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Phantom 4 Pro RTH Problem
1199 31 2018-2-18
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Todd in Chicago
Second Officer
Flight distance : 513757 ft
United States
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Hello folks....

Relatively new Phantom 4 Pro pilot here, and had the drone out for I think my 3rd or 4th flight today (Sunday 2/18 in the US).  In Chicago, we finally got a break in the weather and UAVForecase gave me a "Good to Fly", so I took out the P4P to fly 2 batteries today.

On one particular flight I had flown out pretty far and was on my way back to the launch site when I encountered a series of disconnects.  I think it was just video, but I don't remember for sure.  In any event, considering where my battery was and the distance I needed to cover, I figured I would use the RTH function so even if I disconnected the aircraft would continue it's RTH function.  Well I was quite surprised when in my monitor, I saw the view spin around about 180 degrees from it's home path trajectory and start heading out!  Luckily I still had control was able to cancel the RTH.  I was pretty freaked out as RTH has never failed on any of my DJI drones, so I flipped it into Sport mode and hightailed it back manually.  The P4P had gone approximately 40 feet or so in the completely OPPOSITE direction of the homepoint before I was able to cancel the RTH.

I know I still have a lot to learn about the aircraft and also about reading the logs, but I don't seem to see anything in the logs which gives me an idea of what may have happened.

I'm really hoping somoene here can take a look at the logs and let me know what I'm missing.

You can see at the 14m 55s mark the status of Go Home.  The distance from the home point at that time is 2,357.  You can see that the distance climbs to 2,393 - about 36 feet before I stopped it.  You can see it goes back from Go Home to P-GPS and then you can see I flip it into Sport mode and bring it quickly back.

http://www.phantomhelp.com/LogViewer/PZZWLS7HKASMKHR857G0/

Anyone have any thoughts on this (other than I shouldn't have flown it that far to begin with)?

I'm not really seeing any errors.  You can see that the home point was updated 3 seconds after takeoff, and based on my flight record the home point was correct.  I was able to land with 29% battery, but I had a bad feeling when it started going the other way.

Thoughts?

Thx..

Todd in Chicago

2018-2-18
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Timinator
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Flight distance : 212359 ft
Canada
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What were the winds aloft like?  It looks to me like it just didn't have the horses to get home until you kicked it into sport mode. I always make a point to fly into the wind so that if I lose the signal and trigger RTH, it will get home.
2018-2-18
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Timinator
lvl.4
Flight distance : 212359 ft
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PS, nice move on recognizing you were in trouble and hitting sport mode! Had you not done that it could have been a "Lost my drone today when RTH kicked in" kind of post.
2018-2-18
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Bashy
Captain
Flight distance : 549140 ft
United Kingdom
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Does it not normally show the Home Point on the map? i cannot find it, i can see it in the table but not on the map?
Looking at your top speed on sports mode,  strong winds at 75m?
2018-2-18
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Todd in Chicago
Second Officer
Flight distance : 513757 ft
United States
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Timinator Posted at 2018-2-18 17:56
What were the winds aloft like?  It looks to me like it just didn't have the horses to get home until you kicked it into sport mode. I always make a point to fly into the wind so that if I lose the signal and trigger RTH, it will get home.

Thx Timinator.....

I think I was coming back at a nice cruising speed of between 10 and 15 mph hour until I hit some disconnects.

But, keep in mind, I actually observed the aircraft turning around and heading the opposite direction.  If you might be thinking the wind was too strong for it, it would simply be blown backwards, but this was not the case.  It actually performed a 180 degree turn and started flying in the opposite direction of the home point.

And thx on thx on the kudos.  Once I saw it heading the wrong way I immediately went into "save the aircraft" mode.  ;-)

Cheers...

Todd in Chicago
2018-2-18
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Geebax
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Todd in Chicago Posted at 2018-2-18 21:26
Thx Timinator.....

I think I was coming back at a nice cruising speed of between 10 and 15 mph hour until I hit some disconnects.

