- Tue Feb 08, 2005 11:16 pm
Sheesh, I wrote all that and forgot to address Russ' problem.
Russ, what you're trying to do is generally called "integration." In theory, if you add up all of the measurements you get from a rate sensor over time, you end up with the position. And if your position is zero, then you're back where you started. Unfortunately, integrated signals are notorious for drifting. Noise in the system will make your results less and less accurate over time. So, it's good to have a second sensor to compare against, which doesn't drift as much. In this case, an accelerometer fits the bill pretty nicely.
Another issue with gyros is that any rotation on an axis on the than the gyro axis becomes noise. Suppose I have a gyro on the vertical axis, like a turntable. I tip it sideways 90 degrees, and it doesn't detect any movement. Now it's only detecting forward-backward rotation. So I can rotate it on the vertical axis 90 degrees, and it won't detect any movement. Now it's only detecting side-to-side rotation. So I can tip it backward 90 degrees. That done, it's now back on the vertical axis, 90 degrees off of its original heading, and it hasn't detected any movement.
I hope I got that description right. Anyhow, it's an extreme case, but it shows how you can confuse a gyro by moving it on axes other that the axis that it's measuring. If you're tilting your IMU in your hand, subtle off-axis movements of your hand are probably adding to the noise and confusing the gyro. Again, there needs to be a second sensor (like an accelerometer) to compensate for drift.
Redmond WA USA