Arduino: Putting servos in my class causes them to rotate all the way to one side

Question

I am trying to create a new class that controls two servos. My code compiles just fine. However, when I run it, the servos just turn all the way to one direction. This seems to happen when I try instantiating the class (when in the constructor, I attach the servos in the class to pins).

In My class's header file, I have [UPDATED]

#ifndef ServoController_h
#define ServoController_h

#include "Arduino.h"
#include <Servo.h>

class ServoController
{
    public:
        ServoController(int rotateServoPin, int elevateServoPin);
        void rotate(int degrees);
        void elevate(int degrees);
    private:
        Servo rotateServo;
        Servo elevateServo;
        int elevationAngle;
        int azimuthAngle;
};

#endif

Code so far for my Class:

#include "Arduino.h"
#include "ServoController.h"

ServoController::ServoController(int rotateServoPin, int elevateServoPin)
{
    azimuthAngle = 0;
    elevationAngle = 0;
    elevateServo.attach(elevateServoPin);
    rotateServo.attach(rotateServoPin);
}


void ServoController::rotate(int degrees)
{
    //TO DO
    rotateServo.write(degrees); 
}


void ServoController::elevate(int degrees)
{
    //TO DO
    elevateServo.write(degrees);    
}

And finally my arduino sketch so far is just:

#include <ServoController.h>
#include <Servo.h>

ServoController sc(2 , 3);

void setup()
{

}

void loop()
{
}

I'm pretty sure the circuit I am using is fine, since if I do not use my class, and just use the servo library directly in my arduino file, the servos move correctly.

any ideas why this might happen?

[UPDATE]

I actually got this working. In my constructor, I have removed the lines to attach the servos to pins. Instead, I have added another method to my class which does the attachment.

ServoController::ServoController(int rotateServoPin, int elevateServoPin)
{
    azimuthAngle = 0;
    elevationAngle = 0;
//  elevateServo.attach(elevateServoPin);
//  rotateServo.attach(rotateServoPin);
}


void ServoController::attachPins(int rotateServoPin, int elevateServoPin)
{
    azimuthAngle = 0;
    elevationAngle = 0;
    elevateServo.attach(elevateServoPin);
    rotateServo.attach(rotateServoPin);

}

I then call this in my sketch's setup() function:

void setup()
{
  sc.attachPins(2,3);

}

It seems like if I attach my servos outside of the setup() function, my problem occurs.

[UPDATE July 27 9:13PM]

Verified something with another test:

I created a new sketch where I attached a servo before setup():

#include <Servo.h>

Servo servo0;
servo0.attach(2);

void setup()
{

}


void loop() // this function runs repeatedly after setup() finishes
{
  servo0.write(90);
  delay(2000);  
  servo0.write(135);
  delay(2000);
  servo0.write(45);
  delay(2000);
}

When I try to compile, Arduino throws an error:

"testservotest:4: error: expected constructor, destructor, or type conversion before '.' token"

So there was an error, but it was not thrown when the attach method was called from a class

Thanks very much

Are you sure you are not doing something bad accidentally with the two Servo objects? Like premature destruction, attaching them to the same pin, etc.? — user529758
You need to post actual code where you are instantiating your class, above looks fine to me. May be it is something else. — praks411
In the code provided you never actually set the set the position of the Servos. So they are presumably in an undefined initial state. — Craig
In my setup(), I have added sc.rotate(90); sc.elevate(45); but still the same thing happens. Thanks — user2526712
I actually got this working. In my constructor, I have removed the lines to attach the servos to pins. Instead, I have added another method to my class called attachServos(int rotateServoPin, int elevateServoPin) which does the attachment. I then call this in my setup() function. It seems like if I attach my servos outside of the setup() function, my problem occurs. Does that make sense? — user2526712

Jai Jai · Accepted Answer · 2013-08-26T23:11:31

The call to servo0.attach() needs to be inside the setup routine:

#include <Servo.h>

Servo servo0;

void setup(){
    servo0.attach(2);
}

As you discovered with your attachServo routine. You don't need the extra routine, just call attach method inside the setup.

Arduino: Putting servos in my class causes them to rotate all the way to one side

2 Answers