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GPS Signal lost, Switched to ATTI Model, Flew the drone home
1812 22 2018-5-14
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djiuser_PEp4mLwh74c7
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I flew my drone in the coast and tried to take some photo of a small island.  It is only about 300m direct distance from home point, and about 3500m to a military NFZ (see the figure in red square, blue is military NFZ). Drone was taken off smoothly with GPS level about 14. I started to fly to the small island with altitude about 110m in P mode. Before the drone reached to center of the island, all GPS signal suddenly lost. The compass was abnormal and IMU abnormal. The drone switched to ATTI Mode, RTH function disabled.  The drone floated within 8miles/h wind and flew far and far.  The battery level was about 85%.
  
I was a little bit panic, but fortunately I trained myself how to fly with ATTI Mode, I found out the orientation and so I can enter the correct stick commands to offset the drift from the wind. After struggle for about 8 minutes, I pulled the drone back to the home point safely. During the way home, the RC didn’t gain any GPS, and still showed compass error and IMU error. After I came back to home, I re-calibrate all.
  
  
What I learned are:
  
1.     Training yourself with ATTI Mode until you can control the drone smoothly with 5-10 miles per hour wind;
  
2.     Do not panic, and find correct stick commands, then controlling the drone becomes easy;
  
3.     Nerve try to fly 5 miles near NFZ.
  
4.     Do not fly drone over a big bridge (I flew my drone and took photos over a key bridge and an overpass, and lost GPS signal. I flew back in ATTI Mode too).

One question:

In ATTI Mode, whether the drone is going to be enforced landing when it drifts into NFZ?
  


NearNFZ

NearNFZ
2018-5-14
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Timinator
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Good job getting it back.  Definitely important to know how to fly atti mode. What was the surface you took off from? Grass? Concrete? something else?
2018-5-14
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djiuser_PEp4mLwh74c7
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Timinator Posted at 2018-5-14 11:52
Good job getting it back.  Definitely important to know how to fly atti mode. What was the surface you took off from? Grass? Concrete? something else?

It was grass surface on a restaurant's backyard.  I do think it is the reason of military NFZ, not related to the site I took the drone off.
2018-5-14
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Hellsgate
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You werent actually flying in an nfz i dont think that was the cause of it.
Even if you were to fly into an nfz the issues you stated having should not have happened.
Its great you got the drone back in one piece but i think you need to find the real cause of the problem.
Perhaps upload the flight log there maybe some clues in there.
2018-5-14
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hallmark007
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Yeah good job getting it back,

But my guess is you lost gps because of compass problems. These problems could have occurred before you got off the ground, although it would help to see your flight log.

Just click on link below and follow instructions come back here and post your link .

http://www.phantomhelp.com/LogViewer/Upload/
2018-5-14
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Labroides
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You need to find out what you are doing wrong that is giving you compass errors that cause the drone to switch to atti.
That's not normal at all.
4.     Do not fly drone over a big bridge (I flew my drone and took photos over a key bridge and an overpass, and lost GPS signal. I flew back in ATTI Mode too).
Flying over a bridge won't cause any problems at all.
I'd be more concerned about where you launched from.
2018-5-14
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djiuser_PEp4mLwh74c7
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Labroides Posted at 2018-5-14 15:07
You need to find out what you are doing wrong that is giving you compass errors that cause the drone to switch to atti.
That's not normal at all.
4.     Do not fly drone over a big bridge (I flew my drone and took photos over a key bridge and an overpass, and lost GPS signal. I flew back in ATTI Mode too).

I am sure it was not from the setting:

1. My friend flew a Mavic Pro Platinum who experienced the exact situation as me.
2. When we drove 3 miles away  from the spot to another site (away from the military NFZ), we both flew well: All GPS/Compass/IMU were normal.
2018-5-14
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Labroides
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djiuser_PEp4mLwh74c7 Posted at 2018-5-14 15:43
I am sure it was not from the setting:

1. My friend flew a Mavic Pro Platinum who experienced the exact situation as me.
1. My friend flew a Mavic Pro Platinum who experienced the exact situation as me.
All the more reason to suspect your choice of launching spot.
What was the launch spot like?

It had nothing to do with the NFZ.  That's not how they work at all.
You have another problem that you need to sort out.
2018-5-14
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DJI Susan
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Nice rescue! Thanks for sharing with us. It is recommended to keep away from the NFZ.
The drone will enter landing mode as long as she found herself in NFZ when GPS signal is enough.
2018-5-14
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djiuser_PEp4mLwh74c7
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Labroides Posted at 2018-5-14 19:22
1. My friend flew a Mavic Pro Platinum who experienced the exact situation as me.
All the more reason to suspect your choice of launching spot.
What was the launch spot like?

I set the launching spot between the forth and the fifth fishing deck. The pavement is made from concrete and stones. About 80m away from the right side, there is a watchtower. About 15m away, there are line of residents home or restaurants. Nothing special, but 3000m away is NFZ of Martin military airport. Sorry I cannot upload the screenshot due to image size matters, but it locates 1902 Chesapeake ave, Baltimore.
2018-5-14
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Labroides
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djiuser_PEp4mLwh74c7 Posted at 2018-5-14 20:16
I set the launching spot between the forth and the fifth fishing deck. The pavement is made from concrete and stones. About 80m away from the right side, there is a watchtower. About 15m away, there are line of residents home or restaurants. Nothing special, but 3000m away is NFZ of Martin military airport. Sorry I cannot upload the screenshot due to image size matters, but it locates 1902 Chesapeake ave, Baltimore.

