Compass calibration

[beno]

After firmware upgrade to 3.0 compass was completely wrong (by almost 180 degrees). We did somehow managed calibration in flight, with very steep turns. After that it was 10-20 degrees off, but generally working.

I did try now to calibrate it on the ground. By my surprise, it was possible to calibrate only south and east directions, north and west was not reachable. Direction displayed in degrees on calibration screen was completely wrong. Compass directions are now approx 10 degrees off.

ADAHRS is located after the seat, and there are no steel or magnetic parts near it. It is oriented correctly, with pneumatic ports forward. Is it possible, that ADAHRS is internally magnetized or otherwise faulty? Is such behaviour normal, or I have to replace ADAHRS.

 

[jakej]

Beno

How far aft of the seat ?

 

[beno]

Approx 20cm, I as far as I remember.

 

[jakej]

Maybe you had something ferrous/metallic in your pockets ? or cell phone ?

I've never had an 'issue' with existing correct compass cal after upgrading to vers 3.0. Have done 5 so far.

 

[cmarbach]

Can you describe your compass calibration method? Do you use a compass rose painted at an airport, or do you align the aircraft with a separate compass? Do you use the aircraft mag compass or an external one?

 

[dynonsupport]

What software version did you have before 3.0?

 

[beno]

I had 2.6 before.

At calibration on ground I did use Garmin GPSMAP 62 handheld with magnetic compass. Garmin 62 was mounted near tail.

 

[Taigajoe]

Hello,

I have the same problem.

First I had V2.6 and I did not calibrate the compass after installing. Then I updated to V3.0 and yesterday I calibrated the first time my compass on ground as described in the manual.

After successful calibration I left the plane at the same position aligned to one main direction and I had immediately a difference of about 19°. I repeated several times the calibration procedure. No success.

During flight I have a difference also between 10 to 20°.

There are no ferromagnetic parts in the near - only carbonfiber and the window.

 

[Taigajoe]

Dear Dynon, do you have an explanation for this behavior and a workarround? Thanks!

 

[beno]

I checked again calibration. Uncalibrated compass direction can be read from calibration screen. At some directions it is 90 degress off, therefore I cannot reach North and West directions. It is acting like, it would have magnetic field around, but I think this is not the case (normal compass at same location is OK).

I have read somewhere in this forum, that more than 15 degress difference between real direction and uncalibrated direction is maximum which is still normal.

 

[mmarien]

I had trouble with my compass calibration. Same symptoms - only two directions in the calibration screen. I used another compass to try and find a magnetic source near the ADAHRS without a lot of luck. It turns out that the bolts that I used were metal. The guy I had helping built the mount didn't understand what the ADAHRS did and gave me some AN bolts. I just assumed they were brass. After a lot of checking  I put the compass right on the bolt but it would still just barely swing the compass. I replaced the bolts with brass and all was fine.

Because the symptoms are the same as what I had I would suspect some weak magnetic interference really close that is difficult to detect with a handheld compass.

 

[beno]

That is very logical. We already did done some experiments in that way, but possibly not enough precise. We will check again, trying to remove mounting and to see then uncalibrated directions.

 

[dynonsupport]

These are the first reports we've heard, and so we don't think there's a systemic issue here. But we've been wrong before.

Taigajoe: your issue does sound like straightforward magnetic interference of some kind.

beno: the "steep turns" part of your calibration is making me think that you may be misunderstanding part of the calibration. When you calibrate for any given direction, you should be straight and level, if you're doing the calibration in flight. An inflight cal also isn't ideal as you usually don't have an accurate heading reference (GPS is only correct in a true no wind situation)

 

[beno]

I would like to do calibration on the ground, because it would be much more precise. Possibly, my airplaine on the ground is not exactly level but tail is a little lower (with frontwheel however). Strange is such huge difference between uncalibrated and true heading: for example true 340, uncalibrated skyview 060.

 

[beno]

A did already mentioned, I cannot reach North and West to calibrate (only South and East), because uncalibrated direction is so strange. We did that in flight to trick the system somehow to calibrate to North and West also. The result is (logical) very unprecise however, but is much better than uncalibrated.

 

[Highlander1]

I just completed an installation of a 7" Skyveiw in my Highlander and initially installed the ADAHRS under the co-pilot seat where I had the EDC-10A installed before I upgraded to the Skyview. It would absolutely not calibrate. The only direction that would come in during the setup on a compass rose was north. The fix to the problem was locating the ADAHRS behind the baggage compartment where my boy scout compass showed a magnetically clean area. I made one complete calibration circuit as is called for in the setup and it has worked fine ever since.

Cant wait for the rest of the candy the Skyview is supposed to come out with.

 

[beno]

Today I checked again ADAHRS position, also with simple handheld magnetic compass. System for ailerons is approx. 25cm from ADAHRS but greatly influences compass. When moving ADAHRS further from that metallic system (additional 20 cm) compass direction was much better (before 80 degress off, then 20 degress off).

Skyview and ADAHRS are obviously perfectly OK. Now we just have to find better position for ADAHRS.

 

[jakej]

beno

Great to hear you're on track with the 'issue' - that's why I asked recently about how far from the seat it was, because of the possible magnetic influences.

Jake J

 

[beno]

We were so confident, that 25cm is enough (and that ailerons system is less magnetic) that didn't think of that possibility. Thank for advice, it was very helpful.

 

[Taigajoe]

I had indeed a straightforward magnetic interference - of my old magnetic compass. After removing it the calibration process runs fine and the result is perfect. How embarrassing...