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Unread 20-04-2010, 21:28
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Chris Hibner Chris Hibner is offline
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Re: Picking a gyro for field-centric swerve control

Here are my random thoughts on a few things brought up in this thread:

-You should probably integrate the 1500 deg/s gyro in a very fast loop (1 ms if you can) and the 300 deg/s gyro in a slower loop. Doing this will provide plenty of oversampling to gain a few bits of resolution to make it nearly as accurate as the 300 deg/s gyro at a slower sample rate. The only thing is that you'll need to guarantee a very accurate bias calculation for the 1500 deg/s gyro with a lot of samples - you may not want to use the stock bias routine.

-due to noise in the angular rate signal, you'll probably want to check against the 1500 deg/s gyro when above 70% of saturation value of the 300 deg/s gyro (or thereabouts depending on the noise level). Any noise causing saturation of the output voltage will cause your calculated integral to have a permanent offset, and you really don't want that. On top of that, you can get some strange effects when internal op-amps saturate before the on-board filter. I don't want to get too deep into that but I had to do a big study on these affect in accelerometers for a past job - these issues can be pretty hard to track down, so be conservative when getting anywhere near saturation.

- If the A/D converter uses the same reference voltage as the angular rate sensor (i.e. gyro), you're usually good to go. By sharing the same reference voltage, the A/D conversion will be ratiometric to the the gyro signal (i.e. as the gyro signal changes, so will the A/D conversion and the errors will cancel out).

That's all I can think of for now - the commercial is almost over, so it's back to my TV show for now.
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Last edited by Chris Hibner : 20-04-2010 at 21:56.