Almost lost the drone ... compass error?

[Monsterfez]

Okay so been flying all day no problems, was my 68th flight or so.

Set up, calibrate compass all is well and off I go. Flying close to where I am, 20+ mph but no problem in GPS mode.

All of a sudden, compass error, ATTI mode. Drone is drifting over the water and I panic, keep calm hit RTH. It starts coming home, then again compass error atti mode, again and again about 6 times, eventually get the drone above me. Brining it down to land was the hardest thing I've done so far, it was blowing all over the place, like taking the toy drones out in the wind. 20+ was a bit much for the confined place I took off from, in ATTI mode atleast.

Eventually landed it all okay, brown trouser moment for sure, one thought that went through my head was kamakazi it into a metal fence so it didn't hit mine or my mates car, luckily didn't have too.

So any ideas, did being near the boat cause this, had no error pre-flight or whilst setting up/calibration?

DJI_0382 by Adam Powell, on Flickr

 

[Monsterfez]

HealthyDrones.com - Innovative flight data analysis that matters

 

[RodPad]

Hello, if you calibrate a lot, you should read this.

Compass Calibration, A Complete Primer

I think my last calibration was in May 2016
A compass error can make RTH fail.

Rod

 

[Monsterfez]

Hello, if you calibrate a lot, you should read this.

Compass Calibration, A Complete Primer

I think my last calibration was in May 2016
A compass error can make RTH fail.

Rod

Yeah going to stop calibrating every flight, I only do as usually always in a new spot. But will head to the fields near mine, calibrate and leave alone unless asked for.

 

[RodPad]

Yeah, scary stuff, should load up your log to here
https://www.phantomhelp.com/LogViewer/Upload/
And you can share it with others by copy and past the url here.

Here is a couple on RTH, and IMU.

Best Method to RTH?
Lost signal (but not really)
Lesson learned from crash by RTH because flying with a low battery
I almost read every RTH post.

IMU CALIBRATION AND WARMING UP
IMU Calibration (PDF)

Stay away from trees, they don't move out of the way, and they usually win in a fight.
Rod

 

[fastfed]

I used to calibrate every flight, now only once in a blue moon.

 

[RodPad]

I used to calibrate every flight, now only once in a blue moon.

Have you every captured a Blue Moon on your Phantom?
Now that's a challenge!

Rod

 

[SimonH78]

Sorry for your scare but a pilot error far to windy if it was 20+ mph !! as you Shouldnt even take off! Did you check the Kp index? - You need to plan for emergencies and not rely on GPS - will fly fine in ATTI with the right winds - Don't blame the machine. The boat at altitude would not effect the Phantom.

 

[Numone]

I've calibrated 3 times in 9 months. I haven't calibrated even when I've flown in different countries. I let the AC hover for 20/30 secs after T/O and then do some close manoeuvres before flying off. The last time I calibrated, it was the app that told me there was a compass error during the hover so I work on the basis it'll tell me again if I need to. Additionally, I practice flying and returning in ATTI mode in case it happens during a flight. On the first and only occasion it did happen, i did panic a bit, but I then switched to and kept it in ATTI and brought the AC back - all that practice paid off. So I moved 50 feet, popped in a fresh battery, T/O once again and it flew perfectly.

 

[Monsterfez]

Sorry for your scare but a pilot error far to windy if it was 20+ mph !! as you Shouldnt even take off! Did you check the Kp index? - You need to plan for emergencies and not rely on GPS - will fly fine in ATTI with the right winds - Don't blame the machine. The boat at altitude would not effect the Phantom.

Flown in 20 mph winds before no issue and it really isn't in GPS mode, aslong as you are not planning a distance flight.

 

[Numone]

Flown in 20 mph winds before no issue and it really isn't in GPS mode, aslong as you are not planning a distance flight.

I'd only caution if it's 20mph at ground level, it'll be much higher at 50 or 100 feet. I t/o once with 10-12 mph at ground level. Got up to 300ft and it was <30mph. I know this as it was stationary at full throttle when I tried to return. I kept it at full throttle and began to decend. It started to slowly accelerate and I managed to get it to 10mph and got it back safely. Not going to do that again!

