GPS and connection lost

[Chris_LSZO]

Hi Guys

Today I has fly my bird in some canyons and it loose first GPS and after this the connection to the controller. RTH doesn't work without GPS, so the Mavic hover and then after one minute it descend and try to land. I was lucky, the terrain war very rough and the drone stay in the air few centimeters above ground. After about 3 minutes, the GPS comes back but still no connection to the controller. RTH still doesn't work because the drone was in landing mode. After about 8 minutes I found a place to reconnect the drone, cancel the landing question "yes/no" and fly back home.

Is there any possibility by using the debug mode to change this behavior? I would like, the drone climb byself after loosing the connection without GPS. Hover and then try to land ist very bad....

Chris

 

[rickw]

if you set things up properly the drone will come when it loses signal with rc

 

[Former Member]

OP, if your drone loses connection with the GPS, it doesnt know where home is.

I think you should stay away from those canyons, you might lose your drone if it loses GPS signal and you lose video feed.

 

[Chris_LSZO]

And there is no way to configure the drone like I asked above?

Chris

 

[Former Member]

Is there any possibility by using the debug mode to change this behavior? I would like, the drone climb byself after loosing the connection without GPS. Hover and then try to land ist very bad....

Chris

And there is no way to configure the drone like I asked above?

Chris

You want the drone to try and return home without using it's GPS?

Check out this thread.

What if you lose GPS flying and no line of sight to return home?

 

[Chris_LSZO]

No, I want the drone climb to a configured height after GPS and connection are lost. Even if the GPS signal is lost, the drone knows the current height.
Or if this is not possible configure to not auto land after one minute without GPS and connection (then if the GPS comes back, RTH works again).

Chris

 

[Keule]

I want the drone climb to a configured height after GPS and connection are lost.

The flight controller (FC) is programmed as follows:

- If GPS lost, the FC switches to ATTI mode in which the aircraft can still be controlled by operators stick input. Aircrafts altitude is controlled by the internal barometric sensor.
- If RC connection is lost, the FC executes it's failsafe RTH (i.e. climb to user defined altitude and the aircraft flies to the home coordinates)

But now, these two incidents (ATTI mode and RC link lost) are worst case scenario, therefore the aircraft will land wherever it is.

There is no way to alter that procedure.

 

[Chris_LSZO]

But now, these two incidents (ATTI mode and RC link lost) are worst case scenario, therefore the aircraft will land wherever it is.

On one of my last flight this worst case are happened and after lost GPS and RC the drone hover for one minute and then try to land. But the ground was very rough, so it hover few centimeters above the ground. Then the GPS comes back (still no RC connection) but the drone stay in this "landing mode" and don't perform RTH byself.

Ok, last try: Is there any possibility (by debug maybe?) to extend or avoid the time between lost connection and initiate the auto land? Just one minute are very short.

Chris

 

[Keule]

after lost GPS and RC the drone hover for one minute and then try to land. But the ground was very rough, so it hover few centimeters above the ground.

You had landing protection ON, aircraft will hover until critically low battery. (Then land anyways)

the drone stay in this "landing mode" and don't perform RTH byself.

I assume battery level was critical, therefore aircraft stayed in forced landing mode

Is there any possibility to extend or avoid the time between lost connection and initiate the auto land?

RC connection lost action can be set to RTH, Hover or Land.

There is no way to alter the pre-set time of 3 seconds after link lost to execute above mentioned actions.

 

[sar104]

On one of my last flight this worst case are happened and after lost GPS and RC the drone hover for one minute and then try to land. But the ground was very rough, so it hover few centimeters above the ground. Then the GPS comes back (still no RC connection) but the drone stay in this "landing mode" and don't perform RTH byself.

Ok, last try: Is there any possibility (by debug maybe?) to extend or avoid the time between lost connection and initiate the auto land? Just one minute are very short.

Chris

The auto land response to losing connection applies when the aircraft is in ATTI mode, and the reason for it to land promptly is that it will be drifting with the wind. I've not seen an editable parameter that determines the duration of lost uplink that triggers auto land.

One question - you mentioned that GPS returned but you had no RC connection, so how did you determine that it had reacquired GPS?

