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Mavic Air Fly Away

Trickydicky

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Ok. I've flown DJI phantom for three years now and thought I'd try out the Mavic Air. So I did the usual pre flight stuff and took it out to the local park for my first flight. Less than six minutes in the drone disconnected and flew away. I've been talking to DJI but they are being less than helpful, they don't answer questions and just keep saying the flight data indicates the drone crashed into the water. Perhaps the silly thing I did was fly over water, but I thought that there were no obstacles and I could get the hang of the drone.

Anyway I was hoping that someone might be able to look over the flight record and tell me what they think happened, the data DJI keep throwing at me is contradictory at best so any thoughts from the experts here would be gratefully received.

I can copy the dialogue I've had with DJI but it seems to me that much of it is fairly standard, like they have templates for responses.
 

msinger

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Please upload your TXT flight log here and post a link back here. You'll find instructions for locating your TXT flight log at that link.
 
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JDawg

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"It did not disconnect and fly away - you landed it in the water at 4.069282 W, 55.87173 N, by repeated application of down throttle:"

Oops! I have been reading almost all of these kinds of posts on the forum for months now and the vast majority of the time (99%?) it is operator error. And most of the time (90%?) the poster starts out thinking it is the Drone's fault.
 
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ac0j

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Or the firmware, or the software, or DJI, Its always one of these that gets the blame.
With 3 years experience with the phantom, I find this mistake a bit hard to believe. But, its right there in the log.....
 

Trickydicky

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Thanks for the comments, not surprisingly this is exactly what DJI said, but I'm afraid I don't understand why you think the drone ended up in the water. I was applying the down throttle because I was bringing the drone in to land. The drone was about a 100 metres away from me and in plain sight. It was still maybe 20ft in the air when it disconnected. Can you tell me at what time you think the drone hit the water and what data supports this? You see the problem I have is that I think the flight log shows the drone disconnected at 5.54.7 and then reconnected at 5.56.3 and then immediately disconnected again. So for the last 1.6 seconds of the recorded flight it wasn't connected. I also have a problem with the height of the drone being recorded at -8.7metres at the end of the flight. I was standing at the water's edge and maybe half a metre above the water. So the final height would put the drone 8 metres under water.
 

sar104

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Thanks for the comments, not surprisingly this is exactly what DJI said, but I'm afraid I don't understand why you think the drone ended up in the water. I was applying the down throttle because I was bringing the drone in to land. The drone was about a 100 metres away from me and in plain sight. It was still maybe 20ft in the air when it disconnected. Can you tell me at what time you think the drone hit the water and what data supports this? You see the problem I have is that I think the flight log shows the drone disconnected at 5.54.7 and then reconnected at 5.56.3 and then immediately disconnected again. So for the last 1.6 seconds of the recorded flight it wasn't connected. I also have a problem with the height of the drone being recorded at -8.7metres at the end of the flight. I was standing at the water's edge and maybe half a metre above the water. So the final height would put the drone 8 metres under water.
I can only tell you what the log shows. Looking at the pitch and roll data, first contact with the water was at 353.7 s, leading to an abrupt change in attitude. The signal disconnect occurs 1 s later, consistent with a water impact. When the downlink briefly reconnects 1.6 s later, the roll angle is 67°. I can assure you that the aircraft was not airborne at that time. The negative barometer readings are most likely because the aircraft was in the water and the sensors were wet.

2018-05-24_[14-32-26]_03.png
 
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Trickydicky

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I can only tell you what the log shows. Looking at the pitch and roll data, first contact with the water was at 353.7 s, leading to an abrupt change in attitude. The signal disconnect occurs 1 s later, consistent with a water impact. When the downlink briefly reconnects 1.6 s later, the roll angle is 67°. I can assure you that the aircraft was not airborne at that time. The negative barometer readings are most likely because the aircraft was in the water and the sensors were wet.
Thanks sar104. I really do appreciate the analysis. I haven't seen these graphs before but now I think I understand what they are showing and I understand why both DJI and yourself think the drone crashed into the water. The problem I have is that the drone didn't crash.

If I understand what the data is showing the drone is flying forward with the nose pitched down about 14 degrees, at 353.7 to 354.2 the nose pitches up to about 18 degrees stays up till 354.8 then the drone disconnects. Between these times the drone doesn't roll at all but by the time it reconnects the roll angle is 67 degrees. What the data also shows I think is that I was constantly applying down throttle between 353.7 and 354.7d. If you look at the height data it shows that before 353.7 the drone was descending at just less than 1ft per tenth of a second. After this time when the drone was supposedly hitting the water and rearing it's nose up, it continues to descend at the same rate until it disconnects at 354.8. The final reading at 356.3 shows the same rate of descent. So the height information shows that the drone was descending at a rate consistent with me applying down throttle until the final disconnection. How is this possible if the drone hit the water.

