Challenge_4.md

Challenge 4

In this challenge students will use the distance sensors to control how far the robot moves backwards from an object before coming to a stop.

Success Criteria

1. My robot drives in a straight line for 1m
2. My robot comes to a standstill then turns 90 degrees
3. My robot does this exactly 4 times to make a square

Before You Begin

1. Complete Module 6: Loopy loops!
2. Complete Blockly Level 4 to apply the algorithm visually.

Flowchart Of The Algorithm

flowchart TD
    A[Start Program] --> B[Setup Robot]
    B --> C[Initialize variables]
    C --> E{Is counter less than target?}
    E -->|Yes| F[Drive Forward until time ends]
    F --> G[Apply brake to stop robot]
    G --> H[Rotate Right]
    H --> I[Apply brake to stop robot]
    I --> D[Increment counter by 1]
    D --> E
    E -->|No| J[End Program]

    style A fill:#e1f5fe,color:#000000
    style B fill:#000000,color:#ffffff
    style C fill:#000000,color:#ffffff
    style D fill:#ffcdd2,color:#000000
    style E fill:#ffecb3,color:#000000
    style F fill:#fff3e0,color:#000000
    style G fill:#e3f2fd,color:#000000
    style H fill:#e1bee7,color:#000000
    style I fill:#e8f5e8,color:#000000
    style J fill:#e1f5fe,color:#000000

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Step 1

1. Make sure your battery power switch is off.
2. Navigate to https://lab-micropython.arduino.cc/.
3. Sign in with Google (use your @education.nsw.gov.au account).
4. Follow these instructions to connect, code and save:

Step 2

Extend your code from Challenge 2 to use the ultrasonic sensor to determine whether the robot needs to reverse in order to position itself 1000mm away from the object it started next to. The robot should measure its distance, then reverse as needed until it is 1000mm from the starting object.

Important

The ultrasonic sensor will return -1 if it is too close (less than 20mm) or too far (more that 2000mm) or in an error state.

from aidriver import AIDriver, hold_state

import aidriver

aidriver.DEBUG_AIDRIVER = True
my_robot = AIDriver()

while my_robot.read_distance() == -1:
   print("Robot too close, too far or sensor is in error state")

my_counter = 0
target_counter = 4
wheel_speed = 200
speed_adjust = 0
forward_time = 0
turn_speed = 200
turn_time = 0

while True:
   while my_counter < target_counter:
      my_robot.drive_forward(wheel_speed - speed_adjust, wheel_speed + speed_adjust)
      hold_state(forward_time)
      my_robot.brake()
      hold_state(3)
      my_robot.rotate_right(turn_speed)
      my_robot.brake()
      my_counter = my_counter + 1
   hold_state(1)

Use hold_state(seconds) any time you want the robot to keep doing the same thing (driving, braking, or turning) for a short time and also record that pause in event_log.txt.

If you see syntax or name errors while fixing this starter code, check Common_Errors.md.

Step 3

Your challenge is to:

1. Review the code and modify the values assigned to the setup variables to achieve the success criteria.
2. Once you have achieved it, modify the code so:
   1. The robot does not turn at the end of the last run of the square.
   2. The 1000mm distance is calculated using the ultrasonic sensor.

Caution

To avoid damaging your computer or robot, first save your main.py file. Next, disconnect your robot from your computer, then place it on the floor in an area with enough space for it to move safely before powering it on.

Debugging Tips – Test Small, Test Often

• This starter code intentionally contains some mistakes – fix one error at a time.

• After each fix, run the code and read the first line of any error message.

• Use temporary markers like:

  print("HERE 1")

  to see which part of the program is executing.

• Keep a copy of the last working version of your square, and extend from there.

Step 4 Save Your Code

1. Copy all your code from main.py.
2. Paste it in your portfolio under "Challenge 4".