paper: Take-Back-Half Shooter Wheel Speed Control

[Ether]

Originally Posted by tr6scott

The code is labview, more info from this link. http://www.chiefdelphi.com/forums/sh...d.php?t=113954

Doh. I remember our conversation now. I am starting to show my age. Sorry 'bout that.

[tr6scott]

Me too. NP.

[The Doctor]

I have found this to be an acceptable take-back-half algorithm:

cval -= (cval - goodval) / 2;

Where cval is the current value of [whatever] and goodval is the ideal point (what you want it to be at)

cval += constrain(-(cval - goodval) / 2,-max,max);

This also works, but is constrains the value to within a maximum speed, the variable max. Function constrain below:

float constrain(val,min,max) {
          return val>max?max:val<min?min:val;
}

This seems a lot simpler than the previously posted code, and I was wondering if they are equivalent?

[Ziv]

Originally Posted by The Doctor

I have found this to be an acceptable take-back-half algorithm:

cval -= (cval - goodval) / 2;

Where cval is the current value of [whatever] and goodval is the ideal point (what you want it to be at)

Where's the feedback here? How do you find goodval? The fact that you're setting cval suggests it's an output, and if you somehow knew the ideal output (namely goodval) then you wouldn't need closed loop control in the first place.

Now, if you instead have

cval -= (sensorval - goodval) / 2;

which seems to be what you were getting at, then what you secretly have is an integral controller (just the I from PID) with coefficient 1/2.

[Ether]

Originally Posted by Ziv

Now, if you instead have

cval -= (sensorval - goodval) / 2;

which seems to be what you were getting at, then what you secretly have is an integral controller (just the I from PID) with coefficient 1/2.

Yes.

And, just because it's an integrator, and its gain is 1/2, does not make it a TBH algorithm. The hallmark of TBH is the unique way that the output is reset at each zero crossing.