Build an Obstacle-Avoiding Robot: Sense, Scan, and Steer
A robot that roams on its own—sensing obstacles, scanning for openings, and turning toward clear space—built from parts you understood and tuned in simulation first.
An obstacle-avoiding robot is the natural next build after a line follower. A line follower follows—it tracks a line someone drew for it. This robot decides: with no track and no map, it senses the space around it and chooses where to go. That one difference—reacting to the world instead of following it—is the first real taste of autonomy, and it is still simple enough to understand completely.
This build path treats it as exactly that: a path. You start by understanding the sense–scan–decide–turn loop, add the components a mobile robot needs and learn what each one does, then—before spending anything or risking a miswire—tune the avoidance behaviour in the browser simulator until it navigates a cluttered space cleanly. Only then do you wire the real robot and transfer what you found.
Follow the tech tree below top to bottom. Each node opens once its prerequisites are done, and your progress is saved on this device, so you can build the robot over a weekend without losing your place.
Project roadmap
The build path
Follow the tech tree from parts to a robot that follows a taped line. Each node unlocks when its prerequisites are done, and your progress saves on this device.
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Components
- ControllerArduino UnoThe forgiving 8-bit board most people meet robotics through.
- SensorHC-SR04 Ultrasonic SensorA sonar ping in a two-dollar package—how a robot feels for obstacles.
- ActuatorSG90 Servo MotorThe nine-gram servo behind most robot arms, grippers, and steering.
- DriverL298N Motor DriverThe dual H-bridge that turns weak logic pins into motor power.
- ActuatorDC Gearmotor (TT Motor)The yellow gearbox motor that turns a bare chassis into a moving robot car.
- Chassis2WD Robot ChassisThe deck two motors, a free caster, and your electronics all bolt onto.
- PowerRobot Battery & Power PackThe difference between a robot that runs and one that keeps resetting.
Tutorials in this path
- Beginner · 22 minThe Obstacle-Avoidance Algorithm: Sense, Scan, Decide, TurnThe sense–scan–decide–turn loop that lets a robot avoid obstacles on its own.
- Beginner · 20 minRead an HC-SR04 Ultrasonic Sensor: Reliable Distance in CodeTurn ping-and-echo into a steady distance in cm—with a timeout and a median filter.
- Beginner · 18 minServo-Scan an Ultrasonic Sensor to Find Open SpaceSweep an HC-SR04 on a servo to find the clearest direction before you turn.
- Beginner · 18 min readControl DC Motors with PWM and an H-BridgeWire and control a brushed DC motor safely using PWM, an H-bridge, and realistic current limits.
- Intermediate · 20 min readDifferential-Drive Odometry from Wheel EncodersIntegrate left and right wheel motion into a mobile robot pose, then identify and calibrate drift.
Practise before you wire
Tune it in the live simulator
The build path routes through a browser lab. Find gains that follow the track cleanly here, then transfer them to the real robot.
Frequently asked questions
How does an obstacle-avoiding robot work?
It drives forward while an ultrasonic sensor watches the distance ahead. When something is closer than a set threshold, the robot stops, sweeps the sensor left and right on a servo to measure distance in each direction, and turns toward whichever way is most open—then resumes driving. The whole thing is a short sense–scan–decide–turn loop running many times a second.
Which sensor is best for an obstacle-avoiding robot?
The HC-SR04 ultrasonic sensor is the default: it's cheap, easy to wire, and reliable out to a few metres. A time-of-flight sensor gives a tighter, faster, more precise reading if you need it, but for a first obstacle-avoider the ultrasonic is the right balance of cost and simplicity.
Do I need to buy parts before I start this project?
No. The sensing and the avoidance logic run in the browser simulator, so you can understand and tune the behaviour before buying anything. Only the final build steps—wiring and assembly—need the physical Arduino, HC-SR04, servo, driver, motors, chassis, and battery.
Why isn't my obstacle-avoiding robot working?
The three usual culprits are a noisy or blocked ultrasonic reading (add a median filter and keep the sensor unobstructed), reading the sensor before the servo has finished moving (add a short settle delay), and powering the motors straight from the Arduino instead of through the driver (which browns out and resets the board).
How is this different from a line follower?
A line follower follows a track laid out for it; an obstacle-avoiding robot has no track and must decide where to go. It adds a scanning sensor and a real decision loop, which makes it the natural second robot to build after a line follower.