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OTG Disconnection while airborne
880 16 2018-2-5
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NormSpark
Second Officer
United States
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I used OTG all the time without any issues with the latest firmware, app, iOS but today, I had a worrisome experience. I never thought OTG setup will suffer disconnection. I was not far from the home point, reached 395 ft without any warnings except reaching max altitude so I stopped going up, stayed at this altitude for a while then suddenly, the DJI app showed an error message "Weak Image Transmission" then the "Disconnected" message.
For at least 4 minutes the Spark just hovered in the distance while I figured out how to connect again. I unplugged the OTG then connect using WIFI to no avail so I decided to shutdown app and reconnected with WIFI. Press RC's RTH right away then manual land since I know the battery was getting low. Whew, Spark made it home safely. I checked the two logs - before and after disconnection and did not see anything to cause the disconnection. Any ideas?
First Log
Second Log


2018-2-5
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heliman
First Officer
Denmark
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It sounds to me as phone to rc disconnected, while rc to spark still worked.
And that’s why it did not RTH.
Did you try to fly it with the rc or use it’s RTH button?
2018-2-5
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NormSpark
Second Officer
United States
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heliman Posted at 2018-2-5 12:52
It sounds to me as phone to rc disconnected, while rc to spark still worked.
And that’s why it did not RTH.
Did you try to fly it with the rc or use it’s RTH button?

If you look at the logs, you will notice more or less 4 minutes of gap between first and second log which during this time, the drone just hovered in one place without communicating to RC. I want to add, image transmission stopped as well.

4 minutes later, I was able to connect again using WIFI then I pressed the RC's RTH to go home.
2018-2-5
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NormSpark
Second Officer
United States
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heliman Posted at 2018-2-5 12:52
It sounds to me as phone to rc disconnected, while rc to spark still worked.
And that’s why it did not RTH.
Did you try to fly it with the rc or use it’s RTH button?

Going back to your post again...are you saying if RC to phone got disconnected, I can still use my Iphone to bring the drone home even without image transmission? I thought being disconnected means no communication with the drone at all whether RC or iPhone.
2018-2-5
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heliman
First Officer
Denmark
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Yes. The rc normally works even when the phone disconnects.

The log links go through facebook, so I didn't dare to look.
Now I have peeked anyway. If phone and rc connection failed simultaneously, I would suspect an rc malfunction.
But that would not stop the spark from logging. I don’t know how to read the black box in the spark. I’m sure somebody else does.
Just my ideas.
2018-2-5
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DJI Elektra
Administrator
China
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Sir, OTG cable may cause unexpected problem. Please fly with wifi connection and keep us updated, our engineers are working on OTG cable, please wait patiently. Thanks for your support.
2018-2-5
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Kloo Gee
Captain
Flight distance : 13736932 ft
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United States
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Based on your description, I agree with heliman that it is very likely that your phone became disconnected from the RC while the RC was still connected to your Spark.  If that was indeed the case, the RC will still work to control the aircraft even if your phone itself is disconnected and not displaying any flight information.

In that situation, did you try to use the RC at all to try to bring it back home?  I think while you were in that situation, you very likely could have used the sticks on the RC and the aircraft would have responded accordingly.  
2018-2-5
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NormSpark
Second Officer
United States
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Kloo Gee Posted at 2018-2-5 21:47
Based on your description, I agree with heliman that it is very likely that your phone became disconnected from the RC while the RC was still connected to your Spark.  If that was indeed the case, the RC will still work to control the aircraft even if your phone itself is disconnected and not displaying any flight information.

In that situation, did you try to use the RC at all to try to bring it back home?  I think while you were in that situation, you very likely could have used the sticks on the RC and the aircraft would have responded accordingly.

It was the first time it happened to me so I kind of panicked. I thought if I press the RC RTH, I need to confirm it on the screen so I guess, confirmation is only needed if I press RTH on the app, correct? Thank you for this tip.
2018-2-6
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NormSpark
Second Officer
United States
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heliman Posted at 2018-2-5 12:52
It sounds to me as phone to rc disconnected, while rc to spark still worked.
And that’s why it did not RTH.
Did you try to fly it with the rc or use it’s RTH button?

