Litchi mission: lost my Air into the sea?

[bikelike]

On the very first flying day of my bike journey I lost my beloved Air. I carefully planned the mission to go high, higher than allowed actually,. Certain sections looked so amazing in Google Earth.

My biggest concern for a next mission: was my speed set too high?

Earlier that day I noticed sea gulls were quite interested in my bird... This picture is what I got when I asked Litchi to find her. I'd say that is after I lost connection, which happened - as far as I remember - after the turn around the lighthouse.

Here is the CSV log from Litchi.

 

[Meta4]

On the very first flying day of my bike journey I lost my beloved Air. I carefully planned the mission to go high, higher than allowed actually,. Certain sections looked so amazing in Google Earth.

Flew around until 81% battery when you engaged RTH to bring the drone back.
It was 320 metres away and 148 metres high.
RTH was bringing it back at 8 metres/sec.
At 823.5 seconds, there's a big problem with the battery.
It was full at the start of the flight but at 823.5 sec the voltage suddenly drops from 12V to 10.8V and the % indicator changes from 81% to 17%.
The drone is 297 metres away and still 148 metres up.

At 832.8 you cancel RTH and leave the drone hovering.
At 841.1 the drone starts landing, probably as it's reached critical low battery level.
It's 220 metres from home.

You do nothing to bring the drone closer and signal is lost at 871.1 with the drone still 65 metres up.

The battery drop from 81% to 17% at 823.5 seconds is the big problem and what caused that is a mystery.
You could probably have brought the drone back at that point as it was only 300 metres away.
You would have had to start descending and flying straight to home or the shore at full speed but that didn't happen and it ended up splasjing down.

 

[bikelike]

The battery drop from 81% to 17% at 823.5 seconds is the big problem and what caused that is a mystery.
You could probably have brought the drone back at that point as it was only 300 metres away.
You would have had to start descending and flying straight to home or the shore at full speed but that didn't happen and it ended up splasjing down.

I don't know how this logging works. So are you saying that in the end it did connect to the controller again? I did get a low battery warning and I did accept the return to home option. But as far as I remember once the connection was lost, it never re-established.
The thing is, the flight was 10 minutes so it was in the air for almost 14 minutes when the **** hit the props.

How do I actually view the log file, since it is no TXT file? Excel just gives me a bunch of numbers.

Thanks!

 

[Meta4]

I don't know how this logging works. So are you saying that in the end it did connect to the controller again?
The recorded data shows a connection from launching until 871 seconds when signal was lost.

How do I actually view the log file, since it is no TXT file? Excel just gives me a bunch of numbers.

The recorded flight data is just lots of numbers and Excel is the way to view them.
I summarised the story they tell.

 

[sar104]

Flew around until 81% battery when you engaged RTH to bring the drone back.
It was 320 metres away and 148 metres high.
RTH was bringing it back at 8 metres/sec.
At 823.5 seconds, there's a big problem with the battery.
It was full at the start of the flight but at 823.5 sec the voltage suddenly drops from 12V to 10.8V and the % indicator changes from 81% to 17%.
The drone is 297 metres away and still 148 metres up.

At 832.8 you cancel RTH and leave the drone hovering.
At 841.1 the drone starts landing, probably as it's reached critical low battery level.
It's 220 metres from home.

You do nothing to bring the drone closer and signal is lost at 871.1 with the drone still 65 metres up.

The battery drop from 81% to 17% at 823.5 seconds is the big problem and what caused that is a mystery.
You could probably have brought the drone back at that point as it was only 300 metres away.
You would have had to start descending and flying straight to home or the shore at full speed but that didn't happen and it ended up splasjing down.

Actually there was no problem with the battery - the long periods of connection loss just make it look that way.



There are only a couple of data points between 200 seconds and 820 seconds, and the associated battery data are unreliable. When the link comes back at around 823 seconds the battery level is at about exactly the level that you would expect - as shown by the dotted red trace extrapolating the initial battery depletion rate. It's down very close to the smart autoland battery level, and goes to autoland just 9 seconds after that.

The aircraft behaved properly - the waypoint mission profile exceeded the available battery capacity.

 

[Meta4]

Actually there was no problem with the battery - the long periods of connection loss just make it look that way.There are only a couple of data points between 200 seconds and 820 seconds, and the associated battery data are unreliable. When the link comes back at around 823 seconds the battery level is at about exactly the level that you would expect.

Correct .. That's what I get for reading the data without being able to see the track.
plot.
The rest of my assessment above appears to be correct.
The drone could have been brought back

 

[sar104]

Correct .. That's what I get for reading the data without being able to see the track.
plot.
The rest of my assessment above appears to be correct.
The drone could have been brought back

Agreed - it looks like it should have been able to return under manual control before it lost connection due to autolanding descent, as shown by the dotted orange extrapolation of RTH shown below.

 

[bikelike]

I am highly interested in learning from this lesson. Thank you, guys! I love Litchi because it enables me to fly and film cinematically (first shot), which is quite difficult for me as a beginning pilot, but I am trying (second shot).

