Driving an Adafruit motor shield and a bluetooth module with Arduino Uno

Question

I am creating a simple 4 wheel robot (BO Motors 200 RPM) with Adafruit Motor Shield and Arduino Uno V3. I am trying to use a Bluetooth module to control the robot. However, unlike Mega, I do not have TX1 and RX1 pins on Uno, only 1 pair of TX and RX pins. So, it's a bit difficult to connect the bluetooth module because I realize that it needs soldering, jumper connection won't be possible.

I have following 3 questions. Any help is appreciated.

1. Which Arduino pins are actually used by the Adafruit Motor Shield? If I want to do Serial IO through SoftwareSerial, which Digital pins are safe (free/unused) to use?
2. If I continue to use the Arduino's Tx/Rx pins instead of using SoftwareSerial via Digital ports, will that be a problem? Are those pins available for use when the shield sits on top of Arduino?
3. Following is my code. When the robot runs, I only get one rear wheel running for almost any Serial input. Rest of the motors doesn't run. Will you please take a look at the code and see if anything looks wrong here.

#include <AFMotor.h>
char incomingByte;
int LED = 11;
#define MAX_DISTANCE 2000
#define MAX_SPEED 240
#define COLL_DIST 25
#define TURN_DIST COLL_DIST + 10
// Motor Drive Shield, set to 1kHz PWM frequency
AF_DCMotor motor1(1, MOTOR12_8KHZ);
AF_DCMotor motor2(2, MOTOR12_8KHZ);
AF_DCMotor motor3(3, MOTOR12_8KHZ);
AF_DCMotor motor4(4, MOTOR12_8KHZ);
int pos = 0;
int maxDist = 0;
int maxAngle = 0;
int maxRight = 0;
int maxLeft = 0;
int maxFront = 0;
int course = 0;
int curDist = 0;
String motorSet = "";
unsigned long timeNow = 0;
int maxOffsetSpeed = 20;
int right = 0, left = 0, front = 0, back = 0;
int issettings = false;
void setup() {
  Serial.begin(9600); // initialization
}

void loop() {
  if (Serial.available() > 0) { // if the data came
    timeNow = millis();
    incomingByte = Serial.read();
    if (issettings == true) {
      maxOffsetSpeed = incomingByte;
      return;
    }
    if (incomingByte == 's') {
      issettings = !issettings;
      return;
    }
    if (incomingByte == '1') {
      // front
      if (front < MAX_SPEED && back == 0) {
        back = 0;
        front = front + 40;
        moveForward(front);
      } else if (back > 0) {
        front = 0;
        back = back - 40;
        moveBackward(back);
      }
    }
    if (incomingByte == '2') {
      // back
      if (front > 0 && back == 0) {
        back = 0;
        front = front - 40;
        moveForward(front);
      } else if (back < MAX_SPEED) {
        front = 0;
        back = back + 40;
        moveBackward(back);
      }
    }
    if (incomingByte == '3') {
      if (back > front) {
        turnLeft(back);
        moveBackward(back);
      } else {
        turnLeft(front);
        moveForward(front);
      }
    }

    if (incomingByte == '4') {
      // right
      if (back > front) {
        turnRight(back);
        moveBackward(back);
      } else {
        turnRight(front);
        moveForward(front);
      }
    }

    if (incomingByte == '5') {
      // right
      front = 0;
      back = 0;
      stopRunning();
    }
  }
}

void moveForward(int speedSet) {
  motor1.setSpeed(speedSet + maxOffsetSpeed);
  motor2.setSpeed(speedSet + maxOffsetSpeed);

  motor3.setSpeed(speedSet);
  motor4.setSpeed(speedSet);
  motor1.run(FORWARD);
  motor2.run(FORWARD); // turn it on going forward
  motor3.run(FORWARD);
  motor4.run(FORWARD); // turn it on going forward
}

void moveBackward(int speedSet) {
  motor1.setSpeed(speedSet + maxOffsetSpeed);
  motor2.setSpeed(speedSet + maxOffsetSpeed);
  motor3.setSpeed(speedSet);
  motor4.setSpeed(speedSet);
  motor1.run(BACKWARD);
  motor2.run(BACKWARD); // turn it on going forward
  motor3.run(BACKWARD);
  motor4.run(BACKWARD); // turn it on going forward
}

void turnRight(int speedSet) {
  if (speedSet < 200) {
    speedSet = 200;
  }
  motor1.setSpeed(speedSet + maxOffsetSpeed);
  motor2.setSpeed(speedSet + maxOffsetSpeed);
  motor3.setSpeed(speedSet);
  motor4.setSpeed(speedSet);
  motor1.run(FORWARD);
  motor2.run(FORWARD); // turn motor 1 forward
  motor3.run(BACKWARD);
  motor4.run(BACKWARD);
  delay(200);
}

void turnLeft(int speedSet) {
  if (speedSet < 200) {
    speedSet = 200;
  }
  motor1.setSpeed(speedSet + maxOffsetSpeed);
  motor2.setSpeed(speedSet + maxOffsetSpeed);
  motor3.setSpeed(speedSet);
  motor4.setSpeed(speedSet);
  motor1.run(BACKWARD);
  motor2.run(BACKWARD); // turn motor 1 backward
  motor3.run(FORWARD);
  motor4.run(FORWARD); // turn motor 2 forward
  delay(200);
}

void stopRunning() {
  motor1.setSpeed(0);
  motor2.setSpeed(0);
  motor3.setSpeed(0);
  motor4.setSpeed(0);
  motor1.run(RELEASE);
  motor2.run(RELEASE);
  motor3.run(RELEASE);
  motor4.run(RELEASE);
}```

Answer 1

You did not mention which version of the Adafruit Motor Shield you are using, assuming it is a V2 as the V1 is now discontinued.

Which Arduino pins are actually used by the Adafruit Motor Shield? If I want to do Serial IO through SoftwareSerial, which Digital pins are safe (free/unused) to use?

If you take a look at the Motor Shield schematics, you can find that most digital pins are up for grab except D9 and D10 which are used for the stepper motors outputs.

If I continue to use the Arduino's Tx/Rx pins instead of using SoftwareSerial via Digital ports, will that be a problem? Are those pins available for use when the shield sits on top of Arduino?

It shouldn't be a problem to use the Arduino built-in UART, according to the official documentation the main UART is on D0 and D1 which are unused on the motor shield.

Following is my code. When the robot runs, I only get one rear wheel running for almost any Serial input. Rest of the motors doesn't run. Will you please take a look at the code and see if anything looks wrong here.

The first thing I notice is wrong is the library you are using is obsolete and shouldn't be used with Adafruit's V2 version for the Motor Shield.

Why don't you take a look at their tutorial for driving DC motors with the new library?

If you are in fact using a V1 motor shield, there are a lot more pins used for driving the motors but it looks like the UART would still be free to use. They also have a tutorial for that version, have you tried simple examples without the serial logic to verify each motor can be driven correctly?