Robot Sensors Explained: How Robots See, Feel and Measure the World
A plain guide to the main robot sensors: distance, vision, motion, touch and position. What each one measures, what it is good for, and where it fails.
A robot cannot act sensibly if it cannot sense. Sensors turn the real world into numbers a program can use. Here are the main kinds, in plain language.
Distance sensors
Ultrasonic sensors send out a burst of sound above human hearing and time the echo. Longer echo means farther object. The common HC-SR04 is cheap and perfect for beginners. It struggles with soft surfaces that absorb sound and with angled surfaces that bounce it away. See ultrasonic sensor.
Infrared (IR) sensors use light. They work well at short range and as line sensors, but bright sunlight can confuse them.
Lidar spins a laser to measure distance in many directions, producing a map-like scan. It is accurate but costs more.
Vision sensors
Cameras give rich information: colour, shape, text. Software must interpret the image, which is harder. Depth cameras also give distance for each pixel. See Computer Vision for Robots.
Motion and orientation sensors
An IMU (inertial measurement unit) measures acceleration and rotation. It tells a robot if it is tilting or turning. Balancing robots and drones depend on it. Its weakness is drift: small errors add up over time.
Position sensors
An encoder counts how much a wheel or joint has turned. With it, a robot can drive a set distance or hold a joint angle. Wheels can slip, so encoders alone can drift from the truth.
Touch and force sensors
Bump switches tell a robot it has hit something. Force sensors measure how hard a gripper squeezes, which lets a robot hold an egg without crushing it.
Why robots use several sensors together
Each sensor has weak spots. Combining them, called sensor fusion, gives a more reliable picture. A self-driving car mixes cameras, lidar and radar for this reason. See LiDAR vs Radar vs Camera.
What goes wrong with the wrong sensor
- An ultrasonic sensor on a robot driving over a fluffy carpet may read nothing at all.
- A camera-only robot struggles in the dark.
- A robot that relies only on wheel encoders will slowly lose track of where it is.
Quick picker for beginners
| I want my robot to... | Use |
|---|---|
| Avoid walls | Ultrasonic or IR distance sensor |
| Follow a line | Two or more IR line sensors |
| Know how far it drove | Wheel encoders |
| Stay balanced | IMU |
| Recognise objects | Camera + Raspberry Pi |
Frequently asked questions
What is the best sensor for a beginner? The ultrasonic sensor: cheap, easy, and teaches distance sensing.
Can a robot work with just one sensor? Yes, for simple tasks. Complex tasks need several.
What is sensor noise? Random error in a reading. Good code averages or filters readings to reduce its effect.
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