Joystick filtering gone horribly wrong...help!

[JBotAlan]

Hey all,

I was asked to make the robot have a curved response in the drive motors, i.e. pushing the joysticks halfway gets you about quarter speed, but pushing them full gets you full speed. I was advised that this will make the drivers' jobs easier. However, it seems to be making my job more complicated...

I have a basic lookup table solution in place right now...but it doesn't work. Ideally, I want to be able to input a number of points on the curve (right now, I have 7) and have the code extrapolate the points in between. I would be able to tweak this curve, adjust the constants in code, recompile, and blast the code down again to have filtered joysticks.

Now, at this point in time, I am getting strange results. The code I have is trying to set outputs to values like 360-something or greater, and I can't figure out why (I know it's out of range. I know PWMs only go up to 254...). I am seeing this code get more and more complex, and I need some help implementing KISS in this situation.

Here's the code I've got right now:

unsigned char DRV_GetFilteredValue(unsigned char joystick)
{
	static const unsigned char lookup[] = {127,135,140,145,165,200,254};
	int temp_joystick = (((int)joystick-127)/21.1);
	printf("temp_joystick = %d\r\n",(int)temp_joystick);
	printf("joystick is %d\r\n", (int)joystick);
	if (temp_joystick >= 7) { temp_joystick = 6; }
	if ((joystick < 130) && (joystick > 124)) {
		return 127;
	} else if (temp_joystick < 0) {
		printf("lookup[temp_joystick] = %d, lookup[temp_joystick-1] = %d, output is %d\r\n", (int)lookup[temp_joystick], (int)lookup[temp_joystick-1], (int)((joystick - lookup[temp_joystick-1])*(lookup[temp_joystick] - lookup[temp_joystick-1]) / 21) + lookup[temp_joystick-1]);
		return ((joystick - lookup[temp_joystick-1])*(lookup[temp_joystick] - lookup[temp_joystick-1]) / 21) + lookup[temp_joystick-1];
	} else {
		temp_joystick = -temp_joystick;
		printf("lookup[temp_joystick] = %d, lookup[temp_joystick-1] = %d, output is %d\r\n", (int)lookup[temp_joystick], (int)lookup[temp_joystick-1], (int)254-((joystick - lookup[temp_joystick-1]) * (lookup[temp_joystick] - lookup[temp_joystick-1]) / 21) + lookup[temp_joystick-1]);
		return 254-((joystick - lookup[temp_joystick-1]) * (lookup[temp_joystick] - lookup[temp_joystick-1]) / 21) + lookup[temp_joystick-1];
	}
}

(If you can weed through that, you get a cookie)

You don't even have to look at that code. I just need something that I can put in place to filter the joysticks.

Thanks in advance for any help you can provide.

And I'm willing to throw out the code I've got; I just need *something* to work.

JBot