DJI Mavic, Air and Mini Drones
Friendly, Helpful & Knowledgeable Community
Join Us Now

Crash - was it wind speed?

diggs

Member
Joined
Feb 26, 2020
Messages
21
Reactions
18
Age
42
Location
Canada
I'm new to owning a drone and I had a crash with my drone a couple of weeks back after only a few flights (I was fortunate to be able to recover it with the find my drone functionality, and a little climbing through the snow!). I'm assuming it was wind speed at higher altitude overpowering the drone (from ~35m) but there were also power lines near by, so wondered if they might have played a part? Would anyone be happy to review the logs and verify?

It all happened very quickly, and was a pretty bad feeling knowing it could have easily been well out of recovery. But also it got me starting to research and then to these forums and I feel very fortunate to have recovered the drone after realizing how risky this flight was (and now realizing how little I knew and so many of the basics I wasn't doing).

It really should be mandatory to read these forums for newbies like myself before our first flights if we value our investment!

[Edit] Adding narrative on advice of @Doppler:

Here's what happened (as I remember) - I was at the bottom of a hill with a small stream running through it hoping to get some video of a sunset/mountains. There were large power lines in the area but I thought I would be far enough away to have any issues. Was planning to go straight up, take the video, then come down. (Was just looking for the video/photo!).

I set the drone down and used the take off button. I know now that sats weren't great at take off, but within a few seconds RTH was set and GPS turned green. I went straight up with the drone for what seemed only a very short moment (maybe 10 or 20 seconds).

I was looking at the screen and clicking to start the video (bird had been doing straight up fine) when the screen titled on a weird angle (to the left I think - but I didn't end up starting the recording so don't know) and I couldn't tell what the drone was pointed at. When I looked up I couldn't see the drone (but could hear it) so tried very timid down to see if the drone responded and then right to see if the screen view moved but it didn't seem that I was having much impact. Then the drone was on its side at the bottom of a tree (see photo). From noticing the screen tilting to crash seemed like less than 10 seconds.

Don't have much more to add as was very quick and I was new so wasn't even watching the map or movement away from me...

I managed to find it with the find my drone and it was up the side of the bottom of the mountain (had to climb up to get it). So looks like it crashed straight into the side of the hill or the trees on the hill anyway.
 

Attachments

  • DJIFlightRecord_2020-02-09_[17-18-04].txt
    55.4 KB · Views: 23
Last edited:
  • Like
Reactions: GregE
Welcome to Mavic Pilots! :) Enjoy the forum!Thumbswayup
I have placed your thread in the appropriate area.;)
 
  • Like
Reactions: Thomas B
7 connected satellite is very low
Yeah, very low and I didn't realize that at the time - learnt a lesson there and I won't do that again!

However, at approx 35m the drone tilted (on the monitor) and then was in the hill with little input from me... Assuming that wouldn't be related to the GPS/satellites?
 
However, at approx 35m the drone tilted (on the monitor) and then was in the hill with little input from me... Assuming that wouldn't be related to the GPS/satellites?
Yeah what happens Mr. diggs is your bird goes into ATTI Mode when the number of satellites drop into single digits. That means it has no GPS holding it in place so inertia takes over and it will drift until you make a course correction or stick movement. There are no satellites to lock it in place and hold it still . . .
 
  • Like
Reactions: diggs
This log is not making any sense to me. For example, no throttle input is registered until 24s in to the flight but OSD height steadily increases from 3 to 41m in that time.
1582702518922.png

Another case of corrupted data?

EDIT: Looking at the OSD:height field together with the flyCState and the NotEnoughForce flag, it looks like the descent correlates with the "NotEnoughForce" flag being set to "True". So perhaps another case of an uncommanded descent? Also, the log ends with the flyCState changing from GPS_Atti to ForcedLanding. You did hold the throttle stick full down for nearly 3seconds before the log ends. Did that trigger forced landing at 28m height? I am not sure. Like I said, I am not entirely sure the data is trust worthy. Time to call on @sar104.
1582703308277.png

Also Mr. diggs, an advice: it is better to provide a detailed narrative account of the incident together with the log. Makes interpreting the data a lot easier.
 

Attachments

  • 1582703076250.png
    1582703076250.png
    21.1 KB · Views: 7
Last edited by a moderator:
  • Like
Reactions: diggs
Also Mr. diggs, an advice: it is better to provide a detailed narrative account of the incident together with the log. Makes interpreating the data a lot easier.
Thanks for the advice.

Here's what happened (as I remember) - I was at the bottom of a hill with a small stream running through it hoping to get some video of a sunset/mountains. There were large power lines in the area but I thought I would be far enough away to have any issues. Was planning to go straight up, take the video, then come down. (Was just looking for the video/photo!).

I set the drone down and used the take off button. I know now that sats weren't great at take off, but within a few seconds RTH was set and GPS turned green. I went straight up with the drone for what seemed only a very short moment (maybe 10 or 20 seconds).

