VISUAL · BLOCKS → PYTHON

React and Avoid

Build a reactive rule-based behavior using conditionals so the rover avoids an obstacle and still reaches the goal with zero collisions.

01Challenge

Same rover, goal now 4.0 m ahead, but a wall blocks the direct route. Reach the goal without ever touching the wall. You have a new sensor, proximity, that reports how close an obstacle is ahead. Use if/else to react to it: no planning, no map, just react to what you see right now. Try it before the video.

Predict firstWith only a proximity sensor and if/else reactions — no map, no planning — can the rover get around the wall to the goal with zero collisions?

02Model

A thermostat controls a whole house's temperature with no map, no plan, no memory. It follows one rule: too cold, turn on; warm enough, turn off. It just reacts to the reading in front of it, over and over. That's a reactive controller, and it's enough to hold a house steady for years.

Give the rover the same idea: if something's close ahead, steer; otherwise head for the goal. It never plans a route around the wall. It keeps reacting, and the route emerges. Later you'll teach it to plan; not yet. Master the reflex first.

A rule (if / else) reacts to what the sensor sees.

03Guided practice

Step 1 (worked): the proximity branch is slotted into your 1.1 loop (if proximity < 0.6: steer else: drive). Step 2 (faded): rebuild the branch and pick the threshold and turn sharpness. Step 3 (independent): tune so the rover clears the wall AND re-aims at the goal, sharp enough to clear, gentle enough that the else branch recovers heading.

04Feedback

PASS WHEN Reached the goal (range <= 0.25 m) with zero collisions, the proximity branch read every tick inside the loop.

If your run fails, check:

FAIL: clipped the wall. Your turn starts too late; raise the proximity threshold toward 0.6 m so the rover reacts before it arrives.
FAIL: avoided the wall but never returned toward the goal. The turn is too sharp; reduce the pivot so the else branch can recover heading.
FAIL: ran out of step budget circling the wall. Make proximity rise back above the threshold once clear so the else branch takes over.

05Retrieve & space

Carry-forward: re-place the 1.1 stop-on-goal check into a fresh stack (not pre-filled).
Name-the-phase harder: is read_proximity SENSE or DECIDE? (SENSE.) Is `if proximity < 0.6` SENSE or DECIDE? (DECIDE.)
Reactive-vs-deliberative: of 'follows a precomputed path / flips on the current reading / stores a map', which is reactive? (The second.)

06Mastery & project

From the fixed seed, the rover reaches the goal with zero collisions using a conditional that reads proximity every tick inside the loop (L1: closes a reactive loop).

Contributes the reactive AVOID behavior; in Module 2 you rebuild this reflex as a state in an FSM, and in Module 4 the proximity read becomes an ADC interrupt.

← The Embodied Loop Blocks Are Python →

VISUAL · BLOCKS → PYTHON

React and Avoid

Add an if/else that reads proximity every tick so the rover reacts around the wall.

You read

the same obs values, read as blocks

You change

the blocks you snap together inside control

Fixed

the loop, the rover, and the physics