Quote:
Originally Posted by dyanoshak
Taken directly from the Jaguar source code:
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Reading the code is not my problem.
The code can only actually execute so fast.
PID loop performance is partially dictated by how fast the controller can respond...and it's not a function of your CPU clock (at least not entirely).
The entire reason we want to use the PID loop in the Jaguar is because last year a talented student and myself implemented a complete special case PID loop in Java on the cRIO and eventually it became monumentally clear the cRIO's software payload makes something like this problematic *PARTICULARLY* because of massive code execution speed issues. I want to avoid having to ever try to do something like this during a build season again. Not only because the actual control theory takes up volumes and I have to cut corners explaining it, but because these students are under immense external pressure and it's not fair to toss them under this bus without the mathematics to cover for it.
You can't get the parameters I want like this...unless you can assure me...how many steps of integration and derivative you'll make and how long each iteration called every...apparently 1ms...takes.
The question I'm basically asking is how fast can the Jaguar actually integrate in response to a change in the input and how fast can it do the derivative. Not whether or not the code can actually do it.
If you tune using a closed loop, you can only tune within the context of the limits of instability you observe or happen to measure. If you tune using the open loop performance as key criteria you can tune so that the system will be able to close the loop as best it can because you're also working within the parameters of the actual controller, not merely some information you gathered once upon a time in a galaxy far...far...away that 'seems to work'.
Please read this:
http://www.jashaw.com/pid/tutorial/pid3.html
Specifically:
"Units used to set integral or reset" and the section that follows if immediately about the derivative.
I would like to find out or be told how to measure:
I repeats per minute and the D rate in minutes for the Jaguar PID loop.