EDIT: Solved, by changing the following in this file: AP_Compass_HMC5843.cpp
change this line (274): cal[2] > 0.7f && cal[2] < 1.3f) {
to this: cal[2] > 0.7f && cal[2] < 1.35f) {
(Issue reported here: https://github.com/diydrones/ardupilot/issues/606) (thx James)
I bought a HMC5883L external compass and installed it on my APM2.5, v3.0.1 equipped quad, cutting the trace on the board as required and mounting it raised above the frame. Seemed to work OK but I noticed that on occasion the toiletbowling and erratic Loiter was still present.
Anyway to cut a long story short, my compass is technically functioning all the time while APM is booted, as evidenced by slight but constantly fluctuating Mx, My, Mz and Mag Field Strength values consistent with the behaviour of an electronic compass.
The weird thing is that sometimes the APM sees those values and updates the yaw heading in conjunction with the inertial navigation system and shows the correct heading on start-up. Loiter works great and all is well. More often than not though, the APM ignores these working valid compass values and shows only the inertial navigational yaw output, heading is zero degrees on start-up and Loiter is useless.
There is no pattern as to when or why this happens.
The graphs below shows the two times when I was able to log the problem. In both cases I detached the magnetometer from the frame and secured it independently, then, first I rotated the APM and frame while keeping the magnetometer stationary and in the second instance I rotated the magnetometer while keeping the APM and frame stationary. The first graph clearly shows the compass rotating but APM doesn't register it. The second is the opposite.
I have cleaned any flux off the boards and triple checked all the connections, visually and electrically, I didn't have a I2C plug so I have carefully soldered the 4 wire cable onto the I2C pins on the back of the board and there's a 4 pin header on the magnetometer side. The compass check shows no issues when the APM "sees" the compass and a "compass not initialized" error when it doesn't.
I have ordered another mag but it will take two weeks to arrive, in the meantime I fear that the new one might exhibit the same problem especially if the problem is not actually with the mag but with the APM or something else hence this appeal for some insight into this problem now.
APM does not "see" the changing magetometer Y value:
APM "sees" the changing Y value and updates the heading accordingly:
Replies
Hi James, don't know if you saw Randy's comments in the issue you posted but maybe you'll see this note.
Graham
Ok, so after a little chasing from Graham, I've looked into this issue and there are a few theories about why people are having problems:
So basically I'm proposing #1 and I think that'll fix the problem. Thoughts?
-Randy
I'm getting the following Arduino errors for the compass test?:
J:\unzipped\ArduCopter-3.0.1\libraries\AP_Compass\AP_Compass_HMC5843.cpp: In member function 'virtual bool AP_Compass_HMC5843::init()':
J:\unzipped\ArduCopter-3.0.1\libraries\AP_Compass\AP_Compass_HMC5843.cpp:239: error: 'Serial' was not declared in this scope
J:\unzipped\ArduCopter-3.0.1\libraries\AP_Compass\AP_Compass_HMC5843.cpp:274: error: 'Serial' was not declared in this scope
Do I need to add another #include or #define?
I've been reading your posts as well but it does seem very specific to this particular set-up and hardware. It's likely failing during the compass initialisation, the APM sees that failure and ignores it from then on. It perhaps continues to read in the values it's providing but because the initialisation failed it means that the compass's configuration might be incorrect so it's best that it ignores it actually.
Hi Graham,
I realise that this must be frustrating for you but in light of the fact that there are many of us now using an external compass without any issues, I suspect that the fault lies in your setup specifically rather than with APM or Arducopter in general. From what I can tell from your description, the compass intermittently fails to initialise. I would suspect: 1. Your external compass is faulty. 2. There is a intermittent connection problem between the external compass and the APM (bad solder joint/broken wire etc). 3. The on board compass is not fully disconnected and is intermittently connecting to the bus and corrupting the data.
I have gone over the compass code in an effort to see if anything more can be determined from a failed initialisation. In the file AP_Compass_HMC5843.cpp around line 237 there is a compiler directive to enable/disable some additional output from the initialisation routine. If you alter this line: "#if 0" to be "#if 1" and re-compile the compass test application that I pointed you to last time, you should get additional output at the beginning of the serial stream when the compass is initialised. You may also want to add the following after the line "/* useful for debugging */"
Serial.print("numAttempts: ");
Serial.print(numAttempts);
Serial.print("good_count: ");
Serial.print(good_count);
Also adding this after "_i2c_sem->give();" at approx line 268 (before the above mods) and before the line "return;"
Serial.println("Failed re-initialisation");
I have attached the amended file if this is more convenient.
I have not done a lot of SPI programming (other than tinkering with existing examples) and I am not sure why the code assumes a bad connection and allows for up to 20 attempts (numAttempts) but this might be a useful figure to monitor in your situation. Let me know how you go....
AP_Compass_HMC5843.cpp