 

[Chris_LSZO]

I assume battery level was critical, therefore aircraft stayed in forced landing mode

No, was still at 60%

One question - you mentioned that GPS returned but you had no RC connection, so how did you determine that it had reacquired GPS?

Its logged in the flight log.
DJI Flight Log Viewer - PhantomHelp.com
2:13 lost GPS
3:13 perform auto land (I can see it in the recorded Video)
4:41 regain GPS
11:15 reconnect RC, cancel auto land manually

Chris

 

[sar104]

No, was still at 60%


Its logged in the flight log.
DJI Flight Log Viewer - PhantomHelp.com
2:13 lost GPS
3:13 perform auto land (I can see it in the recorded Video)
4:41 regain GPS
11:15 reconnect RC, cancel auto land manually

Chris

No - you have misunderstood the log. It switched to ATTI when it lost GPS at 133.6 seconds (2:13) but it did not initiate autoland and did not descend - it stayed in ATTI mode under your control until 281 seconds (4:41) when it switched back to P-GPS. However, it had not regained GPS lock (GPS health was still at zero) and was using vision positioning instead. At 355 seconds (5:55) you lost RC connection while it was still in P-GPS (VPS).

When the link was regained at 675 seconds (11:15) the aircraft was in autoland with GPS health still at zero and VPS on. With VPS on it would switch back to P-GPS but we cannot see from the log how long VPS had been on, and the following few seconds show that VPS was going on and off - which accounts for the autoland state rather than P-GPS state. You applied throttle to climb, and flew the aircraft in P-GPS with VPS until 745 seconds, at which point it reacquired GPS lock.

 

[Chris_LSZO]

No - you have misunderstood the log.

You are right, I was confused because the recorded video start 3 min after take off. And yes, now I see, that GPS was active at the moment of loss the RC. BTW: The grafic you attached are very helpful, how you extract this?

Ok, now step by step: GPS was lost and then regain but was still locked, VPS active. Why? Not enough satellites? But the drone are in P-GPS mode... Thats confusing to me. Could you explain this behavior a bit more please?

In the recorded video I can see, the drone stop moving at the moment of loss the RC. Few seconds later I has try a little bit to climb (move the stick) but I has think, this will sure not work. But in the Video I can clearly see the drone accept this command and climb a bit (I upload the video on youtube, maybe this is interesting for you to see).
One minute later the drone descend byself (the difference in height between loss RC and regain is exactly this level). I'm pretty sure, this was the initiation of auto land because after reconnect later to RC autoland was active and I has to cancel it. The drone was in P-GPS mode but VPS was still on. In this circumstances the drone try to land I think. Could someone confirm this maybe?

Thanks so much for now

Chris

 

[sar104]

You are right, I was confused because the recorded video start 3 min after take off. And yes, now I see, that GPS was active at the moment of loss the RC. BTW: The grafic you attached are very helpful, how you extract this?

All the data fields that I plotted are in the txt flight log. That's just a small subset of them relevant to this event.

Ok, now step by step: GPS was lost and then regain but was still locked, VPS active. Why? Not enough satellites? But the drone are in P-GPS mode... Thats confusing to me. Could you explain this behavior a bit more please?

P-GPS doesn't (despite the name) mean that the aircraft has a GPS position lock - it simply means that it is position-aware through either GPS or VPS. If its GPS solution is inadequate (generally not enough satellites) then it will use VPS. In this case the satellite count dropped to 4, which is totally inadequate:

In the recorded video I can see, the drone stop moving at the moment of loss the RC. Few seconds later I has try a little bit to climb (move the stick) but I has think, this will sure not work. But in the Video I can clearly see the drone accept this command and climb a bit (I upload the video on youtube, maybe this is interesting for you to see).

It's possible that the uplink continued after the downlink was lost, and so the aircraft may have responded to stick input at that time. It won't be recorded in the log with no downlink however.

One minute later the drone descend byself (the difference in height between loss RC and regain is exactly this level). I'm pretty sure, this was the initiation of auto land because after reconnect later to RC autoland was active and I has to cancel it. The drone was in P-GPS mode but VPS was still on. In this circumstances the drone try to land I think. Could someone confirm this maybe?

