Your first robot in a weekend

Who this is for

This is for beginners new to robotics who have never wired a circuit, though some comfort with a computer helps. You do not need to solder if you pick parts with screw terminals or plug-in headers. Check the seller's page for the current price and specifications of anything you buy, because they change.

The plan at a glance

Step by step

1. 1. Know the five part types

   A controller board runs your program. A motor driver takes small signals from the board and switches the larger current that motors need. Two geared DC motors with wheels move the robot. A chassis holds everything. A battery pack (four AA cells in a holder is a safe start) powers the motors.

2. 2. Assemble the chassis

   Mount the motors so the wheels sit on opposite sides and in line. Add a ball caster or a slider at the back or front for a third point of support. Make sure nothing hangs below the frame where it can catch.

3. 3. Wire with the power off

   Battery positive and negative to the driver's power input. Each motor to its own output on the driver. The driver's input pins to the controller pins, and the driver's ground to the controller's ground. Put the battery switch off while you work. Compare every wire to the driver's diagram twice.

4. 4. Test one motor at a time

   Lift the robot so the wheels spin in the air. Run a short program that turns the left motor forward for a second. Then the right. If one spins the wrong way, swap that motor's two wires at the driver.

5. 5. Write the driving program

   Combine forward, turn and stop into functions and call them in order. Keep each action short while testing.

6. 6. Tune and repeat

   Change one number at a time, run again and write down what happened.

Worked example: a two-motor robot that drives and turns

A robot with two powered wheels steers by running them at different speeds. Both forward: it goes straight. Left reversed and right forward: it spins to the left on the spot. Here is a first program in the style of the Arduino language, with the pins as examples you would change to match your wiring.

// Example pins: change these to match your wiring
const int LEFT_FWD = 5;
const int LEFT_BACK = 6;
const int RIGHT_FWD = 9;
const int RIGHT_BACK = 10;

void setup() {
  pinMode(LEFT_FWD, OUTPUT);
  pinMode(LEFT_BACK, OUTPUT);
  pinMode(RIGHT_FWD, OUTPUT);
  pinMode(RIGHT_BACK, OUTPUT);
  delay(3000); // time to put it on the floor
}

void stopAll() {
  digitalWrite(LEFT_FWD, LOW);
  digitalWrite(LEFT_BACK, LOW);
  digitalWrite(RIGHT_FWD, LOW);
  digitalWrite(RIGHT_BACK, LOW);
}

void forward(int ms) {
  digitalWrite(LEFT_FWD, HIGH);
  digitalWrite(RIGHT_FWD, HIGH);
  delay(ms);
  stopAll();
}

void turnLeft(int ms) {
  digitalWrite(LEFT_BACK, HIGH);
  digitalWrite(RIGHT_FWD, HIGH);
  delay(ms);
  stopAll();
}

void loop() {
  forward(2000);
  delay(500);
  turnLeft(600);
  delay(500);
}

Timed moves are rough, but they are a fine start. To estimate how far the robot goes, measure the wheel diameter. For a 65 mm wheel, the circumference is π × 65 = 204 mm. If the wheel makes 5 turns, the robot travels 5 × 204 = 1020 mm, a little over a meter. Going the other way, 1000 mm needs 1000 ÷ 204 = 4.9 turns.

To find out how fast your robot actually moves, run forward(2000) on a tape measure and note the distance. Say it covers 0.50 m in 2 s. Its speed is 0.50 ÷ 2 = 0.25 m/s, so a 1 m drive needs 1 ÷ 0.25 = 4 s, which is forward(4000). Test it, because battery level changes the speed.

If something goes wrong

• Nothing happens. Check the battery switch, the cell orientation and that the program uploaded.
• One wheel spins the wrong way. Swap the two wires of that motor at the driver.
• It veers when going straight. The motors are not identical. Run the faster one for a shorter time or reduce its speed with PWM.
• The controller resets when the motors start. The batteries are weak or the power wiring is loose; replace the cells first.
• A part gets hot. Switch off and disconnect the battery. Find the cause before you try again.

Keep it going

Next, make it drive a square, then add a distance sensor so it stops before a wall. Learning the basics of electronics, a coding path and a simulator will make each step faster. If you get stuck on a wiring diagram, DuckyHelper can see your screen and talk through it while you keep working, but always compare to your parts' own documentation.