I was looking at the screen and clicking to start the video (bird had been doing straight up fine) when the screen titled on a weird angle (to the left I think - but I didn't end up starting the recording so don't know) and I couldn't tell what the drone was pointed at. When I looked up I couldn't see the drone (but could hear it) so tried very timid down to see if the drone responded and then right to see if the screen view moved but it didn't seem that I was having much impact. Then the drone was on its side at the bottom of a tree (see photo). From noticing the screen tilting to crash seemed like less than 10 seconds.

Don't have much more to add as was very quick and I was new so wasn't even watching the map or movement away from me...

I managed to find it with the find my drone and it was up the side of the bottom of the mountain (had to climb up to get it). So looks like it crashed straight into the side of the hill or the trees on the hill anyway.
 

Attachments

  • DJI_0080.JPG
    DJI_0080.JPG
    3.7 MB · Views: 36
Last edited:
I wrote a response earlier thanking you for the additional info and inquiring if you had the corresponding DAT file of the flight. When I clicked "Post Reply", the forum told me the thread no longer exists. What's with that?
 
I wrote a response earlier thanking you for the additional info and inquiring if you had the corresponding DAT file of the flight. When I clicked "Post Reply", the forum told me the thread no longer exists. What's with that?
Not sure why the forum would give that error?

Unfortunately I don't have the DAT file (folder is empty)...
 
This log is not making any sense to me. ...
Another case of corrupted data? ...

Hmm, I get it up neat & proper ... strange?

Without the DAT this will not be confirmed unfortunately ... but for what it's worth & you the OP saying that you perhaps should have gathered a bit more knowledge before take off ...

All looks like a Yaw/magYaw disagreement coming up to approx 30m due to starting in a magnetic interfered area which got the Yaw to be off to reality during IMU initiation. Pitch & roll gets disturbed approx at 16sec & the heading speeds rise rapidly (look further down in the chart). Winds were very mild with only just over 1m/s

Messages in the log:

1582734003821.png

Nice "Toilet bowl" flight path?

1582734044652.png

And the stick inputs, mostly throttle for ascending but then later on some small positive rudder inputs & negative throttle. The navHealth reached 4 so that shouldn't been a problem.

1582734715019.png

*EDIT* Might add that the force landing in the end most probably were initiated by the long negative throttle as the VPS sensors had locked on close to the ground high up in the slope just before the crash moment.

1582735839362.png
 
Last edited:
All looks like a Yaw/magYaw disagreement coming up to approx 30m due to starting in a magnetic interfered area which got the Yaw to be off to reality during IMU initiation. Pitch & roll gets disturbed approx at 16sec & the heading speeds rise rapidly (look further down in the chart). Winds were very mild with only just over 1m/s
This is so helpful thanks @slup!

Do you think it would be possible that around the height of 30m, I actually hit the magnetic field for the powerlines or do you think it was to do with launching in the wrong calibration? I wondered if I had hit the field which might have caused such a sudden issue after ascending very smoothly up until that point?

That was my very first thought after the crash, but after reading more and more about the MM vs wind assumed maybe that was it.
 
This is so helpful thanks @slup!

Do you think it would be possible that around the height of 30m, I actually hit the magnetic field for the powerlines or do you think it was to do with launching in the wrong calibration? I wondered if I had hit the field which might have caused such a sudden issue after ascending very smoothly up until that point?

That was my very first thought after the crash, but after reading more and more about the MM vs wind assumed maybe that was it.

As the first lines in the log flags for compass errors the interference were already present there, my bet is that everything went haywire already at startup.

The thing with magnetic interference already at power up of the drone is that the IMU sets the YAW equal to the magYaw (compass) then... everything seems fine as long as you remain in that same strong interference, IMU & compass agrees. This potential upcoming catastrophe can be seen if you look at the drone icon on the map in the app ... it's heading will not align with reality.

Taking of in this situation will be fine to start with usually, as long you are in the interference ... but once out of it the compass correct itself, but not the IMU. This means a disagreement in the information regarding the AC heading direction to the flight controller ... the drone suddenly doesn't know in which direction it points. Then something effects the drone so it need to counteract, wind for instance ... now lost heading wise, the drone spin up/down motors to correct the position but fail to complete the action due to not knowing any direction. This leads to a kind of a snowball effect, the position corrections doesn't succeed so it rev up motors even more still in wrong direction, loses position even more ... & so on.

The flight path in these cases look like circling down a toilet bowl with an increasing speed, usually uncontrollable, eventually ending up in a crash.

You can't calibrate your compass out from this issue & think you can avoid this Yaw/magYaw disagreement. The calibration just teaches the compass to consider the magnetic interference from it's own internal components.

If you get a notice to calibrate your compass always move away to another take off location well separated from the first well away from all magnetic objects ... if several locations tried out then calibrate, check then the drone icon on the map in the app & make sure so it aligns with reality.
 