You are correct, if it was simply strong wind, it would not have turned around. My guess is that the home point was somehow set to a location far away from where you were, this does happen from time to time. I don't know if the flight record contains the home point that is set at the beginning of the flight, but it would be good to be able to see it.
2018-2-18
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Todd in Chicago
Second Officer
Flight distance : 513757 ft
United States
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Bashy Posted at 2018-2-18 21:05
Does it not normally show the Home Point on the map? i cannot find it, i can see it in the table but not on the map?
Looking at your top speed on sports mode,  strong winds at 75m?

Hi Bashy...

Yes, you should see the homepoint on the map.  And you can see it afterwords in the flight records as well.

Yes, I'm sure the winds were strong (I've flown in much worse), even though UAVForecast gave me the go ahead.  When flying around close by, I did not see the P4P struggle at all.

As I mentioned to the Timinator, don't forget, the aircraft wasn't blown backward, it actually made a 180 degree turn to point in the opposite direction away from home and started in that direction.

That is what is puzzling me.

Cheers...

Todd in Chicago.
2018-2-18
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Bashy
Captain
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Ah, dont mind me, just found it, i didnt zoom in far enough lol
2018-2-18
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Jenee 2
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Australia
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Todd in Chicago Posted at 2018-2-18 21:32
Hi Bashy...

Yes, you should see the homepoint on the map.  And you can see it afterwords in the flight records as well.

The only thing I can see in the flight record is that several GPS Mismatch errors occurred before the RTH. I can't be certain but I wonder if this caused it to lose its home location.
2018-2-18
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tompahr
Second Officer
Flight distance : 1653848 ft
Croatia
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I do not think he lost his Home position, he lost his position! GPS on your dron might be problematic, at the moment of activation RTH he thought it was southeast of Home position and headed northwest! On the other hand Home distance seems correct! Very strange! Anyway, you've reacted perfectly and switched to sports mode! Thank you for sharing the log because it shows how to react and what we can expect if "GPS Position NoMatch" appears.
2018-2-18
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tompahr
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Try to open a log from Phantom, located on the SD card in Phantom (.dat). It's harder to read but write a lot more parameters!
2018-2-18
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Todd in Chicago
Second Officer
Flight distance : 513757 ft
United States
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Jenee 2 Posted at 2018-2-18 22:17
The only thing I can see in the flight record is that several GPS Mismatch errors occurred before the RTH. I can't be certain but I wonder if this caused it to lose its home location.

Yes!

I forgot to mention that, never saw those GPS mismatch errors in a log before.  Does anyone know if there is a resource which identified errors in the logs and explains them better?

If not, maybe we can start a sticky post and add to as folks find more errors and full length descriptions.

I wonder if I should open a case with DJI to see if they can figure out what happened.

Tompahr......what do you open the DAT file with?

Thx...

Todd
2018-2-19
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tompahr
Second Officer
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.dat file is stored on the internal memory on your AC (not on SD card like I mentioned before-sorry). When you connect yor AC and computer with USB cable, open Assistan 2 software and then you can download and read .dat file. .dat reader is part of Assistant 2 software. This file contain more flight parameters but it is not user friendly like LogViewer.
Tom.
2018-2-19
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Todd in Chicago
Second Officer
Flight distance : 513757 ft
United States
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Tompahr....

Thx.... I'm friend downloading DAT file this evening and taking a look.  I think the problem is in the GPS no match error unfortunately just don't know what that means.

Cheers....

Todd in Chicago
2018-2-19
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Nigel_
Captain
Flight distance : 388642 ft
United Kingdom
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I think you lost the communications so it set off retracing its route to try to regain communications, you then pressed RTH which had no effect since it never received the message, then you regained the signal and saw it heading back the way it had come, which was not what you expected.   Pressing RTH at that point would probably have brought it back, or if it hadn't regained the signal then it would have changed its mind and set off back home at RTH altitude (although it was already higher).

The RTH location was correctly set to the point you were standing and the wind did not seem to be an issue.  There is some missing log data where communications were lost.
2018-2-19
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Todd in Chicago
Second Officer
Flight distance : 513757 ft
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Geebax Posted at 2018-2-18 21:31
You are correct, if it was simply strong wind, it would not have turned around. My guess is that the home point was somehow set to a location far away from where you were, this does happen from time to time. I don't know if the flight record contains the home point that is set at the beginning of the flight, but it would be good to be able to see it.

