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After RTH landing, MP started to take off, got force landing msg

ScottyV

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Weird thing happened the other day.
I was doing a RTH landing and the MP was landing on my deck where I had taken off from.

It landed fine, exactly where it was supposed to. But then the props started to spin up and it started to very slowly lift off the deck by itself about 6 inches. I know I wasn't giving any input on the controls. I looked at the DJI app (on iPad) and saw a dialog that said "force landing" so I hit it immediately. Happened so fast that I didn't notice any other information it might have been giving.

Any ideas why that happened? Did the downward sensors possibly see through the cracks in the deck, so it wasn't sure it was actually on the ground?

(another lesson that it's often best to just land the thing yourself :eek:)

Let me know if anyone has any ideas, thanks.
 

msinger

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Any ideas why that happened?
Check out your TXT flight log to see if it explains what happened. You can upload and view it online here. If you'd like other people to review and comment on your flight log, then please post a link back here after you upload it.
 
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ScottyV

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Check out your TXT flight log to see if it explains what happened. You can upload and view it online here. If you'd like other people to review and comment on your flight log, then please post a link back here after you upload it.

Ok, will do. However, I'm having issues with Assistant 2 (I might be able to get it connecting on a different laptop, I'm working on that). I haven't retrieved log files before, can I get the logs off the Mavic without it Assistant 2? (sorry, I'm sure there are answers about that on the forum...figured I'd just ask)
Thanks for the help.
 

MavicCF

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Ok, will do. However, I'm having issues with Assistant 2 (I might be able to get it connecting on a different laptop, I'm working on that). I haven't retrieved log files before, can I get the logs off the Mavic without it Assistant 2? (sorry, I'm sure there are answers about that on the forum...figured I'd just ask)
Thanks for the help.
The txt. flight logs are actually stored on your phone/tablet and not on the Mavic. If you go to his link, you will see instructions on how to pull those logs off your device.
 

Jayfdee

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(another lesson that it's often best to just land the thing yourself :eek:)

Have to agree, I am better at landing than any automated version.
I will be interested to know what our knowledgeable friends diagnose.
 

ScottyV

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The txt. flight logs are actually stored on your phone/tablet and not on the Mavic. If you go to his link, you will see instructions on how to pull those logs off your device.

Ok, thanks. I'll take a look and post a link
 

ScottyV

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Here is my flight log. It looks like it was sensing negative IMU altitude just as it was landing. I'm assuming that's why it started to lift back up, but don't know why the sensors read that. (first time I've looked at a flight log too) Let me know if anyone has any ideas. thanks.

DJI Flight Log Viewer - PhantomHelp.com
 

MavicCF

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Here is my flight log. It looks like it was sensing negative IMU altitude just as it was landing. I'm assuming that's why it started to lift back up, but don't know why the sensors read that. (first time I've looked at a flight log too) Let me know if anyone has any ideas. thanks.

DJI Flight Log Viewer - PhantomHelp.com
I'll check it out tomorrow if no one else has looked into it. Good night y'all.
 

HWCM

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Does your deck have spaces between the boards? The downward sensors could have been seeing through the spaces and didn't know it had landed.
 

Lake_Flyer

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Probably Landing Protection acting up. Switch that off in the app, you don't need it.
My friendly advise: Return and land yourself, always. RTH is fine for emergencies. But it isn't 100% flawless.
 

MavicCF

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As others have been saying, it seems to have been due to the VPS.
The mavic was in Autolanding mode using precision landing, when it sensed and avoided an obstacle, temporarily switching it to GPS/ATTI mode again. It then switched to Forced Landing and completed the landing. takes off again.PNG
 
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Lake_Flyer

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But why would it sense and avoid an obstacle after it had already landed on the deck?
What would have triggered that? For me it's the repeated proof that we can never 100% trust the DJI algorithms in play here. Again, always fly it yourself, don't trust the DJI 'intelligence' behind obstacle avoidance, RTH, precision landing, landing protection and so on.
 

Lake_Flyer

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Does your deck have spaces between the boards? The downward sensors could have been seeing through the spaces and didn't know it had landed.
But the barometer would have shown no change in altitude hence it should have known it had landed on a solid surface.
 

ScottyV

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ok, thanks for the feedback. As everyone has said, seems due to the VPS.
The deck does have the typical spacing between the deckboards which you can see through, so I'm guessing that's why.
And not the best idea to auto-land in a fairly confined space too...not gonna do that again! (going to land myself from now on)
Thanks MavicCF for taking a look at the data.
 

MavicCF

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But why would it sense and avoid an obstacle after it had already landed on the deck?
What would have triggered that? For me it's the repeated proof that we can never 100% trust the DJI algorithms in play here. Again, always fly it yourself, don't trust the DJI 'intelligence' behind obstacle avoidance, RTH, precision landing, landing protection and so on.
Good thought, sorry I didn't catch that.
The AC wasn't actually down and landed until the very end of the log, up until at point it was still reporting to be in "sky" mode (vs ground mode). I assume that as it was about to fully land, it sensed the obstacle and switched to GPS to avoid it. When it switched out of GPS it "took off again" although really it had never actually finished its landing. It than gave the operator the option to force land which he did.
I'm not sure which sensor sensed the obstacle, so it could very well have thought the deck cracks made it "unsuitable to land," that would also explain why it suddenly throttled up again.
 

ScottyV

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I'm not sure which sensor sensed the obstacle, so it could very well have thought the deck cracks made it "unsuitable to land," that would also explain why it suddenly throttled up again.

I'm not sure if forward looking sensors would come into play here, but there were definitely obstacles close enough to trigger them. The deck railing was probably 4 ft in front of the MP. And I don't know if specific senser data is part of the flight logs...

I also had a question for you: how did you create the graph that you posted in #13? I looked around log viewer site that I uploaded the file to, and on this forum, but can't figure that one out. Thanks for the help.
 

MavicCF

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I'm not sure if forward looking sensors would come into play here, but there were definitely obstacles close enough to trigger them. The deck railing was probably 4 ft in front of the MP. And I don't know if specific senser data is part of the flight logs...

I also had a question for you: how did you create the graph that you posted in #13? I looked around log viewer site that I uploaded the file to, and on this forum, but can't figure that one out. Thanks for the help.
The most common way is to use a program called CsvView to read the txt./DAT files off the the Mavic or phone. Its a cool program, and lots of fun to use.
 
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msinger

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when it sensed and avoided an obstacle, temporarily switching it to GPS/ATTI mode again
Where did you see that in the flight log?

The Mavic was auto landing before it switched back to P-GPS mode. Since obstacle avoidance is disabled while landing, the Mavic shouldn't have tried to avoid any obstacles.
 
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