  • Like
Reactions: diggs
Can't thank you enough for taking the time to explain all this @slup!

The thing with magnetic interference already at power up of the drone is that the IMU sets the YAW equal to the magYaw (compass) then... everything seems fine as long as you remain in that same strong interference, IMU & compass agrees. This potential upcoming catastrophe can be seen if you look at the drone icon on the map in the app ... it's heading will not align with reality.

Such good learning for me, as that is completely the case here! Now that you mentioned that, in reality, the drone was facing East (to the right of the picture aligned with the train tracks), however, the drone icon on the map is facing the wrong way (it's facing South West). So good to know I could have avoided the whole issue.

1582746745805.png

Taking of in this situation will be fine to start with usually, as long you are in the interference ... but once out of it the compass correct itself, but not the IMU. This means a disagreement in the information regarding the AC heading direction to the flight controller ... the drone suddenly doesn't know in which direction it points. Then something effects the drone so it need to counteract, wind for instance ... now lost heading wise, the drone spin up/down motors to correct the position but fail to complete the action due to not knowing any direction. This leads to a kind of a snowball effect, the position corrections doesn't succeed so it rev up motors even more still in wrong direction, loses position even more ... & so on.

The flight path in these cases look like circling down a toilet bowl with an increasing speed, usually uncontrollable, eventually ending up in a crash.

You can't calibrate your compass out from this issue & think you can avoid this Yaw/magYaw disagreement. The calibration just teaches the compass to consider the magnetic interference from it's own internal components.

This makes complete sense and explains what I experienced. And now I understand the original "toilet bowl" flight path :)

If you get a notice to calibrate your compass always move away to another take off location well separated from the first well away from all magnetic objects ... if several locations tried out then calibrate, check then the drone icon on the map in the app & make sure so it aligns with reality.

Thanks again @slup - I still wouldn't have learned such a valuable lesson if you hadn't taken the time to explain this all out for me. Very much appreciated and hopefully my lesson can help someone else out there avoid a similar issue!
 
  • Like
Reactions: slup
As the first lines in the log flags for compass errors the interference were already present there, my bet is that everything went haywire already at startup.

The thing with magnetic interference already at power up of the drone is that the IMU sets the YAW equal to the magYaw (compass) then... everything seems fine as long as you remain in that same strong interference, IMU & compass agrees. This potential upcoming catastrophe can be seen if you look at the drone icon on the map in the app ... it's heading will not align with reality.

Taking of in this situation will be fine to start with usually, as long you are in the interference ... but once out of it the compass correct itself, but not the IMU. This means a disagreement in the information regarding the AC heading direction to the flight controller ... the drone suddenly doesn't know in which direction it points. Then something effects the drone so it need to counteract, wind for instance ... now lost heading wise, the drone spin up/down motors to correct the position but fail to complete the action due to not knowing any direction. This leads to a kind of a snowball effect, the position corrections doesn't succeed so it rev up motors even more still in wrong direction, loses position even more ... & so on.

The flight path in these cases look like circling down a toilet bowl with an increasing speed, usually uncontrollable, eventually ending up in a crash.

You can't calibrate your compass out from this issue & think you can avoid this Yaw/magYaw disagreement. The calibration just teaches the compass to consider the magnetic interference from it's own internal components.

If you get a notice to calibrate your compass always move away to another take off location well separated from the first well away from all magnetic objects ... if several locations tried out then calibrate, check then the drone icon on the map in the app & make sure so it aligns with reality.

This does look like a classic case of a compass error at startup - the problem manifested as soon as the FC started to apply corrections to hold position:

Delta_V.png

Position.png
 
  • Like
Reactions: diggs
Thanks @sar104. I don't fully understand those graphs, but assuming it's not a good thing when the IMU and GPS are saying different things!!

Really appreciate the info from everyone.
 
Thanks @sar104. I don't fully understand those graphs, but assuming it's not a good thing when the IMU and GPS are saying different things!!

Really appreciate the info from everyone.

Correct - integrating the IMU velocities with respect to time and comparing with the position data is one way to visualize that disagreement. The other graph is the converse approach - differentiate position with respect to time and compare with IMU velocity. They show the same thing in different domains.
 
  • Like
Reactions: diggs
I wrote a response earlier thanking you for the additional info and inquiring if you had the corresponding DAT file of the flight. When I clicked "Post Reply", the forum told me the thread no longer exists. What's with that?
Not this is going to help find a .dat file, but what if you were replying to thread and your browser thought it was still in the thread that the mod moved here from where it was originally?

If that doesn't make any sense to anybody, that fine with me... ;)


Rod
 
Lycus Tech Mavic Air 3 Case

DJI Drone Deals

New Threads

Forum statistics

Threads
130,600
Messages
1,554,287
Members
159,607
Latest member
Schmidteh121