Crash during auto take-off

[lengthlord]

That both the takeoff locations that you used would have significant magnetic distortion.

What seems more likely?

1. The AC shipped with a faulty compass. This fault didn't affect the firsts couple of flights but caused the 2 crashes.
2. The iron ore in the soil and possible rebar in the picnic table caused significant magnetic distortion, which caused the 2 crashes. The compass was damaged by the crashes.

Is compass damage the type of damage typically sustained in a crash?

I'd like to add that I was able to calibrate the compass in a field today. It took a very long time and only worked when moving the AC in an orientation different to that displayed in the DJI Go 4 app. After calibratation I saw an intermittent Compass Error message in the DJI Go 4 app.

 

[lengthlord]

If you are able to test in the same area; go back to the picnic table,turn on the Mavic, note that the direction Go 4 shows it is pointing is accurate, then pick the Mavic up away from the table and see if the indicated direction remains accurate. It seems that if rebar in cement can affect the compass then iron ore in the soil may also affect it.

I don't know if you can raise it high enough manually but you did mention that the fault occurred while still low in the air.

I'm currently abroad so unfortunately I'm not able to test this. However the direction of the AC shown in the flight history in the DJI GO 4 app appears correct, for both crash flights. Screen shots below.

 

[lengthlord]

That both the takeoff locations that you used would have significant magnetic distortion.

The distance between the 2 crash locations is only about 50 metres.

 

[sar104]

The distance between the 2 crash locations is only about 50 metres.

Most magnetic distortion is much shorter range than that. Just to clarify - in the screenshots above, the directions indicated by the aircraft arrows are the directions it was pointing at takeoff?

 

[lengthlord]

Most magnetic distortion is much shorter range than that. Just to clarify - in the screenshots above, the directions indicated by the aircraft arrows are the directions it was pointing at takeoff?

Yes that's the direction it was pointing at takeoff.

 

[BudWalker]

Yes that's the direction it was pointing at takeoff.

I’m on my iPad for next couple of days, so I’m doing this from memory. In the first flight wasn’t left aileron applied shortly after launch and the Mavic moved SE. That implies that it actually had a SW heading.

 

[lengthlord]

I’m on my iPad for next couple of days, so I’m doing this from memory. In the first flight wasn’t left aileron applied shortly after launch and the Mavic moved SE. That implies that it actually had a SW heading.

Yes I applied left aileron to counter the AC movement to its right. This had no affect on the AC. Possibly because it was still in auto takeoff mode? The heading of the AC was NE as shown in the screenshot. I was standing behind the AC with it facing away from me when I initiated auto takeoff.

 

[BudWalker]

Yes I applied left aileron to counter the AC movement to its right. This had no affect on the AC. Possibly because it was still in auto takeoff mode? The heading of the AC was NE as shown in the screenshot. I was standing behind the AC with it facing away from me when I initiated auto takeoff.

View attachment 36404

Maybe I was a bit hasty in my assessment regarding that these both looked like a launch from a geoMagnetically distorted site. In addition to a compromised Yaw (which apparently didn’t happen) there was the compass error that occurred after the Mavic got to about .5 meters (?). This happens if the launch site is geoMagnetically distorted. After launch when the Mavic clears the distortion the Compass becomes correct. But the Yaw value remains incorrect because it’s determined mostly from the IMU data. It’s this difference that causes the compass error to be issued.

Too bad there aren’t any .DATs for these flights. I assume you included the entire MCFlightLog directory? The tablet .DATs can sometimes be split and/or have names that don’t make since.

 

[BudWalker]

Thank you for your reply and advice. It is a wooden picnic table. The hill where I tried to takeoff is called Paddock Mound and is man made. There is a sign by the mound that mentions that the mound is made from clay, and built on top of a capped mine shaft. I've just found this web page, that says the mound "was formed by coal and iron ore working in the 18th century". Anyway the DJI GO 4 app didn't prompt me to calibrate the compass.



I calibrated the compass the day before in a different location, only a few hundred metres away. The drone flew perfectly after the calibration. After the crash, when I tried to re-calibrate the compass I was on the mound. The only metal object nearby was a different picnic table about 10 metres away.

The Disclaimer and Safety Guidelines is a little confusing about compass calibration. Under Safety At a Glance - 2. Pre-flight Checklist on page 4 it writes "Only calibrate the compass when the DJI GOTM app or the status indicator prompt you to do so". Then on page 7 under another section titled Pre-flight Checklist it states "Follow the on-screen instructions to calibrate the compass".

Should I calibrate the compass before every flight, or just when prompted by the app?