You launched from concrete?
Reinforced concrete?
Welcome to the club of hundreds of Phantom owners that caused compass problems for their flights.
If you launched from reinforced concrete (which is half steel) that's the cause of your issues.
2018-5-14
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Timinator
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Labroides Posted at 2018-5-14 21:08
You launched from concrete?
Reinforced concrete?
Welcome to the club of hundreds of Phantom owners that caused compass problems for their flights.

This.

In a pinch, you can also launch from the carrying case to prevent any compass problems in the future.  Still preferable to launch without any iron beneath it.
2018-5-15
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Christine96
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Labroides Posted at 2018-5-14 21:08
You launched from concrete?
Reinforced concrete?
Welcome to the club of hundreds of Phantom owners that caused compass problems for their flights.

Wouldn't the compass problem go away once the drone was high enough above the concrete?  
2018-9-1
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Geebax
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Christine96 Posted at 2018-9-1 18:26
Wouldn't the compass problem go away once the drone was high enough above the concrete?

Nope, because that's not the way it works. The issue is to do with initialisation of the aircraft systems at power on. The compass devices are at the bottom of the legs, so if the aircraft is sitting on concrete with a lot of steel in it, when you power up the aircraft, it initialises the  compass(s), which are influenced by the steel rebar, and thinks this is normal for the compass. Once you get airborne, it then realises that the compass readings make no sense any more, so it decides to ignore the compass and GPS and switches the aircraft into ATTI mode. From then on, whether you realise it or not, you are flying purely manually, no position holding, nothing but altitude stabilisation.
2018-9-1
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Alvaro L
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Thanks for telling us about it.

One question I have is how you can detect an spurious compass setting before taking off? Maybe checking it against a hand bearing compass?
2018-9-2
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Christine96
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Geebax Posted at 2018-9-1 19:00
Nope, because that's not the way it works. The issue is to do with initialisation of the aircraft systems at power on. The compass devices are at the bottom of the legs, so if the aircraft is sitting on concrete with a lot of steel in it, when you power up the aircraft, it initialises the  compass(s), which are influenced by the steel rebar, and thinks this is normal for the compass. Once you get airborne, it then realises that the compass readings make no sense any more, so it decides to ignore the compass and GPS and switches the aircraft into ATTI mode. From then on, whether you realise it or not, you are flying purely manually, no position holding, nothing but altitude stabilisation.

Ok that makes sense.  Now when I first open DJI go 4 app I get the little popup that indicates normal for the compass.  At that point I do not need to calibrate the compass?  
2018-9-2
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rwynant V1
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You can end up in a NFZ when you have loss of GPS signal.

The NFZ is GPS Located........no GPS,  No NFZ

2 AC, same issue......  did you check the KP Index where you were flying??

Randy
2018-9-2
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Labroides
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Alvaro L Posted at 2018-9-2 00:37
Thanks for telling us about it.

One question I have is how you can detect an spurious compass setting before taking off? Maybe checking it against a hand bearing compass?

Simple way is to make sure you never launch from a steel or reinforced concrete surface.
2018-9-2
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Labroides
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Christine96 Posted at 2018-9-2 07:49
Ok that makes sense.  Now when I first open DJI go 4 app I get the little popup that indicates normal for the compass.  At that point I do not need to calibrate the compass?

You should never need to calibrate the compass.
If you ever think the app is tellling you to, read the message carefully.
It will say Magnetic Field Interference - Move aircraft or calibrate compass.
The compass will be warning that it has detected an abnormal  magnetic influence.
The solution is always to move away from that.
Calibrating the compass won't fix anything.

2018-9-2
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Labroides
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rwynant V1 Posted at 2018-9-2 10:04
You can end up in a NFZ when you have loss of GPS signal.

The NFZ is GPS Located........no GPS,  No NFZ
Your comments about NFZ/GPS are correct but the incident was not related to any NFZ.
did you check the KP Index where you were flying??
If the K-index was responsible, it would be the first time that's happened.
The K-index is hype and has never been responsible for any flight incidents.
2018-9-2
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Geebax
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Christine96 Posted at 2018-9-2 07:49
Ok that makes sense.  Now when I first open DJI go 4 app I get the little popup that indicates normal for the compass.  At that point I do not need to calibrate the compass?

No, in fact you do noit need to calibrate the compass at all. It is a hangover from earlier design machines where you could hang various accessories on the aircraft. From the P3 onward, it is not necessary. Many people do not understand this.
2018-9-2
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Christine96
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Labroides Posted at 2018-9-2 14:12
You should never need to calibrate the compass.
If you ever think the app is tellling you to, read the message carefully.
It will say Magnetic Field Interference - Move aircraft or calibrate compass.

I'll keep that in mind thanks.
2018-9-2
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Christine96
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Geebax Posted at 2018-9-2 16:08
No, in fact you do noit need to calibrate the compass at all. It is a hangover from earlier design machines where you could hang various accessories on the aircraft. From the P3 onward, it is not necessary. Many people do not understand this.

I think I was confusing the Mavic Air with P4P.  
2018-9-2
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