Geebax...

That is sure what it seemed like...like somehow the it thought the homepoint was set somewhere else.  

And to answer your question, Yes, the logs from PhantomHelp do show the homepoint updated in the correct location at the beginning of my flight, which coincides with my flight record on my device.  There are no additional updates on the flight record on my device or from Phantom Help which provide any data that the homepoint was set to something else.  So I'll keep digging.

Cheers...

Todd in Chicago
2018-2-19
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Todd in Chicago
Second Officer
Flight distance : 513757 ft
United States
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Folks...

Here is a quick vid of when the RTH kicked in and the P4P turned around and went in the wrong direction.

At 29 seconds in, you'll the P4P stop, I think that is the first time I lost my connection, and then again at 55 seconds.  Around 1:24 you'll see the RTH function kick in and spin the drone around about 180 degrees.



Cheers...

Todd in Chicago
2018-2-19
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Geebax
Captain
Australia
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Todd in Chicago Posted at 2018-2-19 19:37
Folks...

Here is a quick vid of when the RTH kicked in and the P4P turned around and went in the wrong direction.

Yes, pretty much as you described it.
2018-2-19
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Bashy
Captain
Flight distance : 549140 ft
United Kingdom
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Could the Smart RTH have some bearing on this?
2018-2-19
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djiuser_iGJqCoTNTQSa
Second Officer
United States
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I've this happen once before, I immediately hit cancel when I saw it 180 to the wrong direction. Not sure why it does this, but I didn't have any issues after that.
Did you take off from concrete?
2018-2-19
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Nigel_
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Bashy Posted at 2018-2-19 20:23
Could the Smart RTH have some bearing on this?


Like I said above, there is an 11.1 second gap in the log file due to loss of communication, the next record shows that it has already entered GoHome mode and has decided to retrace its route to get out of the shadow of whatever obstacle is blocking reception and thus regain the signal before actually going home.  This is why it turns to face backwards (to where it has come from).  We don't actually see it retracing its path because the GoHome is cancelled by the pilot almost immediately it starts to accelerate.

Not sure if this counts as Smart RTH, since it was still trying to require the signal, not really in RTH mode, the original Smart RTH features are for when it is actually heading back home.
2018-2-20
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Bashy
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HI Nigel, There was some brightness, is there a chance that the smart rth thought there was an obstacle because of sunlight hitting the sensors? just a thought is all, just chucking it out there lol
2018-2-20
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Nigel_
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Bashy Posted at 2018-2-20 02:54
HI Nigel, There was some brightness, is there a chance that the smart rth thought there was an obstacle because of sunlight hitting the sensors? just a thought is all, just chucking it out there lol

I think if there was an obstacle then it would reverse a little while keeping its eyes on the obstacle, then rise above the obstacle, then continue.  It would not turn around and fly back the way it came.

Flying back the way it came is the expected behaviour on loosing contact with the controller, if it had not turned around and headed away from the home point then there would have been something wrong, what it did was correct.
2018-2-20
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iFoxRomeo
First Officer
Flight distance : 1011916 ft
Germany
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It was smart RTH. Todd activated RTH while still under control. Smart RTH initiated (unless it was intentionally deactivated in battery settings).
Check RTH function on https://store.dji.com/guides/how-to-use-the-djis-return-to-home/


Fox
2018-2-20
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Nigel_
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iFoxRomeo Posted at 2018-2-20 03:42
It was smart RTH. Todd activated RTH while still under control. Smart RTH initiated (unless it was intentionally deactivated in battery settings).
Check RTH function on https://store.dji.com/guides/how-to-use-the-djis-return-to-home/


Presumably you are guessing, because the only time that "Go Home" mode appears in the log file, it starts on the same line that has the message "Downlink Restored (after 0m 11.1s)", so RTH could not have been activated while still under control, it must have been activated while the downlink was down.  Also, the only time that the aircraft will fly away from the registered home point while in "Go Home" mode is while it is attempting to reacquire communications after a loss of signal, it does this automatically and can't be activated by the remote control other than by turning the remote control off.

