spherical positioning

[ahecht]

Originally Posted by Cuog

a good gyro does 2 axis(left right forward backward) so u would only need 2 placed perpendiularly

Well, not quite. A gyro (or actually an Angular Rate Sensor) measures speed of rotation, not translational acceleration, so a 2 axis accelerometer would measure pitch and roll, yaw and pitch, or yaw and roll.

Originally Posted by Cuog

no matter what u use it will be effected by acceleration because down and gravity is an acceleration(9.8m/s/s)

it is infact this acceleration that makes the gyro work just remember that

Umm, no. The gyros measure just your rate of rotation, using a tiny tuning-fork like device and the Coreolis effect. They are not affected in any way by gravity, and would work just as well in a zero-g environment.

Back to the original poster, a 3-axis gyro array would give you only orientation, not position. However, as you said, there is some drift (although over short periods of time, it's not too bad). 190s 2k5 robot used a rate gyro so that we could have field-oriented controls, and the drift over the 2 minute match was minimal. However, using a 3-axis accelerometer array in tandem with the gyro array would give you the ability to recalibrate which way is down while you are standing still.