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Mavic Flyaway problems
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2wenty
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I dont even know what to do at this point. My Mavic had a fly away a night ago and I have a job I need to do in 5 days out of state. Not sure I want to spend anymore money on DJI and Im seriously doubting this can be resolved in such a short amount of time.
The detalis on the flyaway are, as soon as it lifted off it just took off out of control and ended up slamming itself into the side of a mountain hovering a few feet off the ground. Thank god this wasnt inside a customers house or on their property. The flight log showed it going 28 mph which is the fastest its ever gone by at least 6 mph.

I dont know what to do. I cant afford to get sued if this happends agian.

Customer service wasnt any help of course.

Also extra thanks to DJI for nothing having spell check work in here and for forcing me to upload an avatar.
2018-4-23
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hallmark007
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If you want other forum members to help you need to upload your flight logs to link below.

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

http://www.phantomhelp.com/LogViewer/Upload/
2018-4-23
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ghostrdr
First Officer
Flight distance : 1272723 ft
United States
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The one thing you're probably right about is that it won't be resolved in five days.
2018-4-23
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Suren
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Flight distance : 6839144 ft
South Africa
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Follow advise given by Hallmark and upload the flight log.
2018-4-23
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2wenty
lvl.2
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Thank you. Heres the log.

http://www.phantomhelp.com/LogViewer/S7NRP0VDOIHHOQG49F4V/
2018-4-23
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2wenty
lvl.2
Flight distance : 72316 ft
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Just bought a new Mavic. Seriously not happy since Im forced to dump $900 on something that isn't my mistake. This job has my hands tied. Also the drone was purchased Jan 17th 2017. Guessing DJI is gonna say it doesn't matter since the drone is out of warranty.
2018-4-23
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2wenty
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Still want DJI to fix the broken one though.
Also flight log on my phone shows no input on the sticks.
2018-4-23
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Bob Brown
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Dang! Sure are alot of those Compass Error right after lift off. now that's freaking crazy!
~ Sorry man I know you were screaming NO NO NO NO NO NO and bouncing around all crazy trying to stop it. At least we know it was not a pilot error thing... but maybe not a DJI issue either?

My best and only guess is that there is maybe some weird magnetic field there for some reason; perhaps lots of metal in those rocks that hate DJI drones and made the drone's magnetic compass get confused; it could not tell where it was and where it was heading. (I do think DJI should find a solution to this... like SHUT OFF THE COMPASS ON CATASTROPHIC ERROR?)

Metal rocks? Maybe you can test the theory? >> How does a normal compass respond to that area? Maybe bring one along and test and see if you can catch true north. If the needle bounces around in that area... then walla! the reason.
2018-4-23
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davidmartingraf
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I would talk to DJI
2018-4-23
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2wenty
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Flight distance : 72316 ft
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I really wish there was a way to avoid this. It should of just hovered in place. It had GPS lock. I tired to press RTH to see if it would stop it but didn't do anything. I just keep thinking if I flew it where people were and it slammed into someones face at 33mph my life would be done.
2018-4-23
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G_Sig
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2wenty Posted at 2018-4-23 15:20
Still want DJI to fix the broken one though.
Also flight log on my phone shows no input on the sticks.

How far away was your car when you took off?
2018-4-23
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2wenty
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I mean the thing just accelerated full bore without any input from the controls. I called them on the phone and said to mail it in. Im just really frustrated because I had to buy another one because of something that didn't have to do with me. Even if they fix this Ill now have 2 which I was forced to buy so I don't lose this job.  I know the new one is around the corner too. Also super sketched to fly it now, especially around people.
2018-4-23
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2wenty
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G_Sig Posted at 2018-4-23 16:01
How far away was your car when you took off?

Like 5-6 feet away. Ive done this a lot and never had a problem. Still the thing shouldn't just accelerate out of control.
2018-4-23
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G_Sig
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2wenty Posted at 2018-4-23 16:06
Like 5-6 feet away. Ive done this a lot and never had a problem. Still the thing shouldn't just accelerate out of control.

