const int Speed = 255;
char state;

void setup() {
  pinMode(8, OUTPUT);
  pinMode(9, OUTPUT);
  pinMode(10, OUTPUT);
  pinMode(11, OUTPUT);
  pinMode(12, OUTPUT);
  pinMode(13, OUTPUT);
  Serial.begin(112500);
}

void loop() {

  //Save income data to variable 'state'
  if (Serial.available()) {
    state = Serial.read();
  }

  //If state equals 'F', move forward
  if (state == 'F') {
    digitalWrite(11, HIGH);
    digitalWrite(8, LOW);
    analogWrite(9, Speed);
    digitalWrite(13, HIGH);
    digitalWrite(12, LOW);
    analogWrite(10, Speed);
  }

  //If state equals 'G', move forward-left
  if (state == 'G') {
    digitalWrite(11, HIGH);
    digitalWrite(8, LOW);
    analogWrite(9, int(Speed/2));
    digitalWrite(13, HIGH);
    digitalWrite(12, LOW);
    analogWrite(10, Speed);
  }

  //If state equals 'I', move forward-right
  if (state == 'I') {
    digitalWrite(11, HIGH);
    digitalWrite(8, LOW);
    analogWrite(9, Speed);
    digitalWrite(13, HIGH);
    digitalWrite(12, LOW);
    analogWrite(10, int(Speed/2));
  }

  //If state equals 'B', move backward
  if (state == 'B') {
    digitalWrite(11, LOW);
    digitalWrite(8, HIGH);
    analogWrite(9, Speed);
    digitalWrite(13, LOW);
    digitalWrite(12, HIGH);
    analogWrite(10, Speed);
  }

  //If state equals 'H', move backward-left
  if (state == 'H') {
    digitalWrite(11, LOW);
    digitalWrite(8, HIGH);
    analogWrite(9, int(Speed/2));
    digitalWrite(13, LOW);
    digitalWrite(12, HIGH);
    analogWrite(10, Speed);
  }

  //If state equals 'J', move backward-right
  if (state == 'J') {
    digitalWrite(11, LOW);
    digitalWrite(8, HIGH);
    analogWrite(9, Speed);
    digitalWrite(13, LOW);
    digitalWrite(12, HIGH);
    analogWrite(10, int(Speed/2));
  }

  //If state equals 'L', move left
  if (state == 'L') {
    digitalWrite(11, HIGH);
    digitalWrite(8, LOW);
    analogWrite(9, 0);
    digitalWrite(13, HIGH);
    digitalWrite(12, LOW);
    analogWrite(10, Speed);
  }

  //If state equals 'R', move right
  if (state == 'R') {
    digitalWrite(11, HIGH);
    digitalWrite(8, LOW);
    analogWrite(9, Speed);
    digitalWrite(13, HIGH);
    digitalWrite(12, LOW);
    analogWrite(10, 0);
  }

  //If state equals 'S', stop
  if (state == 'S') {
    digitalWrite(11, HIGH);
    digitalWrite(8, LOW);
    analogWrite(9, 0);
    digitalWrite(13, HIGH);
    digitalWrite(12, LOW);
    analogWrite(10, 0);
  }
}