Arduino line following robot for beginners in C++(Arduino) - c++

Question

I'm working on a school project with very little resources. I need to make a line following robot which finds the way through a maze by turning left when possible. I already have a small body, but the robot doesn't seem to turn left/follow the line when needed. I also have no clue how I can get rid of small deviations and how I can make the robot turn when there are no more lines?
Materials:
Arduino Leonardo
qtr-8a ground sensor
two basic DC motors
Code:
#include <DRV8835MotorShield.h> //setup for motors
DRV8835MotorShield motors;
void setup() {
// put your setup code here, to run once:
motors.flipM1(true);
motors.flipM2(true);
}
void loop() {
//left groundsensor= analogRead(A0);
//rightgroundsensor = analogRead(A2);
//middlegroundsensor = analogRead(A1);
//motorstM1//right weel
//motors.setM2Speed(100);//left weel
if(analogRead(A0) > 750){ //turn left
motors.setM1Speed(100);
motors.setM2Speed(-100);
}
else if(analogRead(A1) > 750){//nothing left, so go straight
motors.setM1Speed(100);
motors.setM2Speed(100);
}
else if(analogRead(A2) > 750){//nothing in the middle, so robot has deviated, turn right a bit, if the deviation is to the rigth, I don't need the next loop
while(analogRead(A0) < 750){//turn right till black line is in the middle again
motors.setM1Speed(-100);
motors.setM1Speed(100);
}
}
else{//if they are all < 750, it's a deviation or a dead end, I will have to watch how the robot deviates so that I can turn let it always turn in the opposite direction
while(analogRead(A1) < 750){//turn right/left till black line is in the middle again
motors.setM1Speed(-100);
motors.setM1Speed(100);
}
}
}

Answer 1

//left groundsensor= analogRead(A0);
//rightgroundsensor = analogRead(A2);
//middlegroundsensor = analogRead(A1);
I'm assuming the line is wide enough that it can not be between 2 sensors and have both sensors report white. Correct?
Lets consider all the cases the car can run into:
Straight line
Ideally left should be white and middle black. In that case drive straight. But the car will drift left or right.
If A0 gets black turn more to the left. If A1 gets white turn more to the right.
Left turn, Left Branch
A0 and A1 both turn black, turn to the left.
4 way cross
A0, A1 and A2 turn black, turn to the left.
Right branch
A2 turns black, keep going straight
Right turn
A2 turns black and a bit later A1 turns white, turn right
As you see A2 can be ignored. And if you merge all the cases you get:
| A0 | A1 | movement
| white | white | turn right
| white | black | straight
| black | white | turn left or right, shouldn't really be happening
| black | black | turn left
So check for those 4 cases in loop() with a small delay and it should solve the maze.
Note: If the car gets stuck turning one direction for a long time you might want to go a bit straight. If the line is too thick you might just turn on the line and never see the edge. If you have white, white driving in a spiral to find the line again could help. Both cases indicate your loop is too slow or your speed to high. You should never loose the edge of the line.