I have seen this on P3 because of bad compass and IMU which was off.
I have been flying a lot inside last two months and there has not been anything other than iron around
and take off from reinforced conecrete and newer had any compass error.
2018-4-23
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hallmark007
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The best way I can explain this is. If you put your Aircraft on the ground in normal circumstances, start it up, then lift it up and turn it 90 degrees to the right your compass heading and IMU will remain at 0.
If you put your Aircraft on the ground and there is magnetic interference only the heading of your compass will change, your aircraft will still take off. But when it clears magnetic interference compass will then move to correct heading which may have happened, but it is likely that you would have then had problems with IMU exceptional heading your Aircraft would have gone to Atti mode, but your aircraft just took off in what is known as TBE the toilet bowl effect.
It is extremely difficult to control, correct action was to pull 100% on left stick until aircraft hit the ground.
You can see in your log you moving right stick to try to bring Aircraft back to you I presume, but these stick movements were short and not effective.
You can also see towards end of your log you pulling down on throttle to lower aircraft but again these movements although you can see in your log aircraft reduce altitude again were to short.
I am not criticizing the way you handled the situation, I’m just explaining what happened.

Lastly looking at the location you launched from, it’s pretty clear that it’s some kind of lay by and in order to get there you most likely had a car with you, if launched within 10/15 metres of your car this could well have caused your compass problems.

I read all the time of users starting their aircraft on top inside and beside their car, this kind of launch can be fraught with problems.

I presume you have started your case with dji, I’m not sure how it will work out for you, but fingers crossed you will have a happy outcome.
Good Luck

This might help in the future.

https://forum.dji.com/forum.php? ... &fromuid=260008
2018-4-24
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hallmark007
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Bob Brown Posted at 2018-4-23 15:40
Dang! Sure are alot of those Compass Error right after lift off. now that's freaking crazy!
~ Sorry man I know you were screaming NO NO NO NO NO NO and bouncing around all crazy trying to stop it. At least we know it was not a pilot error thing... but maybe not a DJI issue either?

Why is compass error not pilot error, surely if pilot does not check compass or launch ground before he flies, he has some responsibility.
2018-4-24
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2wenty
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hallmark007 Posted at 2018-4-24 01:57
The best way I can explain this is. If you put your Aircraft on the ground in normal circumstances, start it up, then lift it up and turn it 90 degrees to the right both your compass heading and IMU will both move together 90 degrees and no problems.
If you put your Aircraft on the ground and there is magnetic interference only the heading of your compass will change, your aircraft will still take off. But when it clears magnetic interference compass will then move to correct heading which may have happened, but it is likely that you would have then had problems with IMU exceptional heading your Aircraft would have gone to Atti mode, but your aircraft just took off in what is known as TBE the toilet bowl effect.
It is extremely difficult to control, correct action was to pull 100% on left stick until aircraft hit the ground.

The reason for stick inputs being short is this was at night and when it tool off it went over where the cliff was. The part where it leaves the roads is a straight drop off. I was worried it was going to be lost. I initially tried to correct and nothing happened. Hit RTH and nothing. So I started running after it so see where it was going to go. I knew it was going to crash since I didn't have control and my only objective was to at least recover it, so I pulled back on the the right stick, which for me makes it go up (my controls are inverted). It lifted just high enough to get back to the road height where it slammed itself into the side of the mountain. I mean if the compass error is so critical why doesn't it pop up on the screen. The thing has a wind warning for god sake. I would think the compass should be a little more important.
2018-4-24
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hallmark007
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2wenty Posted at 2018-4-24 03:36
The reason for stick inputs being short is this was at night and when it tool off it went over where the cliff was. The part where it leaves the roads is a straight drop off. I was worried it was going to be lost. I initially tried to correct and nothing happened. Hit RTH and nothing. So I started running after it so see where it was going to go. I knew it was going to crash since I didn't have control and my only objective was to at least recover it, so I pulled back on the the right stick, which for me makes it go up (my controls are inverted). It lifted just high enough to get back to the road height where it slammed itself into the side of the mountain. I mean if the compass error is so critical why doesn't it pop up on the screen. The thing has a wind warning for god sake. I would think the compass should be a little more important.

It will not always give you warning, this is why it is so important to check that compass is ok before taking off, you can do this by checking small red triangle in bottom left hand corner of your telemetry, it should be pointing on the same heading as your aircraft.

What happened to you is most likely that when you put your Aircraft on the ground and started up your compass received some magnetic interference causing it to change its heading resulting in taking off with bad compass.

