Four DC toy motors controlled with Arduino Pro Micro (similar to Leonardo), HC-06 Bluetooth module and L293B motor driver.

BluetoothControlOfFourMotors.ino

//Four DC toy motors controlled with Arduino Pro Micro (similar to Leonardo), HC-06 Bluetooth module and L293B motor driver.
//Motor settings:
const int pwmMotorLeft = 6;
const int in1MotorLeft = 14; 
const int in2MotorLeft = 15; 

const int pwmMotorRight = 10;
const int in1MotorRight = 16; 
const int in2MotorRight = 9;  

const int pwmMotorTower = 3;
const int in1MotorTower = 8; 
const int in2MotorTower = 2; 

const int pwmMotorArm = 5;
const int in1MotorArm = 7; 
const int in2MotorArm = 4; 

void setup() {
  Serial.begin(9600);
  Serial1.begin(9600);//Serial1 is required to use RX pin of pro micro to receive data from HC-06 TX pin.  
  delay(1000); //For the following println to work
  Serial.println("Setup finished.");
}

void stopMotors() {
  digitalWrite(in1MotorLeft, LOW);
  digitalWrite(in2MotorLeft, LOW);
  
  digitalWrite(in1MotorRight, LOW);
  digitalWrite(in2MotorRight, LOW);
  
  digitalWrite(in1MotorTower, LOW);
  digitalWrite(in2MotorTower, LOW);
  
  digitalWrite(in1MotorArm, LOW);
  digitalWrite(in2MotorArm, LOW);
}

void goForward() {
  digitalWrite(in1MotorLeft, LOW);
  digitalWrite(in2MotorLeft, HIGH);
  digitalWrite(in1MotorRight, LOW);
  digitalWrite(in2MotorRight, HIGH);
}

void goBackward() {
  digitalWrite(in1MotorLeft, HIGH);
  digitalWrite(in2MotorLeft, LOW);
  digitalWrite(in1MotorRight, HIGH);
  digitalWrite(in2MotorRight, LOW);
}

void turnRight() {  
  digitalWrite(in1MotorLeft, HIGH);
  digitalWrite(in2MotorLeft, LOW);
  
  digitalWrite(in1MotorRight, LOW);
  digitalWrite(in2MotorRight, HIGH);
}

void turnLeft() {  
  digitalWrite(in1MotorLeft, LOW);
  digitalWrite(in2MotorLeft, HIGH);
  
  digitalWrite(in1MotorRight, HIGH);
  digitalWrite(in2MotorRight, LOW);
}

void turnTowerRight() {
  digitalWrite(in1MotorTower, LOW);
  digitalWrite(in2MotorTower, HIGH);
}

void turnTowerLeft() {
  digitalWrite(in1MotorTower, HIGH);
  digitalWrite(in2MotorTower, LOW);
}

void lowerArm() {
  digitalWrite(in1MotorArm, LOW);
  digitalWrite(in2MotorArm, HIGH);
}

void raiseArm() {
  digitalWrite(in1MotorArm, HIGH);
  digitalWrite(in2MotorArm, LOW);
}

void loop() {
  int delay_ms = 5;
  int avgSpeed = 8*30;
  if (Serial1.available())   {
    Serial.print("Serial1.available(). data: ");
    char data = Serial1.read();
    Serial.println(data);
    if(data == '1') raiseArm();
    if(data == '0') lowerArm();
    if(data == 'F') goForward();
    if(data == 'B') goBackward();
    if(data == 'L') turnLeft();
    if(data == 'R') turnRight();
    if(data == 'A') turnTowerLeft();
    if(data == 'D') turnTowerRight();
    if(data == 'S') stopMotors();
  }    
  analogWrite(pwmMotorLeft, avgSpeed);
  analogWrite(pwmMotorRight, avgSpeed);
  analogWrite(pwmMotorTower, avgSpeed); 
  analogWrite(pwmMotorArm, avgSpeed);
  delay(delay_ms);  
}