External vs. internal compass (PixHawk v.2.4.6) Help neede with config and compass variance (/inconsistency)


happy New Year , one and all :) !

now upgraded from 3DR APM2.5 to a PixHawk FC.

Have 3D (GPS) lock.

The compass calibration is the same as with the ol'good APM, the difference is I see two coordinates rotating and taking the points.

The values obtained are good and in the range written in the WiKi.

Now I'm unsure how to assign the external compass, so the PixHawk  uses the external compass in the GPS module?

1-  After the calibration success (more than 2000pts) when I move the PixHawk FC, the compass in Mission Planner moves an shows the orientation.

But if I move only the GPS/compass module, (holding the FC still) nothing happens - no movement in MP.

The GPS/compass module config' is compass 1, the internal compass is nr. 2.

I'm wondering what is wrong.

2-  Another strange effect is, that with nothing connected to the PixHawk, only linked to the PC via USB, I get a compass variance error (in MP) from the internal FC compass.

I hope somebody could enlighten me what I have to do to correct this compass problem. Thank you :)

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You can't do that.  The flight controller knows it's not turning so it ignores the compass variance.  External is 1 and internal is 2 and should only use the external one.  The internal one is used during startup as a secondary check.


thank you! Is there a method to check if the two compass are working (both).

Or visualize that.

Will the compass variance (red EKF) disappear after a start in stabilize for example?

I did a new calibration, still have this ^ issue when I move the copter.

No, it wants this to be good as a sanity check.  They have however relaxed the variance in an effort to reduce the issue somewhat.


good to know. Thank you.

Now I have to find out, where *north* is on the GPS/Compass module.

The arrow is in thge same direction as the cable connectio.

Never saw this before (assy' mistake?)

Is there perhaps a rule, where the north direction is, looking to the chip?

I posted something similar to this a few hours earlier; I get a solid red EKF and compass variance messages, even if both compasses get good offsets. Heading is good.

The difference is my internal one is pitched up 90' (AHRS orientation = 24).

Can I just disable the internal one? If I do, I get the same issue as the OP - move the copter and EKF turns orange or red.

Disable the int one and solve the problem.


do you mean physical - cutting a trace like in the APM,  or via software/settings ?

Do you - or someone - know how to identify  the directions on the chip? (pls see the pic above )

But what about the orange and red EKF alerts I get when I do this?

You can disable it in mission planner.

>_< it looks like this even after multiple re- recalibrations.

What is going on ?

sry for the typo (compasses)


Yes you disable in mission planner full params list,

Are you shure that you disable the int one? Its number two, If yes, you are having problems with your ext compass

thank you Cala and Euan for writing.

Without nothing connected to the PixWak, only the USB cable to the PC I also have the *compass variance* in the HUD window.

Is that normal, wrong setup or is that indicating a faulty compass chip?

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