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Unread 20-04-2010, 19:43
EricVanWyk EricVanWyk is offline
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Re: Picking a gyro for field-centric swerve control

Quote:
Originally Posted by Tom Line View Post
I had considered the LM317, but the 'optimal' input to the gyro is 3 volts, even though it can handle 2.6-3.7 or something near that.

One of the problems we have with older gyros we have in the shop is that we don't know their gains. How to FIND those gains is a mystery to me, so we have several gyros that are really not usable because I don't know how to find the gains to put into labview to get accurate readings.

I was concerned that changing the input voltage will also change the gain requirement: I believe in the datasheet I read that it would, but I might be mistaken. If it does, how do I go about find the correct gain value? Trial and error hasn't worked very well for our other gyros. You get some VERY strange readings even with just small changes in gain.

I like the idea of not having to worry about resistors to get the voltage regulator to the correct voltage: if there's an easy way to find the gain I should be using that sounds like a homerun.
Typically:
* Give the gyro an arbitrary gain.
* Zero the gyro.
* Rotate a large, known angle. Typically a dozen revolutions or so.
* Divide actual rotation by measured rotation.
* Apply this to the arbitrary gain.
* Profit!

Varying input voltage will usually affect gain AND offset, so be mindful. Offset error is likely to have a bigger impact.

Resistors are pretty stable over time, but have large birth error. So, I hate using them to set voltages in production ( and almost always go for fixed regulators if I have the choice ), but don't mind them in one-off situations.

As a reminder, you can see what choices I made for the KoP gyro by looking here: http://usfirst.org/roboticsprograms/....aspx?id=16337
To be honest, the unity gain stages are more to protect against mis-wiring than anything else. If I were to do this as a one off or for a more controlled audience, I'd probably skip the output buffering entirely.