|
Re: Picking a gyro for field-centric swerve control
Are you sure you want a pitch and roll gyro? If you use it to track field orientation you'll have to mount it sideways and "throw away" one output (unless like Golto you have some use for an inclination angle).
If you choose to go with the LM317 you'll need more external components than you might otherwise. I'd consider using the COM-00526 that they offer instead (fixed 3.3V). Be sure to check the reference design shown on the data sheet to see what external parts (typically capacitors) you'll need in either case.
Regarding drift, the only clues are in the datasheet. The "rate noise density" and "sensitivity change vs. temperature" are the parameters of interest based on your question. In theory you can predict drift vs. time based on those parameters, but as a practical matter the answers you get would only apply in laboratory settings. Even if you place very little dollar value on your time, you'll quickly have spent more in doing a formal analysis than in just buying the part and having fun with it. Analog purists who do noise analysis for fun will surely disagree. If one offers to help, by all means accept.
The resolution of the cRIO NI-9201 analog module is 12 bits over a 20V span, which equates to 4.88mv/bit, so even using the 4X output you'll want to add a gain stage to the output of the module if you *really* want the lower end of the 1500 deg/sec. The downside is that any gyro output noise will also be amplified. You might choose to use a gain of about 20 (resulting in 13.4mv/deg/sec, or about 3 LSB). You'll then also need to be careful about how you prototype the circuit (proper grounding, signal routing, filtering, etc.) to minimize its susceptibility to noise pickup from external sources (like motor controllers).
Before you go to the lengths of adding a non-unity gain stage, you might want to try using the 4X output directly into the NI-9201 despite the resolution mis-match, just to see if you can live without the slow rate resolution you are "throwing away". You might be surprised. For what it's worth, we've never been able to saturate even a 150 deg/sec gyro on a real robot, so 1500 deg/sec could indeed be overkill unless you are planning to do something really exotic.
Hope that helps...
__________________

Last edited by ayeckley : 20-04-2010 at 19:15.
Reason: Clarification about the trade-off.
|