We are told in our manual all the pitfalls regarding the envoirment we fly in and the need to be clear of all interference, I will leave link below that may help in the future with preflight checks, although it won’t help in this case it’s a worthwhile exercise to use when preparing to fly.
https://forum.dji.com/forum.php?mod=viewthread&tid=104222&fromuid=260008
2018-4-24
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2wenty
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hallmark007 Posted at 2018-4-24 03:49
It will not always give you warning, this is why it is so important to check that compass is ok before taking off, you can do this by checking small red triangle in bottom left hand corner of your telemetry, it should be pointing on the same heading as your aircraft.

What happened to you is most likely that when you put your Aircraft on the ground and started up your compass received some magnetic interference causing it to change its heading resulting in taking off with bad compass.

If you look though. There was no compass error when it was on the ground it happened right after it took off. So at what point am I supposed to avoid that? Also shouldn't it have fixed itself when it moved away at least. It traveled fairly far.
2018-4-24
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hallmark007
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2wenty Posted at 2018-4-24 03:54
If you look though. There was no compass error when it was on the ground it happened right after it took off. So at what point am I supposed to avoid that? Also shouldn't it have fixed itself when it moved away at least. It traveled fairly far.

Well first you should be clear of all magnetic interference, you said you were 5/6 feet from your car, this is not good and is most likely the cause of magnetic interference, you should always check that compass is on correct heading before taking off.

You will not always get compass warning, in the case of those who for instance who start craft away from interference and then bring or put aircraft on the ground where it can pick up interference , you will not get compass warning.
2018-4-24
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2wenty
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hallmark007 Posted at 2018-4-24 04:05
Well first you should be clear of all magnetic interference, you said you were 5/6 feet from your car, this is not good and is most likely the cause of magnetic interference, you should always check that compass is on correct heading before taking off.

You will not always get compass warning, in the case of those who for instance who start craft away from interference and then bring or put aircraft on the ground where it can pick up interference , you will not get compass warning.

Im also curious why it would just take off on its own. There was no input for it to go in any direction. I only lifted it. It headed in a direction in full force on its own. Seems like a s h itty design flaw to me and very dangerous. Even if I wanted to correct the error it doesn't even seem like there is a way to do it.  
2018-4-24
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hallmark007
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2wenty Posted at 2018-4-24 04:11
Im also curious why it would just take off on its own. There was no input for it to go in any direction. I only lifted it. It headed in a direction in full force on its own. Seems like a s h itty design flaw to me and very dangerous. Even if I wanted to correct the error it doesn't even seem like there is a way to do it.

Simply put compass problem, compass heading and IMU must be the same and if they are not you get this problem with aircraft taking off in this circular motion, your gps count was also on the weak side at 10.
2018-4-24
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Suren
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South Africa
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With all those compass errors from take off it should have been screaming at you on the app.
2018-4-24
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hallmark007
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Suren Posted at 2018-4-24 10:30
With all those compass errors from take off it should have been screaming at you on the app.


That’s not how it works, that’s why it’s important to check compass before you start flying.


Compass error started at 5.9” ,it is possible that magnetic interference from car was picked up at this height.
2018-4-24
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QuadKid
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Flight distance : 482349 ft
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Sorry for your loss. Quote,  I have a job I need to do in 5 days out of state. I am assuming you live in the US. If you are flying commercially you should have a backup for any circumstance, I always presume the worst is going to happen.
2018-4-24
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rwynant V1
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Here's what I'm seeing......... ( not a professional by any means, but I do fly Pro jobs )

68% start.....3.9v/cell    First off that is NOT 68%    ( Always start your flight with fully charged batteries )

In LESS THAN 15 seconds your cell voltage dropped to 3.6v/ cell     In airplane ESCs that very near LOW VOLTAGE CUT OFF

IF,   you sat the Mavic down, got a few sats....then initiated manual take off BEFORE the IMU warmed up enough, then you might not have enough voltage to drive all systems on the AC

Keeping in mind the voltage per cell is basically near done for a 15 minute flight........

SO,  me being an avid motorcyclist, and waited years to ride the Crest due to being washed out, and that being one of the repaired areas.....the AMOUNT OF REBAR in the road surface and on the hillside
is UNBELIEVABLE.    That's going to be the source of most of your compass error.

