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Challenge 5:

In this challenge, students will use the ultrasonic sensor to detect obstacles in front of the robot and program it to avoid them by stopping and turning away.

Success Criteria

  1. My robot drives forward until it detects an obstacle within 300mm.
  2. My robot stops before hitting the obstacle.
  3. My robot turns (left or right) to avoid the obstacle, then continues driving forward.

Before You Begin

  1. Complete Module 8: Functions, fills, and pizza!
  2. Complete Blockly Levels 7 & Blockly Levels 9 to apply the algorithm visually.

Flowchart Of The Algorithm

flowchart TD
    A[Start Program] --> B[Setup Robot and Variables]
    B --> C{Main Control Loop}
    C --> D[Read Distance from Ultrasonic Sensor]
    D --> E{Is distance valid and less than safe_distance?}
    E -->|Yes| F[Apply Brake]
    F --> G[Turn Left]
    G --> C
    E -->|No| H[Drive Forward]
    H --> C

    style A fill:#e1f5fe,color:#000000
    style B fill:#000000,color:#ffffff
    style C fill:#fff3e0,color:#000000
    style D fill:#e3f2fd,color:#000000
    style E fill:#ffecb3,color:#000000
    style F fill:#ffcdd2,color:#000000
    style G fill:#e1bee7,color:#000000
    style H fill:#e8f5
Loading

Step 1

  1. Set up your robot and connect to the coding environment as before.

Step 2

Write code so your robot:

  • Drives forward.
  • Uses the ultrasonic sensor to check for obstacles.
  • If an obstacle is detected within 300mm, the robot stops, turns, and continues forward.
from aidriver import AIDriver, hold_state

import aidriver

aidriver.DEBUG_AIDRIVER = True
my_robot = AIDriver()

my_counter = 0
wheel_speed = 200
speed_adjust = 0
turn_speed = 200
turn_time = 0
safe_distance = 0

def turn_left():
    # implement 90 degree left turn here
    pass


def drive_forward():
    # implement drive forward here
    pass


def brake():
    my_robot.brake()
    hold_state(3)


while True:
    distance = my_robot.read_distance()
    if distance != -1 and distance < safe_distance:
        brake()
        turn_left()
    else:
        drive_forward()

If you get an error when running this, or the names don’t match the AIDriver functions, see Common_Errors.md.

Step 3

  • Test and adjust the distance threshold and turn timing as needed.
  • Try different turn directions or randomize the turn for more advanced behaviour.

Step 4 Save Your Code

  1. Copy all your code from main.py.
  2. Paste it in your portfolio under "Challenge 5".

Debugging Tips – Test Small, Test Often

  • First, make the robot just drive forward and print the distance:

    print("distance:", my_robot.read_distance())

  • Once that works, add the if/else decision to brake and turn.

  • Run your program after every small change so you know which edit caused an error.

  • If behaviour is confusing, add print("HERE 1"), print("HERE 2") inside different branches to see which path the code is taking.