Autonomous decision making

Learn

What you’ll learn

• The difference between remote-controlled and autonomous robots
• The sense–plan–act cycle
• How behaviours combine, with priorities

Remote control vs autonomy

A remote-controlled robot needs a person to make every decision. An autonomous robot makes its own decisions from its sensors. Many real robots are in between: they handle the details themselves and take high-level goals from people.

Sense, plan, act

1. Sense: read the sensors and build a picture of the world (the robot’s model).
2. Plan: decide what to do to reach the goal.
3. Act: move, then sense again.

Simple robots skip the planning and react directly (“too close → turn”). Advanced robots build maps and plan routes.

Behaviours with priorities

A practical way to build autonomy is to stack simple behaviours, with the most important one winning:

Priority	Behaviour	When
1 (highest)	Avoid collision	Something very close
2	Follow the wall	Wall on the right
3	Wander	Otherwise

This is called subsumption: higher behaviours take over (subsume) lower ones when they’re triggered.

Autonomy needs fail-safes

• Stop if sensors give impossible readings.
• Stop if the robot hasn’t moved when it should have (stuck).
• Always have a physical off switch.

Examples

Example: behaviours in code

function loop() {
  if (distance() < 15) return motors(-50, 50);         // 1: avoid
  if (distanceRight() < 30) return motors(60, 55);     // 2: follow wall
  motors(55, 60);                                      // 3: wander (gentle curve)
}

Example: a stuck detector

let lastD = 0, sameSince = 0;
function loop() {
  const d = distance();
  if (Math.abs(d - lastD) > 1) sameSince = millis();
  lastD = d;
  if (millis() - sameSince > 2000) { motors(-50, -50); return; }  // stuck: back off
  motors(60, 60);
}

Practice

Try it

Behaviours

▶ Run↺ Reset

Your code (JavaScript)function loop() { if (distance() < 15) return motors(-50, 50); // avoid if (distanceRight() < 30) return motors(60, 55); // follow wall motors(55, 60); // wander }Load starter code

Robot commands

• motors(left, right): wheel power, −100 to 100
• lineLeft(), lineRight(): true over the black line
• distance(): cm to the nearest thing ahead (max 200)
• distanceLeft(), distanceRight(): cm to the sides
• linePosition(): where the line is, −1 (left) to 1 (right), or null
• millis(): milliseconds since Run
• print(value): show a message below
• setup() runs once; loop() runs 50 times a second

Re-orderEasy

Swap the priorities so “follow wall” comes before “avoid”. What goes wrong? When following a wall into a corner the robot doesn’t turn away in time, because avoiding is no longer the top priority.

Cover the roomMedium

Change the wander behaviour so the robot visits all parts of the room within 60 seconds.

Rate the autonomyHard

Place these on a scale from teleoperated to fully autonomous: a drone flown by remote; a robot vacuum; a Mars rover; a self-driving car with a safety driver. Remote drone (teleoperated) → car with safety driver (semi-autonomous) → Mars rover (mostly autonomous, with goals set from Earth) → robot vacuum (fully autonomous in its small world).

Quick check

1. An autonomous robot…

Needs a person for every decisionMakes its own decisions from sensor dataHas no sensorsOnly works outdoors

2. In subsumption, which behaviour wins?

The first one writtenThe highest-priority one that is triggeredThe slowestA random one

3. Why add a stuck detector?

To save codeAs a fail-safe when the robot can’t moveTo go fasterTo play sounds

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