Robotics

Robot simulator

Write a controller in JavaScript and watch a differential-drive robot run it with ultrasonic, line and encoder sensors.

About 60 min

Ready. Press Run.

Lab goal: 0 / 100 cm without a crash

Rays turn green when an echo returns within 150 cm and red (dashed) when the way is open. Amber dots are line sensors over the tape; the dashed amber ring is the goal zone.

Preset

Cruise, slow down when something is ahead, and turn away from the nearest short ray.

Arena

Controller code (JavaScript)

// Obstacle avoidance with three ultrasonic rays (cm from the robot's edge).
// Wheel commands run from -1 (full reverse) to 1 (full forward, 40 cm/s).
function control(s, memory) {
  const { left, front, right } = s.ultrasonic;
  const nearest = Math.min(left, front, right);
  const speed = front < 30 ? 0.2 : 0.6;           // slow down when something is ahead

if (nearest > 40) {                              // nothing close: cruise straight
    memory.turn = 0;
    return { left: speed, right: speed };
  }

let turn;                                        // +1 turns left, -1 turns right
  if (nearest === front) {
    // Wall ahead: pick the more open side once and keep it until the front clears,
    // so the robot does not flip-flop in front of the wall.
    if (!memory.turn) memory.turn = left < right ? -1 : 1;
    turn = memory.turn;
  } else {
    turn = nearest === left ? -1 : 1;              // turn away from the nearest side ray
    memory.turn = 0;
  }
  const v = front < 15 || nearest < 10 ? 0 : speed; // very close: spin in place
  return { left: v - 0.45 * turn, right: v + 0.45 * turn };
}

Tab inserts two spaces. Press Esc, then Tab, to move on from the editor.

Speed

Telemetry

t: 0.00 s
x: 40.0 cm
y: 40.0 cm
θ: 28.6°
Ultrasonic L / F / R: 159.7 / 216.4 / 135.1 cm
Line L / R: 0 / 0
Encoders L / R: 0 / 0 ticks
Crashed: no

Controller reference

control(s, memory) → { left, right }, each -1..1
s.ultrasonic.left / front / right: cm from the robot's edge (rays at +45°, 0°, -45°)
s.line.left / right: 1 over the tape, else 0
s.encoders.left / right: ticks, 10 per cm
s.yawRate: rad/s, positive turning left
s.pose.x / y / theta: cm and rad (-π..π), y points up
s.goal.x / y: only in arenas with a goal
s.t: seconds since reset
memory: an object kept between calls until Reset

Sensors only change between calls, so a loop that waits for one never ends. Loops stop with an error after 1,000,000 passes in one call; to wait, remember the state in memory and check again next tick.

The loop runs at 100 Hz. Wheel base 12 cm, top speed 40 cm/s, body radius 7 cm. Your code is saved in this browser; Load preset replaces it.