Also if you look at the speed of the drone and its distance from me, it is flying at about 16mph until 353.7, after this it continues to fly at the same speed although slowing slightly to 12 mph at 354.7. In this time it has moved towards me by around 20ft which is consistent with the speeds logged. When the drone reconnects at 5.56.3 it is still flying forward at 8.5 mph and has moved towards me a further 17 feet. So the drone hits the water and continues to move forward at approximately the same speed before disconnecting finally some 37ft away from first impact. How is this possible.

I don't understand why the data shows the drone pitching back the way it does, the height, speed and distance data do not support this movement. Also if you think the drone is pitched nose down so you would expect when it hits the water it would rotate the other way, it's nose would bury in the water and the tail would flip over. Also if the drone pitched back would it not stop and start flying backwards?

I also don't understand why the data shows the drone rolled by 67 degrees when it finally disconnected. The final set of readings show the drone still moving at 8.5mph, this is 2.6 seconds after supposedly hitting the water. The final readings also give an ultrasonic height of 0.4 metres. How was the drone still moving forward, descending and at a height of 0.4 metres yet rolled by 67 degrees.

I think that because I was flying over water the heights recorded are not true heights, as I said when the aircraft disconnected it was still around 20ft in the air. After it disconnected the aircraft turned and flew away, I think the trace of the flight shows the aircraft had turned at the end. I don't understand why the drone didn't return home. However I have noted that the final set of readings show the drone was only connected to 6 satellites so maybe it didn't know where it was.

As I said I think I understand why you think the drone crashed, but I was there and it simply didn't happen. The other data doesn't support the drone crashing into the water. I don't know what happened to the drone that caused it to disconnect and fly off.
 

sar104

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Thanks sar104. I really do appreciate the analysis. I haven't seen these graphs before but now I think I understand what they are showing and I understand why both DJI and yourself think the drone crashed into the water. The problem I have is that the drone didn't crash.

If I understand what the data is showing the drone is flying forward with the nose pitched down about 14 degrees, at 353.7 to 354.2 the nose pitches up to about 18 degrees stays up till 354.8 then the drone disconnects. Between these times the drone doesn't roll at all but by the time it reconnects the roll angle is 67 degrees. What the data also shows I think is that I was constantly applying down throttle between 353.7 and 354.7d. If you look at the height data it shows that before 353.7 the drone was descending at just less than 1ft per tenth of a second. After this time when the drone was supposedly hitting the water and rearing it's nose up, it continues to descend at the same rate until it disconnects at 354.8. The final reading at 356.3 shows the same rate of descent. So the height information shows that the drone was descending at a rate consistent with me applying down throttle until the final disconnection. How is this possible if the drone hit the water.

Also if you look at the speed of the drone and its distance from me, it is flying at about 16mph until 353.7, after this it continues to fly at the same speed although slowing slightly to 12 mph at 354.7. In this time it has moved towards me by around 20ft which is consistent with the speeds logged. When the drone reconnects at 5.56.3 it is still flying forward at 8.5 mph and has moved towards me a further 17 feet. So the drone hits the water and continues to move forward at approximately the same speed before disconnecting finally some 37ft away from first impact. How is this possible.

I don't understand why the data shows the drone pitching back the way it does, the height, speed and distance data do not support this movement. Also if you think the drone is pitched nose down so you would expect when it hits the water it would rotate the other way, it's nose would bury in the water and the tail would flip over. Also if the drone pitched back would it not stop and start flying backwards?

I also don't understand why the data shows the drone rolled by 67 degrees when it finally disconnected. The final set of readings show the drone still moving at 8.5mph, this is 2.6 seconds after supposedly hitting the water. The final readings also give an ultrasonic height of 0.4 metres. How was the drone still moving forward, descending and at a height of 0.4 metres yet rolled by 67 degrees.

I think that because I was flying over water the heights recorded are not true heights, as I said when the aircraft disconnected it was still around 20ft in the air. After it disconnected the aircraft turned and flew away, I think the trace of the flight shows the aircraft had turned at the end. I don't understand why the drone didn't return home. However I have noted that the final set of readings show the drone was only connected to 6 satellites so maybe it didn't know where it was.

