Line Follower Simulator: Tune a Robot in Your Browser

Controls

Use the track presets to establish a baseline, or pause the run and draw directly on the course. Robot speed controls how far the chassis advances per update. Sensor count and spacing change the field of view. The P, I, and D controls change steering response; Step advances one deterministic update while paused.

Start with a moderate speed, five sensors, and the default gains. Change one variable at a time and compare the error, lap time, and time-on-track metrics.

Theory

The sensor bar samples reflectance across the front of the robot. Each active sensor contributes its signed position to a weighted average. The center of the bar is error zero; readings left or right of center produce negative or positive error.

The controller combines three terms:

$$u(t) = K_p e(t) + K_i \int e(t)dt + K_d \frac{de(t)}{dt}$$

The correction $u(t)$ speeds one wheel and slows the other. Proportional control reacts to the current offset, integral control corrects persistent bias, and derivative control damps rapid changes.

Algorithm

1. Sample every sensor at a fixed interval.
2. Compute a weighted line position and normalize it around the center.
3. Reuse the last observed line direction when every sensor loses the track.
4. Update integral and derivative terms using the same fixed time step.
5. Clamp the correction, calculate left and right motor commands, and integrate the robot pose.

Tune proportional gain until the robot follows gentle turns, add derivative gain until oscillation settles, and introduce only enough integral gain to remove a repeatable offset.

Source code

The browser simulator and a microcontroller use the same control shape. A compact Arduino-style loop looks like this:

float integral = 0.0f;
float previousError = 0.0f;

void controlStep(float dt) {
  float error = readWeightedLinePosition();
  integral = constrain(integral + error * dt, -2.0f, 2.0f);
  float derivative = (error - previousError) / dt;
  float correction = kp * error + ki * integral + kd * derivative;

  setMotorSpeeds(baseSpeed - correction, baseSpeed + correction);
  previousError = error;
}

Keep the real control interval stable. A variable delay changes the derivative and integral terms even when the gains stay the same.

Circuit diagram

Connect the sensor outputs to analog-capable inputs, share ground between every module, and drive motors through an H-bridge rather than from controller pins.

Verify the motor supply rating and add local decoupling near the controller and driver. Never route motor current through a development board’s logic regulator.