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Qtr-8a pid

Hi, i am making a line follower robot using arduino nano, pololu qtr8a sensor and tb6612fng dual motor driver.

This is my code:

#include <QTRSensors.h>

#define NUM_SENSORS 8 // number of sensors used
#define TIMEOUT 4 // waits for 2500 microseconds for sensor outputs to go low
#define EMITTER_PIN 13 // emitter is controlled by digital pin 13

//Define the Pins
// sensors 0 through 8 are connected to:

QTRSensorsAnalog qtra((unsigned char[]) {A2,A4, A6,A7,A1,A0,A5,A3 }, NUM_SENSORS, TIMEOUT, EMITTER_PIN);

int IndicatorLED = 13;

//Motor 1
int pinAIN1 = 6; //Direction
int pinAIN2 = 7; //Direction
int pinPWMA = 5; //Speed

//Motor 2
int pinBIN1 = 8; //Direction
int pinBIN2 = 9; //Direction
int pinPWMB = 10; //Speed

//Standby
int pinSTBY = 12;

unsigned int sensorValues[NUM_SENSORS];
unsigned int sensors[8];

int position = 0;
int error = 0;
int m1Speed = 0;
int m2Speed = 0;
int motorSpeed = 0;
unsigned long previousMillis = 0; // time keeping function
int BlinkTime = 300; // blink time
int CycleTime = 1; // used to call for a blink toggle
int BlinkCycle = 1; // used to alternate the LED on and off
///////////////////////PID TUNING//////////////
int lastError = 0;
float KP = 0;
float KD = 0;
int M1 = 50; //base motor speeds
int M2 = 50; //base motor speeds
int M1max = 50; //max motor speeds
int M2max = 50; //max motor speeds
int M1min = 0; //min motor speeds
int M2min = 0; //min motor speeds

//Constants to help remember the parameters
static boolean turnCW = 0; //for motorDrive function
static boolean turnCCW = 1; //for motorDrive function
static boolean motor1 = 0; //for motorDrive, motorStop, motorBrake functions
static boolean motor2 = 1; //for motorDrive, motorStop, motorBrake functions

void setup()
{
//Set the PIN Modes
pinMode(IndicatorLED, OUTPUT);
digitalWrite(IndicatorLED, HIGH);
pinMode(pinPWMA, OUTPUT);
pinMode(pinAIN1, OUTPUT);
pinMode(pinAIN2, OUTPUT);
pinMode(pinPWMB, OUTPUT);
pinMode(pinBIN1, OUTPUT);
pinMode(pinBIN2, OUTPUT);
pinMode(pinSTBY, OUTPUT);

for (int i = 0; i < 400; i++) // make the calibration take about 10 seconds
{
TimeCheck();
delay(5);
qtra.calibrate(); // reads all sensors 10 times at 2500 us per read (i.e. ~25 ms per call)
}

}

void loop()
{
TimeCheck(); //Check to see if it is time to blink the LED

position = qtra.readLine(sensors);

// compute our "error" from the line position
// error is zero when the middle sensor is over the line,
error = position - 3500; /// using an 8 sensor array targeting middle of position 4 to 5

// set the motor speed based on proportional and derivative PID terms
motorSpeed = KP * error + KD * (error - lastError);
lastError = error;
/////////CHANGE THE - OR + BELOW DEPENDING ON HOW YOUR DRIVER WORKS
m1Speed = M1 - motorSpeed; // M1 and M2 are base motor speeds.
m2Speed = M2 + motorSpeed;

if (m1Speed < M1min) //keep speeds to 0 or above
m1Speed = M1min;
if (m2Speed < M2min) m2Speed = M2min; if (m1Speed > M1max) //maximum allowed value
m1Speed = M1max;
if (m2Speed > M2max) //maximum allowed value
m2Speed = M2max;
// set motor speeds using the two motor speed variables above 255

forward(); // run the motors based on error information
}

//////////////////////FORWARD////////
//Drive both motors CW, full speed
void forward()
{
TimeCheck();
motorDrive(motor1, turnCW, m1Speed);
motorDrive(motor2, turnCW, m2Speed);
}

/* //Apply Brakes, then into Standby
motorBrake(motor1);
motorBrake(motor2);
motorsStandby(); */

void TimeCheck() {
unsigned long currentMillis = millis();
if (currentMillis - previousMillis > BlinkTime) {
// save the last time you blinked the LED
previousMillis = currentMillis;

BlinkIt();
}
}

void motorDrive(boolean motorNumber, boolean motorDirection, int motorSpeed)
{
/*
This Drives a specified motor, in a specific direction, at a specified speed:
- motorNumber: motor1 or motor2 ---> Motor 1 or Motor 2
- motorDirection: turnCW or turnCCW ---> clockwise or counter-clockwise
- motorSpeed: 0 to 255 ---> 0 = stop / 255 = fast
*/

boolean pinIn1; //Relates to AIN1 or BIN1 (depending on the motor number specified)

//Specify the Direction to turn the motor
//Clockwise: AIN1/BIN1 = HIGH and AIN2/BIN2 = LOW
//Counter-Clockwise: AIN1/BIN1 = LOW and AIN2/BIN2 = HIGH
if (motorDirection == turnCW)
pinIn1 = HIGH;
else
pinIn1 = LOW;

//Select the motor to turn, and set the direction and the speed
if (motorNumber == motor1)
{
digitalWrite(pinAIN1, pinIn1);
digitalWrite(pinAIN2, !pinIn1); //This is the opposite of the AIN1
analogWrite(pinPWMA, motorSpeed);
}
else
{
digitalWrite(pinBIN1, pinIn1);
digitalWrite(pinBIN2, !pinIn1); //This is the opposite of the BIN1
analogWrite(pinPWMB, motorSpeed);
}

//Finally , make sure STBY is disabled - pull it HIGH
digitalWrite(pinSTBY, HIGH);
}

void motorBrake(boolean motorNumber)
{
/*
This "Short Brake"s the specified motor, by setting speed to zero
*/

if (motorNumber == motor1)
analogWrite(pinPWMA, 0);
else
analogWrite(pinPWMB, 0);
}

void motorStop(boolean motorNumber)
{
/*
This stops the specified motor by setting both IN pins to LOW
*/
if (motorNumber == motor1) {
digitalWrite(pinAIN1, LOW);
digitalWrite(pinAIN2, LOW);
}
else
{
digitalWrite(pinBIN1, LOW);
digitalWrite(pinBIN2, LOW);
}
}

void BlinkIt() {
if (BlinkCycle == 1) {
//Led On
digitalWrite(IndicatorLED, HIGH);
}
if (BlinkCycle == 2) {
//Led Off
digitalWrite(IndicatorLED, LOW);
BlinkCycle = 0; // reset BlinkCycle
}
BlinkCycle++; // Set BlinkCycle to second mode
}

All the robot does is driving fast in circles.

What’s The problem ?

Hello.

There could be many reasons a robot would have that kind of behavior, so unfortunately there is not enough information for me to make any helpful guesses at the cause.

Are you using a white course with a black line? The first thing I would suggest doing is making sure you are getting a good calibration for the line sensors. Please note that you should make sure each sensor sees both the background and the line during calibration. After the calibration has run, could you try printing our your calibrated minim and maximum values for each sensor to the Serial Monitor? You can see how to do this in the “QTRAExample.ino”, from lines 56-72.

Brandon