Edit: That does say "then the drone will retrace its flight path for 30 seconds before it starts to ascend and fly straight back to you." under the user triggered RTH.  Does the P4P actually do that, or have they put it in the wrong section?  I know it does it on loss of signal for all P4, even though it isn't mentioned.  I would be surprised if it did it when user triggered because it would not be what you were expecting and may lead to a crash if things have moved!
2018-2-20
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iFoxRomeo
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Nigel, I quote Todd:
"...I figured I would use the RTH function so even if I disconnected the aircraft would continue it's RTH function.  Well I was quite surprised when in my monitor, I saw the view spin around about 180 degrees from it's home path trajectory and start heading out!  Luckily I still had control was able to cancel the RTH..."


He was under control, he started RTH, so smart RTH is supposed to kick in and perform the manouver it actually did.


Fox
2018-2-20
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Todd in Chicago
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djiuser_iGJqCoTNTQSa Posted at 2018-2-19 22:04
I've this happen once before, I immediately hit cancel when I saw it 180 to the wrong direction. Not sure why it does this, but I didn't have any issues after that.
Did you take off from concrete?

Hi there....

I did not take off from concrete, but rather a snow covered grassy field.

Cheers...

Todd in Chicago
2018-2-20
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Todd in Chicago
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Nigel_ Posted at 2018-2-20 01:31
Like I said above, there is an 11.1 second gap in the log file due to loss of communication, the next record shows that it has already entered GoHome mode and has decided to retrace its route to get out of the shadow of whatever obstacle is blocking reception and thus regain the signal before actually going home.  This is why it turns to face backwards (to where it has come from).  We don't actually see it retracing its path because the GoHome is cancelled by the pilot almost immediately it starts to accelerate.

Not sure if this counts as Smart RTH, since it was still trying to require the signal, not really in RTH mode, the original Smart RTH features are for when it is actually heading back home.

Hmmm....

Very interesting.

I wish the flight logs provided that data.  However, I did not get a chance to do the DAT file last night, but will tonight for sure.  Maybe SMART RTH data is in there.

Cheers...

Todd in Chicago
2018-2-20
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Todd in Chicago
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iFoxRomeo Posted at 2018-2-20 03:42
It was smart RTH. Todd activated RTH while still under control. Smart RTH initiated (unless it was intentionally deactivated in battery settings).
Check RTH function on https://store.dji.com/guides/how-to-use-the-djis-return-to-home/

Thx Fox...

I will check this in my settings this evening as well as looking in the DAT file for SMART RTH data.

Cheers...

Todd in Chicago
2018-2-20
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Nigel_
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I think the aircraft log should say if it received an RTH request in the comments, but I doubt that it did since there was no link at the time and it should have turned around given the 11 second loss of contact.  It was only just getting around to setting off back when you regained the link, hence you seeing it turn.  I think when it regained the link it would have cancelled its RTH itself rather than come home since it regained the link within the 30 seconds.
2018-2-20
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Todd in Chicago
Second Officer
Flight distance : 513757 ft
United States
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Folks...

I was able to download all of my DAT files from the aircraft, and open them in the viewer, but that is not an easy program to use, and I was not really able to learn anything from that.  Also, all that data appears to be numerical in nature meaning values that are changing vs. error messages or conditions.  I'll try again tomorrow but tonight was not really able to make any progress with understanding the DAT files, so nothing happening on that front yet.

When my patience wore down there, I went back to studying the downloaded CSV file from PhantomHelp.

Overall throughout my flight I had very decent satellite coverage with about 14-18 satellites.

One thing I noticed was that I never had any "drops" until I was coming home.  I was literally out to 5,000 feet with no drops.  When I decided to come home, that is when the trouble started.  Even though I was pretty high, about 240 feet or so and only 2,500 feet from home, that is when I started to have the disconnects for who knows what reason (these things happen). Just an interesting note.

