Self Balancing Robot Stopped Working for Unknown Reason

I've been building a self-balancing robot following the schematics and code from this tutorial

The difference in my project is that I am using for my DC motors two uxcell DC 12V 220RPM Encoder Gear Motors and a 12V battery pack to supply power to the motor driver and a 9V batter that came with my Arduino to power the Arduino.

I had followed the code and instructions for building the circuit, and it had worked. However, after mounting the circuit onto the robot's frame, the motors stopped working. I checked the serial monitor, and the Arduino was still detecting the right data from the sensor and outputting a power to the motors, but nothing was happening. I tried replacing parts and wires, but the issue still remains. Does anyone have any ideas?

9V block batteries are unsuitable for Arduino circuitry.

If you continue to have problems after fixing that one, please read the "How to use this forum" post before posting again.

It’s the battery that came with the ELEGOO UNO Project Super Starter Kit

This is the code I am using. I’m still working on the exact PID values to use though.

#include "I2Cdev.h"
#include <PID_v1.h>
#include "MPU6050_6Axis_MotionApps20.h"

MPU6050 mpu;

// MPU control/status vars
bool dmpReady = false;  // set true if DMP init was successful
uint8_t mpuIntStatus;   // holds actual interrupt status byte from MPU
uint8_t devStatus;      // return status after each device operation (0 = success, !0 = error)
uint16_t packetSize;    // expected DMP packet size (default is 42 bytes)
uint16_t fifoCount;     // count of all bytes currently in FIFO
uint8_t fifoBuffer[64]; // FIFO storage buffer

// orientation/motion vars
Quaternion q;           // [w, x, y, z]         quaternion container
VectorFloat gravity;    // [x, y, z]            gravity vector
float ypr[3];           // [yaw, pitch, roll]   yaw/pitch/roll container and gravity vector

/*********Tune these 4 values for your BOT*********/
double setpoint= 177; //set the value when the bot is perpendicular to ground using serial monitor.
//Read the project documentation on to learn how to set these values
double Kp = 21; //Set this first
double Kd = 0.8; //Set this secound
double Ki = 140; //Finally set this
/******End of values setting*********/

double input, output;
PID pid(&input, &output, &setpoint, Kp, Ki, Kd, DIRECT);

volatile bool mpuInterrupt = false;
void dmpDataReady() {
  mpuInterrupt = true;

void setup() {
  //initialize device
  Serial.println(F("Initializing I2C devices..."));

  //verify connection
  Serial.println(F("Testing device connections..."));
  Serial.println(mpu.testConnection()?F("MPU6050 connection successful"):F("MPU6050 connection failed"));

  //load and configure the DMP
  devStatus = mpu.dmpInitialize();
// supply your own gyro offsets here, scaled for min sensitivity

  //make sure it worked (returns 0 if so)
   if (devStatus == 0)
        // turn on the DMP, now that it's ready
        Serial.println(F("Enabling DMP..."));

        // enable Arduino interrupt detection
        Serial.println(F("Enabling interrupt detection (Arduino external interrupt 0)..."));
        attachInterrupt(0, dmpDataReady, RISING);
        mpuIntStatus = mpu.getIntStatus();

        // set our DMP Ready flag so the main loop() function knows it's okay to use it
        Serial.println(F("DMP ready! Waiting for first interrupt..."));
        dmpReady = true;

        // get expected DMP packet size for later comparison
        packetSize = mpu.dmpGetFIFOPacketSize();
        //setup PID
        pid.SetOutputLimits(-255, 255);  
        // ERROR!
        // 1 = initial memory load failed
        // 2 = DMP configuration updates failed
        // (if it's going to break, usually the code will be 1)
        Serial.print(F("DMP Initialization failed (code "));
//Initialise the Motor outpu pins
    pinMode (6, OUTPUT);
    pinMode (9, OUTPUT);
    pinMode (10, OUTPUT);
    pinMode (11, OUTPUT);

//By default turn off both the motors

void loop() {
  // if programming failed, don't try to do anything
  if (!dmpReady) return;

  // wait for MPU interrupt or extra packet(s) available
  while (!mpuInterrupt && fifoCount < packetSize)
        //no mpu data - performing PID calculations and output to motors    
        //Print the value of Input and Output on serial monitor to check how it is working.
        Serial.print(input); Serial.print(" =>"); Serial.println(output);
        if (input>150 && input<200){//If the Bot is falling
        if (output>0) //Falling towards front
        Forward(); //Rotate the wheels forward
        else if (output<0) //Falling towards back
        Reverse(); //Rotate the wheels backward
        else //If Bot not falling
        Stop(); //Hold the wheels still
    // reset interrupt flag and get INT_STATUS byte
    mpuInterrupt = false;
    mpuIntStatus = mpu.getIntStatus();

    // get current FIFO count
    fifoCount = mpu.getFIFOCount();

    // check for overflow (this should never happen unless our code is too inefficient)
    if ((mpuIntStatus & 0x10) || fifoCount == 1024)
        // reset so we can continue cleanly
        Serial.println(F("FIFO overflow!"));

    // otherwise, check for DMP data ready interrupt (this should happen frequently)
    else if (mpuIntStatus & 0x02)
        // wait for correct available data length, should be a VERY short wait
        while (fifoCount < packetSize) fifoCount = mpu.getFIFOCount();

        // read a packet from FIFO
        mpu.getFIFOBytes(fifoBuffer, packetSize);
        // track FIFO count here in case there is > 1 packet available
        // (this lets us immediately read more without waiting for an interrupt)
        fifoCount -= packetSize;

        mpu.dmpGetQuaternion(&q, fifoBuffer); //get value for q
        mpu.dmpGetGravity(&gravity, &q); //get value for gravity
        mpu.dmpGetYawPitchRoll(ypr, &q, &gravity); //get value for ypr

        input = ypr[1] * 180/M_PI + 180;


void Forward() //Code to rotate the wheel forward
    Serial.print("F"); //Debugging information

void Reverse() //Code to rotate the wheel Backward 

void Stop() //Code to stop both the wheels

9V block batteries are unsuitable for Arduino circuitry.

There is still an issue even if I am just powering the Arduino from the computer.

If you continue to have problems after fixing that one, please read the "How to use this forum" post before posting again.

I did read that. I can't give more specifics because I don't know where the issue is.

You have not provided enough information for anyone to understand what the actual problem is. But this strongly suggests that you made a construction mistake:

I had followed the code and instructions for building the circuit, and it had worked. However, after mounting the circuit onto the robot's frame, the motors stopped working.

So, you should go through the entire setup and double or triple check each and every connection for continuity and expected power, ground or signals.

Use a multimeter or oscilloscope for electrical tests.

DIY electronic projects are a "funny thing.' I found that if I took all the parts and assembled them, I get a it doesn't work thingy. Now you got this big chunk of interconnected thingies and you do not know which interconnected thingy is the culprit. I found that it is best to put one subsystem thingy at a time onto, what will be the final assembly, test, troubleshoot, move onto the next sub component thingy.

Also known as the 'small bites' method.
Don't try to eat the whole meal at once. You will fail.
Instead, take small bites. Chew them up properly. Swallow the food.
Only then, take another bite.

Same with your project. (as Idahowalker described above)