How the Navigating by Touch Code Works

How the script roaming_with_whiskers works

The first part of roaming_with_whiskers defines the four navigation functions: forward, left, right, and backwards.  Notice how the left, right, and backwards functions all have a sleep function. Every time each of these functions are called, the cyber:bot moves in that direction for a predetermined amount of time. 750 milliseconds is enough time to back up away from an obstacle, and 500 milliseconds makes about a 90 degree turn to the right or the left.  The forward function does not have a sleep function call inside of it. 

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(750)

def right():
    bot(18).servo_speed(75)
    bot(19).servo_speed(75)
    sleep(500)

def left():
    bot(18).servo_speed(-75)
    bot(19).servo_speed(-75)
    sleep(500)

After the four navigation functions have been defined, the script enters into the while True: loop.  Inside of this loop, we have a four-part if statement.  The first thing it checks is if both whiskers are touching, that is, if both whisker_left and whisker_right are equal to 0.  If this is true, then the program runs through the backwards and right functions making the cyber:bot backup and then turn right, presumably away from the obstacle.

    if whisker_left == 0 and whisker_right == 0:     
        backwards()                                 
        right()

If whisker_right and whisker_left are not touching, then the program goes to the next part of the if statement which says else if (elif) the left whisker is not touching (whisker_left == 1) and the right whisker is touching (whisker_right == 0), then the program executes the backwards and left functions.

    elif whisker_left == 1 and whisker_right == 0:   
        backwards()                                  
        left()

If the if statement has still not found a true condition, then it checks to see if the left whisker is touching (whisker_left == 0) and the right whisker is not touching (whisker_right == 1).  If this it true, the program executes the functions backwards and right.

    elif whisker_left == 0 and whisker_right == 1:  
        backwards()                                   
        right()

Finally, if all three of the above conditions are not met, the program executes the forward function and drives a little bit before once again checking to see if an obstacle is detected.

Compact Code — The script could have lastly checked:

elif whisker_left == 1 and whisker_right == 1:

…instead of using just else:, however, the only condition remaining at the end was that neither whisker was touching (whisker_right and whisker_left are both equal to 1).  Although both of these would have worked, else: is used because it shortens the code.

Compact it More — To make the script even more compact, shorten the variable names used to define each maneuver and to store the whisker I/O pin states.  This could help if want to combine whisker navigation with other sensor input or with piezospeaker sounds.