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DJI Spark Compass Calibration
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<blockquote data-quote="BudWalker" data-source="post: 11628" data-attributes="member: 787"><p>Just got around to viewing this YouTube. Unfortunately, it promotes the misconception that the compass calibration detects and then compensates for magnetic effects external to the AC. This is not correct. In fact, it's mathematically impossible for a calibration to detect and compensate for magnetic effects external to the AC. Whether it's declination, deviation, or whatever it's labelled, if it's external to the AC then it can't be compensated for by a calibration.</p><p></p><p>This misconception has been around for a long time. I suspect it probably stems from this thread</p><p><a href="https://phantompilots.com/threads/compass-calibration-a-complete-primer.32829/" target="_blank">Compass Calibration, A Complete Primer</a></p><p>Lately, I've been attempting to address this starting about here</p><p><a href="https://phantompilots.com/threads/compass-calibration-a-complete-primer.32829/page-8#post-1238065" target="_blank">Compass Calibration, A Complete Primer</a></p><p></p><p>In addition, the video doesn't explain what a calibration actually does. I wrote this sometime back</p><p></p><p>The purpose of the "dance" is to expose each of the three magnetometers to a wide range of magnetic values. After this the "gain" is set for each of the three magnetometers so that there will be a uniform response to the geomagnetic field. To determine what the gain needs to be each of the magnetometers needs to be exposed to a wide range of magnetic values.</p><p></p><p>After rotating 360 degrees in the XY plane the X and Y magnetometers have both seen positive and negative values. By orientating the AC so that the Z axis is now perpendicular to it's original orientation and then rotating the AC 360 degrees the Z axis sees the positive and negative values. The usual nose down (X axis down) brings the Z axis perpendicular to it's original orientation. But, so does side down (Y axis down).</p><p></p><p>The "dance" is just a procedure to insure that the three magnetometers have each been exposed to a wide range of values. It would work equally well if the AC were "tumbled" provided it was placed in enough different orientations. I once did an experiment where the calibration was done upside down. I.e., first rotation was done top side down and the second rotation was done nose up. Didn't make any difference.</p></blockquote><p></p>
[QUOTE="BudWalker, post: 11628, member: 787"] Just got around to viewing this YouTube. Unfortunately, it promotes the misconception that the compass calibration detects and then compensates for magnetic effects external to the AC. This is not correct. In fact, it's mathematically impossible for a calibration to detect and compensate for magnetic effects external to the AC. Whether it's declination, deviation, or whatever it's labelled, if it's external to the AC then it can't be compensated for by a calibration. This misconception has been around for a long time. I suspect it probably stems from this thread [URL="https://phantompilots.com/threads/compass-calibration-a-complete-primer.32829/"]Compass Calibration, A Complete Primer[/URL] Lately, I've been attempting to address this starting about here [URL="https://phantompilots.com/threads/compass-calibration-a-complete-primer.32829/page-8#post-1238065"]Compass Calibration, A Complete Primer[/URL] In addition, the video doesn't explain what a calibration actually does. I wrote this sometime back The purpose of the "dance" is to expose each of the three magnetometers to a wide range of magnetic values. After this the "gain" is set for each of the three magnetometers so that there will be a uniform response to the geomagnetic field. To determine what the gain needs to be each of the magnetometers needs to be exposed to a wide range of magnetic values. After rotating 360 degrees in the XY plane the X and Y magnetometers have both seen positive and negative values. By orientating the AC so that the Z axis is now perpendicular to it's original orientation and then rotating the AC 360 degrees the Z axis sees the positive and negative values. The usual nose down (X axis down) brings the Z axis perpendicular to it's original orientation. But, so does side down (Y axis down). The "dance" is just a procedure to insure that the three magnetometers have each been exposed to a wide range of values. It would work equally well if the AC were "tumbled" provided it was placed in enough different orientations. I once did an experiment where the calibration was done upside down. I.e., first rotation was done top side down and the second rotation was done nose up. Didn't make any difference. [/QUOTE]
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