Object Avoidance

Learn how to avoid objects with BurgerBot.

Avoiding an object

To prevent collisions with obstacles, use bot.distance to measure the distance between the object and your bot. If the measured distance is less than a specified threshold (e.g., 5 cm), stop the bot and move it backward to maintain a safe distance from the obstacle.

Understanding the Distance Sensor

The ultrasonic rangefinder works by sending out sound waves and measuring how long they take to bounce back. The bot.distance property returns the distance in centimeters to the nearest object.

The code:

from burgerbot import Burgerbot

bot = Burgerbot()

while True:  # Infinite loop - runs forever (note: capital T in True!)
    distance = bot.distance  # Get current distance in cm

    if distance <= 5:  # Object closer than 5cm
        print(f"Too close! Distance: {distance}cm")
        bot.stop()
        bot.backward(1)  # Back up for 1 second
    else:
        print(f"Path clear. Distance: {distance}cm")
        bot.forward(0.5)  # Move forward in short bursts

How it works:

1. while True: creates an infinite loop that runs continuously
2. bot.distance gets the current distance reading from the rangefinder
3. If distance is 5cm or less, the robot stops and reverses
4. If distance is greater than 5cm, the robot moves forward
5. Using forward(0.5) instead of forward(1) makes the robot check distance more frequently

Why short bursts? Moving in 0.5-second intervals allows the robot to respond more quickly to obstacles, making navigation smoother and safer.

Common Issues

• Problem: bot.distance returns 0 or very large numbers (like 400)
• Solution: Check that the rangefinder Trigger and Echo pins are wired correctly to GPIO pins

• Why: Incorrect wiring prevents the sensor from sending or receiving ultrasonic signals

• Problem: Robot doesn’t detect objects closer than 2cm
• Solution: This is normal - ultrasonic sensors have a minimum detection range of about 2cm

• Why: Sound waves need time and space to separate transmission from echo

• Problem: Robot doesn’t detect dark or soft objects well
• Solution: Use objects with hard, flat surfaces for testing. Ultrasonic sensors work best with solid, reflective surfaces

• Why: Soft materials (like fabric) and dark surfaces absorb sound waves instead of reflecting them

• Problem: Robot behaves erratically, sometimes ignoring obstacles
• Solution: Ensure you’re using while True: with a capital T. Python is case-sensitive!

• Why: while true: will cause a NameError because true is not defined in Python (it’s True)

• Problem: Robot reverses but doesn’t turn to find a new path
• Solution: This basic algorithm only reverses. You’ll need to add turning logic (covered in later lessons)
• Why: The current code is designed to demonstrate simple avoidance, not full navigation

Try it Yourself

Ready to experiment with object avoidance? Try these challenges:

1. Adjust the detection threshold: Change if distance <= 5: to if distance <= 10:. How does the robot’s behavior change? What about distance <= 3?

2. Add turning: Modify the code to turn left or right after reversing. Hint: Add bot.left(0.5) after the backward command.

3. Variable speed: Make the robot slow down as it approaches objects. Use the distance value to calculate motor speed.

4. Obstacle counter: Keep track of how many objects the robot has avoided. Print this count to the console.

Advanced Challenge: Create a robot that maintains exactly 10cm from a wall as it drives parallel to it. You’ll need to constantly adjust direction based on distance readings!

Following an object

To maintain a consistent distance from an object, first measure the distance between the object and your position. Move forward until the object is at the desired distance, then stop. If the object is closer than the desired distance, move backward until the desired distance is achieved. This process allows you to effectively follow an object while maintaining a set distance from it.

Example

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