Crash help, copter loss of altitude

Log Analysis -- deprecated Copter Logs -- deprecated
1

Hello, recently had to pull the chute on my copter towards the end of an auto mission. It was at the penultimate waypoint, when it reached the waypoint it stopped and lost altitude. The day was windy so there had been altitude deviations several times during the mission and I had attributed this to the wind affecting the barometer. However this time it descended and continued to loose altitude by over 5m. I suspected something was wrong and entered loiter to end the mission and take control. Raised the throttle and tried to regain control. The copter did not respond and maintain altitude and the deceleration accelerated. At this point it was ~35m high and I had two choices, to try althold or manual or to trigger the parachute (a recent addition). My initial reaction was that it was acting like it was low on power, potentially battery issues? And so I took the decision to try the chute as if it is battery issues manual would help regain control.
Pulled chute, it fired, canopy fully formed ~ 15/20 meters and slowed decent to a point where it limited damage to fractured carbon on the landing gear and a small bend in one of the arm mounts.

I think I heard a motor stall at the point where it lost control.
Also the copter was loosing altitude whilst maintaining level so I think think fc was maintaining stability whilst insufficient lift was available… could this point towards a motor or esc issue and thus the loss of this meant the fc has to reduce power on opposite motor and thus insufficient lift?

Immediately after pulling the chute I checked telemetry and voltage seemed to be good. Upon reaching the copter I made it safe and then looked for any initial signs. All motors and escs were cool. Battery voltages good. (2 6s lipos) and no visible cause for the in flight issue.

I am not experienced in reviewing logs, but I have tried to have a look at the logs. What I have noticed is:
that the UAV is slightly underpowered, it would appear average throttle during flight is ~60 %.
Battery voltages seemed ok
I think there may be an esc calib issue.
Towards the end of the flight the fc was asking ch2 for more and more thrust, reaching 100pc several times and then reaching 100pc and staying at the point where the issue occurred.

I cant figure out a route cause for the loss of altitude.
I am experienced at building, but there is always more to learn and I learn things every day. Especially with apm!
Looking at the logs I believe that the copter is slightly underpowered.
I think there was a slight issue with esc calib (if so I am frustrated because I know better!)
I am not really sure how to interpret the logs. I have had a good look through and I cant understand why it had an issue.

I welcome your help and guidance with this, please let me know where I have made mistakes, it helps me learn.

Please see link to log below.

Thanks

2

I should have added more info.

Upon making repairs I have checked function of the electronics and everything seems to be acting as it should.

I have not yet attempted a test fly as I would like to track down and understand the cause so it can be avoided in the future.

3

When a motor fails it usually goes to max and the opposite motor goes low. Didn’t see that in the log. All I see is that the motors are running near capacity throughout the flight. Yes, motor 2 did run a little higher than the rest but did not stay at max throughout.

Maybe the wind picked up and this caused it to start loosing altitude as in auto mode the copter will fall if its under powered and then regain altitude when it reaches the waypoint. Didn’t see that but you had stopped it mid flight.

When I have read about hex and octo’s having a motor failure they tend to loose yaw and start to spin. Yours did not do that. I do not have either type so can’t comment on that.

Mike

4

I had a quick look at your logs at the thing that stands out is the motors nearly at max the whole flight.

I am more surprised you made an entire mission.

The copter is either overweight or underpowered (really three same thing) but the motor outs leave very little room for stabilisation.
Whenever the copter needed extra power to stabilise it would have had to slow motors down because it could not speed any up, so this would have caused loss of lift for the sake of stability.