Mavic pro crashed immediately after take off

[malcolmlinco]

I did "precision" take off and without any input drone started to drift away instead of climbing to 6m.
According to flight logs drone was facing north but I had placed it facing south. When you watch the embedded video then it seems that drone flew backwards but it was flying onward and when it became clear that it will crash the wall then I pulled right stick down to reverse the movement(as you can see from the video). IMU calibration was done 12h before the incident and compass 2h before. When I analysed flight txt log then I noticed that drone took off without problems but shortly had compass error that messed it up. I purchased the drone from DJI on 18.05.2018 and now I am wondering if this is something that could be covered by DJI warranty. As I understand then warranty for MC is 12 months?

The drone is messed up pretty hard. One of legs is broken, camera is broken, one of the forward looking sensor is broken and who knows what else.

So, should I submit a case to DJI?

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[FoxhallGH]

Sorry to hear about the crash ... If you were seeing a difference between the way the compass was pointing, and where the nose of the Mavic was 'actually' pointing, then that may indicate that you took off above something that affected the earth's magnetic field in that immediate location e.g. steel reinforcing rods in a concrete path ... What surface did you take off from??
Calibration of the compass doesn't help in that sort of scenario, as that's not what compass calibration is for - but a difference between the compass pointer direction and the actual aircraft heading (before lift-off), is a definite indication that your Mavic is in an unusual magnetic field.
Did you also wait for the RC Controller & 'voice' to tell you that the GPS positioning had updated before you did the precision take-off??

 

[sar104]

Sorry to hear about the crash ... If you were seeing a difference between the way the compass was pointing, and where the nose of the Mavic was 'actually' pointing, then that may indicate that you took off above something that affected the earth's magnetic field in that immediate location e.g. steel reinforcing rods in a concrete path ... What surface did you take off from??
Calibration of the compass doesn't help in that sort of scenario, as that's not what compass calibration is for - but a difference between the compass pointer direction and the actual aircraft heading (before lift-off), is a definite indication that your Mavic is in an unusual magnetic field.
Did you also wait for the RC Controller & 'voice' to tell you that the GPS positioning had updated before you did the precision take-off??

That's definitely the problem here - a 180° error in the initialized IMU yaw value will cause exactly that kind of motion.



As soon as the aircraft starts to move you see a significant discrepancy between the velocity derived from the IMU position and the velocity computed by the IMU from the accelerometers and rate gyros, which is an unambiguous indicator of magnetic interference at the takeoff point.

 

[conchman]

There wasn't a "magnetic interference" warning or "compass error" message, when you took off?

 

[sar104]

There wasn't a "magnetic interference" warning or "compass error" message, when you took off?

One or two, but by then probably too late for the OP to rescue the situation:

 

[FoxhallGH]

With the take-off point so close to that building, it's very possible that the building construction and foundations include metal reinforcing ...
I've just done a 'street-view' on the site as shown in post #5 above ...

Note the bl**dy great iron gate next to your take-off point! Also that building is probably constructed from steel beams with cladding ...
Not an ideal launch site really!

 

[malcolmlinco]

Did you also wait for the RC Controller & 'voice' to tell you that the GPS positioning had updated before you did the precision take-off??
Do you mean "the home point has been recorded"? Correct me if I'm wrong but you can't do precision take off without that?

Truth to be told, as you can see from sar104 post I took off from parking lot from top of a car. This can be considered as stupid move but I was relying Mavic's sensors. During my previous take off attempts I have several times encountered 'magnetic interference' and compass error and then adjusted the take off terrain for more suitable one until errors disappear. This time there were no errors/warnings while I was waiting(around 20 seconds?) for lock from at least 10 satellites. As there were no errors then I didn't pay any attention on how drone was facing on the mini map. I noticed the wrong rotation only when I started to analyze the logs.

So, the verdict is that I have no chance with DJI? I can't blame Mavic for not warning me about magnetic interference and this crash is all on me? If Mavic doesn't warn me before take off then how can I be sure that it is safe to take off ever?

 

[FoxhallGH]

Again - too late now - but for future reference, the Mavic can't warn you about magnetic interference like this ... When you do the magnetic calibration of the Mavic, all you are doing, is setting up the drone so it can compensate for the way that it, as an electronic device, alters the way that the earth's magnetic field 'flows' around it. So if you sit it down and start it up near to something that is more magnetic than the earth's natural field, and/or with lines of magnetic force going in some other direction, then the Mavic is simply going to take that field as its reference (i.e. it thinks that is the earth's mag' field). It's not until the Mavic rises up and gets away from that [erroneous] magnetic influence, that it suddenly discovers the 'correct' earth's magnetic field, but - since it has already set up the control orientation based on what it knew on the ground - the mag' reference is suddenly out of kilter with the controls. The Mavic tries to compensate, but its points of reference are all off - and instead of correcting itself, it pushes itself into something fatal! - as you found out ...

In a way - the Mavic did warn you but you didn't realise what the significance of the difference between the compass pointer and the aircraft heading actually meant.

 

[sar104]

Again - too late now - but for future reference, the Mavic can't warn you about magnetic interference like this ... When you do the magnetic calibration of the Mavic, all you are doing, is setting up the drone so it can compensate for the way that it, as an electronic device, alters the way that the earth's magnetic field 'flows' around it. So if you sit it down and start it up near to something that is more magnetic than the earth's natural field, and/or with lines of magnetic force going in some other direction, then the Mavic is simply going to take that field as its reference (i.e. it thinks that is the earth's mag' field). It's not until the Mavic rises up and gets away from that [erroneous] magnetic influence, that it suddenly discovers the 'correct' earth's magnetic field, but - since it has already set up the control orientation based on what it knew on the ground - the mag' reference is suddenly out of kilter with the controls. The Mavic tries to compensate, but its points of reference are all off - and instead of correcting itself, it pushes itself into something fatal! - as you found out ...