At 9m 38.9 seconds I received my first series (4 in a row) of mysterious GPS Position NoMatch messages, which Google doesn't seem to know the answer about.  From what I've been able to gather, DJI has not provided the answer for what this message is, nor does it appear on screen when it occurs, it is simply noted in the log files.

At 9m 41.9 seconds I received my second series (3 in a row) of GPS Position NoMatch messages.

10m 20.9 seconds next series (5 in a row) NoMatch messages.

10m 40.9 seconds next series (5 in a row) NoMatch messages.

I received my final series of NoMatch messages for this flight at 10m 52.9 seconds (4 in a row)

See a pattern there?  ;-)

Since all of these messages were received at a xMins xx.9 seconds, this is probably some cyclical timing thing.  Weird, but probably makes sense as I'm guessing GPS is all about timing.

About a minute and a half later I reached my furthest distance of 5,054.10 feet at 12m 5.4 seconds and begin flying back.

I'm coming back at a speed of about 16-17mph.

About almost 2 mins later at 13m 57.7 seconds I lose connection for almost 4 seconds.  I have reduced the distance from my furthest point to my home point to 2,877.8 feet.

About 1 minute 9 seconds later I lose connection again, this time for about 2.5 seconds at 14m 6s.

18 seconds later I lose connection again for 2.3 seconds at 14m 24 seconds.

5 seconds later I lose connection again for 2.2 seconds 14m 29.5 seconds.

About 15 seconds later I lose my connection for the last time, but this time for 11 seconds at 14m 44.7.

The very next entry, which is when the downlink is restored, the flight mode is showing Go Home.  It does not say if that was requested by me or if the aircraft itself initiated the RTH.  At this point my RTH distance has been reduced to 2,358 feet.

At 15m 1.3 seconds the Phantom has turned around and is starting to fly in the opposite direction and makes it as far as 2,393.7 feet which is 36 feet from where it turned around.  I had cancelled the RTH function as I saw that it was flying in the opposite direction, but the logs do not seem to show the cancellation command.

At 15 10.7 seconds P4P is out of RTH mode and back in GPS mode.
At 15 17.3 seconds I switch into Sport mode and try to get back as fast as I can.

Logs show another series of 5 in a row of the NoMatch errors, again on the .9 (16m 10.9 seconds)

At 17m 9.4 seconds I'm back home....roughly 2 minutes after the P4P had started going in the wrong direction.

Whew.

Ok....so I'll do some testing to see what happens if the P4P loses connection to the controller.  Does anyone know if it starts to backtrack, does it actually turn around?  It would seem to me that it would just fly backwards...?

If anyone knows how I can coax the RTH data from the DAT file or can point me to where I can learn to do that, I've to take a whack at it.

Cheers...

Todd in Chicago
2018-2-20
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Nigel_
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Flight distance : 388642 ft
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Todd in Chicago Posted at 2018-2-20 22:35
Folks...

I was able to download all of my DAT files from the aircraft, and open them in the viewer, but that is not an easy program to use, and I was not really able to learn anything from that.  Also, all that data appears to be numerical in nature meaning values that are changing vs. error messages or conditions.  I'll try again tomorrow but tonight was not really able to make any progress with understanding the DAT files, so nothing happening on that front yet.


"Ok....so I'll do some testing to see what happens if the P4P loses connection to the controller.  Does anyone know if it starts to backtrack, does it actually turn around?  It would seem to me that it would just fly backwards...?"

It needs to see where it is going for obstacle avoidance, yes it will turn around while backtracking.  Not all phantoms have eyes on the back of their heads like yours does!

Note that when loosing signal, it doesn't backtrack immediately, it will slow down and wait a while before backtracking and having decided to backtrack it will take a while to get going, if signal returns it will take a while to stop again since a poor signal is likely to come and go, the signal has to be continuous over several seconds for it to decide it is good and then cancel a backtrack.  Your signal came back while it was in the middle of turning around.

I wouldn't be surprised if there was a powerful wifi transmitter nearby that might have been causing communications issues.   What is that big tower down on the beach for?   Ignore the GPS warnings, they are not unusual and will not have been the cause of your issue.
2018-2-21
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