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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Yes, I observed this too.

Ok, so it is indicated to fly with autodec disabled in case of a GPS failure :o

BTW................ is it normal that with the compass (sses) calibrated and showing the correct direction, the EKF for the compass goes orange and red when I pitch and roll the copter ????

In YAW it is always green.

No, not normal - you should be able to get the EKF to stay mainly green.

If it's not then you have an issue.Note that when this happened to me it was because of issues with my current monitor and compass mot - basically my current monitor would not read 0 on USB power and thus the mag readings were all off for USB power. You should also (obvoiusly) check for interference. On a small quad this can happen very easily (e.g. from the battery).

thank you for that input.

I'll check and search what (interference) causes that EKF.

................more test and re-installs and re-configurations done:

The on board compass works fine alone.

Together with the external compass in the GPS module, the EKF still turns red when I tilt the copter in roll and pitch, regardless of the rotation in ° of the external module in relation to the PixHawk and in combination with roll 180° in the config.

I was told to rollback my firmware to version AC 3.2.1.

Of course, the EKF disappears........

Does this make sense? Or will this only hide my external compass problem and put my copter and my flying in to a risk for others and for me??

How you fix the gps? any magnetized bolt near? What happens if you disable the int one?, still turn red?

The GPS module and the PixHawk are still on a wooden board fixed only with blue tac.

There is no metal nor bolts, etc.

This way it is easier to move things around and to calibrate.

With the internal compass disabled, I also get the red bar indicating compass variance.

If you move higher the gps module? wires are ok? orientation it's ok?

Now when you move the gps module you notice a reaction in M Planner?

The GPS is on a little mast as it would on the copter.

I measured the wires, they have continuity from end to end :)

The orientation is shown in the pic attached = up is north.(??)

But I can't swear it of course.

When I move the GPS module, the EKF turns red.

No movement in the HUD (compass)

What do you think could be the cause ???


Hi Bernardo

Your int compass is probably damaged

I exactly had the same issue with 2 differents Pixhawk whom experiment by misfortune few crash. Even by disabling the Internal, still had Error Pos Vert Variance and Error Compass Variance (Full Red on EKF module..

Then i tried with a brand new one but with the same wires and GPS module

Everythings was Ok then


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