Robots use sensors and actuators to interact with the world. Sensors are the input parts that collect information, such as light, sound, distance, touch, temperature, and motion. Actuators are the output parts that make something happen, such as spinning a wheel, moving an arm, lighting an LED, or playing a sound.
Understanding this input, controller, output pattern helps students see how robots sense, decide, and act.
Understanding Sensors and Actuators
A sensor does not give a robot a perfect picture of reality. It produces a signal that must be interpreted. Some signals are digital, meaning they have only two states such as pressed or not pressed.
A bumper switch is a simple example. Other signals are analog, meaning the value can vary over a range. A light sensor may report many brightness levels.
The controller often converts an analog voltage into a number before using it in a program. Students should notice the difference between a measured value and the real quantity. A distance sensor might report a value close to the wall distance, but its reading can include small errors.
Different sensors have limits caused by the environment. Ultrasonic sensors send out sound pulses and measure the time until an echo returns. Soft fabric, angled surfaces, or a narrow object may give a weak or misleading echo.
Cameras collect many pixels, yet they need enough light and careful programming to identify an object. Touch sensors only detect contact after it happens. For this reason, robots often combine several kinds of evidence.
A line-following robot can use light sensors to find a dark line, while wheel encoders measure how far its wheels have turned. Comparing sensor readings helps the controller make safer decisions.
Actuators need more than an instruction from a controller. A controller pin sends a very small electrical signal. Most motors need far more current than that pin can safely supply.
A motor driver sits between the controller and the motor. It uses a separate power source to provide the needed current while following the controller command. The driver can reverse the direction of a direct current motor by changing the direction of current flow.
It can control motor speed by sending short bursts of power. Longer bursts give more average power.
This method is called pulse width modulation. A motor can become hot, stall when blocked, or drain a battery quickly, so power planning matters in every moving robot.
Real robots use feedback to correct their actions. A robot that tells its wheels to run for two seconds assumes both wheels move equally. In practice, one wheel may slip or face more friction.
Encoders can report wheel rotation, allowing the controller to compare the target movement with the actual movement. This is useful in robot cars, lifting systems, automatic doors, drones, and factory machines. When building or programming a robot, test one part at a time.
Record sensor values in bright and dim conditions. Check the actuator with no load before attaching a mechanism.
Use a clear threshold, then test values near that threshold. Small changes in wiring, battery level, surface texture, or object position can change the result.
Key Facts
- Sensors provide input signals to a robot controller.
- Actuators receive output signals from a robot controller.
- Robot action loop: sense, process, act, repeat.
- Speed = distance ÷ time.
- A servo motor usually turns to a chosen angle, often from 0° to 180°.
- A simple control rule can be written as: if distance < 20 cm, then stop motor.
Vocabulary
- Sensor
- A sensor is a device that detects information from the environment and sends it to the robot controller.
- Actuator
- An actuator is a device that changes electrical energy into action, such as motion, light, sound, or force.
- Controller
- A controller is the robot brain that reads sensor inputs, follows instructions, and sends commands to actuators.
- Input
- Input is information entering a system, such as a distance reading from an ultrasonic sensor.
- Output
- Output is the response made by a system, such as a motor turning or an LED glowing.
Common Mistakes to Avoid
- Calling a motor a sensor is wrong because a motor creates motion instead of detecting information.
- Forgetting the controller is wrong because sensors do not usually control actuators directly in a robot system.
- Mixing up analog and digital signals is wrong because some sensors give many possible values while others give only simple on or off states.
- Ignoring power needs is wrong because motors, servos, solenoids, speakers, and bright LEDs may need more current than a small controller pin can safely provide.
Practice Questions
- 1 A robot uses an ultrasonic sensor and measures an object 15 cm away. Its rule is: if distance < 20 cm, stop the DC motor. What should the robot do?
- 2 A robot wheel travels 120 cm in 6 seconds. What is its speed in cm/s?
- 3 A classroom robot has a camera, microphone, touch sensor, DC motor, servo, LED, and speaker. Sort each part into input, output, or controller-related parts, and explain your choices.