Open Source AHRS project: giving away hardware
Pascal Gosselin
pascal at aeroteknic.com
Mon May 12 04:21:10 CEST 2014
On 2014-05-11, 11:28 AM, joerg Reisenweber wrote:
> This all assumes a locked and defined mounting situation for the magnetometer.
> Then yes. For an embedded device however this method tells you nothing about
> the magnetometer heading. The embedded device can change relative orientation
> to the vehicle that's driving.
> PS: you must be very sure about the vehicle moving exactly straight ahead as
> well, for anything but a non-sliding car that's not guaranteed, think boat,
> even airplane
>
We're talking calibration here. Yes the unit should be rigidly mounted
for calibration of the sensors. There are also periods of "stay still
for X seconds" at various points in such a calibration. I have done
and continue to do lots and lots of AHRS calibrations of various types
on aircraft (airplanes and helicopters). I would be more than happy to
share the information that I have on various calibration techniques.
Once the sensors are calibrated (i.e. figuring out the drift of the Rate
Gyros when sitting still) and the magnetic environment of the device is
known, what's left is the alignment procedure. Every time you start the
AHRS code on the device, it would need to be motionless for a while.
Lying the GTA02/GTA04 flat on a table for example for perhaps 2-3
minutes might be sufficient.
I feel that this likely the reason why even the latest mainstream phones
don't have AHRS or IMU capability (an IMU would enable indoor navigation
over only very short distances in a smartphone, given the rather crude
quality of the MEMS sensors and horrific gyro drift expected if you are
bouncing around with the smartphone in your hand and moving rather
slowly without GPS aiding the Kalman filter).
Application for an AHRS on a smartphone would be for enhanced
geo-referencing of photos and "Google Glass" type applications that
don't make you look like a Glasshole. The other obvious application is
as an emergency backup attitude (Pitch and Roll) and Heading indicator
for airplanes and helicopters.... or simply recording of the sensor data
and doing post-processing on a server to process the data later (think
extreme sports, like playing back a skydive for example).
-Pascal
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