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Compass Error During Flight

Discussion in 'Pro/Adv Discussion' started by lil boss, Jul 9, 2018.

  1. lil boss

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    Hi All. Earlier I was approaching a metal silo of sorts to get a close up picture. At about 20 feet out I started receiving a compass error warning. I do not know exactly what the message said as I flew away from the object ASAP. So, my question is, what would happen if I ignored warning and flew closer. I snapped this picture, and after descending a little bit more received the warning.

    DJI_0209finish1440.jpg
     
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  2. quaddamage

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    The drone would rotate a bit when moving near the silo, and would curve its flight if you tried to go straight line near it. Nothing more.

    Well it is a metal object, so it would also block and reflect signal from some GPS satellites and possibly cause greater position changes when hovering.
     
  3. Dronason

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    It would quit the GPS mode and fly in ATTI mode. With no wind, no obstacle and close visual control it would be doable to control it. In other cases could be harder as the wind will push it and it would be to the pilot to compensate for that. If there was no obstacles at same altitude, there is good chance that when it would drift (or you would gain some altitude), the issue with the compass will go away and GPS control will be back.
    Always good to be ready for ATTI scenario when flying close to object.
     
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  4. solentlife

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    Dronason in my opinion has answered best.

    The GPS mode would drop out even though you would still have all the GPS data ... basically because directional input of Compass is lost. You do not get reflected GPS signals of the metal structure strong enough to worry about. Why ? GPS transmissions in fact are extremely low power and any reflected is too weak and is rejected anyway. Think about your Car Satnav ... boats ... trucks ...
    ATTI mode is something that needs to be practiced ... and to note that flying in ATTI mode will need AC to be kept clear of obstacles more than in GPS mode. Because of drift / lack of static position ability.

    An experienced ATTI flyer could in fact fly and photo that silo - making sure of course that silo does not get between Controller and AC ... that would block control signals.
    Keeping close eye on screen - hoping that lag / dropout doesn't occur.... you could fly and then when finished rise up and away to regain compass and GPs Mode once metal interference is lost.

    Nigel
     
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  5. Meta4

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    Try it again and experiment.
    Or on a building with a steel roof.
    Slowly lower the Phantom toward the roof until it starts to slowly spiral rather than hover in place.
    Raise the Phantom until it is back to normal, lower it again.
    It's quite safe as raising the Phantom beyond the magnetic influence eliminates the issue.
     
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  6. With The Birds

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    As meta has said, if you are prepared and don’t panic you won’t have problems. I often launch from my deck, it’s a suspended concrete slab with a ridiculous amount of steel reinforcing- I often have compass errors when launching (have to hand launch from above head height) and when returning but all is good once clear.
     
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  7. solentlife

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    I also have concrete areas wth rebar in that I can launch from ... but I no longer do.

    Why ? I only needed one occasion where it started to go bad to convince me to avoid it. I had Compass Error ... I powered Down ..Lifted above and powered up again ... all seemed fine .. launched and as it moved across above the concrete - it went into a drunken act that luckily I still had enough input to get it to fly away enough for error to stop ...

    I for one - now avoid such launches and take-off locations.

    In flight - that's different because you are steady ... it feels more better and ATTI mode kicking in is usually at height. You are more able to deal with it.

    Thats my view anyway.

    Nigel
     
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  8. lil boss

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    Thanks everyone... It's the 1st time I ever encountered this so it shook me pretty good. My knee jerk reaction was to get the hell away from the silo. That said Dronie was in my line of sight. Silo only about 500 feet away from home. Thanks all. I'll fly ATTI to get a feel for it, and try the silo a 2nd time another day. Wishing you all a super day !!!
     
  9. solentlife

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    Main things to remember when out of P-GPS mode (flying ATTI) :

    1. There is no auto braking effect. If you make AC fly in a direction - it will continue till you give opposite arresting input. This is the biggest factor for inexperienced ATTI flyers to grasp.
    2. There is no steady hover - the AC will drift around under influence of wind / any air movement - often made worse by too coarse control inputs to correct. Often leads to a crass version of the Toilet Bowl Effect !!
    3. The P3P manual talks about A-Mode and being able to RTH if Home Point was recorded and GPS is available, but later adds that if Compass is not available - it cannot RTH.