In a way - the Mavic did warn you but you didn't realise what the significance of the difference between the compass pointer and the aircraft heading actually meant.

It will report a compass error if the external field exceeds some pre-programmed thresholds but often that isn't the case and it really does just interpret it as the earth's magnetic field. As a result it initializes the IMU with an incorrect heading.

 

[Meta4]

So, the verdict is that I have no chance with DJI? I can't blame Mavic for not warning me about magnetic interference and this crash is all on me? If Mavic doesn't warn me before take off then how can I be sure that it is safe to take off ever?

Avoiding launching from steel or reinforced concrete surfaces would prevent 99% of this sort of incident.
It's just asking for trouble launching from somewhere like that.

 

[malcolmlinco]

I guess I will have to swallow this bitter pill and think through my next steps in drone world.

Thank you all for taking time and analysing this crash. Such a great community.

 

[crlmjohnson]

lots of concrete in that picture...where you took off. There is a little graphic indicator on the controller screen, that gives you visual of the direction that the aircraft is pointing as reference to the directions (north, south, west, east), I always check that also, especially whenever I am flying in a new location. especially surrounding concrete buildings and sidewalks. sometimes the controller will give audible warnings and sometimes not. but the little red icon on the graphical display will be jumping around especially if there is some type of interfere with the aircraft or controller. if this is happening, then do not take off from that location, move to another location.

 

[Deleted member 94307]

As soon as I saw the title I thought compass error. Happened to my neighbor on his back deck. He didn’t realize there are metal pipes all underneath. Before he even realized what was happening , the drone quickly drifted in the wind towards his family and then went into a neighbors house. Aside from props no drone damage.. same could not be said for neighbors siding.

He had seen me take off with my phantom but because of a fence didn’t see the part where I turned drone on and checked status and hovered and check out readings ... to him it looked like I just took off so he did the same..

You have to check everything over or crashes will happen. Just like a plane pilot, preflight check list.. check drone for issues , then after powering on at least look at the controller. Good idea to have you battery voltage on main screen. Then hover and check again... then go crazy but keeping height above all obstacles is always safer. Gives you time to react if error or malfunction occurs... just like planes and helicopters.

 

[malcolmlinco]

I can't help myself from wondering if I had slammed that 'pause' button on remote the moment when I noticed that something is not right, would it have made drone hover or it would have kept trying to adjust itself according to new compass readings?

 

[Meta4]

I can't help myself from wondering if I had slammed that 'pause' button on remote the moment when I noticed that something is not right, would it have made drone hover or it would have kept trying to adjust itself according to new compass readings?

No .. the problem was that the drone was unable to hover or follow your controls because it had been initialised within a magnetic field associated with the steel of your car.
Once it left that field, all bets were off.

 

[Egor]

I think you could ... just mix up the joysticks!!! I crash my Mavic Pro by mixing up the joysticks. It flew in the tree instead of climbing up

 

[Bigbird48]

anytime I'm with in 5 or 10 feet of my car I get a compass error. I have to shut the drone off move further away from my car and restart the drone then its fine. Never take off from the metal roof of a car.

 

[m chaussettes]

What a great thread. I had a similar thing happen last week (no unhappy ending) and now I know the cause. One of the first things you learn when getting your IFR license is how to cross-reference your instruments... using the other instruments to verify what you are seeing. So now I know how to cross-reference the compass and to stay away from the metal tool shed. BTW, my M2P logged the home point and as I was increasing the elevation it started to fly backward. I wonder what other indicators can be cross-referenced on the controller?

 

[BrucenYvette]

These three videos were incredibly helpful to my understanding of the delicate balance between “magnetic north”, those “Global Positioning Satellites” orbiting the earth, the compass, IMU, and navigation technologies on board my Mavic Pro.

I see tons of questions about “compass errors”, and many testimonies of crashes and losses of drones that point to a lack of understanding of this particular aspect of our Mavics.

#1: DJI Mavic - Explaining Compass Errors & GPS Issues - Part 1 Flight Mode Basics

#2: DJI Mavic - Explaining Compass Errors & GPS Issues - Part 2 Compass Error

#3: DJI Mavic - Explaining Compass Errors & GPS Issues - Part 3 GPS


It was not before I gained at least a basic understanding of the effects of environmental factors that interfere with these onboard technologies before I began to grow in my skills and confidence in managing an aircraft that has gone awry. I am no “rocket scientist”, and I know that I’m a very long way away from understanding the scientific hows and whys. But, I did finally get “smart-enough” to stop assuming that every bad incident that happens with my Mavic is NOT a DJI defect, but due to my own lack of knowledge and experience.

These 3 videos I think would be of value to every noobie that enters this hobby.

 

[Microwave89]

That dangerous off by 180 degrees situation, can it be reproduced if I haven't more than a manhole cover?
Should I add NdFeB magnets to the manhole cover?
Understandings are that the Mavic will once it got a small GPS error correct it in the wrong direction and thus make it larger.
That in turn will make the Mavic try correct it with increasing speed and thus make the error become even bigger.
I haven't thought about what the controls will do in that situation and whether they're going to be inverted.

I would really love to see this entire behavior myself and attempt to sort it out in time by switching to ATTI.
Has anyone been brave enough to reproduce this?
Are there other fly-away scenarios that should be experienced apart from strong wind in upper air and drifting with or without P-mode?