Thread: My new project

Code:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define pi 3.14159265

struct pos_s{
    int x;
    int y;
    };
int main(){
    float angle;
    struct pos_s pos;
    int i;
    scanf("%d", &pos.x);
    scanf("%d", &pos.y);
    printf("processeing...\n");
    angle = ((atan2((0 + pos.y), (0 + pos.x)))*(180/pi));
    printf("final angle:%f", angle);
    return 0;
    }

OK, but I work without a sign, and this gives the correct answer(haven't check it yet but I think it is correct....)

Compile this code and tell me what you think...

But it doesn't work when y is negative, why? It does work if x is negative, but not y...

I think something is wrong with the quadrants...

Originally Posted by Adak

Your point of reference for the slope can make the slope of the line, negative or positive, depending on which pair of coordinates you use as x1 y1, and which pair you use for x2 y2.

One pair puts you at the bottom of the line, and makes the line in your diagram positive (heading into the first quadrant).

If you change which point is x1 y1, then your point of reference changes, and now you're at the top of the line, and your slope will be negative (heading into the third quadrant). Your angle will always be positive, whatever the slope might be.

I know, but the problem is that my angle is negative , compile my code, try it you're self...

Originally Posted by yann

But it doesn't work when y is negative, why? It does work if x is negative, but not y...

-5.0 / 2.0 = -2.5

atan(-2.5) = -1.19028995 radians = -68.19859051 degrees


what do you mean it doesnt work?

Originally Posted by yann

I know, but the problem is that my angle is negative , compile my code, try it you're self...

It's supposed to be negative, thats why i said you have to check teh signs of the operators to know the quadrant it is in. if X is positive then a negative degree is in quadrant 4, if x is negative then a negative degree is in quadrant 3

crap, I should have read the entire thread.

I believe what he's looking for are angle numbers which are always positive, like on a compass face.

I tend to agree. Mathematicians may use negative angle numbers, but to me, that's like driving your car with a negative steering wheel -- < huh? > doesn't work for me.

I've added a couple lines of code to show how to tweak it for lower right quadrant, (positive x, negative y), entries:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define pi 3.14159265

struct pos_s{
    int x;
    int y;
    };
int main(void){
    float angle;
    struct pos_s pos;
    int i;
    printf("\nEnter the x coordinate: ");
    scanf("%d", &pos.x);
    printf("\nEnter the y coordinate: ");
    scanf("%d", &pos.y);
    printf("\nprocessing...\n");
    angle = ((atan2((0 + pos.y), (0 + pos.x)))*(180/pi));
    //adjustments for lower right quadrant  
    if(angle < 0)
      angle *= -1;
    if(pos.x > 0 && pos.y < 0)
      angle += 90;

    printf("\nfinal angle:%f", angle);
    printf("\n\n\t\t\t     press enter when ready");
    while((i = getchar()) != '\n');
    i = getchar();
    return 0;
    }

OK, i am going to do it in 3D, I have actually done some work, its x and y for left and right and y and z for up and down, and then i am going to make it control a turret... I already have two servos
and a micro controller(that I know how to use...I did some robotics in the 5th grade(11yrs old)...Its strange that here we have a totally different educational system...The best thing about it is that you decide what you want to be when you are about 15/17/etc...

Originally Posted by yann

I already have two servos
and a micro controller(that I know how to use...I did some robotics in the 5th grade

So how does that work? The turret moves in two dimensions -- around the y-axis, and then around the x-axis, with one servo for each?

Can both servos move at the same time?

No, I actually didn't do that yet but here is what i want...The turret first adjust his angle for left and right, and the for up and down, one servo is for left and right and the other one is for up and down...I already made the program that calculates the angle for left and right and up and down, and yes, both servos can move at the same time, it will rock! I think it is gonna fire match rockets(google for it they are awsome)

Originally Posted by yann

No, I actually didn't do that yet but here is what i want...The turret first adjust his angle for left and right, and the for up and down,

Yes, that is what I meant. The left-right is around the y-axis, since the y axis is vertical. The up-down is around the x-axis, since the x axis is horizontal. You are lucky in the sense that w/ 3D graphics, moving something in both those dimensions then involves the z-axis -- if the base of the turret is 0,0,0, the end/nose of the turret will have an x, y, z value (this is where I had to learn some trigonometry*). But if you are calculating the angle for each servo independently, then you do not have to worry about that I think, in quite the same way.

3D for real. Don't hurt anyone.

* my hand rolled wireframe sphere still has a wicked looking (alas, unintentional) "wormhole" like structure running thru the center, pole to pole. AFAIK no one has used it to travel to another universe yet.