Controlling a brushless motor ESC with arduino

Ok, this is what I got now:

#include <Servo.h>

Servo myservo; // create servo object to control a servo

int potpin = A5; // analog pin used to connect the potentiometer
int val; // variable to read the value from the analog pin

void setup() {
myservo.attach(5); // attaches the servo on pin 9 to the servo object
Serial.begin(9600);
}

void loop() {
val = analogRead(potpin); // reads the value of the potentiometer (value between 0 and 1023)
val = map(val, 0, 1023, 0, 180); // scale it to use it with the servo (value between 0 and 180)
myservo.write(val); // sets the servo position according to the scaled value
Serial.println(val); //lets me read the reult from serial monitor
delay(15); // waits for the servo to get there
}

However the motor wont spin in the other direction, do you know how to achieve that?