failure is possible and also it’s not the motor that gave up the crash before
this is the old log https://plot.dron.ee/eug4
now that i see it better there was something wrong with ESC/motor no 1, it was always at 100% :scream:

in the log i can see that motor no 2 (RC10) (btw i switched outputs from RC1-4 to RC9-12 because i’m using Dshot1200) twitched more and more in intensity until the quadcopter became unstable and couldn’t recover and mantain attitude
could it be that the voltage dropped so low that the pids became insufficient to stabilize the quad? :face_with_raised_eyebrow:

I’m using Hobbywing XRotor 45A 4in1, T-motor MT2216-900kv v1 and APC 11x4.7 propellers
any hints on how setup up blheli in case it’s a issue with de-sync?

(RsX) #4

Here we go again :scream:
https://plot.dron.ee/iYB5

this time the quad crashed after just 32min into the flight
It had another 8 minutes of flight time before hitting 20% of remaining capacity, so it cannot be an issue with the battery
Last time motor RC10 and RC12(rear motors) had higher values, now motor RC9 and RC10(diagonal motors) had to work harder and i cannot explain why
Whats more interesting is that exactly these pairs of motors went crazy and caused the crash to occur
I’m really suspecting an issue with motor sync or something really wrong with my PixHawk :persevere:

(Mike Boland) #5

Looking at how the desired and actual diverged, and the CW props working hard and the CCW hardly working at all, it is not surprising to an oscillation set in and cause a crash.

Assuming you have checked that the motors are all square to one another, prop tips in line with each other, and the frame is balanced around the centre of thrust, then this is the second log I have looked this morning where there is a large discrepancy in thrust between CW and CCW.

First step would be to get the thrust figures closer to 1500.
Add some weight or a bigger battery.
then
Try and find why the CW props are not producing the thrust the CCW props are.
then
Do an autotune.