That being said <-- I hate that .........   The bottom line is your battery was DONE when you took off.   BATTERY  BATTERY BATTERY

I hope what I see has helped.

Randy
2018-4-24
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2wenty
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rwynant V1 Posted at 2018-4-24 12:55
Here's what I'm seeing......... ( not a professional by any means, but I do fly Pro jobs )

68% start.....3.9v/cell    First off that is NOT 68%    ( Always start your flight with fully charged batteries )

I was only going straight up to take a photo. So the battery wasn't a big deal. Honestly if the thing fell out of the sky because the battery died id be fine with that. I have my warning set at 30% and it never went off. I can't imagine the battery is what caused it to fly itself into the mountain. There really needs to be a way for this to be avoided. There should be a switch or if you hold RTH that stops it from flying out of control. Its honestly a liability. Theres metal everywhere. I flow around cars even closer and never had a problem. What if you had a car that had an electronic gas pedal that just randomly floored itself if it got some sort of interference?
2018-4-25
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2wenty
lvl.2
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Also what a PITA to re setup the drone. Why isn't there an option to just use the profile I already have in the app. As good as DJI is, there a some major things lacking.
2018-4-25
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Captain Mal
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I think threads like this can be good learning tools for someone like me who is still pretty new to this.  Once you see something like this happen, what can you do to recover? In this case, if the compass was ok on the ground but somehow lost calibration in the air, what can you do when the drone seems to become self aware and wants to escape this Earth as fast as it can?
2018-4-25
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rwynant V1
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2wenty Posted at 2018-4-25 01:18
I was only going straight up to take a photo. So the battery wasn't a big deal. Honestly if the thing fell out of the sky because the battery died id be fine with that. I have my warning set at 30% and it never went off. I can't imagine the battery is what caused it to fly itself into the mountain. There really needs to be a way for this to be avoided. There should be a switch or if you hold RTH that stops it from flying out of control. Its honestly a liability. Theres metal everywhere. I flow around cars even closer and never had a problem. What if you had a car that had an electronic gas pedal that just randomly floored itself if it got some sort of interference?

Look,  I am truly sorry this happened to you,  but the reality is the software seemed to think you had a battery that was holding 68% down to 67%......when INFACT you were at 3.6v/cell which is closer to 10-12%....................... 12 seconds in the air and your load dropped available voltage to 3.6/cell

Basically you installed a dead battery.  

If you have seen any of the threads on the Interweb regarding auto landing in water......taking off and flying for 5 min then hitting WARNING LOW VOLTAGE when you "thought" you put in a fresh pack, and the quad just lands.

In your case,  your quad may have attempted to fly to a RTH altitude, yes all by itself due to it thinking it needed to GO HOME....but with the limited voltage available it squewed off in a partial circle.........please know your battery cells should be starting out at 4.0 to 4.15v under load....( fully charged )..........not 3.9, then dropping to 3.6 under load in less than 15sec.

I have had this percentage/ low voltage warning on my Inspire and actually tested it......it is a known issue with some of these DJI aircraft.   I have not experienced this with my P4 Pro.

BTW,  the BATTERY is always THEE Big Deal,  Always!!

Good luck
Randy
2018-4-25
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2wenty
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rwynant V1 Posted at 2018-4-25 08:19
Look,  I am truly sorry this happened to you,  but the reality is the software seemed to think you had a battery that was holding 68% down to 67%......when INFACT you were at 3.6v/cell which is closer to 10-12%....................... 12 seconds in the air and your load dropped available voltage to 3.6/cell

Basically you installed a dead battery.  

Im confused so are you saying the compass issue is because the battery is bad? The battery had 3 solid lights. So Im not exactly sure how this was an issue. It sounds more like a problem with DJI if anything. The controller told me a percentage over 50% if I remember correctly. The exact same battery hasn't been charged since the crash and still has 2 solid lights with the 3rd blinking. Im just not going to waste my time or money putting a fully charged battery in every time I take off.
2018-4-25
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hallmark007
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rwynant V1 Posted at 2018-4-25 08:19
Look,  I am truly sorry this happened to you,  but the reality is the software seemed to think you had a battery that was holding 68% down to 67%......when INFACT you were at 3.6v/cell which is closer to 10-12%....................... 12 seconds in the air and your load dropped available voltage to 3.6/cell

Basically you installed a dead battery.  

