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ArduIMU with magnetometer HMC5843 and barometer SCP1000-D11

Posted by Yves Gohy on April 3, 2010 at 2:16pm

Hello, I did this because I noticed that the altitude of GPS is not stable. GPS coordinates are correct however.

They remain well within a radius of ten meters around the real point. But the altitude is completely crazy, it depends on the day, and even the moment of day. This is related to the position of satellites, I am in Europe, Is this the problem?.But, it's may be a problem for the stabilization of our plane in altitude. And increasingly it is not very accurate.

And with two I2C devices it works, cool.

What do you think of this approach?

arduimu, hmc5843, scp1000-d11, barometer, magnetometer

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Comments

Zoltan Beldi April 4, 2010 at 8:24pm

Curt, There has to be something seriously wrong there.

The kalman filter slips during constellation changes are only about 10 meters max (+/- 5m) providing you have reasonable sat geometry. For the sort of jumps you're seeing, it suggests that either

a) You have a bad GPS or
b) There is some interference or shielding happening.
3D Robotics

Chris Anderson April 4, 2010 at 7:18pm

Curt,

We have hours of data from the sky and have never seen a deviation of more than ~10 meters. It really depends on how many sats you're seeing. Inside or near buildings you may not have enough for good alt resolution, but in the air it's much better.
Scott Plunkett April 4, 2010 at 9:11am

This is an awesome idea for a remote sensor pod...we could integrate the magnetometer, airspeed sensor and barometric pressure sensor on one small board, then pass all of that thorugh to the ArduIMU; run a filter and cross reference the GPS with the airspeed, altimeter, bearing and location from that unit - it would be VERY robust, but require some additional code and allow us to negate some of the vagaries of using GPS while still reaping the benefits of having it onboard and mitigating our calculations where needed.
Harald Molle April 4, 2010 at 8:28am

Sorry, i did not read the previous comment, with that, my uBlox theory is smashed. A pity, i wanted it to be used in a project, where altitude is an issue.
Harald Molle April 4, 2010 at 8:21am

When i did my ship-experiences, i also logged the altitude for pure curiousity. For over one hour on a lake, (with always the same altitude :-) the readings from the GPS did only vary in some 2-3m. I used the em406. I think, in the air, the changes in attitude of the GPS antenna is a big problem and that may cause lots of "switching" between satellites, which will in turn "stress" the Kalman-filter algorithms. Maybe a circular polarized antenna like on the uBlox module will make it better. Would be interesting to hear from your futire findings.
Curt Olson April 4, 2010 at 6:49am

I have one of the popular new ublox5 gps's ... just sitting still here with no attitude change, I see the altitude wander + and - 200 meters above and below the approximate correct altitude for my location ... so that's a 400m (meter) spread just to be clear. That will probably improve a bit up in the air with a better view of the sky, but makes me a little nervous about any system that does altitude hold purely on gps.
Yves Gohy April 4, 2010 at 4:04am
Yves Gohy April 4, 2010 at 3:34am

P030410_22.050001.JPG

https://storage.ning.com/topology/rest/1.0/file/get/3692026327?profile=original
Developer

Pete Hollands April 4, 2010 at 12:23am

Yves thanks for sharing that. The picture shows the Magnetometer but where is the barometric pressure sensor ?
Yves Gohy April 3, 2010 at 11:45pm

And of course here is the code.
arduimu.zip

https://storage.ning.com/topology/rest/1.0/file/get/3692026307?profile=original