What is a robot? Sense, think, act

A robot is a machine that does three things again and again. It senses the world around it. It thinks: it decides what to do. Then it acts: it moves or changes something. After it acts, it senses again, because the world has changed. Robotics engineers call this the sense-think-act loop.

A toy car with a remote control has motors and a battery. But a person does the sensing and the thinking for it. Give the car a sensor and a small computer, and it can make its own decisions. That is the step from a machine to a robot.

#Sense, think, act on the robot car

The robots on this site share one design: the CoreEngine robot car. Each of its parts has one main job.

#Sense

The HC-SR04 sends a short burst of ultrasound, too high for people to hear. Then it listens for the echo. The longer the echo takes, the farther away the object is. The sensor does not know what the object is. It only knows how far away it is.

Other robots use other sensors. A line sensor sees a black line on a white floor, and a switch can feel a bump. The Line follower uses two line sensors to follow a track.

#Think

The Arduino Uno reads the sensor and runs your sketch, the program you wrote. The sketch holds the robot's rules, for example: "If something is closer than 25 cm, turn away." The Uno checks these rules many times a second.

#Act

The Uno's pins can only give small signals, about 20 mA each. A TT motor needs about 0.3 A while it drives the robot, and up to about 1 A when it is blocked. So the Uno sends its signals to the L298N motor driver. The L298N switches the battery's current to the motors: forwards or backwards, fast or slow.

The robot has no steering wheel. It steers with its two driven wheels:

• Both wheels forwards at the same speed: it drives straight.
• One wheel faster than the other: it drives in a curve.
• One wheel forwards and the other backwards: it spins on the spot.

#Power

Nothing works without energy. The four AA cells give about 6 V. The motors get this power through the L298N. The L298N also has a small 5 V regulator. Its 5 V output powers the Uno and the sensor.

#One pass of the loop

The obstacle avoider shows the loop at work. Its sketch uses these numbers:

1. Sense: measure the distance every 60 ms, about 16 times a second.
2. Think: is the object closer than 25 cm?
3. Act: if not, drive ahead at speed 190 (the scale goes from 0 to 255). If it is closer, drive backwards at speed 160 for 300 ms, spin right at speed 170 for 380 ms, and then drive ahead again.

Then the loop starts again with a new measurement. The robot never stops sensing, not even while it drives backwards and turns. The lesson Programs that never wait shows how the sketch does that.

#What is a microcontroller?

A microcontroller is a complete small computer on one chip. It has a processor, memory for the program, memory for data, and pins that connect it to the outside world. Microcontrollers are in many things around you: a washing machine, a microwave oven, a TV remote control, a car.

The Uno's microcontroller is the ATmega328P:

A laptop has millions of times more memory. The Uno does not need it. It has no screen, no keyboard and no operating system. It runs one program, your sketch, as soon as it gets power.

The program for an Arduino board is called a sketch. You write it in C++ in the Arduino IDE. When you press Upload, the IDE compiles your sketch into machine code and writes it into the flash memory.

The pins connect the sketch to the world. As an output, a pin gives about 5 V (HIGH) or 0 V (LOW), for example to switch an LED on and off. As an input, a pin tells the sketch whether the voltage on it is high or low, for example the signal from a sensor. The lesson Arduino Uno: pins and your first program looks at the pins in detail.

#What the simulator does

CoreEngine is a robot simulator for Windows. In it, you build a robot from the same parts as the real robot car, and you test it before you build it for real.

• Build. You make the body from shapes and place models of real parts on it: the Arduino Uno, the L298N, the HC-SR04, TT motors, the battery holder, a ball caster, an SG90 servo and an LED module.
• Wire. You connect the parts pin to pin, as on the real robot.
• Check. The simulator checks your wiring. It tells you, for example, when there is no battery, when the motor driver has no power, when the grounds are not joined, or when the battery goes to the Uno's 5V pin. That last mistake burns a real board.
• Code. You write the sketch in a built-in Arduino IDE, with Verify and Upload buttons.
• Run. Your sketch is compiled with arduino-cli, which uses the same compiler as the Arduino IDE. The machine code then runs on an emulated ATmega328P: a program that behaves like the real chip. It is the same program a real Uno would run, not a simplified copy.
• Test. The robot drives in an arena with physics. You see a live readout of the distance, the motors and the battery, a Serial Monitor with your sketch's messages, and an event log.

On the desk in the Garage, the Uno runs from the laptop's USB and LEDs light up. So you can try LED projects without a battery.

The simulator does not replace real parts. It lets you try ideas quickly and find mistakes before they cost you a part.

#How to use this site

You can repeat these steps as often as you like. Each new idea starts again at step 1 or step 2.

#Try it now

Open the obstacle avoider and watch sense, think and act happen.

What you will see:

• The robot drives straight ahead.
• The live distance readout gets smaller as a wall comes closer.
• Below 25 cm, the robot drives backwards for a moment, spins to the right and drives on.
• The Serial Monitor prints a new distance about every 60 ms, also while the robot turns.

#Where to go next

1. Arduino Uno: pins and your first program, then the Blink project.
2. Motors and the L298N driver, then the First drive project.
3. Measuring distance with the HC-SR04.
4. Programs that never wait: millis() and states, then the Obstacle avoider.
5. The Keep distance robot, which follows your hand.