const int leftFrontDirection = 28;
const int leftRearDirection = 26;
const int rightFrontDirection = 24;
const int rightRearDirection = 22;
const int leftFrontSpeed = 13;
const int leftRearSpeed = 12;
const int rightFrontSpeed = 11;
const int rightRearSpeed = 10;
const int stop = 0; // the next 4 numbers are for example only
const int slow = 85;
const int medium = 170;
const int fast = 255;
const int forward = 1;
const int reverse = 0;

void setup() {
pinMode ( leftFrontDirection, OUTPUT );
pinMode ( leftRearDirection  , OUTPUT ); 
pinMode ( rightFrontDirection  , OUTPUT ); 
pinMode ( rightRearDirection  , OUTPUT );
pinMode ( leftFrontSpeed  , OUTPUT ); 
pinMode ( leftRearSpeed , OUTPUT ); 
pinMode ( rightFrontSpeed  , OUTPUT );
pinMode ( rightRearSpeed  , OUTPUT );
}

void loop() {
//move forward slow for 1 sec
move(forward, forward, slow);
delay(1000); 
//move forward medium for 1 sec
move(forward, forward, medium);
delay(1000);
//reverse fast for 1 sec
move(reverse, reverse, fast);
delay(1000); 
} 

void move(int leftDirection, int rightDirection, int speed) {
digitalWrite( leftFrontDirection, leftDirection );
digitalWrite( leftRearDirection, leftDirection );
digitalWrite( rightFrontDirection, rightDirection );
digitalWrite( rightRearDirection, rightDirection );
analogWrite( leftFrontSpeed, speed );
analogWrite( leftRearSpeed, speed );
analogWrite( rightFrontSpeed, speed );
analogWrite( rightRearSpeed, speed );
}