Thank you that's a good idea I will watch some videos because I'm not totally clear if I'm doing it correctly, although the drone did fly perfectly after my first calibration.



I'll try flying again without the prop guards. I’d be very glad if someone had a look at the logs beforehand. I'm pretty sure I installed the guards correctly. I watched this DJI quick tip video before installing them.



Good to know, thanks

I just now saw this - I hate it when other people don’t read all the posts in a thread before jumping in

The subterranean iron ore is a possible explanation for the compass error occurring shortly after launch. But, no compromised Yaw....

 

[lengthlord]

I assume you included the entire MCFlightLog directory?

Yes I've included the entire MCFlightLog directory

 

[lengthlord]

What should I do now? Should I initiate a DJI repair request? Will this be covered by the warranty?

Many thanks, Matthew

 

[lengthlord]

there was the compass error that occurred after the Mavic got to about .5 meters (?)

The compass errors happened at around 3 ft (1m) see attached screen shots.

 

[lengthlord]

Too bad there aren’t any .DATs for these flights

I think there is a way of retrieving those .DATs but it requires a rooted Mavic and some advanced knowledge.

Can I somehow get the DATs from the AC? Do you guys know of an online tutorial for this? Does rooting the Mavic invalidate its warranty?

 

[lengthlord]

I guess the most important questions are:

1. What did I do wrong?
2. What can I do to make sure this doesn’t happen again?

 

[BudWalker]

I guess the most important questions are:

1. What did I do wrong?
2. What can I do to make sure this doesn’t happen again?

Re the black box data. I don’t think there is any way to look at this data and it probably wouldn’t add anything to what we already know.

In your first post you stated that you couldn’t calibrate the compass. Was this at the incident site? If so, can you try a calibration at a better site - one without subterranean iron ore. A successful calibration at a different site would be consistent with the iron ore being the cause of the incident.

 

[lengthlord]

Was this at the incident site?

I initially calibrated the compass at a different location about 1 km from the incident site, prior to the incidents. It wasn’t particularly easy to calibrate but it did eventually work, after a few tries. As I’m new to this I assumed user error.

At the incident site after the crashes I tried to calibrate the compass again but could not.

I have since managed to calibrate the compass in the middle of a field no where near the incident site. However it took many rotations and changing the orientation before being prompted before it calibrated.

 

[BudWalker]

I initially calibrated the compass at a different location about 1 km from the incident site, prior to the incidents. It wasn’t particularly easy to calibrate but it did eventually work, after a few tries. As I’m new to this I assumed user error.

At the incident site after the crashes I tried to calibrate the compass again but could not.

I have since managed to calibrate the compass in the middle of a field no where near the incident site. However it took many rotations and changing the orientation before being prompted before it calibrated.

You’re probably pretty good at calibrations by now. So I don’t that’s the problem. TBH, none of the possible explanations seem all that compelling, to me at least. Maybe @sar104 , @msinger or @MavicCF can add something.

 

[sar104]

You’re probably pretty good at calibrations by now. So I don’t that’s the problem. TBH, none of the possible explanations seem all that compelling, to me at least. Maybe @sar104 , @msinger or @MavicCF can add something.

It seems to be a compass error in both flights. Both present as typical CCW toilet bowl type motions, which is especially clear when looking at pitch vs. roll:





The lack of an obvious discrepancy between T₀ yaw and actual takeoff orientation is troubling though. I'll take another look for the mobile device DAT files.

 

[Spy808]

Power up drone n power up remote... Wait till the all ready to take off comes on... Then pick up drone without turning ön motors and turn drone left or right... The icon of ur drone should turn the same time and direction as ur turning the drone if not (delayed or compass error comes on the screen) then I'm afraid the compass module is burnt... It's like when leaving drone on for awhile when updating or calibrating and letting it sit burns up the drone...

 

[lengthlord]

Power up drone n power up remote... Wait till the all ready to take off comes on... Then pick up drone without turning ön motors and turn drone left or right... The icon of ur drone should turn the same time and direction as ur turning the drone

Thanks, I first did a factory reset using the DJI Assistant 2 app and a successful IMU calibration. Then I took the AC to a field and performed your test Spy808. The result was that the arrow icon in the app did not rotate when rotating the AC. Strangely when adjusting the pitch of the AC the direction of the icon did change!

A red Compass Error message appeared in the app several times, disappearing to be replaced with a green Ready to Go message.

It's like when leaving drone on for awhile when updating or calibrating and letting it sit burns up the drone...

I’m not sure I follow you. Do you mean to say that simply powering up the drone, or using the app simulator, which requires the drone to be powered on, can damage the compass?