Beginner 1 st crash....why? log file

[stressor]

Hi I am new. trying to learn what went wrong! Had only 20 flights so far and had a horrible low altitude crash today with some damage. Initially conditions were good, little wind, perfect visibility, blades, controller and battery 100%. GPS lock seemed fine on the ground, did auto take off, recorded home point. Take off seemed unremarkable, but as soon as airbourne MP didnt hover....just started circling clockwise, pretty uncontrollable. Tried to land but unstable....basically crash landed after 30s flight max altitude 58ft but crashed from about 20ft at about 15mph. I didn't move the sticks to cause the circling, only to try and bring it down. I genuinely don't know what caused this irratic behaviour. Looked at the log files got a number of warnings:

A 00m 00s 0.0 ft 0 ft Mode Mode changed to Motors_Started
B 00m 00s 0.0 ft 0 ft Tip Tips__Taking Off
C 00m 00s 0.0 ft 0 ft Warning The aircraft is in a Warning Zone (Recreational airport). Fly with caution here.
D 00m 00s 0.0 ft 0 ft Tip Setting new Return-To-Home altitude to 35m (115 ft). Setting new Maximum Flight Altitude to 222m (728 ft)
E 00m 01s 0.0 ft 0 ft Mode Mode changed to AutoTakeoff
F 00m 01s 0.0 ft 0 ft Tip Tips__Taking Off
G 00m 02s 1.6 ft 1 ft Tip Home Point Recorded. RTH Altitude: 35m.
H 00m 04s 21.7 ft 1 ft Mode Mode changed to GPS_Atti
I 00m 14s 57.4 ft 9 ft Warning Speed Error
J 00m 22s 35.1 ft 104 ft Warning Speed Error
K 00m 28s 4.3 ft 154 ft Warning Speed Error
00m 29s 3.6 ft 158 ft

thank you for your comments/insights.

here is the full log Dropbox - DJIlogs

 

[MacIak]

Cannot open/ view your file from this PC but id almost think of a lost prop. Were they all still attached when the Mav was recovered?

 

[stressor]

yes I thought the same but they were all attached on recovery. One was cracked at tip from impact. I have done a quick test flight post-crash (in a big grass field for safety) and handling is now ok, but MP is damaged at front and camera stabilization and gimble control all damaged (although still records). Anyway even if fixed, I am very nervous to fly now because I don't know why it lost control and am fearing another accident.

 

[stressor]

Any insights anyone? thanks

 

[MacIak]

How about uploading the log to airdata?

 

[SIRWELDALOT]

Any insights anyone? thanks

was it set to follow you,,, was it dark outside??Were sensors on or off? I have found that it can be difficult to land at night with sensors enabled

 

[stressor]

fully light, sensors all on, P mode, not sport, not any sub mode. It careered out of the control from take off (ie hover) without any stick input, without loosing altitude, without loosing a prop, without any significant wind

 

[stressor]

here is the air data track: Airdata UAV - Flight Data Analysis for Drones

 

[MacIak]

here is the air data track: Airdata UAV - Flight Data Analysis for Drones

Looks bad. Speed error is actually speed error and seperate thing from the rotor speeds. Looks like the gps fix, compass or imu (or combo) let you down. It was unable to determine certain parameters and probably could have recovered if given time/altitude. Still being uncertain, you have done a good job bringing it down. I would not be surprised if DJI accepts this as warranty case.
Id start the procedure with em and ship it in if you can. Although there is a lot of negativity about how they deal with this, they are actually pretty darn good in analyzing data and are not afraid of admitting if something was wrong. Update please if/when possible..

 

[f3honda4me]

This sounds like a classic compass issue. My guess is there was a metal object near the drone at the time it was powered on. 95% sure that caused the behavior you described.

 

[f3honda4me]

Can you get the DAT file off of the DRONE itself and upload to to dropbox then provide the link? The logs you provided are just from the RC/device and do not contain the necessary data to determine the cause.

How to retrieve a V3 .DAT File

 

[stressor]

Thank you all, very helpful. I'll have a go at retrieving the DAT file. In the moment, to be honest I wasn't sure whether to climb or descend but I feared by climbing it would fly wildy out of the small park I was in, so I chose descend, with mixed success.

 

[stressor]

ok I am struggling with the DAT file. installed the DJIassistant 2 but it reported "no flight records". Tried this method

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but under advanced > there was no "flight data mode". Probably doing something wrong.

