I installed my magnetometer recently and it seems to be working nicely when looking at the CLI test. havnt flown yet though.
I was curious and decided to compare the magnetometer with a standard needle compass. I found that one of the 2 are about 5-10 degrees out.
Its not a lucky packet or chrismas cracker compass that I have, its quite a decent one so im pretty sure its facing magnetic north.
I might be getting ahead of myself here so the question is, should the front arm of my quad point in the same direction as the compass needle or is there some kind of explination for the slight offset?
I have double checked my declination. it is 17*44' negative. in South Africa, Pretoria.
to compare the arducopter compass and the regular compass, you should set the declination to zero in the CLI. If you don't do this, the ardu mag will show you true north instead of mag north (true north is important for position hold).
the other difference between the two will be the offsets. If you haven't flown your quad yet, the offsets will be all zero and this will lead to some inaccuracy in the headings returned by the ardu mag. If you fly it (or wave it around in the air for more than 4 minutes), the offsets should be updated and saved to eeprom (you can check via the CLi).
after all that I'd expect they'd be pretty close but even then 5 degrees of difference isn't much...we only need it to be accurate enough to stop yaw drift and work for position hold.
Oh yes that actually makes sense now, setting the declination to zero.
Once you put the declination in then the quad should point to true North.
got another quick question regarding the image below.
I cant show the values as I dont have my quad with me to plug in.
somewhere in the place that I have marked in red is a value called Magnetic_DEC or something like that.
What is this value for? Mine was showing 0.309 which is not my magnetic declination of 17,44.
It's a guess but i might be that it's the declination shown in radians. 17.44 degrees = 0.304 radians.
good quess=) I think you may be right! can anyone clarify?