Don’t think your right or in anyway close to right regarding what happened here.

1/ “Aircraft could be initiating RTH” Aircraft was within 20 metres of homepoint it would just land
2/ aircraft battery shows more likely that is was going into hibernation or reducing power cycle, so it’s most likely that opening power values were not correct. Try a battery that has been left for a period of time while in reducing cycle, it may start showing 100% but will drop power very quickly, it is not the same as a freshly charged battery, so this is most likely the explanation for battery drop.
3/ to try and ignore the fact that this was clearly a problem with compass is ludicrous in the face of what can be seen in logs, low battery power 3.6 is nowhere near only 15% , the sudden change in speed and we don’t know what temp battery was could also have caused this sudden drop, you need to go away and check this, it would also show in red in flight log if this was the case.

4/ “it’s always the battery” again where is the proof for this statement. Batteries and having them charged before flying are the responsibility of the controller/Pilot.
“It is a known issue with some dji aircraft” again more ridiculous statements what aircrafts are you talking about and which aircrafts are still having problems with batteries.

It might be wiser to stick to what is in the logs here, instead of trying to put your own spin on something that clearly didn’t happen.
If your answer to everything that goes wrong with drones is the battery, you may need to think that one again.
2018-4-25
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A CW
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hallmark007 Posted at 2018-4-25 10:11
Don’t think your right or in anyway close to right regarding what happened here.

1/ “Aircraft could be initiating RTH” Aircraft was within 20 metres of homepoint it would just land

Totally agree Hallmark.

I'd also add that flying at night (as in this case) massively impacts on the VPS - the drone lost VPS 5 seconds into the flight as couldn't see/detect the ground so OPTI was ineffective too. Adding that to a compass failure upon take off due to not checking the compass reading and taking off next to a car and you're set for a fly away. Also, the home point was set after take off and I believe the recommendation is to wait for 11 sats to be received as a minimum for a true GPS/GLONASS lock - not 10 (reducing in number) as in this case.

OP - I'm sorry you experienced this but there was clearly room for better planning to help prevent this on your part. If you are getting a new one then it's best to follow a more thorough pre flight check list in future. Especially flying at night.

>Check the compass and IMU readings before take off
>Change location/don't take off if the compass is in the red. Calibrate at a new location, away from large metal objects (like cars) to ensure little interference.
>Wait for a home point to set on the map before even arming the motors
>Be prepared for obstacle avoidance and downward vision sensors not to operate effectively in low light - making GPS even more vital
>Wait for at least 11 satellites to be recorded and 3 or 4 bars on the satellite signal graph in the app
>For further safety, I recommend only taking off with a fully charged battery too. Check the cell deviations as part of your checks - cell 3 was inconsistent.

Had you have done the above I'm fairly confident you would still have your drone now. Turn around for DJI repair is usually 2-4 weeks. Fly aways are generally not covered under warranty.
2018-4-25
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rwynant V1
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hallmark007 Posted at 2018-4-25 10:11
Don’t think your right or in anyway close to right regarding what happened here.

1/ “Aircraft could be initiating RTH” Aircraft was within 20 metres of homepoint it would just land

Hallmark,  please see replies below:  RW-

Don’t think your right or in anyway close to right regarding what happened here.
RW-  we all have opinions regarding what we SEE in his flight log

1/ “Aircraft could be initiating RTH” Aircraft was within 20 metres of homepoint it would just land
RW- Not necessarily......I have 1st hand experience with my Inspire that had a physical battery failure
2.5 years after purchase....perfect charge, life = good, cells all good......directly over the home point at 10' the bird shot straight up with a LV warning due to one cell failure.....the battery swelled and became disconnected......the point being when the voltage dropped the bird did something unexpected.
2/ aircraft battery shows more likely that is was going into hibernation or reducing power cycle, so it’s most likely that opening power values were not correct. Try a battery that has been left for a period of time while in reducing cycle, it may start showing 100% but will drop power very quickly, it is not the same as a freshly charged battery, so this is most likely the explanation for battery drop.
RW- agreed.  but the reason for the system not SEEING and reporting low voltage, but instead showing 67% left in the battery......that is a know issue, and the cause of many very short flights when using a used uncharged battery.
3/ to try and ignore the fact that this was clearly a problem with compass is ludicrous in the face of what can be seen in logs, low battery power 3.6 is nowhere near only 15% , the sudden change in speed and we don’t know what temp battery was could also have caused this sudden drop, you need to go away and check this, it would also show in red in flight log if this was the case.
RW- the flight log WOULD have shown RED....IF the system was reporting correct PERCENTAGE, which it was not.  OP stated his 1st stage low voltage warning was set at 30%...alsoI did NOT ignore the compass....I stated I know that area was rebuilt and that the rebar in the ground was UNBELIEVABLE.....Maybe, just mabe that was a contributing factor.

