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Originally Posted by Ether
Thanks Chris. I should have worded my question more precisely.
The high-pass filter would have to have a fairly low cutoff frequency to allow the rate information to pass through for rates typically seen in FRC robots: as you said, perhaps a 30-second time constant. I was wondering what this would do to control loops using the integrated yaw signal.
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That's a good question. With a long enough time constant, it shouldn't have any effect.
The problem with high pass filters is they act like bias-learning. If you turn in one direction long enough, it "learns" a little of that time-averaged yaw rate into the bias of the integration. Then when you stop turning it thinks you're turning a little in the opposite direction even though you're not turning* (see below). If the turning of the robot averages out to zero every 1/5th of a time constant or so, then the effect of the "learning" should be zero and the HPF will not affect the integral or the control loop. If your robot is going to turn a lot more in one direction, the HPF is a bad idea (2008 is a good example of where using an HPF is not good since you're always turning left).
The important part is that the turning averages out to zero in a time period much shorter than the time constant. If you can guarantee this, the HPF will have negligible effect.
I have a lot of data saved from my autonomous simulator. If I find some time over the next day or two I can throw in a high pass filter and post some plots of the before and after.
* - Interesting sidebar for those not familiar with signal processing: The human body is filled with high-pass-filter "bias learning" characteristics. The inner ear is a good one: you spin for a while on a merry-go-round and when you stop spinning, it's hard to stand up because the "HPF" in your inner ear learned the spinning into its bias. When you stop spinning your inner ear thinks you're spinning in the opposite direction so it's difficult to walk.
Another great example is smell: ever notice that after you're near something for a long period of time, you can't smell it anymore, but if you leave the room and come back, you can smell it again. That's due to the HPF effect in your sense of smell.
Your eyes have a similar mechanism - your vision processing uses a spatial HPF (spatial as opposed to a time-based HPF). There are many illusions you can find that use black/white transitions to create interesting effects that make the image appear different than it really is.