Hello everyone.

  
  

I encountered a strange thing recently and was wondering if anyone could explain to me if I did something wrong or if there was a fault with my Mavic Air.

  
  

Let me explain:

  

I started the drone on my second-floor balcony (about 5m above ground). Since it was under cover, it did not pick up enough satellites, so it was displaying Opti. I took off and hovered over the railing. After a few seconds, it picked up GPS and recorded the home point. I increase altitude and started flying the drone away from the house. All of a sudden, I lost control of the drone. It was flying away from me at 14 meters per second. After panicking a bit, I pressed the home button and after a short while, it stopped flying away and returned home.

  
  

Now, if you look at where the drone is in the attached image, the app shows a height of 5 meters, but the house is is about to fly over is easily 9 or 10 meters. In fact, both houses taht it went over are higher than 5 meters. The only time the app showed higher, was when it started returing home at 20 Meters.

This is what’s confusing me.

   

The drone returned home in 1 piece, but I have no idea why I lost control and the numbers don't make sense.

   

Any ideas?

  
Thanks

Bhavesh

You can post your log files and people will be able to help you understand exactly what happened.

The height answer is pretty easy though.  Where you take off from becomes altitude of 0.  So if you took off 5 meters above the ground, the drone sees that as 0.  Hence, when the drone says it is at 5 meters, it is really at 10.  The ground below your balcony would be -5.

JEZ2 Posted at 6-18 06:50
You can post your log files and people will be able to help you understand exactly what happened.

The height answer is pretty easy though.  Where you take off from becomes altitude of 0.  So if you took off 5 meters above the ground, the drone sees that as 0.  Hence, when the drone says it is at 5 meters, it is really at 10.  The ground below your balcony would be -5.

Thanks a stack for the quick response.

Where do I find the log file?

Here's a way to get  find the log file and post it.  https://www.phantomhelp.com/logviewer/upload/

Alternatively, you can use Airdata.

JEZ2 Posted at 6-18 07:04
Here's a way to get  find the log file and post it.  https://www.phantomhelp.com/logviewer/upload/

Alternatively, you can use Airdata.

Awesome. I uploaded the logs and about to review them. Much appreciated.

BhaveshD Posted at 6-18 07:14
Awesome. I uploaded the logs and about to review them. Much appreciated.

Feel free to post the link here if you want.  There are some forum members who are particularly good at reading logs and determining what happened to  a flight.

The link to the  Airdata  log

https://app.airdata.com/flight/5042c1df8590f0246427f04b037d969b/GENERALOverview

BhaveshD Posted at 6-18 11:06
The link to the  Airdata  log

https://app.airdata.com/flight/5042c1df8590f0246427f04b037d969b/GENERALOverview

Hiya,

Your out of control due to a compass error.

Normally the 2 lines yaw and ref yaw have equal values, where they apart in the chart your MA started to move away.
guess lots of iron around the drone on that balcony....

cheers
JJB

JJB* Posted at 6-18 11:53
Hiya,

Your out of control due to a compass error.

Wow you are so correct. There is a lot of metal on the balcony.

Thanks a stack for explaining

BhaveshD Posted at 6-18 22:28
Wow you are so correct. There is a lot of metal on the balcony.

Thanks a stack for explaining

thanks, another issue is that when you fly away in OPTI mode, and after awhile HP is set ; dependinh how far the drone is away already HP is set to that position,

So in case of a real RTH (lost contact) drone will fly back to a HP wich is mayby not a suitable HP to fly too.....

Happy many landings,
cheers
JJB

Hello there Bhavesh. I am sorry to know what happened to your previous flight with your DJI Mavic Air and it is good to know that you were able to retrieve the drone with no issue. Can you please fly your DJI Mavic Air to a different location with less interference to see if the issue will still persist? The said DJI drone might have picked up magnetic interference on the ground, and you took off from close to a buildings with rebar concrete metal objects on it. Thank you.

JEZ2 Posted at 6-18 06:50
You can post your log files and people will be able to help you understand exactly what happened.

The height answer is pretty easy though.  Where you take off from becomes altitude of 0.  So if you took off 5 meters above the ground, the drone sees that as 0.  Hence, when the drone says it is at 5 meters, it is really at 10.  The ground below your balcony would be -5.

Hi, hope your issue is resolved. Always check for iron arou d the drone and also signal towers as they disturb the compass of the drone. I had once flown mine near the aignal tower and it started to decend automatically,  i had to retrieve it in sports mode.

djiuser_ZBUEP5AjDXcM Posted at 6-20 04:25
Hi, hope your issue is resolved. Always check for iron arou d the drone and also signal towers as they disturb the compass of the drone. I had once flown mine near the aignal tower and it started to decend automatically,  i had to retrieve it in sports mode.

Always check for iron arou d the drone and also signal towers as they disturb the compass of the drone. I had once flown mine near the aignal tower and it started to decend automatically
The only way that a signal tower could disturb your drone's compass would be to get closer than one metre to the tower.
Whatever caused your drone to descend, it had nothing at all to do with the tower.
What it was could probably be identified from your flight data.

Hi BhaveshD
The compass is used in a sensor fusion with the IMU to provide the "odometry" of a "robot" (drone here). The IMU+Compass work independently of GPS and provide the short term localization info (relative to the previous status) while the GPS the long term  localization info (absolute position). If there's a compass shift (due to nearby metallic structures) then the drone favors the compass because it gives real time information while the GPS gives periodic readings. When these mismatch then you get a compass warning and you better gain altitude to keep clear of any source of interference.

The safe distance from ferroic objects depends on their mass and can range from a couple of feet to some dozens of feet. So in your situation I don't believe you experienced compass  misbehavior; because it would manifest as soon as you traveled above the balcony railings (like the one showing just before landing at 2.41), but probably wind gust instability which can be very violent. Mind you that there's also wind acceleration and turbulence around large structures too.

If you insist on taking off from your balcony it's better that you hand launched, and never take off if the wind is close to the limit (for mavic air 22mph/35kmh)

Safe flights