Chief Delphi - H-Drive Programming

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Chief Delphi (http://www.chiefdelphi.com/forums/index.php)

- Java (http://www.chiefdelphi.com/forums/forumdisplay.php?f=184)

- - H-Drive Programming (http://www.chiefdelphi.com/forums/showthread.php?t=133110)

Ether

27-01-2015 22:06

Re: H-Drive Programming

Quote:

Originally Posted by kinganu123 (Post 1434921)

Yes, exactly this

@kinganu123: Is the following a correct interpretation of what you meant?

Let X be the value of the joystick strafe axis,
in the range 0 to +1 for strafe right.

Let G(X) be your Gaussian taper function, such that G(0)=4 and G(1)=1.

Let Xt(X) be the tapered value of X: Xt(X)=X*G(X).

If so, would you be so kind as to post your G(X) function.

kinganu123

28-01-2015 19:02

Re: H-Drive Programming

Our formula is e^(gaussianInput^2/-.18) where the gaussianInput is the polar degrees from 0 to pi where pi/2 is 0, 0 is 1, and pi is -1.
I'm putting the code below, in case what I've typed doesn't make sense, here's the code:

Code:

        centerCurrent = xAxis;

             double gaussianInput=angleToGaussianInput(Math.atan2(yAxis, xAxis));

             leftCurrent =gaussianConversion(gaussianInput)+rotate;

             rightCurrent=leftCurrent-2*rotate;



        private double gaussianConversion(double gaussianInput) {

                return Math.exp(Math.pow(gaussianInput, 2)/(-.18));

        }



        private double angleToGaussianInput(double rad) {

                if(rad>Math.PI)

                        rad-=Math.PI;

                return (rad-Math.PI/2.0)/(Math.PI/2.0);

        }

Ether

28-01-2015 23:22

Re: H-Drive Programming

Quote:

Originally Posted by kinganu123 (Post 1435377)

Our formula is...

OK, to see if I'm understanding your formula correctly, can we take a simple numerical example?

Suppose the driver pushes the joystick to Y=1, X=0.5, rotate=0. What will be the "tapered" value of X?

kinganu123

29-01-2015 20:03

Re: H-Drive Programming

Oh, sorry, I meant to say that the y-axis is the one that is modified, not the x.
So, x will be .5 and y will be 0.9702, or e^(((atan(1/.5)-pi/2)/pi/2)^2/-.18).

Ether

29-01-2015 22:39

Re: H-Drive Programming

4 Attachment(s)

Quote:

Originally Posted by kinganu123 (Post 1435852)

Oh, sorry, I meant to say that the y-axis is the one that is modified, not the x.
So, x will be .5 and y will be 0.9702, or e^(((atan(1/.5)-pi/2)/pi/2)^2/-.18).

I believe you left out a pair of parentheses:

e^(((atan(1/.5)-pi/2)/(pi/2))^2/-.18)

This is quite different from the previous description.

See attachments.

Have you guys driven with this yet? How is it working?

kinganu123

30-01-2015 01:15

Re: H-Drive Programming

Yes, I didn't realize that he specified the strafe axis, which would result in the confusion.
And we haven't been able to test it yet since the mechanical guys are currently assembling the elevator on the robot, so we're losing a few days on testing and tuning this.
Also, I thought I'd note here that we tweaked the code above, in case anyone else wanted to try our stuff out, because I noticed a slight flaw in getting the y values

Code:

centerCurrent = xAxis;

double gaussianInput=angleToGaussianInput(Math.atan2(yAxis, xAxis));

double scaledGaussianOutput=yAxis*gaussianConversion(gaussianInput)

leftCurrent =scaledGaussianOutput+rotate;

rightCurrent=scaledGaussianOutput-rotate;

Ether

30-01-2015 09:00

Re: H-Drive Programming

Quote:

Originally Posted by kinganu123 (Post 1435992)

Yes, I didn't realize that he specified the strafe axis, which would result in the confusion.

It's not just the axis; the gains are quite different from what was described.

I'm a math enthusiast, so don't take this wrong, but why the complicated function with exponential and inverse trig? Wouldn't a simple linear interpolated 6x6 LUT do the job... and be far more easily tuned to compensate for actual behavior once you've done your testing?

kinganu123

30-01-2015 18:30

Re: H-Drive Programming

So we do have a simpler version coded up with some sort of linear adjustment instead of this one (I had some of the other students write that as a backup), but the main reasoning behind this method was to allow y to increase significantly to make up the lost y speed as the driver went at a smaller angle (with respect to the front of the robot).

Ether

03-02-2015 17:16

Re: H-Drive Programming

4 Attachment(s)

Instead of using arctangent and exponential functions, why not just multiply the X axis by a factor of 4, clip it at 1, and normalize the resulting X,Y pair?

Code:





void adjust(float Xj, float Yj, float *Xa, float *Ya){



        float mag;



        *Ya=Yj;

        

        if (Xj<=-0.25) *Xa=-1; 

        else if (Xj<0.25) *Xa=4.0*Xj;

        else *Xa=1.0;



        // normalize adjusted values:

        mag=sqrt(*Xa**Xa+*Ya**Ya);

        if (mag>1) {*Xa/=mag; *Ya/=mag;}

}

See attached Excel spreadsheet. The 100 tab shows an overview of adjusted XY pairs (cyan cells) for the entire first quadrant. The 25 tab zooms in for a closer look for small joystick values.

The attached plot shows a family of Xa vs Xj curves for Yj=0 to 1.

Or you could make the X gain a function of Yj, like so:

Code:





void adjust(float Xj, float Yj, float *Xa, float *Ya){



        float mag, gain;



        gain=1+3*Yj;



        *Ya=Yj;

        

        *Xa=gain*Xj;

        if (*Xa>1) *Xa=1;

        else if (*Xa<-1) *Xa=-1;



        // normalize adjusted values:

        mag=sqrt(*Xa**Xa+*Ya**Ya);

        if (mag>1) {*Xa/=mag; *Ya/=mag;}

}

See attached plots for Xa vs Xj for Yj=0 to 1
and Ya vs Yj for Xj=0 to 1

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