ATTI mode mid flight - causing the Mavic to almost crash

John Locke · Nov 25, 2016

Mr Spock said:
Does the mavic have course lock like the p3a p3ps? In atti mode would help get it back easier?

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Course lock doesn't work in atti mode. That mode needs a compass and GPS.

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John Locke · Nov 25, 2016

generaltso said:
So, is it likely that calibrating the IMU without calibrating the compass is what caused me to switch to atti mode mid-flight? If I calibrate the compass before the next flight, is it unlikely to happen again?

It's possible that's the cause. It's also possible you flew into an area that had a magnetic anomaly that confused the dual compass. This scenario is rare, but possible. For instance, flying too close to a locomotive, which has a massive electro magnetic field around it.

These compass issues are more common on P3p craft that have a single compass, less common on p4 with dual compass, like Mavic.

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Jeff Gilbert · Nov 26, 2016

John Locke said:
Course lock doesn't work in atti mode. That mode needs a compass and GPS.
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Ever since introduced on the Naza, I've used CL as a controlled method for flying back to HP.
CL requires only compass.
FWIW, HL requires GPS and compass...
That's why CL desirable when GPS is lost...

erkme73 · Nov 26, 2016

The Editor said:
The number of satellites is pretty immaterial. Everybody gets hung up on 'oh I had 15 satellites'
It is the HDOP/VDOP that is important not number of birds your GPS/Glonass RX can 'see'. This is indicated by the small bargraph display next to the number. DJI will say in the manual this is a 'signal strength' - it isn't. It is the quality of the positioning derived from timing errors.
12 or 16 sats with poor HDOP/VDOP is worthless.
DJI actually removed the number from the Go app around 14 months ago but so many people complained because they needed their number back that they reinstated it (wrongly in my opinion) since it gives a false sense of security.
If there are a large cluster of sats low on the horizon then then you will have a large horizontal dilution of precision and hence the positioning errors (or worse for some, the aircraft drops into Atti).
Pay attention to the bargraph/signal strength style display not some meaningless number.

What do you do if you're showing full signal strength on the GPS indicator, and then suddenly, without warning or cause (nothing blocking the bird at 400') it drops to red with a single tick? Of course, that's AFTER it's left GPS mode and has aimlessly started drifting?

In this screen grab of my flight path/log, go to the 1 min mark, and watch how my MP was already drifting well to the east before the GPS ever dropped:

I don't know what causes the GPS to go from FULL to unusable, but there is literally no warning. And when that happens at a critical moment, it can end badly.

The Editor · Nov 26, 2016

erkme73 said:
What do you do if you're showing full signal strength on the GPS indicator, and then suddenly, without warning or cause (nothing blocking the bird at 400') it drops to red with a single tick? Of course, that's AFTER it's left GPS mode and has aimlessly started drifting?

In this screen grab of my flight path/log, go to the 1 min mark, and watch how my MP was already drifting well to the east before the GPS ever dropped:

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I don't know what causes the GPS to go from FULL to unusable, but there is literally no warning. And when that happens at a critical moment, it can end badly.

That circular motion is TBE (toilet bowl effect) so you had a bad compass calibration.
Also, if your aircraft switches to Atti you just carry on flying, so long as you are competent flying in Atti mode - it doesn't end badly, it is just non GPS assisted flight.
In your case though, it went into Atti, suffered TBE because of a bad compass calibration.

J-Dub · Nov 26, 2016

Interference from flying over the housing development?? Each home its own bubble of electronic signals???

Gerald Ellis · Nov 26, 2016

mattmjm said:
Thank you for your replies and recommendations guys. I plan to calibrate in an open field tomorrow afternoon and I'll post a more detailed reply then (Wednesday, November 23rd)..

I'm not totally positive the following tip does any good but I know with my P3P when I calibrated the compass I put something on the ground like a spare prop or handkerchief and then instead of walking around in a circle, I actually rotated the drone over that position on the ground as close as possible. IOW circled the item on the ground. For me, that completely stopped the slight drifting when yawing in place even when it was gusty wind.

