Who has had a play with fluxgate compasses?

krypton_john

Senior Member
Hi All,

There's a couple of cheap i2c compasses available, and I'm thinking of making a compass for use in an aircraft*. On the face of it, the project is very simple - a PICAXE, an i2c compass and an LCD display to show the heading.

However in an aircraft, you are tilting in the turns and pitching on climbs and descents, and I wonder if this generates an error the non gimballed compass reading? If so, would it be possible to use some sort of solid state rate gyro to correct this?

Thanks in advance for any comments!
JohnO

* don't worry - it needn't be attached to the aircraft power and it is not going be relied apon for navigation!
 

MFB

Senior Member
There is now a wide choice of electronic compass chips and some even have onboard signal condition that outputs data over a serial port, but all they have an inherent error of about two degrees in heading for each degree of tilt. For near static applications this error can be compensated with the aid of a tilt sensor. However, this sensor will be affected by dynamic acceleration and can only be used on slowly moving vehicles (e.g. submersible) not an aircraft.
 

krypton_john

Senior Member
Hi and thanks.

So how come the tilt error under acceleration cannot be compensated by using a tilt sensor or accelerometer?

Aircraft usually use a directional gyro which is unaffected by turns and acceleration. The only problem is that it drifts and has to be set to the compass periodically. Therefore presumably a solid state gyro could be used with the fluxgate compass resetting it when not turning?
 

BCJKiwi

Senior Member
Well it can but requires complex math, or additional hardware sensors. see a resonable discussion here;
http://www.patentstorm.us/patents/6836971-description.html

Off the shelf 3-axis tilt compensated compasses are available starting at > US$250.

The tilt compensation is good for 45 to 60 degrees (depending on the model) so I'm not sure it would be adequate for an aircraft unless not engaged in sharp turns or loops.

Other than that, mount the compass in a gimbal!
 
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krypton_john

Senior Member
Thanks BJ

45 degree turns are not used in aircraft unless you are having fun instead of navigating!

Unfortunately the gimbal won't help as it will align to the g-forces in the turns rather than aligning to gravity which I presume is what's required.

Looks like tilt compensated fluxgates are getting cheaper though - fluxgateworld.com (!) have them for £70 in quantity.

Cheers,
JohnO
 
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