Compass chips

Depends on your application! In a car its usually an OK assumption. The bigger problem, as others mentioned above, is even with a perfect sensor the compensation and/or environmental interference may yield unusable results. We had a test aircraft where raising the landing gear swung the compass ~20 degrees!

Let us know how you make out, Best Regards, Dave

Reply to
Dave Nadler
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You haven't been for a drive with me :)

--
Clifford Heath. 
Traction is optional, velocity not.
Reply to
Clifford Heath

When you're sliding, you're probably not concerned that the GPS display has the wrong orientation ;-)

Reply to
Dave Nadler

Or a flight with me :) I've got to do this again soon, where the "aircraft departs from controlled flight".

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So do 14 year old pilots, before they are allowed to go solo.

Tom Takeoff is optional, landing isn't.

Reply to
Tom Gardner

GPS + IMU + some lateral vehicle acceleration will give you your heading.

As soon as the kalman filter sees some lateral acceleration on the GPS that it can correlate with accelerometer readings, it knows which way you're pointed.

(Assuming you're in a gravity field)

--
Tim Wescott 
Control system and signal processing consulting 
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Reply to
Tim Wescott

Almost once a week I wish that my car GPS had a built-in compass. The usual situation is I want to drive to some address, so I enter it into the GPS while the car is parked. The GPS figures out the route from where I am, but because it doesn't know which way the car is facing, it can't tell me which way to start driving. Garmin made some hiking GPS's with built-in compasses but I've never seen a car GPS with one. I'd buy it if they made it.

Regarding sensors:

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has some kind of compass sensor that they say is better than a fluxgate. They used it in a line of car compasses and instrumentation boards a while back, and I wrote some code that ran one of the instrumentation boards.

Reply to
Paul Rubin

Steer one direction with the rudder and the opposite with the elevators and you can get a dead-air heading several degrees off straight, and off vertically too.

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umop apisdn 

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Reply to
Jasen Betts

True, but you don't need to sideslip. Try ridge flying in a glider :) Or even just uncoordinated flying, using the rudder without ailerons :) Or just a strong 90 degree crosswind approx the same as your airspeed :)

Reply to
Tom Gardner

I question the accuracy without a compass; the alternative is to determine the angle by integrating the angular rotation. That is, of course, highly sensitive to noise, drift and zero offset.

Solid measurements would be appreciated.

Gravity isn't required - you need angular rotation.

Reply to
Tom Gardner

Interesting to see how you would negate the field distortion due to being surrounded by a large hunk of iron! Even then it wouldn't be accurate near Kiirunavarra, even neglecting the magnetic dip at high latitudes

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Vaguely what kind of measured performance were you able to achieve? Did you rely on sensor fusion, i.e. use other instruments as well?

Reply to
Tom Gardner

Car compasses correct for that. When you first install the compass, you press a calibrate button, then drive the car around in a circle. The changing part of the field is due to the earth, and the fixed part is due to the car. So it can subtract out the fixed part. I've had some compasses that did that (Precision Navigation Wayfinder), and they worked pretty well.

Of course with a compass and gps in the same box, it could know that you were near Kiirunavarra and make appropriate corrections.

Reply to
Paul Rubin

OK, thanks.

I very much doubt there the device contains sufficient localised knowledge. Supposedly Kiirunavarra was discovered when someone hiking put his knife down, and found it surprisingly difficult to pick up. The mountain is now being systematically removed, and IIRC will eventually turn into a very big hole!

What I don't understand is given that the heavier elements were all formed in supernovae, how come there is a concentration of them? Surely they should be uniformly distributed.

Reply to
Tom Gardner

It is not a uniform distribution, but a random distribution, which by its very nature has "concentrations" (clusters) and "holes". It is like a PRNG returning 2 five times in a row. It is improbable, but it still may happen.

--
Nils M Holm  < n m h @ t 3 x . o r g >  www.t3x.org
Reply to
Nils M Holm

Having an engine out also often results in some amount of slip, particularly at lower speeds. Assuming a multi-engine aircraft, of course...

Reply to
Robert Wessel

I once flew a track in the eastern arctic that magnetic error was briefly exactly -90 degrees. (Straight east of the magnetic pole) I was close enough to the magnetic pole that the magnetic error changed >1 degree / hour in a PBY.

w..

Reply to
Walter Banks

My father worked for a mining company called Cominco. At one point in the late 1970s they were developing a lead-zinc mine on Little Cornwallis Island, which is about 100 miles north of the magnetic pole, so the compass variation would have been 180 degrees!

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He used to joke about renaming it "Palm Island" to improve recruiting. ;)

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

The truly heavy elements are, indeed, distributed almost uniformly. That's what makes them so bloody hard to mine for.

This is, among other things, the reason why it use to make sense to base currencies on gold: the occasional gold rush set aside, gold is actually distributed quite thinly, yet evenly all over the place. This means that to dig up a certain amount of gold takes essentially the same amount of work, no matter where in the world you do it. This meant the value of gold stayed relatively fixed over time --- until industrialized mining blew up that concept.

Another example are the so-called "rare earths" (chemically: lanthanides), which are currently mined almost exclusively in one place in China --- with some nasty political consequences to boot. Yet it doesn't really matter much where you open such a mining operation: the yield will be pretty similar basically everywhere.

So why is there almost no other mine which might give the Chinese some competition? Well, that's because to get useful amounts of these ores involves going through incredibly large amounts of dirt, and using some seriously dangerous physical and chemical processing to first isolate the extremely diluted rare-earth ores from the rest of the dirt, then to separate individual ores them from each other. So you can mine for rare earths wherever you want, but you'll get serious amounts of pollution coming from some fricking _huge_, ugly holes in the ground if you do. This eventually got this kind of mining choked off by environmental protection rules, or flat-out closed by the government, almost everywhere.

Reply to
Hans-Bernhard Bröker

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