Servos not working properly with joystick

Question

So, I was working with a project in which I used a joystick module to control two servos at the same time. The joystick controls the servos in a way that when the joystick is moved along x-axis, both servos move in the same direction but when joystick moves in y-axis, the servos move in different directions. I have this program:

#include <Servo.h>
Servo servo1;
Servo servo2;
int joyx = 0;
int joyy = 5;
int joyval;
int joyvalx; 
int joyvaly;
void setup() {
    Serial.begin(9600);
    servo1.attach(3);
    servo2.attach(5);

}

void loop() {
    Serial.println(joyvalx + "," + joyvaly);
    int x = analogRead(joyx);
    int y = analogRead(joyy);
    if(x != joyvalx){
        joyval = map(x, 0, 1023, 0, 180);
        servo1.write(joyval);
        servo2.write(joyval);
    } 
    if (y != joyvaly){
        joyval = map(y, 0, 1023, 0, 180);
        servo1.write(joyval);
        servo2.write(1023-joyval);
    }
}

However, the servos don't seem to work properly. One servo works fine but the other just gets stuck. Also, if I use the code for only one direction (x-axis or y-axis) by removing the code for the other, then both servos work good. I can't understand the problem. If anyone does, please help me.

score 2 · Accepted Answer · answered Jul 08 '18 at 20:44

The problem, as jsotola pointed out, is that your code writes totally different values to the servos very fast. You don't combine the two values from the joystick, but just overwrite the previous servo value. So this cannot work.

As I interpret your description, you want the x axis to move both servos the same amount in the same direction (in unity), while the y axis determines the difference of position between them. If you move the y axis to one side, the first servo will go a bit clockwise, while the other goes a bit counter-clockwise. When you then move the x axis, both servos will move to the corresponding direction, while maintaining their position difference.

It is better to first write a formula, how you will calculate each servo position from the given joystick values. The above behavior can be described with these formulas:

servo_1_value = mapped_x + mapped_y;
servo_2_value = mapped_x - mapped_y;

Now you have to map the joystick values correspondingly:

mapped_x = map(x, 0, 1023, 0, 180);
mapped_y = map(y, 0, 1023, -90, 90);

Note, that you should change the parameters for mapping y to the values you need. In the above code they are set to the maximum (meaning that moving the y axis to either end will effectively disable the x axis, since the servo cannot move past 0 or 180 degrees).

You don't really need to check, if the value changed. But if you really want to, you should check the calculated values for each servo separately. Something like this:

if(servo_1_value != old_servo_1_value){
    servo1.write(servo_1_value);
}
if(servo_2_value != old_servo_2_value){
    servo2.write(servo_2_value);
}

But you don't really need to check for a change here.

Servos not working properly with joystick

1 Answers1