Problems with Line-Follower code

Using Arduino Programming Questions
1

I am making a line follower robot for high school, i am using:
-qtr-8rc sensors
-Aduino Uno R3
-LN298N Motor Drive

My electric system is right but the code is failing me, i think i didn't call the functions in the right way in the void loop. Here is the code:

#include <QTRSensors.h>
QTRSensorsRC qtr;
const uint8_t SensorCount = 6;
uint16_t sensorValues[SensorCount];

float Kp = 0.028; //set up the constants value
float Ki = 0;
float Kd = 0;
int P;
int I;
int D;

int lastError = 0;
//Increasing the maxspeed can damage the motors - at a value of 255 the 6V motors will receive 7,4 V 
const uint8_t maxspeeda = 200;
const uint8_t maxspeedb = 200;
const uint8_t basespeeda = 180;
const uint8_t basespeedb = 180;

//Set up the drive motor carrier pins
int pin_in1 = 7;
int pin_in2 = 8;
int pin_ena = 6; // PWM speed control
int pin_in3 = 9;
int pin_in4 = 10;
int pin_enb = 5; // PWM speed control
int FULL = 255;

void setup() {
  Serial.begin(9600);
  //Set up the sensor array pins
  QTRSensorsRC((const uint8_t[]){A0, A1, A2, A3, A4, A5}, SensorCount);
 pinMode(pin_in1, OUTPUT);
 pinMode(pin_in2, OUTPUT); 
 pinMode(pin_ena, OUTPUT); 
 pinMode(pin_in3, OUTPUT); 
 pinMode(pin_in4, OUTPUT); 
 pinMode(pin_enb, OUTPUT); 
}

void loop() {
manual_calibration();
PID_control();
}

void PID_control() {
  uint16_t position = qtr.readLine(sensorValues);
  int error = 3500 - position;

  P = error;
  I = I + error;
  D = error - lastError;
  lastError = error;
  int motorspeed = PKp + IKi + D*Kd;

  int motorspeeda = basespeeda + motorspeed;
  int motorspeedb = basespeedb - motorspeed;

  if (motorspeeda > maxspeeda) {
    motorspeeda = maxspeeda;
  }
  if (motorspeedb > maxspeedb) {
    motorspeedb = maxspeedb;
  }
  if (motorspeeda < 0) {
    motorspeeda = 0;
  }
  if (motorspeedb < 0) {
    motorspeedb = 0;
  } 
  //Serial.print(motorspeeda);Serial.print(" ");Serial.println(motorspeedb);
}

void manual_calibration(){

int i;
for (i = 0; i < 250; i++) 
{
qtr.calibrate(QTR_EMITTERS_ON);
delay(200);
}

}
2

why do you call manual calibrate in loop() instead of setup()? doesn't is only need to be done once?

presumably 3500 is some expected intensity from the sensor tracking the bright line vs a dark background. how was this value determined? (try using Sreial.println() to display the measured sensor values and manually move the 'bot

are you sure the sign of the error produces the desired affect resulting in a left/right turn, or is it opposite

where are the motor speeds actually written to the controller?

may be better to label the variables left/right speed

3

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