Compass or Gyro

[Darkbluestar]

I am working on an omni directional robot and I am going to be using a single laser mouse placed in the exact center of the robot in order to find out the robot's x,y location. I figured that I need to know what direction I am facing and that I would need either a compass or a gyro. However, I am not exactly sure which one would be best for my application. I only need to run the robot for about 3 minutes at a time and it will hopefully be moving pretty fast.

[Kohanbash]

Hi
I would recommend the compass as they are usually easier to use, and you don't need to deal with the gyros drift (a cheap gyro can drift degrees per second).

[Darkbluestar]

How does this one look?

http://acroname.com/robotics/parts/R117-COMPASS.html

[mpuvdd]

There is also this one by Parallax.
http://www.parallax.com/Store/Sensors/CompassGPS/tabid/173/CategoryID/48/List/0/Level/a/ProductID/98/Default.aspx?SortField=ProductName%2cProductName

[Kohanbash]

The parallax one looks nice even thou I don't see the resolution anywhere...

[Darkbluestar]

The parallax chip looks nice but I am already using the only serial interface on my mcu. I am using the ATMEGA644. I was thinking about the acroname one because it has an I2C interface which I have room for.

[Admin]

If you are only running it for 3 minutes than a gyro would be infinitely better (drift will be insignificant in short time spans). The problem with a compass is that motors and nearby objects affect the reading.

Are you doing a three wheel or four wheel omni robot?

Make sure your laser mouse is always perfectly flush with the ground, or it won't work.

[Darkbluestar]

Thanks for the info. This is for a competition and other robots will be around so that might influence the compass. I am going to be using a four wheel, pretty much like your omni Admin, and I am going to try and put some sort of suspension on it(ME member on my team is working on it). I am planning on putting the mouse on a suspension system as well so it will always contact the ground(I'm working on that). What would be a good choice for a gyro? I am not really familiar with them and I don't really understand which one I should use. I am mostly going to use the gyro to keep the robot from rotating. I do not want the robot to rotate at all, that's why I am going to use omni wheels.

[Darkbluestar]

I found a compass with SPI and analog interface, how does it look? http://www.sparkfun.com/commerce/product_info.php?products_id=8372

[Admin]

I found a compass with SPI and analog interface

you mean gyro?

do you need SPI?

what would you consider acceptable error in degrees? (you will always have error)

[Darkbluestar]

Yes gyro sorry I don't need SPI, but my mcu has an SPI interface so I was just noting that. I am trying to look for as small an error as possible. I am not really sure what would be acceptable. I just need it to be accurate enough so that if my robot accidentally rotates I can compensate for that change. I need my robot to always face the same direction.