Nearly lost my Mavic Air this morning - Home Point changed randomly

[MavicCF]

It did not give me an option and in any event I had not moved an inch from the launch point - so home point and current location would presumably have been the same.. I had certainly been nowhere near the randomly generated home point which was out of the park and 500 yards up the road in someone's front garden. I had a strong gps signal on my mobile phone (Huawei Mate 10 Pro running the most current version of Android).

Something certainly went wrong, whether you reset the home point or not. In your settings you can reset the HP once the Mavic is already flying either to where the Mavic currently is, or to where you currently are (this works only if your device has GPS but is good if you a moving around a lot). What happened to you was definetly not the HP being reset to the Mavic's location. However as I said above, in the case of "home point me" your device can potentially report the wrong position and think its in a completely random place, resulting in the new HP being set in a random location. However, the real question here is why it randomly decided to reset the HP. Did your device crash just before you hit RTH or anything like that?

 

[Bondaneka]

Thank you - so my understanding of this is that my mobile device generated a wildly inaccurate home location sometime after take-off and for whatever reason the RTH point was updated accordingly. Presumably - and I appreciate you can only hazard a guess - if I had ended up losing the drone DJI would not have accepted responsibility (although hard to see how they reach this position given that the flight log doesn't provide proof ether way)? This has really put me off using the RTH mode in future so line-of sight, a pair of binoculars, a strobe and manual flying seem the most sensible way to proceed.

 

[Bondaneka]

My mobile device did not crash at any time but thanks for your thoughts/interest - much appreciated from you all.

 

[msinger]

@Bondaneka, can you answer my question above?

 

[MavicCF]

@Bondaneka, can you answer my question above?

Sorry, I'll shut up.

 

[sar104]

@msinger is correct. The homepoint was reset at 114.6 s to a spurious location generated by the app. Note from the plot below that the app GPS location was all over the place during the flight. The aircraft then flew to that new HP and attempted to land, but the pilot applied throttle at 552 s, causing the aircraft to climb, and then applied several extended periods of elevator starting at 612 s that caused the aircraft to fly off to the NE.

 

[Bondaneka]

Thank you so much for your analysis - does this mean that the gps in my (new and expensive) mobile phone may be too unreliable to ever use with the controller or could this be a one-off event?

 

[Mossiback]

I will leave analysis to the greater minds and just ask; did you try the cancel button on the RC?

 

[Bondaneka]

There isn't a cancel button as far as I am aware but I suppose with hindsight I should have pressed the pause button and then ran towards its last known location to see if I could spot it hovering.

 

[Bondaneka]

It all happened so quickly!

 

[msinger]

Sorry, I'll shut up.

And I guess I should stop asking

 

[Mossiback]

There isn't a cancel button as far as I am aware but I suppose with hindsight I should have pressed the pause button...

The pause button is what I was referring to. Pressing it institutes emergency braking effectively cancelling whatever flight was happening. Switching it into and out of Sport mode also cancels RTH. Now that you have your Mavic back (yea!), you can get to a wide-open area and test it.

 

[MavicCF]

@msinger is correct. The homepoint was reset at 114.6 s to a spurious location generated by the app. Note from the plot below that the app GPS location was all over the place during the flight. The aircraft then flew to that new HP and attempted to land, but the pilot applied throttle at 552 s, causing the aircraft to climb, and then applied several extended periods of elevator starting at 612 s that caused the aircraft to fly off to the NE.

View attachment 34460

Sorry to keep bugging you @sar104, I had about half of what you have on your graph worked up on mine but now I'm curious how your are getting the app GPS? I didn't realize that was in this file. Thanks! -CF

 

[Bondaneka]

Thanks Mossiback - I will. Just a thought, my mobile phone's Location services menu offers a choice of selecting "Use GPS only" as opposed to the default and in use during all my flights thus far "Use GPS, Wi-Fi and mobile networks". I wonder whether I could ensure greater GPS accuracy of the app/controller and therefore the RTH location by switching to "Use GPS only" ?

 

[sar104]

Sorry to keep bugging you @sar104, I had about half of what you have on your graph worked up on mine but now I'm curious how your are getting the app GPS? I didn't realize that was in this file. Thanks! -CF

The mobile device txt file continuously logs aircraft location, home point location, app location and RC location (if applicable).

 

[MavicCF]

The mobile device txt file continuously logs aircraft location, home point location, app location and RC location (if applicable).

So that would be in the txt. download, not the csv?

 

[sar104]

Thank you so much for your analysis - does this mean that the gps in my (new and expensive) mobile phone may be too unreliable to ever use with the controller or could this be a one-off event?

If I recall correctly, there have been numerous issues in the past, especially under Android, with mobile device GPS data and the Go app, even when other apps clearly reported good GPS location data. I thought that was resolved in a previous app update. You appear to be using the latest version (4.2.8) so I'm not sure what is going on. Is your phone accurately reporting position in Google maps, etc.?

 

[sar104]

So that would be in the txt. download, not the csv?

It's in the txt but whether or not it makes it into a csv file depends on how the csv is generated. For example, PhantomHelp and Airdata csv files only include a small fraction of the data in the log file.

 

[MavicCF]

It's in the txt but whether or not it makes it into a csv file depends on how the csv is generated. For example, PhantomHelp and Airdata csv files only include a small fraction of the data in the log file.

That must be my problem as I downloaded the csv. from PhantomHelp. I'll try the txt. and run it through CsvView. Thanks! -CF

 

[MavicCF]

Sure enough, that was it! Ran the txt. through CscView and exported it, now I have way more to play with! Thanks a bundle!