Maybe it is just paranoia and has nothing to do with a more accurate calibration but I've followed that tip with other drones and it seems to work better on all of them.

BudWalker · Nov 26, 2016

erkme73 said:
What do you do if you're showing full signal strength on the GPS indicator, and then suddenly, without warning or cause (nothing blocking the bird at 400') it drops to red with a single tick? Of course, that's AFTER it's left GPS mode and has aimlessly started drifting?

In this screen grab of my flight path/log, go to the 1 min mark, and watch how my MP was already drifting well to the east before the GPS ever dropped:

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I don't know what causes the GPS to go from FULL to unusable, but there is literally no warning. And when that happens at a critical moment, it can end badly.

Would it be possible to get the .DAT from this flight? If so, then it may be possible to determine the cause of the incident in this flight. The .DAT is on the Mavic Pro itself. To retrieve it use DJI Assistant 2 and go to the Flight Record tab. After confirming that it's OK to put the Mavic in Flight Data mode a list containing the recent flights will appear. Select just the Flight Control File of the incident flight and then press Save To Local. Ultimately a file with a name something like DJI_ASSISTANT_EXPORT_FILE[2016-10-27 22-40-28].DAT will be created. That file can't be attached here so you'll have to Dropbox it and post the link.

I'll use DatCon to convert this .DAT to a .csv file. If you've been on PhantomPilots P3 forum you may know about DatCon which reads and converts the P3 .DAT files. DatCon has been extended to work with Mavic .DAT files. I plan to relaease it in a week or so. But, I wanted to look at your incident while there is still the opportunity to retrieve that .DAT

erkme73 · Nov 26, 2016

BudWalker said:
Would it be possible to get the .DAT from this flight? If so, then it may be possible to determine the cause of the incident in this flight. The .DAT is on the Mavic Pro itself. To retrieve it use DJI Assistant 2 and go to the Flight Record tab. After confirming that it's OK to put the Mavic in Flight Data mode a list containing the recent flights will appear. Select just the Flight Control File of the incident flight and then press Save To Local. Ultimately a file with a name something like DJI_ASSISTANT_EXPORT_FILE[2016-10-27 22-40-28].DAT will be created. That file can't be attached here so you'll have to Dropbox it and post the link.

I'll use DatCon to convert this .DAT to a .csv file. If you've been on PhantomPilots P3 forum you may know about DatCon which reads and converts the P3 .DAT files. DatCon has been extended to work with Mavic .DAT files. I plan to relaease it in a week or so. But, I wanted to look at your incident while there is still the opportunity to retrieve that .DAT

Ugh. Where were you 24 hours ago...

As soon as I saw your instructions, I immediately download and installed DJI Assistant 2, and followed your directions. Unfortunately, it looks like we missed the 11/21 flight record - by a day. My oldest record is 11/22. That's Murphy. Sorry. Would have LOVED to get to the bottom of this. On the upside, I'll know how to do this for the next event.

The Editor · Nov 26, 2016

erkme73 said:
Ugh. Where were you 24 hours ago... As soon as I saw your instructions, I immediately download and installed DJI Assistant 2, and followed your directions. Unfortunately, it looks like we missed the 11/21 flight record - by a day. My oldest record is 11/22. That's Murphy. Sorry. Would have LOVED to get to the bottom of this. On the upside, I'll know how to do this for the next event.

The bottom of it is......Bad compass data!

erkme73 · Nov 26, 2016

The Editor said:
The bottom of it is......Bad compass data!

I'll defer to your expertise on that - though DJI was blaming low light on VPS and poor GPS signal/interference for the 'drift away'. It just seems like a 'bad compass' is a too-convenient catchall for unwanted flight behavior. I walked out into the middle of a grassy field and conducted the compass calibration to the "T", and still I have "bad compass data". It's just getting a tad frustrating.