    The upshot in my opinion then is while close to the Silo - you are the only control factor to get it home / fly safely. Once you move sufficient away from the Silo - you should regain P-GPS mode and AC will have its failsafe factors available again..... Yes I know ... just confirms what we've all been saying already !

    Nigel
     
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  10. lil boss

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    Excellent Advice Nigel... Everything Duly Noted !!! Have Yourself A Fine Day Sir !!!
     
  11. Quest-So

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    Your case reminded me that I had a similar one some days ago, but got no warning on the screen. Namely I was in a descending procedure from a higher altitude and came at say 40 m over the church’s metal roof. I deviated to the yard and all went well down to landing. But uploading the flight data to AirdataUAV I noticed the AC has recorded a compass error warning exactly when the bird had to deal with the large church’s metal roof.

    Ideea is the compass doesn’t like at all any large metal surfaces, so you would better avoid flying over such. There are known cases (see on YT) with drones that crashed following a flight over / around a ship, the huge metal surfaces compromising permanently the compass.

    I had to fly these days around a huge Liebherr 1600 crane, involved on a highway construction. Uploading the flight to AirdataUAV, I found that the max compass turn rate per 0.1 seconds became 11.50 value which is huge compared to values as 3.50-6.00 I usually get. This is still inside the acceptable span of 15-16 degrees per 0.1 seconds, but it’s obvious the bird didn’t liked at all the vicinity of the crane.
     
  12. lil boss

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    Very Interesting... And funny in a way, as a few weeks ago, I was snapping photos of a large crane sitting on a barge docked in the Delaware River. Not sure of the model or size. I appreciate your reply and would be interested in viewing my compass data. I do have a Free account with Airdata... will I be able to see the compass data ? Thanks again... Have an awesome day !!
     
    #12 lil boss, Jul 11, 2018
    Last edited: Jul 11, 2018
  13. Quest-So

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    Airdata provides a list of all warnings / alarms the system has generated during the flight in General -> Notifications. Since you’ve noticed on the screen a compass error warning while you were close to the silo, it should be present in the list.
     
  14. Fly Dawg

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    Don't count on Airdata's information for details. These are only compilations and not a complete reflection as to the actual data involved. For the most part, it is usable for basic information but any more than that you have to look at the actual data files for a comprehensive view.
     
  15. Quest-So

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    True, Fly Dawg, for detailed flight analysis DAT files are the solution.
     
  16. Fly Dawg

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    That is correct, however under many circumstances the device logs will be fine, unless there is complete signal loss, or if there is an anomaly that is not recorded in the device file. The device logs can be analyzed in a similar manner as the aircraft .dat files. That was just a comment on the compilation of the Airdata information.
     
  17. lil boss

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    Thanks for all you help.

    I uploaded the flight record and looked at the data...

    There were multiple compass errors.. they were "repeated" numerous times. One was repeated 18 times and another 20. Not sure exactly what that means. I don't remember that many warnings popping up...

    Also Maximum Turn Rate was 6.10.
    (I only screen printed the last portion of the flight).

    Looks like all comments were on the money.

    Notifications.jpg

    Compass.jpg
     
    #17 lil boss, Jul 11, 2018
    Last edited: Jul 11, 2018
  18. lil boss

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    REALLY? If there is any chance of permanently damaging the compass then why are we even discussing this? What about flying near bridges, buildings, etc??
     
  19. solentlife

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    I wouldn't go so far as Quest-So in his statement of permanent effects - but yes it can happen, but only when a serious magnetic unit or material has been placed near a compass.

    Example : Ships carrying Iron Ore can actually be excused from carrying a magnetic compass in the past .. because the Iron Ore would cause massive deviation of the standard compass rendering it pretty useless. It was not only the Iron Ore but also the loading operation where the Ore would hit the steel structure of the vessel causing shifts in magnetic fluxlines.

    Such ships would often have their standard compasses re swung after such cargoes to ascertain the NEW residual effects.

    Passing a strong magnet near a compass can do this ... after passage of the magnet - the compass is off by some degrees. It is due to re-alignment of the flux.

    But loss of a Phantom because of residual effects to compass after passing a bridge / ship etc. ? Unlikely. The loss is most likely due to pilots inability to fly ATTI mode.

    Nigel
     
  20. lil boss

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    Whew.... A sigh of relief !! :D Thanks Man !! (And Thanks To Everyone Else) Cheers !!
     
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