4/ “it’s always the battery” again where is the proof for this statement. Batteries and having them charged before flying are the responsibility of the controller/Pilot.
“It is a known issue with some dji aircraft” again more ridiculous statements what aircrafts are you talking about and which aircrafts are still having problems with batteries.
RW- "its always the battery"      I was only discussing this situation. The battery for all these Drones/Quads/Hexacopters is what powers ALL the various systems and redundant systems on these aircraft.   Battery = fuel.....not enough fuel, and bad things happen.

It might be wiser to stick to what is in the logs here, instead of trying to put your own spin on something that clearly didn’t happen.
RW- Opinions are like........everyone has one
If your answer to everything that goes wrong with drones is the battery, you may need to think that one again.
RW- Go take a battery class,  they are online on the interweb.     I have 17 model aircraft ranging in power from 4s to 12s power.  All powered by LiPo batteries.  some are 2# and some are 15# wingspans from 40" to 78"........I would NEVER EVER put a battery in one of my planes that was showing less than 4v/cell....EVER.    So go out and learn something about LiPo batteries and the load they can take and still provide the needed voltage to run all systems.
2018-4-25
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rwynant V1
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Gentlemen,  Please also note,  since we have NOT done this yet....Mathmatics,  no OPINION HERE.

Fully charged battery = 12.6vdc

Recorded Battery voltage in the log  10.852vdc

That puts this quad in the air with  13.873% battery power   

Again,  2Wenty, I am sorry......If your quad is under a year old, contact DJI and find out why the system reported incorrect Battery power. Maybe they can help the situation.
2018-4-25
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rwynant V1
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"Don’t think your right or in anyway close to right regarding what happened here."

One more addition to this mystery......It appears his location, which also has not been addressed, is a few hundred feet from a TUNNEL.  Concrete and rebar.  The road has been rebuilt with rebar in and under it, in an attempt to hold that area together.   This may also be a major contributing factor in the compass failure.  Angeles Crest Highway was closed for years due to the rains and wash outs in the mid 2000s.

There are several contributing factors here.  It is entirely possible the battery had nothing to do with this,  or the rebar in the ground and near the take off point + car........but when you put all these points on the table.....we have an unhappy customer.  And a crashed aircraft.
2018-4-25
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HedgeTrimmer
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Bob Brown Posted at 2018-4-23 15:40
Dang! Sure are alot of those Compass Error right after lift off. now that's freaking crazy!
~ Sorry man I know you were screaming NO NO NO NO NO NO and bouncing around all crazy trying to stop it. At least we know it was not a pilot error thing... but maybe not a DJI issue either?

(I do think DJI should find a solution to this... like SHUT OFF THE COMPASS ON CATASTROPHIC ERROR?)

Not sure how DJI would compensate for Compass that goes awry after take off.  Other than system ignore compass changes that are too rapid.
Going with input from acceleromters for axis rotation vs. movement along axis.  
GPS won't help since it would not detect changes in orientation, only changes in location.
Being it was dark at time, optic sensors would be of no help either.  

2018-4-25
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HedgeTrimmer
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rwynant V1 Posted at 2018-4-25 19:01
"Don’t think your right or in anyway close to right regarding what happened here."

One more addition to this mystery......It appears his location, which also has not been addressed, is a few hundred feet from a TUNNEL.  Concrete and rebar.  The road has been rebuilt with rebar in and under it, in an attempt to hold that area together.   This may also be a major contributing factor in the compass failure.  Angeles Crest Highway was closed for years due to the rains and wash outs in the mid 2000s.

