Deadzone Programming

Technical C/C++
1

I looked around a bit but couldn’t find any resources on this for c++
How do you program in a deadzone for a attack 3 joystick?
I wrote this code but it doesn’t seem to be working.

	void driving(){
		double y;           //variable for forward/backward movement
		double x;           //variable for side to side movement
		double turn;        //variable for turning movement
		if(driverStick.GetY()>0.3||driverStick.GetY()<-0.3){
			y=driverStick.GetY();
		}
		if(driverStick.GetX()>0.3||driverStick.GetX()<-0.3){
			x=driverStick.GetX();
			}
		if(driverStick2.GetX()>0.3||driverStick2.GetX()<-0.3){
			turn=driverStick2.GetX();
			}
2

Try this, you need to set default values. Also I just cleaned it up a bit.


void driving(){
	double y = 0;           //variable for forward/backward movement
	double x = 0;           //variable for side to side movement
	double turn = 0;        //variable for turning movement
	double deadzone = 0.3;	//variable for amount of deadzone

	if(driverStick.GetY() > deadzone || driverStick.GetY() < -deadzone) {
		y = driverStick.GetY();
	}

	if(driverStick.GetX() > deadzone || driverStick.GetX() < -deadzone) {
		x = driverStick.GetX();
	}

	if(driverStick2.GetX() > deadzone || driverStick2.GetX() < -deadzone){
		turn = driverStick2.GetX();
	}
3

Ok, thanks, I’ll try that at practice on monday.
Also, how does setting default values for those variables change it?

4

Well, if you don’t and you try to use it later after the if statement failing the value is set to null and you’ll get an error.

5

We’ve found the following to work great for dead zones. The main advantage is you can still generate values between 0 and .3. With the previously posted solution once you get out of the dead zone you’re instantly outputting .3 or 30%. If you notice we have a lot of 127s in the middle of the array. Those provide the dead zone but we shift everything else over so that once your out of the dead zone it doesn’t go straight to .3.

This was written on the old control system. Technically the cRio has enough power to run the equation we are using to generate the array. We’ve just never taken the time to switch it over.


const char inputShape[255] = {0,1,3,4,5,6,7,9,10,11,12,13,15,16,17,18,19,21,22,23,24,25,27,28,29,30,31,
	        33,34,35,36,37,38,40,41,42,43,44,46,47,48,49,50,52,53,54,55,56,58,59,60,61,62,
	        64,65,66,67,68,70,71,72,73,74,76,77,78,79,80,82,83,84,85,86,88,89,90,91,92,94,
	        95,96,97,98,100,101,102,103,104,106,107,108,109,110,112,113,114,115,116,117,
	        118,119,120,121,121,122,123,123,124,124,125,125,125,126,126,126,126,126,127,
	        127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,
	        128,128,128,128,128,129,129,129,130,130,131,131,132,133,133,134,135,136,
	        137,138,139,140,141,142,144,145,146,147,148,150,151,152,153,154,156,157,158,
	        159,160,162,163,164,165,166,168,169,170,171,172,174,175,176,177,178,180,181,
	        182,183,184,186,187,188,189,190,192,193,194,195,196,198,199,200,201,202,204,
	        205,206,207,208,210,211,212,213,214,216,217,218,219,220,221,223,224,225,226,
	        227,229,230,231,232,233,235,236,237,238,239,241,242,243,244,245,247,248,249,
	        250,251,253,254,255};
*/
float InputShape(float userValue)
	{
		int iUserValue;

		iUserValue = (int)(userValue * 127);
		iUserValue += 127;
		iUserValue = inputShape[iUserValue];
		userValue = iUserValue - 127;
		userValue /= 127;
		return userValue;
	}

--SNIP--

ly = InputShape(stick->GetRawAxis(2)); 
ry = InputShape(stick->GetRawAxis(5));
6

Quick question abotu the code, where does the variable userValue come from?

7

It comes from whatever line calls the InputShape() function.

8

Gah, wasnt paying attention lol

9

Instead of checking for both the positive and negative deadzone, you can just take the absolute value. In addition, you can reduce the number of function calls to GetX() and GetY() by assuming the value is valid and handling the exceptional situations.

#include <math.h>

...

void driving() {
    double y = driverStick.GetY();
    double x = driverStick.GetX();
    double turn = driverStick2.GetX();
    double deadzone = 0.3;

    if(fabs(y) < deadzone)
    {
        y = 0;
    }

    if(fabs(x) < deadzone)
    {
        x = 0;
    }

    if(fabs(turn) < deadzone)
    {
        turn = 0;
    }

...

}

Or, if you prefer the compact Arithmetic If operator:

#include <math.h>

...

void driving() {
    double y = driverStick.GetY();
    double x = driverStick.GetX();
    double turn = driverStick2.GetX();
    double deadzone = 0.3;

    y = ((fabs(y) < deadzone) ? (0) : (y));
    x = ((fabs(x) < deadzone) ? (0) : (x));
    turn = ((fabs(turn) < deadzone) ? (0) : (turn));

...

}
10

Thanks! Also, did you mean abs() instead of fabs()?

11

abs() takes an int and returns an int. fabs() takes a float and returns a float.

Since Joystick::GetX() and GetY() return floats, he did mean fabs().

12

Ah, thanks for the correction.

13