Navigating by Touch

In previous navigation programs, our scripts only made the cyber:bot execute a list of movements predefined by you, the programmer.  Now that you can write a script to make the cyber:bot monitor whisker switches and trigger action in response, you can also write a script that lets the cyber:bot drive and select its own maneuver if it bumps into something. This is an example of autonomous robot navigation.

Whisker Navigation Overview

The roaming_with_whiskers.py script makes the cyber:bot go forward while monitoring its whisker inputs, until it encounters an obstacle with one or both of them.  As soon as the cyber:bot senses whisker electrical contact, it uses an if…elif…else statement to decide what to do.  The decision code checks for various whisker pressed/not pressed combinations, and calls navigation functions to execute back-up-and-turn maneuvers.  Then, the cyber:bot resumes forward motion until it bumps into another obstacle.

Example Script: roaming_with_whiskers

Let’s try the script first, and then take a closer look at how it works.

• Open a script you have previously used with the cyber:bot baord, like whiskers_detect_test or cyberbot-template-with-blink.hex.
• Set the project’s name to roaming_with_whiskers, update the script so that it matches the one below, and then click Save.
• Click Send to micro:bit.  
• Disconnect the cyber:bot from its programming cable, and set the cyber:bot board’s PWR switch to 2.
• Put the cyber:bot on the floor, and try letting it roam.  When it contacts obstacles in its path with its whisker switches, it should back up, turn, and then roam in a new direction.
• Set the cyber:bot board’s PWR switch back to 0 when you are done testing.

# roaming_with_whiskers

from cyberbot import *        
        
def forward():
    bot(18).servo_speed(75)
    bot(19).servo_speed(-75)

def backwards():
    bot(18).servo_speed(-75)
    bot(19).servo_speed(75)
    sleep(1000)

def right():
    bot(18).servo_speed(75)
    bot(19).servo_speed(75)
    sleep(800)

def left():
    bot(18).servo_speed(-75)
    bot(19).servo_speed(-75)
    sleep(800)

while True:
    whisker_left = bot(7).read_digital()
    whisker_right = bot(9).read_digital()
    
    if whisker_left == 0 and whisker_right == 0:     
        backwards()                                 
        right()
    elif whisker_left == 1 and whisker_right == 0:   
        backwards()                                  
        left()
    elif whisker_left == 0 and whisker_right == 1:  
        backwards()                                   
        right()
    else:                                           
        forward()