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Is it possible to align a mems gyro to approximately true north with no external data input - ie nothing input by the user. I want to put a mems gyro/acc ship on a board and mount the board to a ceiling and have it recognize the approximate direction of north, ignoring mechanical misalignments.

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    \$\begingroup\$ No compass or something? No. \$\endgroup\$
    – Eugene Sh.
    Dec 4, 2017 at 17:41
  • \$\begingroup\$ Get one with a magnetometer in it, then you can do the "spin around 3 times" alignment procedure. \$\endgroup\$
    – Ron Beyer
    Dec 4, 2017 at 17:44
  • \$\begingroup\$ Do you want to put it in a stationary home? Just draw an arrow on the ceiling. \$\endgroup\$
    – Eugene Sh.
    Dec 4, 2017 at 17:47
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    \$\begingroup\$ @HarrySvensson I guess some context would be nice... Quite a few years ago I had a car with a compass in the dashboard that had to be calibrated by driving around in a circle 3 times in one direction, and then 3 times in the opposite direction. Even now, Google recommends using a "figure 8" pattern" to calibrate the compass (align the magnetometers). \$\endgroup\$
    – Ron Beyer
    Dec 4, 2017 at 17:52
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    \$\begingroup\$ @Whit3rd Right. Now try to detect it with MEMS gyro and make the necessary calculations to find the north and do it in reasonable time... \$\endgroup\$
    – Eugene Sh.
    Dec 4, 2017 at 22:39

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MEMS gyros are not (yet) accurate (and stable) enough to do that, but laser-based gyros (FOGs and RLGs) are capable of directly measuring the 0.004166°/sec rotation of the Earth and determining the axis of that spin, thereby aligning themselves to true North.

If you'd like to learn more, search on the phrase "Strapdown Gyrocompass Alignment".

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  • \$\begingroup\$ "true north". Is north where the south pole of earth's magnetic field converges? Or is north a point where earth's axis of spin is penetrating? - Maybe it doesn't matter.. It's just the first time I hear "true north", which would indicate that the other would be the "false north". I wonder if John Snow would be sad if he was King of the false north. \$\endgroup\$ Dec 5, 2017 at 0:17
  • \$\begingroup\$ @HarrySvensson: I can't tell how serious you're being. True north is the Earth's spin axis, of course -- the only "north" that's relevant to navigation. Magnetic north is used as an approximation only because it's easy to measure with a compass. \$\endgroup\$
    – Dave Tweed
    Dec 5, 2017 at 4:51
  • \$\begingroup\$ No, I was being serious - Woaw, I never knew that. Now when you're saying it, it kind of makes sense. \$\endgroup\$ Dec 5, 2017 at 5:11
  • \$\begingroup\$ I thought he also asked "in jest". Google "compass deviation" and you'll see the difference may be 5-6 degrees. \$\endgroup\$
    – Larry_C
    Dec 5, 2017 at 15:20
  • \$\begingroup\$ With an RLG or FOG, does heading only alignment require a maneuver, or rotation of the platform for alignment? \$\endgroup\$
    – Larry_C
    Dec 5, 2017 at 15:22

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