High compass offset values


I keep getting relatively high compass offset values with a standard carrier board, Cube black, and ~6" compass pedestal.


I tried calibrating at home in my house and thought i might be getting some interference from my house wiring or even my steel table, but I just tried going out to a nearby soccer field with nothing within >100’ and only saw negligible results.

I tried looking in the arducopter documentation, but I cant seem to determine which compass is #1, #2 and #3.

I am 90% positive that compass #1 is automatically the external compass; but I am wondering how the offsets could be be so much higher for an external compass than the other two (which I assume are internals) especially considering how high off the frame it is mounted.

Are these numbers typical? They seem high to me. Am I missing something? Do I need to make a grounded shield underneath my HERE2?


Another thing for me to ask Michael about :slight_smile:
Those offset numbers are fine.



Sorry, I didn’t really know where the issue, if any, existed.

I’m glad to hear that those numbers are in line.

Am I wrong to be a bit concerned by the fact that the external compass mounted 6" up has significantly larger offsets than the internal compasses?


Not at all. The offsets are related to the physical constants of the area, as long as they are constant, it’s not important


Cool; that’s reassuring. It definitely didn’t change an appreciable amount when I went out to the field, and that was a completely different macro environment. (outside; noting within >100ft; open sky above) same micro environment, though cause it was right down the street.

So I guess that shows some consistency in results…

1 Like

now that you have had a fly, check the logs to see how much the magnetic field changed/mag field strength. you can do this in the dataflash log viewer


Unfortunately, I haven’t flown yet due to really in-opportune timing between when I ordered my cube and the grounding SB.

I recently went out to a massive soccer field to try a Re-calibration. No flight yet, but I’ll be sure to check the mags in the logs once I feel comfortable to fly.


These still feel high - How are these offsets so high and inconsistent even when 6" above the frame? This was just a little no-takeoff flight on my deck to verify stick input directions, and Im seeing a variation of 400+

2019-05-15 21-01-40.bin (1.6 MB)


Would a ground plane shield under my GPS module help?


Have you done a compass MOT yet?


No, that is next. I’d also like to look into compass learn which is a new feature since I’ve gotten back into arducopter. (my last build was back in the apm days)

My intuition is just telling me these are high. Idk. Hopefully I’m wrong.

How is it possible that the two internal compasses which are significantly closer to not only the flight controller electrical noise, but also the power dust and escs, are that much lower in magnitude?


The Log auto analysis is also identifying my compass offsets as high and the compass test is a big fat FAIL:

Log File G:\2019-05-15 21-01-40.log
Size (kb) 3618.662109375
No of lines 42385
Duration 0:11:02
Vehicletype ArduCopter
Firmware Version V3.6.8
Firmware Hash 2f409678
Hardware Type
Free Mem 0
Skipped Lines 0
Test: Autotune = UNKNOWN - No ATUN log data
Test: Brownout = GOOD -
Test: Compass = FAIL - FAIL: Large compass offset params (X:196.08, Y:-371.85, Z:485.55)
FAIL: Large compass offset in MAG data (X:196.00, Y:-371.00, Z:485.00)
mag_field interference within limits (4.94%)

Test: Dupe Log Data = GOOD -
Test: Empty = FAIL - Empty log? Throttle never above 20%
Test: Event/Failsafe = GOOD -
Test: GPS = GOOD -
Test: IMU Mismatch = GOOD - (Mismatch: 0.17, WARN: 0.75, FAIL: 1.50)
Test: Motor Balance = UNKNOWN - tuple index out of range
Test: NaNs = FAIL - Found NaN in CTUN.DSAlt

Test: OpticalFlow = FAIL - FAIL: no optical flow data

Test: Parameters = FAIL - ‘THR_MIN’ not found
Test: PM = GOOD -
Test: Pitch/Roll = GOOD -
Test: Thrust = GOOD -
Test: VCC = UNKNOWN - No CURR log data


Did a compass mot - got a max of 5.

according to the documentation, that is well within the “good” range of 0-30%:

Check the % of interference displayed. If it is less than 30% then your compass interference is acceptable and you should see good Loiter, RTL and AUTO performance. If it is 31% ~ 60% then the interference is in the “grey zone” where it may be ok (some users are fine, some are not). If it is higher than 60% you should try moving your APM/PX further up and away from the sources of interference or consider purchasing an external compass (or GPS+compass module (some of these)).