Android / Arduino Remote Control Car

In this post we build a remote control car using Arduino, Bluetooth, and an Android device. The Android device serves as the controller. One cool factor of this project is our Android app uses the position of the Android device to control the car!

RC Car Schematic

/* This sketch is for a remote controlled car with four electric motors that uses the Arduino Uno, RN42 Bluetooth module, and an
Adafruit Motorshield. This code is free for anybody to use or modify
*/

#include <Wire.h> //needed for motors and motor shield
#include <Adafruit_MotorShield.h> //needed for motors and motor shield
#include "utility/Adafruit_PWMServoDriver.h" //needed for motors and motor shield
#include <ctype.h>

int con = 0; //global variable to track connection status
// Create the motor shield object with the default I2C address
Adafruit_MotorShield AFMS = Adafruit_MotorShield(); 
// create an object for each motor and assign it to a port on the shield 
Adafruit_DCMotor *M1 = AFMS.getMotor(1);
Adafruit_DCMotor *M2 = AFMS.getMotor(2);
Adafruit_DCMotor *M3 = AFMS.getMotor(3);
Adafruit_DCMotor *M4 = AFMS.getMotor(4);
int count = 0; //counts how long its been since comms from joystick
 String uDSpeed = "500"; //create global variables to hold speed and direction info
 String lRSpeed = "500"; //defulat is 500 because that is stop condition

//setup code only executed once
void setup() {
  Serial.begin(115200); //start serial commm
  
  //This loop runs until a connection from another RN42 is complete and a "#" is recieved from the car
  //The joystick RN42 is the slave
  while(!con) { 
    if((char)Serial.read() == '#') { con = 1; }//once connected change "con" to true
    delay(5);
  }

 AFMS.begin();  //Start motor shield object, create with the default frequency 1.6KHz
} 


void loop() {
  
  //check if a full speed / direction frame is ready to be read
  if(Serial.available() >= 6) {
    String temp; //temperary string to hold incoming data
    char c = (char)Serial.read();
    if(c == 'u') { //If a 'u' was read this is start of an up / down data frame
      for(int i=0; i<5; i++) { //loop to read 5 other bytes of frame
        if(i < 4) { //reads the speed portion of frame into string 
          temp += (char)Serial.read();
        }
        else { //look for end of frame 'd' character, if it is there save this reading as new speed
          if((char)Serial.read() == 'd') { 
           uDSpeed = temp; 
           count = 0; //just got speed so reset count
          }
        }
      }
    }
    else if(c == 'l') { //If a 'l' was read this is start of an left / right data frame
      for(int i=0; i<5; i++) { //following code is the same as above except for direction frame
        if(i < 4) {
          temp += (char)Serial.read();
        }
        else {
          if((char)Serial.read() == 'r') { 
           lRSpeed = temp; 
           count = 0; //just got speed so reset count
          }
        }
      }
    }
  }
  
  delay(1);
  //the following code will stop the car if no comms with joystick for 150ms
  count++;
  if(count > 20) {
    setMotorSpeed(500,500);
  }
  
  //function call to set motor speeds
  setMotorSpeed(uDSpeed.toInt(),lRSpeed.toInt());
}

//This function clears all bytes out of arduino serial read buffer
void clearSerialBuf() {
 while(Serial.available()) { Serial.read(); }
}

//This function uses the ADC values from the joystick and turns them into motor speeds for going 
//forware, right, left, and reverse. Inputs are the left/right and up/down joystick axis
void setMotorSpeed(int upDown, int leftRight) {
  int lR = 0;
  int bF = 0;
  
  //If left/right is 500 no turn 
  if(leftRight == 500) {
    lR = 0;
  }
   else if(leftRight > 500) { //If greater than 500 this is a right turn
     lR = 1;
     leftRight = leftRight - 500;
   }
   else { //less than 500 this is a left turn
     lR = 2;
     leftRight = 500 - leftRight;
   }
   
   if(upDown == 500) { //500 no up/down direction
      bF = 0;
   }
   else if(upDown > 500) {//more than 500 go forward
     bF = 1;
     upDown = upDown - 500;
   }
   else { //less than 500 go backward
     bF = 2;
     upDown = 500 - upDown;
   }
   
