Obstacle Avoidance — Block Coding Guide

You can do everything in this session with blocks instead of typing Python. Pybricks shows the matching Python next to your blocks (live preview), so the block track and the Python track end up at the same place — you can peek at the Python any time to see what your blocks turned into.

Same robot, same ideas. Blocks and Python are just two ways to give the robot the same instructions.

1. Switch to blocks

In code.pybricks.com, make a new block program (choose blocks instead of Python when you create it). You’ll see a blocks canvas with a palette of blocks on the side and a live Python preview.

2. Set up the robot (add the distance sensor)

Use the setup / configuration area to tell Pybricks about your robot. This is the block version of the hub, Motor, DriveBase, and sensor lines in the Python:

1. Add the hub.
2. Add your two drive motors and set the port for each (same as earlier sessions). Keep your calibrated wheel diameter and axle track.
3. Add the distance / ultrasonic sensor and set its port — match the port the sensor is actually plugged into. Give it a name like eyes.

This is the block equivalent of:

eyes = UltrasonicSensor(Port.C)

3. Read the sensor

From the sensor blocks, find the “distance” value block for your distance sensor. Drop it into a print block to watch the number:

Move your hand toward the sensor and watch the number drop. With nothing in front of it, it reads 2000 — that’s the “no object” value.

4. Repeat forever with a “forever / while” loop

Use a forever (repeat-forever) loop block. Everything inside it runs over and over until you press Stop:

forever:
    (check the sensor and decide)

That’s the block version of:

while True:
    ...

It runs forever. A forever / while True: loop does not stop on its own. Use the editor’s Stop button to end it.

5. Decide with an “if / else” block

Put an if / else block inside the forever loop. In the if part, use a comparison block to test the distance value, and fill the two halves with what to do:

forever:
    if  distance (mm)  <  200 :
        drive straight -100 mm   (back up)
        turn 90 degrees          (turn away)
    else:
        drive 150 mm/s, turn 0   (forward)

That’s the block version of:

while True:
    if eyes.distance() < 200:
        robot.straight(-100)
        robot.turn(90)
    else:
        robot.drive(150, 0)
    wait(10)

Remember: 200 mm is a guess you tune on the real course, not a correct answer.

6. Tune the trigger (same as the Python track)

Tuning is identical no matter which track you use:

1. Run the program and drive toward an obstacle.
2. Stops too far away? Make the trigger number smaller. Bumps the wall first? Make it bigger.
3. Run again on the real course until it stops where you want.

Write your trigger distance on the worksheet.

Ready to try Python?

Look at the live Python preview next to your blocks — that’s real code your blocks made. When you’re curious, start a Python program and type the commands from the main session page. Same robot, same results.