Mad_Angler1 · Nov 27, 2016

Make sure people are not wearing Apple watches or any other smart watch when calibrating as this will cause havoc and all the legs are fully out not folded when you calibrate.

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niclariv · Nov 27, 2016

Is a metal belt buckle going to cause a bad calibration? If so, that will make for some awkward calibrations..

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J3ffrey · Nov 27, 2016

Never had to worry about a watch or phone in a pocket or a belt buckle on ANY other drone... why is this one so sensitive. Or is this just people inventing old wives tales?

MavicMo · Nov 27, 2016

I'm really curious about this part of the thread regarding never taking off from Concrete. I've never head that before. I regularly take-off from concrete driveways, sidewalks, empty roads, and have never had an issue with any of my drones. I know there is rebar in most concrete structures which "may" have an affect on a drone.

You seem to make a distinction between "concrete" and "pavement", but the dictionary definition of pavement includes concrete as part of pavement...

Just curious...

msinger said:
The pavement most likely has no metal in it.

msinger · Nov 27, 2016

MavicMo said:
You seem to make a distinction between "concrete" and "pavement", but the dictionary definition of pavement includes concrete as part of pavement...

Sorry for the confusion. I'm from the US. If you're British though, then it could also mean a sidewalk.

Techcop50 · Nov 27, 2016

Pavement generally means asphalt where I'm from, and asphalt doesn't generally contain steel. I fly from concrete on occasion, but not if I get a compass error before takeoff. If I do get the compass error, I'll move to the grass and see if I still get the error. Most often it goes away.
Never had an issue with asphalt.

Michal T · Nov 27, 2016

J3ffrey said:
Never had to worry about a watch or phone in a pocket or a belt buckle on ANY other drone... why is this one so sensitive. Or is this just people inventing old wives tales?

This is my first DJI commercial drone. However, I have been building drones for about two years with various controllers ranging from pixhawk to Naza and flown 3DR solo. They all required compass calibration, but it was always a one time thing that rarely had to be repeated. Frankly, tuning took way more time than compass calibration did. I never used to worry about belt buckles, keys in my pocket or rebars near by.
Unless I had a freaking magnet in my pocket none of the electronic devices near by would cause any problems. I am also surprised by some of the advice on here, especially related to electromagnetic interference. Our Mavic is certified by FCC meaning it is supposed to accept ANY electromagnetic interference from nearby devices like Apple watches smartphones wifi boosters etc. Does everyone have the same issues with P3s and P4s?

m0j0 · Nov 27, 2016

niclariv said:
Is a metal belt buckle going to cause a bad calibration? If so, that will make for some awkward calibrations..

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I remove everything metal including belts. Takes a little planning but it is a process that works for me.

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m0j0 · Nov 27, 2016

Michal T said:
This is my first DJI commercial ..... Does everyone have the same issues with P3s and P4s?

I have been flying DJI for about a year. I remove all metal. Including rings when I calibrate. I don't know that it is necessary. I have been doing it that way since I started last November. I have flown close to 500 miles since then on a number of aircraft. Only once did I have any type of compass error. It was likely due to magnetic interference in a location I was flying. I calibrate sparingly pretty much exactly as directed in the compass thread. Which for me means I calibrate when traveling more than 200 miles or if I notice any issues or abnormalities with flight.. I have not had many issues though. So I will continue to follow the advice in that thread. The Mavic having dual compasses like the P4 is incredibly stable. Thus far one good calibration and I haven't done it since.

The methods might be over the top. They may be unnecessary but thus far they work. Now back to another issue. Coming from 3dr or any other platform you have to understand something. DJI products are going to have more reported issues... not because it is a lesser product. To the contrary, they are fantastic which is why there are probably 10 Phantoms for every competitors product. Every product has thousands of operators resulting in more reports. These products are stable.

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