   //If direction variables are both 0 the car is stopped
   if(lR == 0 && bF == 0) {
     motorStop();
   }
   else if (bF==1) { //if forward variable is true
     if(lR == 0) { //no turn so go straight forward
       goForward(scaleSpeed(upDown));
     }
     else if(lR == 1) { //go forward and right
       goTurn(scaleSpeed(scaleTurn(upDown,leftRight)), scaleSpeed(upDown), 1);
     }
     else { //go forward and left
       goTurn(scaleSpeed(upDown),scaleSpeed(scaleTurn(upDown,leftRight)), 1);
     }
   }
   else if (bF==2) { //if backwards variable is true
     if(lR == 0) { //go straight backwards
       goBackward(scaleSpeed(upDown));
     }
     else if(lR == 1) { //go backward and right
       goTurn(scaleSpeed(scaleTurn(upDown,leftRight)), scaleSpeed(upDown), 0);
     }
     else { //go backward and left
       goTurn(scaleSpeed(upDown),scaleSpeed(scaleTurn(upDown,leftRight)), 0);
     }
   }
   else { //if no forward or back then just turn
     if(lR==1) { //Right turn, left wheels forward and right wheels backwards
       goRight(scaleSpeed(leftRight));
     }
     else { //left turn, right wheels forward and left wheels backwards
       goLeft(scaleSpeed(leftRight));
     }
   }
}

//function to stop the motors
void motorStop() {
  M2->run(RELEASE);
  M4->run(RELEASE);
  M1->run(RELEASE);
  M3->run(RELEASE);
}

//function to tell motors to go forward, input is speed
void goForward(int mSpeed) {
  M1->setSpeed(mSpeed);
  M2->setSpeed(mSpeed);
  M3->setSpeed(mSpeed);
  M4->setSpeed(mSpeed);
  M2->run(FORWARD);
  M4->run(FORWARD);
  M1->run(FORWARD);
  M3->run(FORWARD);
}

//function to tell motors to go backward, input is speed
void goBackward(int mSpeed) {
  M1->setSpeed(mSpeed);
  M2->setSpeed(mSpeed);
  M3->setSpeed(mSpeed);
  M4->setSpeed(mSpeed);
  M2->run(BACKWARD);
  M4->run(BACKWARD);
  M1->run(BACKWARD);
  M3->run(BACKWARD);
}


//function for left or right turn. inputs are speed for left tires and speed for right tires
//and whether we are going forward or backwards
void goTurn(int rTire, int lTire, int forward) {
  
  M1->setSpeed(rTire);
  M2->setSpeed(lTire);
  M3->setSpeed(rTire);
  M4->setSpeed(lTire);
   //code to turn Right
  if(forward) {
    M2->run(FORWARD); //M2 and M4 are left tires
    M4->run(FORWARD);
    M1->run(FORWARD); //M1 and M3 are right tires
    M3->run(FORWARD);
  }
  else {
    M2->run(BACKWARD);
    M4->run(BACKWARD);
    M1->run(BACKWARD);
    M3->run(BACKWARD);
  }
}

//right turn function, no forward or backwards motion
void goRight(int tSpeed) {
  tSpeed = tSpeed - (tSpeed*.2); //reduce speed by 20%
  M1->setSpeed(tSpeed);
  M2->setSpeed(tSpeed);
  M3->setSpeed(tSpeed);
  M4->setSpeed(tSpeed);
   //code to turn Right
  M2->run(FORWARD); //left tires
  M4->run(FORWARD);
  M1->run(BACKWARD); //right tires
  M3->run(BACKWARD);
}

//left turn function, no forward or backwards motion
void goLeft(int tSpeed) {
  tSpeed = tSpeed - (tSpeed*.2); //reduce speed by 20%
  M1->setSpeed(tSpeed);
  M2->setSpeed(tSpeed);
  M3->setSpeed(tSpeed);
  M4->setSpeed(tSpeed);
   //code to turn Right
  M2->run(BACKWARD); //left tires
  M4->run(BACKWARD);
  M1->run(FORWARD); //right tires
  M3->run(FORWARD);
}

//This function scales the speed values from the joystick ADCs to the speed values of the motors
int scaleSpeed(int scale) {
  float r = ((float)scale/500)*250;
  return int(r);
}

//This scales the turns based on the forward / backward speeds
int scaleTurn(int fBSp, int lRSp) {
  float r =(float)fBSp*(1 - (float)lRSp/500);
  return int(r);
}