int motorAdir = 8;
int motorApwm = 9;

int motorBdir = 11;
int motorBpwm = 10;

int forward = 1;
int backward = 0;

int delayTime = 100;//increase this if you want the change in speed to be slower
//decrease if you want the change in speed to be faster

void setup()
{
  // put your setup code here, to run once:
  pinMode(motorAdir, OUTPUT);
  pinMode(motorBdir, OUTPUT);
  pinMode(motorApwm, OUTPUT);
  pinMode(motorBpwm, OUTPUT);

  Serial.begin(9600);
}

void loop()
{
  // put your main code here, to run repeatedly:
  digitalWrite(motorAdir, forward); //we declared forward up top
  digitalWrite(motorBdir, forward);
  for (byte i = 0; i <= 255; i++) {//start at 0 and increase to 255
    analogWrite(motorApwm, i);
    analogWrite(motorBpwm, i);
    Serial.print("Forward: ");Serial.println(i);
    delay(delayTime); //again delayTime is up top

  }
  //By now the PWM values for both motors are 255, max speed.
  delay(delayTime);

  for (byte i = 255; i >= 0; i--) {//start at 255 and go down to 0
    analogWrite(motorApwm, i);
    analogWrite(motorBpwm, i);
    Serial.print("Forward: ");Serial.println(i);
    delay(delayTime);
  }
  delay(delayTime);

  //Now we do the same but backwards
  digitalWrite(motorAdir, backward); //we declared forward up top
  digitalWrite(motorBdir, backward);
  for (byte i = 0; i <= 255; i++) {//start at 0 and increase to 255
    analogWrite(motorApwm, i);
    analogWrite(motorBpwm, i);
    Serial.print("Backward: ");Serial.println(i);
    delay(delayTime); //again delayTime is up top
  }
  //By now the PWM values for both motors are 255, max speed.
  delay(delayTime);

  for (byte i = 255; i >= 0; i--) {//start at 255 and go down to 0
    analogWrite(motorApwm, i);
    analogWrite(motorBpwm, i);
    Serial.print("Backward: ");Serial.println(i);
    delay(delayTime);
  }
  delay(delayTime);
}