Compass calibration? - earth magnetism changes everywhere !

Discussion in 'General Discussion' started by CrashALot, Apr 7, 2019.

  1. CrashALot

    CrashALot Member

    Oct 17, 2018
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    yuneec and others say you only need to calibrate compass every 50 or 150 mi or however far they say.

    well honestly, i have taken a compass out in a clear field and even within 6 ft, 'north' changes, sometimes 5-10 degrees, another 10 ft it swings a diff direction, up north in higher latitudes in USA 'north' is 10+- degrees 'constantly' off from 'true' north, as is any location in high latitudes on earth, i suspect worse in some areas, so a fairly sizable change, nowhere near wiring or metal only earth dirt !

    as i tell others, 'North' you get to choose which north you like, i aim a satellite dish often when I travel and 'north' just gets you kinda close, the satellite is fixed (at least from 23k mi away) so compass is just a good guess/starting point !

    so these 'compass' are really elec magnetometers, which measure in 3D and all we are doing is trying by spinning uav in all directions to 'cancel' out local magnetic disturbance and thus be able to 'reliably' detect motherEarthBitch's magnetic flux lines, no ?

    not really north but all relative to gps and magnetic flux lines and accelerometer, maybe a barometer, and any other 'sensor' used for position and altitude.

    so why NOT have to 'calibrate' every time at a new site more than a few hundred feet from last OR why EVER calibrate ?

    why just some seemingly arbitrary distance, land composition varies tremendously and much less than 50mi so ..... ?

    and honestly, why not just spin a uav in a slow level circle, in calibration mode and have system inside do an auto calibrate, why the manual spinning ?

    can someone explain it all ?

    ps: only once have i had TH complain about compass, and it really could not stabilize near ground, fine up higher so landing was very iffy and simply chose to 'land now it seems almost stable', shut down engines asap & made it w/o tipping over !
     
  2. HarveyH54

    HarveyH54 Active Member

    You couldn't calibrate with the motor spinning, antennas transmitting, because all would be emitting an electromagnetic field, stronger than the Earth's.. You need to calibrate away from powerlines, and metal (that can act like an antenna) for the same reason, the compass will pick up the strongest source of a magnetic field, and call that north. There is a lot of iron in the ground, terrain varies a great deal, as you change locations. Usually, it's not going to cause any problems, doubt point true north is mission critical, basically just need to point in the general direction. I never pulled out a compass, and stood facing exactly north when I calibrated, and don't calibrate very often. My choice, accept any minimal risks involved, hasn't been an issue, yet... I'd suspect that correct compass heading is more important to the 'Smart' mode functions, which I don't use, occasionally RTH.

    Basically, depends on where, and what you plan on doing, but it's simple enough to do, to ensure a better flight experience, and protect your investment.
     
  3. CrashALot

    CrashALot Member

    Oct 17, 2018
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    sorry but this sound ludicrous !! matter of fact, it should be BETTER to calibrate while motors are running and all elec running, then you actually COULD NULLIFY everything out and get rid of both uav and earth dirt 'interference' !!!!

    btw what made you think i did not understand the principle of compass calibration ??

    as i said if so 'sensitive' to interference then EACH AND EVERY FLIGHT SHOULD HAVE CALIBRATION OF COMPASS, NOT JUST EVERY 50 MI OR 500 MI, seems rather silly either way, no ??

    so back to the uav should do a self compass calibration by slowly spinning and nullifying interference and then detect actual flux lines from earth's metal core !!

    and of course, GPS should NEVER be disabled by uav if it was disabled, direction should be obvious via a few gps sats, OR the 15+ i normally get.

    yuneec either has poor systems s/w guys or maybe some 'real' reason for uav to ever disable gps and run away looking for 'north', seems BS at best, silly in the least !!!

    Hell GPS is far more reliable than compass, and what about accelerometer, and inertial navigation, 3 ways to find 'north' NEVER EVER reason to runaway !!!!! silly & stupid programming me thinks or not enuf ram or not enuf skill !!!

     
  4. HarveyH54

    HarveyH54 Active Member

    You do realize that the GPS satellites are about 200 miles overhead, and the signal is particularly strong? You gain and lose satellites, as you move around. A compass is fairly stable and reliable. A little redundancy is usually a good thing. If you lose too many, or all GPS, you still have a basic heading to work with from the compass. Not sure, but there probably are other redundant sensors for altitude, and exceleration. I lose GPS in my car briefly on occasion, no big deal. If I miss a turn or exit, I can get back on track, and the GPS will give directions when It's back in business. If you loose GPS while flying, probably not a big deal, unless you rely on the Smart mode functions or flying FPV. I don't do either, and fly by sight, not that GPS dependent.

    Do other UAVs auto-calibrate? Are other brands GPS only? I haven't looked to upgrade in a few years, and only a passing interest in new models as the roll out, but don't recall these features. Not something I'm looking for anyway, maybe I missed something.
     
  5. Sureshot

    Sureshot Member

    Feb 21, 2019
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    FWIW: Magnetic north can not only be off true north by declination, but also by inclination.
    The FC has a map table to compensate nagnetic north to true north by Lat/Lon.
    I have found that if the plane is 10 to 20 feet away from local magnetic interference, The compass calibration gives good results. If I get within 10 feet of steel beams for example, the FC has trouble navigating.
    I was flying my old CX20/F450 too close to some big steel, The result was sudden toilet-bowl circling.
     
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