 

[DanMan32]

AC in theory should be able to figure out heading from GPS as long as its moving and work that way for the time being. If it's compass still reads but is offset different than it expects based on GPS, then it can still use that too temporarily with the offset, as long as it isn't totally erratic relative to heading determined by GPS.
If it forced ATTI, don't use RTH as that needs compass as well as GPS. Use your map instead to get your LOS bearings.
Learn to get your bearings in LOS by flying forward (right joystick up), then yaw in the same direction as it appears to be flying left or right. When it stops moving left or right while still flying "forward", it is heading towards you so you can stop yaw. Saw that on a couple videos and practiced on my X5. I don't bank/slip right/left much anymore since.

Sent from my HTC 10 using PhantomPilots mobile app

 

[Numone]

AC in theory should be able to figure out heading from GPS as long as its moving and work that way for the time being. If it's compass still reads but is offset different than it expects based on GPS, then it can still use that too temporarily with the offset, as long as it isn't totally erratic relative to heading determined by GPS.
If it forced ATTI, don't use RTH as that needs compass as well as GPS. Use your map instead to get your LOS bearings.
Learn to get your bearings in LOS by flying forward (right joystick up), then yaw in the same direction as it appears to be flying left or right. When it stops moving left or right while still flying "forward", it is heading towards you so you can stop yaw. Saw that on a couple videos and practiced on my X5. I don't bank/slip right/left much anymore since.

Sent from my HTC 10 using PhantomPilots mobile app

Yeah, good point re ATTI and RTH DanMan, plus the bearing tip. Learning a degree of manual flight skill has saved my AC on one occasion. Because of that, I try to fly in full manual using the radar, direction indicator and the map of course to get it back on at least one flight on every trip.

 

[Meta4]

So any ideas, did being near the boat cause this, had no error pre-flight or whilst setting up/calibration?

No .. being near the ship didn't have any effect (unless you calibrated your compass right beside one).
The place you calibrated is the problem.
I'm guessing it's close to a lot of steel - probably right on reinforced concrete?
It sounds like you were re-enacting this guy's flight:

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[Meta4]

Sorry for your scare but a pilot error far to windy if it was 20+ mph !! as you Shouldnt even take off! Did you check the Kp index?

The Phantom can easily handle 20+ mph winds and maintain position.
If the pilot knows what they are doing this should not be a problem.
Kp index is irrelevant and has never been shown to have any effect on Phantom flying.

 

[SimonH78]

The Phantom can easily handle 20+ mph winds and maintain position.
If the pilot knows what they are doing this should not be a problem.
Kp index is irrelevant and has never been shown to have any effect on Phantom flying.

Well obviously did'nt and you don't rely on GPS - Kp can have an effect, its included in aerial training, as is flying in ATTI mode comfortably in case it cause pear shaped.

 

[David Chan]

I am well aware of calibrating the compass around metal will cause error. What I didn't know is the take off point also matters, at least for me. Once I calibrated and took off about 200 feet from a pier and the whole flight was fine. For the second flight I went ahead to take off on the pier itself knowing the compass was already calibrated. But I got compass error on and off just like the guy in the video the Meta4 linked above so I landed it right away. Not sure if this is already well known or I might have missed it in the manual, but most of the thread I read above compass error here the suggestion was not to calibrate around metal. From my experience, taking off around metal will also cause compass error. Not sure if others have experience the same.

 

[DanMan32]

By the way to be clear,my theory is what the firmware could be designed to do and not what I believe it is doing.

Sent from my HTC 10 using PhantomPilots mobile app

 

[peter west nz]

I have had errors like this when flying above some steel light poles at about twice their height. Continuous compass errors, changing in and out of atti. Good job I can fly atti. It was still a frightening flight.
In your case, a steel ship moving in the earth's field distorts the field by the back emf generated in it's hull by that moving, so my advice is - stay up high! I don't think they de-gause ships any more

 

[Meta4]

From my experience, taking off around metal will also cause compass error. Not sure if others have experience the same.

Definitely. There have been several incidents that show clearly that takeoff from steel or reinforced concrete can be very bad.
This post explains why: Looking for Trouble ??