So the image and data suggest that it crashed right behind me? I can hardly believe that because it was behind the tip if the peninsula within two minutes or so. The whole flight was estimated as 10 minutes and in Google EarthPro it's much faster. That is why I thought this was a well designed route. Also I don't understand the sharp corner at the very west, it's not how I designed it at all. Maybe there is a key to understand?

I did get a battery warning though after some 10 minutes and I panicked from there. But by then it should have been back, or almost. In my panic I missed the cancelling of auto-landing and also to check on the map where the aircraft was located, rather than staring to anything moving in the sky.

 

[sar104]

I am highly interested in learning from this lesson. Thank you, guys! I love Litchi because it enables me to fly and film cinematically (first shot), which is quite difficult for me as a beginning pilot, but I am trying (second shot).

So the image and data suggest that it crashed right behind me? I can hardly believe that because it was behind the tip if the peninsula within two minutes or so. The whole flight was estimated as 10 minutes and in Google EarthPro it's much faster. That is why I thought this was a well designed route. Also I don't understand the sharp corner at the very west, it's not how I designed it at all. Maybe there is a key to understand?

I did get a battery warning though after some 10 minutes and I panicked from there. But by then it should have been back, or almost. In my panic I missed the cancelling of auto-landing and also to check on the map where the aircraft was located, rather than staring to anything moving in the sky.

It didn't crash - it autolanded in the sea just north of the peninsula. The sharp corners don't reflect the actual flight track because downlink was lost on a couple of occasions. If you look at the actual track data points recorded you can see that the corner is where the connection was lost, and a straight line connects it to the next received position data point.

 

[bikelike]

It is still totally unclear to me why my dear drone took that much time and taking that much battery power for such a small distance. That makes me hesitant to make future Litchi missions, anyways missions where I lose connection and / or eyesight.

 

[sar104]

It is still totally unclear to me why my dear drone took that much time and taking that much battery power for such a small distance. That makes me hesitant to make future Litchi missions, anyways missions where I lose connection and / or eyesight.

Without seeing your Litchi mission profile I cannot help you with that question.

 

[bikelike]

Here it is: Mission Hub - Litchi

 

[Meta4]

I am highly interested in learning from this lesson. Thank you, guys! I love Litchi because it enables me to fly and film cinematically (first shot), which is quite difficult for me as a beginning pilot, but I am trying (second shot).

So the image and data suggest that it crashed right behind me? I can hardly believe that because it was behind the tip if the peninsula within two minutes or so. The whole flight was estimated as 10 minutes and in Google EarthPro it's much faster. That is why I thought this was a well designed route. Also I don't understand the sharp corner at the very west, it's not how I designed it at all. Maybe there is a key to understand?

I did get a battery warning though after some 10 minutes and I panicked from there. But by then it should have been back, or almost. In my panic I missed the cancelling of auto-landing and also to check on the map where the aircraft was located, rather than staring to anything moving in the sky.

Your litchi flight route was about 4 kilometres long, which should have been an easy flight distance to achieve on one battery.
Here's a display of what data we have for the flight: DJI Flight Log Viewer - PhantomHelp.com
The plot is a little confusing because the straight east-west line near waypoint 6 is just joining the dots between where signal was lost and where it reconnected.
This distance appears to be approx 500 metres but the time the drone took from where signal was lost to where it reconnected was10.5 minutes.
This is where the battery was burnt up from 81% to 17%.
At the cruising speed you set, it should have taken less than one minute to travel that distance.
But in 10.5 minutes it could have traveled approx 6 kilometres.

So what was the drone doing for 10.5 minutes that used up so much battery?
Your flight plan shows that you set the finish action as Reverse which doubles the length of the flight.
This means that while signal was lost, the drone kept flying all the way back to waypoint 10 (right next to where you launched) and then started fling the mission in reverse until signal was regained near waypoint 7.
The actual speed flown between waypoints 2-4 was only about 20 km/hr, suggesting a significant headwind when the drone was flying toward the north.
This would have used up some additional battery on the return flight.

You said that the planned flight time was 12 minutes which would be about 8 kilometres at the cruise speed of 37 km/hr.
This suggests you intended to fly the route out and reverse.
But the planned flight time is in still air and does not allow for wind, which was significant at your flying altitude.
With the slow flight against a headwind for parts of the route, the drone would not have had enough battery to complete the reverse flight as programmed.

But if you had maintained signal and monitored the flight, you would have known it was burning too much battery and cancelled and brought it home easily.
Or you still could have brought it back when signal was regained at 17% but it would have required quick action.
The drone was lost because of a lack of situational awareness and leaving it fighting headwinds at high altitude.
Losing signal for >10 minutes turned out to be a fatal mistake.
The distance was never very far from the home point so it should have been a simple matter to maintain signal.

