int servoPin = A3;
Servo jamesServo;
int servoPos = 0;

void setup() {

  // attaches the servo on the A3 pin to the servo object
  jamesServo.attach( A3 );

   //Register our Particle to control the servo
   Particle.function("servo", servoControl);
   
   // Keep a cloud variable for the current position
  Particle.variable(  "servoPos" , &servoPos , INT );

}

int servoControl(String command)
{
    // Convert
   int newPos = command.toInt();
   // Make sure it is in the right range
   // And set the position
   servoPos = constrain( newPos, 0 , 180);

   // Set the servo
   jamesServo.write( servoPos );

   // done
   return 1;
}