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Compass Error on attempting yo take off at canal lock

Discussion in 'Pro/Adv Discussion' started by Skylark, Oct 11, 2015.

  1. Skylark

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    This afternoon, I thought I could get some really cool footage of my local canal and chose a flat spot near a canal lock to take off. After the usual preflight checks, I turned on the phantom only to be bombarded with a compass error warning and a suggestion to move elsewhere. Unbeknownst to me I moved to a nearly canal bridge but still got the same compass error readout. On further inspection of the lock and the bridge I found their was massive reinforced iron in both structures so I decided to abort the mission. I contemplated whether it would be possible to take of in ATTI mode, if that were possible, but was reluctant to do so due to the enclosed nature of the canal bordered by high trees. I foresaw losing LOS and saying goodbye to my bird.

    Now my question which I would like to ask the more experienced on the forum. Could I have started in ATTI mode and flown the mission safely by bypassing the start up procedure that gave me all the compass errors in PGP? Many thanks for informed revise in advance.
     
  2. ianwood

    ianwood Taco Wrangler
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    Don't take off near metal.
     
  3. EPT160

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  4. Chris P Duck

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    Compass and GPS are different.

    ALL modes use compass.

    GPS = position hold, stops it drifting (not affected by nearby metal)

    Compass = orientation hold, stops it spinning (affected by metal)


    ETA, GPS I'll not be able to hold position without the compass.
     
  5. EPT160

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    I certainly understand that.

    So is the Inspire 1 guidance system the same as the P3P?

    I only have the P3P but the navigational specs seem the same??
     
  6. Chris P Duck

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    As far as I know they're the same.
    I've also seen video's of P3's launching from ships, fly thing through/under metal bridges etc.
    At a guess it would depend if the metal is ferrous or not.
     
  7. Skylark

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    Thanks for the replies so far. I have seen a number of videos showing Inspire taking off from metal hulled boats/ships as well as footage taken using ATTI mode in metal warehouses. My question is whether you can take off safely in ATTI mode and whether you can start up the initiation process in ATTI thereby bypassing the compass error message you get if the controller is set to PGP?
     
  8. emilewski

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    (edited) The answer is no. I took off from a bridge yesterday and had compass error. I took off in ATTI anyway and it flew, but in hindsight it was stupid to do that. I regretted it and landed in ATTI right away again as it was drifting too much with a lot of trees about and not a large landing area. I then started up off the bridge and was fine (a much better idea). Taking off with a compass error can be done but it is not a smart thing to do and just asking for trouble in retrospect.
     
    #8 emilewski, Oct 12, 2015
    Last edited: Oct 12, 2015
  9. Chris P Duck

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    The answer is no.

    All modes use the compass (as I said) you may be able to take off, but only expect "I told you so" when you post after of a flyaway that destroyed your P3.
     
    ranges likes this.
  10. Skylark

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    Your recent replies intrigue me as I don't know how an Inspire 1 was used to take shots of the inside of a meal structure (warehouse).
     
  11. Chris P Duck

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    If the warehouse was non ferrous metal then it would not have been a problem.
    If it was ferrous metal I believe that that large chunks of metal in one location would be much worse than the thin-ish metal used in a warehouse (assuming it was some sort of corrugated metal?) evenly spread over a wide area.
    Even if it was ferrous metal, and it was a large chunk in 1 location it may have been ok.

    I'm not saying don't try these things (though don't blame me if they go wrong) what I am saying is believe it's for a reason when it says compass error and/or won't let you take off.
    For info the worse thing you can do is try to calibrate the compass near a big source of interference, the "calibration" may mask the source of the interference, but as soon as you fly AWAY from the interference you'll get problems as it won't know which way is which.

    P-mode will be MORE of a problem as it will try to hold position as well as orientation. However atti still uses a LOT of tricks to keep it in the air and stable. So it still needs the data fed to the controller from its sensors to be accurate.
     
  12. edonovanl

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    Learn to fly competently in ATTI first so you are prepared for when it happens - drift will always occur in this mode.
     
  13. ianwood

    ianwood Taco Wrangler
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    Sometimes people get lucky. The only difference is the Inspire compass is further from the ground than the P3. I would keep both Inspire and P3 at least a couple feet from any metal and I would only be comfortable with that if I did a full magnetic assessment first.
     
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  14. Skylark

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    Hi Guys,

    The video I was referring to shot in a warehouse is this. I just don't know how it was shot in any mode given the likelihood of large amounts of ferrous material. The video was taken by Wild Rabbit Productions an excellent professional company based in LA.
     
    #14 Skylark, Oct 12, 2015
    Last edited: Oct 12, 2015
  15. joebar.rc

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    Actually, a compass is only needed for heading, it works together with the GPS to determine the path, heading and bearing. In atti mode it is probably fused with the gyro/act but heading is not kept.
    I don't really see how the reports of compass error in atti mode could lead to a crash other than that the weight of the compass values in the sensor fusion is wrong in that mode.

    A not calibrated compass in GPS hold will often cause a toiletbowl effect and that 'can' lead to overcompensation and crash

    Drift is not an effect of the compass error, drift is because atti does not use the GPS for position hold.
     
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  16. Chris P Duck

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    " ATTI flight mode does not use GPS for position hold, while the compass, gyroscopic and barometer controls maintain attitude of the craft keeping it level and holding a constant bearing (the way it is facing) when the control sticks are centered."
     
  17. ianwood

    ianwood Taco Wrangler
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    Winner winner, chicken dinner. The compass is used for both heading AND orientation in GPS mode. In ATTI mode it is still used but I suspect it is less weighted which is why ATTI mode is the best move for compass based issues.

    Regardless, it's the conflict between GPS and compass that causes TBE which then stresses the attitudinal stability control which is also compromised by the compass. Remove GPS and there's nothing to start the reaction.
     
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  18. joebar.rc

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    Yeah, that is what I said ain't it :), if used in atti, probably only for keeping the yaw fixed. Most flight controller code, even the L1 adaptive attitude which I suspect dji is using does is like that if a magnetometer is available.

    Anyways, better be safe than sorry, keep away from ferrous areas while flying or calibrating
     
  19. Wibble

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    If you take off in ATTI then switch to GPS once you are in the air wouldn't that be ok?
     
  20. Skylark

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    I am not sure to be honest. If you see the whole video sequence of the one I posted you will note the close proximity of the Inspire 1 to metal beams and rafters, yet the control of the pilot was as shady as a rock. This footage was taken inside so P-OPTi or ATTI were the only options.