Maze-solving robot

Learn

What you’ll build

A robot that drives through a maze made of walls (cardboard boxes or planks), following the right-hand wall until it reaches the exit.

Parts

Your 2WD car, with two distance sensors: one facing forward and one facing right. Two HC-SR04s work (trigger them one after the other so they don’t hear each other’s echoes), or small ToF sensors such as the VL53L0X.

Build a test maze

• Corridors at least 2–3 times the robot’s width.
• Walls at least as high as the sensors.
• Start simple: an L-shape, then a U-turn, then add dead ends.

The algorithm

The right-hand rule (see Navigation):

Front	Right	Action
Blocked	—	Turn left (on the spot)
Clear	Gap (far)	Turn right gently
Clear	Too close	Steer left a little
Clear	Good distance	Straight

Tuning tips

• Turn into gaps gently, or the robot clips the end of the wall.
• Slow down: maze solving rewards reliability, not speed.
• A wall at a slant confuses ultrasonic sensors; keep walls square to the robot’s path.

Examples

Arduino wall follower

maze-solver.ino

const int ENA = 5, IN1 = 7, IN2 = 8, ENB = 6, IN3 = 9, IN4 = 10;

void setMotor(int en, int a, int b, int speed) {   // speed -255..255
  digitalWrite(a, speed > 0);
  digitalWrite(b, speed < 0);
  analogWrite(en, min(abs(speed), 255));
}

void drive(int left, int right) {
  setMotor(ENA, IN1, IN2, left);
  setMotor(ENB, IN3, IN4, right);
}

void setupMotors() {
  int pins[] = {ENA, IN1, IN2, ENB, IN3, IN4};
  for (int p : pins) pinMode(p, OUTPUT);
}

const int F_TRIG = 3, F_ECHO = 2, R_TRIG = 12, R_ECHO = 4;

float readCm(int trig, int echo) {
  digitalWrite(trig, LOW);  delayMicroseconds(2);
  digitalWrite(trig, HIGH); delayMicroseconds(10);
  digitalWrite(trig, LOW);
  long us = pulseIn(echo, HIGH, 20000);
  return us == 0 ? 300 : us * 0.0343 / 2;
}

void setup() {
  setupMotors();
  pinMode(F_TRIG, OUTPUT); pinMode(F_ECHO, INPUT);
  pinMode(R_TRIG, OUTPUT); pinMode(R_ECHO, INPUT);
  delay(2000);
}

void loop() {
  float front = readCm(F_TRIG, F_ECHO);
  delay(10);                                 // let echoes die down
  float right = readCm(R_TRIG, R_ECHO);

  if (front < 15) drive(-150, 150);          // wall ahead: turn left
  else if (right > 30) drive(170, 110);      // gap: gentle right
  else if (right < 10) drive(110, 170);      // too close: steer left
  else drive(170, 170);
}

Practice

Try it in the simulator

Maze solver

▶ Run↺ Reset

Your code (JavaScript)function loop() { if (distance() < 15) motors(-40, 40); else if (distanceRight() > 30) motors(60, 40); else if (distanceRight() < 12) motors(40, 60); else motors(60, 60); }Load starter code

Robot commands

• motors(left, right): wheel power, −100 to 100
• lineLeft(), lineRight(): true over the black line
• distance(): cm to the nearest thing ahead (max 200)
• distanceLeft(), distanceRight(): cm to the sides
• linePosition(): where the line is, −1 (left) to 1 (right), or null
• millis(): milliseconds since Run
• print(value): show a message below
• setup() runs once; loop() runs 50 times a second

Reach the goalEasy

Run the wall follower and note the time it takes to reach the goal.

Beat 45 secondsMedium

Tune the speeds and distances to reach the goal in under 45 s.

Remember the wayHard

Real maze robots explore once, then race the shortest route. Describe how your robot could record its turns on the first run and remove dead ends for the second run. Record each decision as L, R, S (straight) or U (U-turn). A sequence like “L U L” can be replaced by “S”.

Quick check

1. Which two directions do the sensors face for a right-hand wall follower?

Front and rightBack and leftUp and downLeft and right only

2. Why trigger two ultrasonic sensors one after the other?

So they don’t hear each other’s echoesTo save codeTo go fasterIt doesn’t matter

3. The robot clips wall ends when turning into gaps. Fix?

Turn more gentlyDrive fasterRemove the right sensorUse brighter LEDs

Check my answers