What does not make sense about compass is it was fine on the ground and fine until 6.1 seconds into flight and until reaching 5.9 feet off ground.  
Changes in magnetic field, moving away from ground, and into air one would expect opposite to happen.**  Doubtful that a person would miss a magnet floating in air about 6 feet off the ground.  
The parked car should have caused compass problems prior to take off and had most effect couple of feet before the 5.9 feet off ground.  If car was causing compass problem, it should have stopped as drone got away from car.

Still it would be worth taking a regular compass out to Angeles Crest Tunnels turnout area.  Parking same vehicle in same spot as before.
Then holding compass at drone launch point about 4-inches off ground.  Then slowly raising compass (need a step ladder) to see if compass starts spinning or alternating directions.  
Followed by repeating process by hand with drone powered up to see if compass goes crazy again.

**Magnetic field strength is general taken to be I = 1/d3.  d is distance and I is field strength.  Whether use I = 1/d2 or I = 1/d3 depends on whether we are talking monopole or dipole source.  Either  way magnetic field strength rapidly decreases with increase in  distance.

2018-4-25
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hallmark007
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HedgeTrimmer Posted at 2018-4-25 19:43
What does not make sense about compass is it was fine on the ground and fine until 6.1 seconds into flight and until reaching 5.9 feet off ground.  
Changes in magnetic field, moving away from ground, and into air one would expect opposite to happen.**  Doubtful that a person would miss a magnet floating in air about 6 feet off the ground.  
The parked car should have caused compass problems prior to take off and had most effect couple of feet before the 5.9 feet off ground.  If car was causing compass problem, it should have stopped as drone got away from car.

The best way I can explain this is. If you put your Aircraft on the ground in normal circumstances, start it up, then lift it up and turn it 90 degrees to the right both your compass heading and IMU will stay at 0.
If you put your Aircraft on the ground and there is magnetic interference only the heading of your compass will change, your aircraft will still take off. But when it clears magnetic interference compass will then move to correct heading which you would think was great. But No, what happens is IMU is then conflicted and confused because of this sudden movement by compass, so you receive IMU exceptional heading warning compass error yaw error etc, your aircraft cannot deal with data conflict so decides to switch to Atti mode dropping gps in favour of compass simply because aircraft can fly without gps but not compass.

Si it’s the magnetic interference that causes problem with compass and the compass puts IMU out of whack,

Calibration gives the compass the information it needs to determine which magnetic influences are part of the Mavic / MavAir and what is the earth's normal magnetic field.
The compass doesn't lose calibration and doesn't ever need re-calibration unless you add or remove equipment to/from the Mavic/MavAir  although we see more often MavAir needing calibration I believe this is due to over sensitized warnings given by MavAir.




2018-4-26
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HedgeTrimmer
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hallmark007 Posted at 2018-4-26 02:00
The best way I can explain this is. If you put your Aircraft on the ground in normal circumstances, start it up, then lift it up and turn it 90 degrees to the right both your compass heading and IMU will both move together 90 degrees and no problems.
If you put your Aircraft on the ground and there is magnetic interference only the heading of your compass will change, your aircraft will still take off. But when it clears magnetic interference compass will then move to correct heading which you would think was great. But No, what happens is IMU is then conflicted and confused because of this sudden movement by compass, so you receive IMU exceptional heading warning compass error yaw error etc, your aircraft cannot deal with data conflict so decides to switch to Atti mode dropping gps in favour of compass simply because aircraft can fly without gps but not compass.

But when it clears magnetic interference compass will then move to  correct heading which you would think was great. But No, what happens is  IMU is then conflicted and confused because of this sudden movement by  compass,

I can go along with first part.  But sudden compass change conflicting with output single axis (Yaw) of Inertia Measurement Unit, should be dealt with firmware of drone.  The drone should have slowly rotated left or right, then stopped rotating.

Instead the drone waits about 2.5 seconds, then suddenly takes off accelerating as if it is being commaned too.   In this case the drone stayed in P-GPS mode, at least according to log posted, and didn't switch to ATTI.  What was going on behind scences is unknown.  Perhaps drone did start flying as if it was in manual flight mode, without indicating as such.

Assuming drone's compass was confused by removal of magnatic interfence, which then conflicted with Yaw axis input of IMU, and GPS output being over-ridden to drone's aggregated navigation system, which resulted in motor controls for props changing in speed, causing the drone to accelerate out of control, then it is a safety issue that needs to be addressed by firmware.
2018-4-26
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