So if the RC disconnects from Spark, will the drone go back to homepoint automatically?
2018-2-6
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tonyyng
lvl.4

Canada
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NormSpark Posted at 2018-2-6 07:20
It was the first time it happened to me so I kind of panicked. I thought if I press the RC RTH, I need to confirm it on the screen so I guess, confirmation is only needed if I press RTH on the app, correct? Thank you for this tip.

Press and hold the RTH button on the Remote Controller.  It has to be longer than a quick click of the button.

I'd suggest you try it on your next flight to get used to how it works.
2018-2-6
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tonyyng
lvl.4

Canada
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NormSpark Posted at 2018-2-6 07:21
So if the RC disconnects from Spark, will the drone go back to homepoint automatically?

Yes.  After a disconnection from the RC, the Spark should go into RTH after 3 seconds.

Remember the other factors.  It needs to have GPS lock and be more than 20m away.  Less than 20m, it will just land.
2018-2-6
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kRx md
First Officer
Flight distance : 158914 ft
Philippines
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tonyyng Posted at 2018-2-6 07:37
Yes.  After a disconnection from the RC, the Spark should go into RTH after 3 seconds.

Remember the other factors.  It needs to have GPS lock and be more than 20m away.  Less than 20m, it will just land.

thank you for pointing this out. As I have to remember to launch with a 20m radius that is clear of any structure, so that when it disconnects for any reason within 20m, any automatic landing is safe.
2018-2-6
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S.J
Captain
Flight distance : 322454 ft
Kuwait
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kRx md Posted at 2018-2-6 07:50
thank you for pointing this out. As I have to remember to launch with a 20m radius that is clear of any structure, so that when it disconnects for any reason within 20m, any automatic landing is safe.

yes, that is absolutely good decision .
Most of the flyaways can be avoided if the pilots set the home point before long journeys and use the RTH button on the RC for returning back instead of the app "RTH" button
2018-2-6
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Grmachine
Second Officer
United States
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Correct me if I'm wrong, but wouldn't the controller still have a green indicator, even if the Mobile device to RC connection was lost? The indicator is for the RC to AC connection correct?
2018-2-6
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bjr981s
Captain
Flight distance : 129528 ft
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Australia
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hmm I will chime in here is it appear that most people don't know how the connections for both Wifi And OTG work.

The Wifi and OTG connection works from the SmartDevice to the Transmitter. Neither go to the aircraft.

The Transmitter acts as the network gateway for all signal transmission.

OP you lost signal because you lost signal it had nothing to do with OTG it was a loss of signal from the Transmitter to the aircraft.

If you want to know more about how this operates read the Phantom 2 video transmission issues threads. You can read how the Transmitter is the WiFi gateway to the Aircraft.

It is the same as when you have an internet link at home. You can connect to the Modem / Gateway (RC Transmitter) by either a hard cable or Wifi. The aircraft is the Internet.   


2018-2-7
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Jezmo
Second Officer
United States
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bjr981s Posted at 2018-2-7 05:21
hmm I will chime in here is it appear that most people don't know how the connections for both Wifi And OTG work.

The Wifi and OTG connection works from the SmartDevice to the Transmitter. Neither go to the aircraft.

Your post brings up an interesting question. Why didn't the Spark return home when the controller disconnected. I thought after loss of signal from the RC it would automatically initiate RTH after 3 seconds.
2018-2-7
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bjr981s
Captain
Flight distance : 129528 ft
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Australia
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Jezmo Posted at 2018-2-7 13:27
Your post brings up an interesting question. Why didn't the Spark return home when the controller disconnected. I thought after loss of signal from the RC it would automatically initiate RTH after 3 seconds.

Could  be a any number of reasons.

The first one that springs to mind is the issue most Failsafe radios systems appear not to work sometimes.

The Failsafe has 3 seconds. If the signal is intermittent. i.e. gets one clear frame through every  2 seconds. The failsafe will never activate.

You need to switch off your TX to activate failsafe in this scenario. Or manually select the failsafe RTH command.

Bad compass is another in that it will be confused and not be able to determine how to go home.

Remember that it is a 2 way transmission in that the controller talks to the aircraft and then the aircraft responds to the controller.

If you lose the aircraft to controller link. The aircraft still thinks it is OK. But the TX shows disconnected.

I don't know if DJI have implemented a bidirectional transport layer. I would doubt it.

I would think the first scenario is the most likely in that its an intermittent connection to the aircraft.

2018-2-8
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