Guys I need your help, APM 2.5 is new for me it´s the first time.  When I connect my usb cable to my bixler on the field, the red plane on the mission planner is opposite (almost everytime) to the true north.

What I did to solve the problem:

1- Check on “enable” magnetometer in MP/Configuration/hardware

2- Correct the declination and confirm in MP/configuration/adv parameter

That solution didn’t work completely, what I mean with that is that it corrects the orientation a little bit.

I don´t have an external magnetometer.

The question is:

What I have to do so that when I power up my APM 2.5 in the field and my bixler is pointing to N,E,W or S, in the mission planner that little red plane point to the same direction? 

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Where is your APM board located, is it near the motor? There are magnets in the motor which may affect the magnetometer.

Then the canopy is locked in place by two magnets, another possibility for error.

Have you calibrated the compass?

Hi Picea,

 My board is located away from motor and at least 10 cm from the magnets of the canopy. Its located above the wings in the bixler. 

Craig, Thx.

  Yes, I´ve calibrate my compass as fallow:

MP/cofiguration/hardware/check on enable magnetometer and then add my declination. This only helps a bit, let say that it was 180° opposite, doing that it will reduce to 150° opposite.

This may be something you've obviously double-checked but is your APM pointing the right way in the plane?

follow the calibration procedure here

https://code.google.com/p/ardupilot-mega/wiki/APM2RCSetup

4) Configure your hardware

In this tab, you can tell APM what optional sensors you have connected. Just click the check box for any sensor you're using. (Sonar is not currently supported with APM; it's primarily used for ArduCopter)

For the magnetometer (compass), you have a choice of calibration options once you enable the sensor:

  1. You can do nothing, and the code will try to figure out all the offsets and declination by comparing the compass readings with the GPS and IMU readings over time in flight. Pro: No user effort. Con: It takes a few minutes of flying to get right, so the compass is inaccurate at first launch.
  2. Manual calibration in the Mission Planner (above). You can enter your Declination as instructed below and then press the "Live Calibration" button and move and rotate your aircraft around for 30 seconds while it records the data and does some math to calibrate the sensor. Pro: It works. Con: it's a little awkward, especially for big aircraft. Also it doesn't reflect the magnetic interference that can occur when the motors are going in flight.
  3. Replay a flight log. This is a very cool option, shown above as Log Calibration, where you can just replay a previously recorded flight log (.tlog) and the code will compare the GPS and IMU readings with the compass reading and make the necessary corrections. Pro: Works great. Con: You must have already flown, if you load a .tlog file where you didn't actually fly you'll mess up your calibration and will have to do it again or risk poor flight performance.

To manually enter a declination for your geographic location, you can find the correct value by clicking on the link to open a web browser. Enter your location and it will give you a declination, as circled below:

In this case, I would enter "14.13" into the magnetometer line (the software converts from decimal to degrees/minutes).

Picea

I did the test off the bixler and the result is the same, so I think is not a matter of magnets.  

Hi Graham,

Yes, My APM is pointing the right way (input rail towards the nose of the plane) 

Graig, 

I did this, my declination is -11°55´ I put it into the magnetometer line as -11.55 the I check in the adv parameter COMPASS_DEC it says 0.207 which is ((11+ 55/60)/ (180/PI))

Now, if the APM 2.5 has a internal magnetometer. Why should I have to enable it in "Hardware options"?

You can choose not to use the compass for navigation and rely solely on the GPS.

Do the live calibration described in the instructions above.

Keshan,

Post a copy of your parameter file please. I had the same concerns as you and started a discussion here. It turned out for me to be quite simple.....I just went and flew the plane. I made sure all my parameters were set correctly (thus the reason why I want you to post your param file) and turned on COMPASS_LEARN, and voila all was good!

The problem started for me on a windy day where I couldn't fly, so I decided to work on some other issues with my antenna tracker. A buddy if mine was walking the plane around the field (quite comical) and I was observing the operation of the tracker all the while recording the telemetry on my laptop.

Later while replaying the tlog I noticed that the plane icon in the Mission Planner was pointed 180 degrees opposite the direction of travel. I was really concerned about this and afraid to fly till Pieter gave me the good advice to just go and fly it! I did and the direction indication corrected itself before I even left the ground.

So I would suggest you do two things, first upgrade the firmware to 2.73, second post your param file here and lets check it to be sure all your parameters are set correctly.

Regards,

Nathaniel ~KD2DEY

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