Hi all, 
I can't find a good description of how to calibrate your compass and I also have some problems with my compass' readings.

I have a Pixhawk autopilot module and a 3DR uBlox GPS/compass module. Connecting this module is simple (my compass is connected through the I2C splitter so not directly to the Pixhawk). In mission planner I want to set-up my compass so I did the following: 

1. Connect via COM to Pixhawk

2. Go to: 'Initial setup' -> 'Mandatory Hardware' -> 'Compass'. 

3. Choose the option: 'APM with External Compass' AND select 'rotation_none' from the drop down menu next to 'Manual'. I selected 'rotation_none' because my GPS/compass module is upside down and the arrow is pointing in the same direction as the arrow on the Pixhawk, so a belly-to-belly set-up. 

4. Click 'Live Calibration' and turn a bit with the Pixhawk.


But.... when I now check my compass readings in 'Flight Data' I get this very weird result: North is not were North is AND East and West are switched. So if I turn 90degrees clockwise starting from North my compass says he is looking to the West... 


Note: how do you know if the new settings "external compass" have been saved? Because when I open the compass tab a second time the checkbox is at 'Manual' again and not 'External'

Also, I've read that if you connect the uBlox module to Pixhawk, the internal compass is automatically turned off, although I have a fealing that both are turned on, because if you turn (yawing) either of the two modules seperately the measured heading in mission planner changes.

Can anyone help me?

Note to webdesigners: Is it possible to make a new category with 'Compass'? 

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@Menno,

If you are using the GPS/Compass module with a Pixhawk, why are you selecting "AMP with External Compass"?

You should be selecting the Pixhawk/PX4 option at the top of the selection list.

Regards,

TCIII ArduRover2 Developer 

Because that option shows a picture of the uBlox GPS/compass module that I'm using. And because my compass is external.... Should I select Pixhawk/PX4 then? But how does mission planner then know that I also have an external compass connected to the I2C port on the Pixhawk?

@Menno,

You have a Pixhawk. Read these Wiki instructions for the Pixhawk: GPS/Compass

Select the Pixhawk/PX4 option for the compass setup.

Regards,

TCIII ArduRover2 Developer

I followed the instructions.. but the compass gives bad readings. I'll put a picture below of how the compass is mounted (the arrows of both the pixhawk and ublox are pointing to the left). Since the ublox is upside down here (and the compass is upside down in the ublox) I should select "rotation none" right?
PS, I clicked "yes" when mission planner asked "FW version greater than APM:copter 3.01"?
The picture below shows my selections before I click "Live Calibration" to configure the compass:



@Menno,

Is it necessary to have the GPS/Compass attached to the bottom of the Pixhawk?

I do not recommend that configuration.

Mount the GPS/Compass so that it is right side up and facing the same direction as the Pixhawk arrow.

Regards,

TCIII ArduRover2 Developer

It's not necessary and I don't know yet how it will be in the final set up, but this is easy if you want keep both modules parallel during the configuration.... But no matter how they are mounted in the end, the compass should work, but it doesn't

That's the GPS orientation for those of us in the Southern Hemisphere Thomas.

Is this a joke, or is there hemispheric dependence? Note that I'm talking about the compass (not GPS).

I've found the problem. Apparently the compass was not in the right orientation. Now it is exactly alligned with the pixhawk board (tops up, arrows pointing in the same direction). 

One remark though, I still need to figure out how to configure it if I do change their orientation.
And I have to figure out how to disable the pixhawk internal compass, because he doesn't switch that off automatically upon detection of an external compass (as stated in several guides and discussions). It now mixes/filters the two readings. If that makes it more accurate or faster I don't know....

This mixing was of course the reason why I had problems in the first place when the ublox was mounted 180degrees w.r.t. pixhawk....mixing misaligned compass' readings makes of course no sense at all.

Menno,
PS, how to close (but not delete) this discussion or mark it as 'solved' or something.

Hi,

I'm having issues with an external compass calibration on my apm2.5.     

I'm in the southern hemisphere and was wondering if the magnetic inclination (I'm not talking about declination) which points up here (down in the NH) would effect the compass calibration. I don't know how mission planner calibrates the compass, but my guess is that the vertical magnetometer (pointing in opposite directions in each hemisphere) is compared to the accelerometer g vector (always down) during calibration(?).

Julian

There is no hemisphere difference. The calibration works the same in both northern and southern hemispheres.

In fact, the current compass calibration code was developed by people in Australia.

Cheers, Tridge

Today I got the same problem with apm2.5( http://www.quadkopters.com/product/apm-2-52/) with an ublox external compass( http://www.quadkopters.com/product/ublox-6m-gps/). when I calibrate it shows offset of -23 -24 130 . In gauge I see north and south heading is ok but if I turn my quad to East it shows West and vice versa.i have placed the external compass module just beside of apm.One problem is that my compass module have no direction arrow but I have tried and calibrated the compass with all four orientation but still the problem exist..But one thing I see as I compare the compass gauge with a real analog compass the reading is looks very similar but in the apm mission planner(http://ardupilot.com/downloads/?did=82) the heading of uav shows wrong direction for east and west.Any body have got any solution of this problem or any advice is highly appreciable.   

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