Gyro Compass

[Nathan]

For top secret purposes this year we need a compass. Do to the fact that compass sensors that rely on the Earth's magnetic field are unreliable at best, we are looking for a compass that uses a gyro.

Now I know that such a compass exists, I remember finding one on the Internet but do to momentary stupidity did not bookmark it. I also know that we could "build" this ourselves by using a regular gyro sensor and an interrupt port, but would much rather buy a gyro that does all the math on board it's chip and just returns a 0-359.9 degree value.

Could anyone help me find this elusive chip?

Thanks a lot,
Nathan

[Gboehm]

Well my experiance flying has taght be a little bit about gyroscopic instruments. Remember that a Directional Gyro is subject to gyroscopic precession. Also a gyro will have to be set prior to each match, also if you compete at more than one event it will have to be set for that new arena.

[JohnC]

Or, you can put in your Teleop_Init() some code to initialize the starting position variable of the gyro, and do your calculations based on that.

[Nathan]

John, that's what we were planning on doing. We would just initialize it before the match with all the other sensors.

We know there would be some gyroscopic precession, but hopefully it won't be too bad.

Has anybody found one of these yet?

[ZZII 527]

97 is trying something similar, though we are going for the DIY approach of matching the kit gyro and a cheap digital compass to get the heading. The problem, if I understand it correctly, is: Compass is unreliable instantaneously because of noise, but good for long-term averaging. Gyro is good for short duration, but long-term it will drift away. So, there is a clever and simple to program filter that will combine the best of both into a clean heading signal.

http://www.chiefdelphi.com/media/papers/2010

You will have to use your imagination to take it from the vertical case, with an accelerometer measuring gravity, to the horizontal case, with a compass measuring heading, but I think it works. Here is a high-level diagram of what we're thinking about:

http://web.mit.edu/first/www/semiOLcontrol.pdf

Some off-board processing, but you could probably do it all on the IFI RC too. There are also other problems like magnetic interference and tilt errors, but maybe these can just be thrown into an offset factor?

[Nathan]

Ok, thank you for the info guys.

I was really hoping to find an off the shelf solution so that we didn't have to waste time doing R&D.

Thanks again,
Nathan