 

[sar104]

Here it is: Mission Hub - Litchi

It looks as if it should have been able to finish, but it didn't achieve the cruising speed that you set (10.3 m/s) for parts of the flight:

 

[sar104]

Your litchi flight route was about 4 kilometres long, which should have been an easy flight distance to achieve on one battery.
Here's a display of what data we have for the flight: DJI Flight Log Viewer - PhantomHelp.com
The plot is a little confusing because the straight east-west line near waypoint 6 is just joining the dots between where signal was lost and where it reconnected.
This distance appears to be approx 500 metres but the time the drone took from where signal was lost to where it reconnected was10.5 minutes.
This is where the battery was burnt up from 81% to 17%.
At the cruising speed you set, it should have taken less than one minute to travel that distance.
But in 10.5 minutes it could have traveled approx 6 kilometres.

So what was the drone doing for 10.5 minutes that used up so much battery?
Your flight plan shows that you set the finish action as Reverse which doubles the length of the flight.
This means that while signal was lost, the drone kept flying all the way back to waypoint 10 (right next to where you launched) and then started fling the mission in reverse until signal was regained near waypoint 7.
The actual speed flown between waypoints 2-4 was only about 20 km/hr, suggesting a significant headwind when the drone was flying toward the north.
This would have used up some additional battery on the return flight.

You said that the planned flight time was 12 minutes which would be about 8 kilometres at the cruise speed of 37 km/hr.
This suggests you intended to fly the route out and reverse.
But the planned flight time is in still air and does not allow for wind, which was significant at your flying altitude.
With the slow flight against a headwind for parts of the route, the drone would not have had enough battery to complete the reverse flight as programmed.

But if you had maintained signal and monitored the flight, you would have known it was burning too much battery and cancelled and brought it home easily.
Or you still could have brought it back when signal was regained at 17% but it would have required quick action.
The drone was lost because of a lack of situational awareness and leaving it fighting headwinds at high altitude.

Good spot - the reverse finish action was almost certainly the problem. It most likely did finish the mission, went into reverse, hit the smart battery RTH level on the way back, and then autolanded. That times out about right. The only puzzle in that case is why it did not reconnect earlier.

 

[bikelike]

Thanks again for looking into this thoroughly, I already bought a new drone and I have a long journey ahead.

The reverse setting is a very good one. I left it accidentally active from previous flights, which btw never worked. And I always make sure I set the end point there where I will be at that moment, in this case I did not move so same as start point.

My questions:

1. Looking at it now, the end point was some 50 meters from me which actually is too much, I now realise. Is it possible I did not hear it? Not much ambient noise like cars were around. My ears are OK.

2. No connection to the remote? A cable / connector malfunction, would that give the same result as signal loss? I never trusted the short cable so much, that is why I use a short cable from the big USB to usb-c (phone). Because of fear for this, I was sitting paralysed, trying to hold the remote with no movement.

3. Why did the reverse command never worked and now all of a sudden it did?

 

[Meta4]

1. Looking at it now, the end point was some 50 meters from me which actually is too much, I now realise. Is it possible I did not hear it? Not much ambient noise like cars were around. My ears are OK.

Could you hear the Mavic 50 metres away with a breeze from the north taking the sound away from you?

2. No connection to the remote? A cable / connector malfunction, would that give the same result as signal loss? I never trusted the short cable so much, that is why I use a short cable from the big USB to usb-c (phone). Because of fear for this, I was sitting paralysed, trying to hold the remote with no movement.

One likely explanation was that you were not aiming the controller toward the drone as it kept flying around the waypoint route.
Another factor ... did you have a clear, unobstructed line of sight between the controller and drone or were there buildings etc that could have blocked it?

3. Why did the reverse command never worked and now all of a sudden it did?

No idea but you could do a little testing on a small waypoint route where you can see the drone at all times to see if the reverse command usually works.
Since there was no data recorded for 10.5 minutes, we can only guess that it did actually reverse and go all the way out and some of the way back.
But it's hard to think what else could have happened for that time, so following the route that was programmed is most likely.

 

[bikelike]

Testing day for all three options.

1. I just tested the sound on 50 meters next to a road with a good bit of low speed traffic. I could not hear it until 30 meters. So that one is checked as part of the cause.

2. Back to the start - end point i should have had connection, so maybe that was a connector thing, even though I tested it for many minutes with all kinds of movements and it would not go out of connection.

3. I made two little missions, one with reverse and one without. However, the drone does not reverse, I've let it in the air for several minutes. The screen stays occupied, with the red button enabled to cancel, as below. The mission without return ends differently, as expected: Litchi is available for a next task.

 

[sar104]

Extrapolating forwards from the last data point on the way out - if it had completed the route at the set cruising speed and then reversed, with no lost time, and then entered RTH at the intersection of the return line with the profile, then it would have arrived at the reconnection point at around 660 seconds. It actually arrived there at 820 seconds, leaving. just 160 seconds to account for with slower speeds and track reverse actions etc. It seems pretty compelling that that's what happened.

 

[bikelike]

Mmn, another reason not to believe it reached the end point, since I did not touch the sticks once.