 

[f3honda4me]

ok I am struggling with the DAT file. installed the DJIassistant 2 but it reported "no flight records". Tried this method

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but under advanced > there was no "flight data mode". Probably doing something wrong.

I don't know about the video but the link I provided gave instructions.

 

[Blacksails]

As mentioned before, the circling is known as Toilet Bowl Effect, and is almost always down to compass issues. If the mavic had a user selectable Atti mode, things like this could be avoided. I'll never understand why DJI didn't include it.

 

[stressor]

As mentioned before, the circling is known as Toilet Bowl Effect, and is almost always down to compass issues. If the mavic had a user selectable Atti mode, things like this could be avoided. I'll never understand why DJI didn't include it.

Thank you for this link! I have now read up on the toilet bowl effect and this seem to fit perfectly. In fact I had forgetten that 5mins before I went to another location, powered up but got an error "MAG" something which I had never seen before nor understood, but it was enough to not take off and find another location (park). In the park I didn't get any error on taking off....so I presumably all was well until it spiralled out of the control after about 15secs and crashed into the ground. I now assume MAG error message was initial magnetic interference which whilst reduced might have still been a problem, although I couldn't know this at the second location.

 

[BudWalker]

Thank you for this link! I have now read up on the toilet bowl effect and this seem to fit perfectly. In fact I had forgetten that 5mins before I went to another location, powered up but got an error "MAG" something which I had never seen before nor understood, but it was enough to not take off and find another location (park). In the park I didn't get any error on taking off....so I presumably all was well until it spiralled out of the control after about 15secs and crashed into the ground. I now assume MAG error message was initial magnetic interference which whilst reduced might have still been a problem, although I couldn't know this at the second location.

What was the aircraft heading when you launched it? The .txt shows that it was -6.8 degrees. Is this correct?


If the heading indicator is incorrect before launch it means that the AC has an incorrect Yaw value and erratic flight, possibly a fly away is almost guaranteed. An incorrect Yaw is almost always caused by some ferrous material at the launch site interfering with the compass. It's not caused by a flawed compass calibration. This can be confirmed if you could retrieve the .DAT from the Mavic.

 

[BudWalker]

..... If the mavic had a user selectable Atti mode, things like this could be avoided. I'll never understand why DJI didn't include it.

There is something else that might be related, although I'm not sure quite how. The P3 would switch into ATTI mode at the slightest hint of a possible compass error. Often in situations where there was no actual compass error. But, the Mavic will sometimes remain in GPS+ATTI and attempt to "fix" the error by rotating the Mavic but holding the Yaw value constant. When the compass agrees with Yaw rotation is stopped and the error is "fixed". This will usually work if the error is not too large to begin with. But if it is too large it seems that after about 8 secs the FC will give up and then switch into ATTI mode.

Another thing is that several pilots report that Mavic ATTI in this situation is different from P3 ATTI. Specifically, that the Mavic isn't just drifting with the wind - the FC is trying to move the Mavic. I've not experienced this, but I've heard it enough times to believe it.

 

[stressor]

What was the aircraft heading when you launched it? The .txt shows that it was -6.8 degrees. Is this correct?
View attachment 25179

If the heading indicator is incorrect before launch it means that the AC has an incorrect Yaw value and erratic flight, possibly a fly away is almost guaranteed.

If I understand you correctly you are asking if the direction of the MP on the ground was exactly the same as a the digital compass on screen? Unfortunately this is not a check I can ever recall making because it was my naive assumption the two would always line up. I do a check for a number of things, but I wouldn't check things that are never out of true (by my beginners assumptions). BTW I have calibrated the compass the day before and there was no flag to do this again, although I appreciate it is always good practice.

 

[f3honda4me]

If I understand you correctly you are asking if the direction of the MP on the ground was exactly the same as a the digital compass on screen? Unfortunately this is not a check I can ever recall making because it was my naive assumption the two would always line up. I do a check for a number of things, but I wouldn't check things that are never out of true (by my beginners assumptions). BTW I have calibrated the compass the day before and there was no flag to do this again, although I appreciate it is always good practice.

Actually, you should generally never calibrate the compass unless it tells you to do so or you are trying to fix a compass related issue. It is actually bad practice to calibrate it when not needed as you risk screwing something up.