I've had my Mavic for a year now. It has served me well, even though the included mini USB-Lighthing cable gave me trouble with loss of video feed (original cable solved this). Anyway; I brought my Mavic to a hike today on a local mountain top (1000 m) and flew couple of flights while hiking up. At the top, after 18 minutes, I got the following error messages:
«Compass Error. Exit P-GPS Mode» and «In flight, working IMU encounters heading exception, please switch to atti mode if craft behave abnormally».
The main video feed on my iPhone 6S+ also prompted «weak GPS signal», even though there was not anything blocking the Mavic from the sky (we were still at the top). Shortly after this another error message appeared: «Weak GPS signal. Positional accuracy may be compromised. Please fly with caution».
For a couple of seconds the Mavic would not respond to horizontal commands, only vertical. The error messages repeated themselves before I managed to land safely. As I’ve never encountered anything like this before I got a little scared, I therefor want to share my experience with you guys so I can learn something from todays happy little accident.
The aircraft worked perfecly up to this moment. This was also the first time I tried the "Follow me terrain" mode.
Basic information:
- No obstacles around the aircraft, only partly clouded skies.
- I´m on the latest FW.
- I calibrated the compass to days ago (as I moved across the country).
- The mountain we climbed mainly contains Quartzite with a varying amounts of iron.
- I will also provide the flight data extracted from todays flight (.DAT file) if requested.
Compass error IMU exceptional heading go to Atti mode, is usually a problem with compass magnetic interference.
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, 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.
While I can’t be certain you picked up interference from the ground or surrounding area it is the most common cause.
hallmark007 Posted at 2018-7-9 14:22
Compass error IMU exceptional heading go to Atti mode, is usually a problem with compass magnetic interference.
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.
Very well said. And agree most likely what happened. A mountain can most definitely cause a compass problem.
Dude, one more thing, you should never calibrate the compass UNLESS the app ask you do it, no matter how far you travel. I even travelled to different continents and I never calibrated the compass!
I understand the cause of this problem, but I´ve never experienced this during a flight. I guess there was magnetic interference from the mountain which caused it. I will report back if it happens again in the future.
As for the calibration; old habit from my time with the P3 Pro. I will avoid it in the future, unless the app asks me to.
What about the GPS signal? Any reason why the signal suddenly became "weak" (ref. video in first post). I had the Mavic in sight - and as previously described, I was flying on a flat mountain top.
behansen Posted at 2018-7-15 13:11
What about the GPS signal? Any reason why the signal suddenly became "weak" (ref. video in first post). I had the Mavic in sight - and as previously described, I was flying on a flat mountain top.
Thanks again,
I have run into the same problem now three times. Flying remotely in Forested areas. Start up procedure never changes. Wait for unit to locate itself. Usually calibrate the compass however I might stop doing that. First time my drone flew away and I got it back after it was 2km away and finally used RTH. That night I calibrated the IMU. Seemed to work perfectly for the next year then back in February and again the other day, same problem. Compass error and IMU heading error. Drone just went where it wanted to go. Just flying away. Do not believe there was any metal interferrence. I will be conscious about take off then turning the unit quickly.
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