As I said I think I understand why you think the drone crashed, but I was there and it simply didn't happen. The other data doesn't support the drone crashing into the water. I don't know what happened to the drone that caused it to disconnect and fly off.
So just to be clear - you are saying that you positively saw the aircraft well above the surface, after the disconnect, flying away?
 

Trickydicky

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absolutely, it was only about a hundred metres away from me and I was watching it as it descended. I expected it to return home, but it didn't, then I waited for 20 minutes to see if it would return home at low battery, but it didn't, then I drove to my actual home half expecting it to fly there - it had headed off in that direction - silly to think that but I'd flown it there the night before.

The other reason I think the heights are all wonky is that DJI say there is an ultrasonic height of 2.4 metres at 354 and then the ultrasonic height at 356.3 is 0.4 metres, a difference of 2 metres, but in the same time the barometric height changes from -1.5 to -8.7 metres, a difference of 7.2 metres. Surely they should be almost the same.
 

sar104

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absolutely, it was only about a hundred metres away from me and I was watching it as it descended. I expected it to return home, but it didn't, then I waited for 20 minutes to see if it would return home at low battery, but it didn't, then I drove to my actual home half expecting it to fly there - it had headed off in that direction - silly to think that but I'd flown it there the night before.

The other reason I think the heights are all wonky is that DJI say there is an ultrasonic height of 2.4 metres at 354 and then the ultrasonic height at 356.3 is 0.4 metres, a difference of 2 metres, but in the same time the barometric height changes from -1.5 to -8.7 metres, a difference of 7.2 metres. Surely they should be almost the same.
I understand that you watched as it descended, but then what, exactly, did you actually see it do? And at some point you obviously lost sight of it. When did that happen, and why? Did it climb? Did it fly off at constant altitude? What direction? Fast? Slow?

The VPS height values over water are not reliable - there is no point worrying about those discrepancies.
 
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Trickydicky

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I understand that you watched as it descended, but then what, exactly, did you actually see it do? And at some point you obviously lost sight of it. When did that happen, and why? Did it climb? Did it fly off at constant altitude? What direction? Fast? Slow?

The VPS height values over water are not reliable - there is no point worrying about those discrepancies.
Ok. So it was flying towards me and descending when it disconnected. I only realised it had disconnected when it stopped (I think) turned about 120 degrees to the right and headed off. It stayed at the same height and I wouldn’t say it was flying fast. I watched it as it flew across the lake. It stayed at the same level and on the same heading at all times after disconnecting. I eventually lost sight of it when it became too small to see.
 

Jameslavis

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I’m not sar by any means but I fly over water all but time and I’d bet it dropped into gnat drink due to inaccurate height report in the app or the water messing with readings.
 

sar104

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Ok. So it was flying towards me and descending when it disconnected. I only realised it had disconnected when it stopped (I think) turned about 120 degrees to the right and headed off. It stayed at the same height and I wouldn’t say it was flying fast. I watched it as it flew across the lake. It stayed at the same level and on the same heading at all times after disconnecting. I eventually lost sight of it when it became too small to see.
Is there any chance that at some point it landed in the water but recovered and took off again without you noticing?
 

Trickydicky

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Afraid not. It was still well above the water when it disconnected and I had eyes on it all the time because I was bringing it in to land. I'm interested to know why you think it was in the water?
 

sar104

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Afraid not. It was still well above the water when it disconnected and I had eyes on it all the time because I was bringing it in to land. I'm interested to know why you think it was in the water?
I was just wondering if it had got wet if that might have accounted for the telemetry discrepancies and disconnect. Right now there seems to be no way to reconcile your observations with the flight data, which is not a situation that I've seen before.
 
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Jeff7577

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It looks like you were trying to fly close to the water. You did it!
 

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Did you happen to to have it's failsafe set mto land instead of RTH or maybe had it set to return at current altitude in which case if was 100 meters away it would land on the spot? any case sorry for your loss..
 

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I was just wondering if it had got wet if that might have accounted for the telemetry discrepancies and disconnect. Right now there seems to be no way to reconcile your observations with the flight data, which is not a situation that I've seen before.
To me the log also looks like controlled flight into the water. Maybe because the drone flew low over the water it scared a bird that flew away. The drone hit the water and OP looked at the bird flying away thinking it was his drone?

if it really did turn 120 deg and flew off at the same height (low above the watter) it would have hit the trees on the south shore.
 

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