The log doesn't record the transition to ATTI and then auto land (due to loss of VPS) since the link was down. However, we can compare the altitude when the link was lost with the altitude when it returned, and note that the aircraft had only descended 12 m over that period. That implies that auto land was only initiated a short time before the link came back at 675 seconds. If it had commenced auto land one minute after loss of downlink then it would have descended far more than that at the default descent speed. Or perhaps it was going in and out of ATTI/autoland during that period. I would have thought that you might be able to see exactly what happened on the video.

 

[Chris_LSZO]

The log doesn't record the transition to ATTI and then auto land (due to loss of VPS) since the link was down. However, we can compare the altitude when the link was lost with the altitude when it returned, and note that the aircraft had only descended 12 m over that period. That implies that auto land was only initiated a short time before the link came back at 675 seconds. If it had commenced auto land one minute after loss of downlink then it would have descended far more than that at the default descent speed. Or perhaps it was going in and out of ATTI/autoland during that period. I would have thought that you might be able to see exactly what happened on the video.

What program you use for visualisation the logged data?

Well, now the Video are available at yt:

At 2:10 the Signal are lost till 7:45
At 2:25 you can see some movement, there I has command something without downlink
At 3:10 the drone initiate autoland

What do you think about it?

And one more question about the logged data: When the drone has loose GPS, why VPS are still low all the time without GPS?


Chris

 

[sar104]

What program you use for visualisation the logged data?

Well, now the Video are available at yt:

At 2:10 the Signal are lost till 7:45
At 2:25 you can see some movement, there I has command something without downlink
At 3:10 the drone initiate autoland

What do you think about it?

And one more question about the logged data: When the drone has loose GPS, why VPS are still low all the time without GPS?


Chris

Okay - that explains several things. Correlating the video to the flight log, the sudden climb at 7:48 (468 s) in the video occurs at 678 s in the log, so the offset is 210 seconds.

The link was lost at 355 s in the flight log, which corresponds to 2:25 (145 s) in the video, not 2:10 s.

We can see autoland start at 3:13 in the video (193 s) which, adding 210 s, corresponds to 403 seconds in the flight log. In other words it started 48 s after the downlink was lost. The reason that it only descended 12 m is that it was near the bottom of the gorge anyway, and had nowhere to go. The vision system prevented landing.



I analyzed and displayed the data using Wavemetrics Igor Pro.

 

[Chris_LSZO]

Great analyse! Thank you so much. There is just still one question:
About the logged data: When the drone has loose GPS, why VPS are still low all the time without GPS? It comes high at the same Moment P-GPS comes high again. This make no sense to me...

 

[sar104]

Great analyse! Thank you so much. There is just still one question:
About the logged data: When the drone has loose GPS, why VPS are still low all the time without GPS? It comes high at the same Moment P-GPS comes high again. This make no sense to me...

Because VPS is what the aircraft is using to operate in P-GPS mode when it has no GPS lock. When VPS becomes available at 282 seconds the aircraft switches from ATTI to P-GPS because it now has positioning capability.

 

[Chris_LSZO]

I really don't understand the difference between VPS and ATTI. So I have to find out this now, thanks for the moment. Great forum!

Chris

 

[sar104]

I really don't understand the difference between VPS and ATTI. So I have to find out this now, thanks for the moment. Great forum!

Chris

VPS is the vision positioning system - a set of cameras and sensors that allows the aircraft to hold position or move relative to its surroundings, even though it doesn't know where it is (no GPS coordinates).

P-GPS is a flight mode in which the aircraft uses either GPS (primary) or VPS (secondary) to hold position or navigate. If you release the sticks in that mode then the aircraft will stop and hold position, altitude and heading.

ATTI is a flight mode where the aircraft doesn't know where it is, either absolutely (GPS) or relative to its surroundings (VPS). In that mode it simply stabilizes attitude - pitch and roll are kept at zero (i.e. level), yaw is held steady (no rotation) and altitude is held constant barometrically. As a result it will make no attempt to stop or remain stationary if you center the sticks, and will drift with the wind unless you manually correct with pitch and roll.