YOU LEARN HERE...

how a robot can repeat certain command sequences and how you can structure your programmes better with named programme blocks (functions).

EXAMPLES

Example 1: Moving a square To move a square, the robot must move forwards a distance four times and turn 90°. You use a repeat loop for the repetitive movement. This is introduced with repeatfollowed by the number of repetitions and a colon. The commands that are to be repeated must be indented.

Program: [► WebTigerPython]

from callibot import *
            
repeat 4: 
    forward()
    delay(2000)
    left()
    delay(550)
stop()

Run the programme in simulation mode first. In real mode, you may have to adjust the time when turning left.

In contrast to the turtlegrafics, in which the turtle can draw a square exactly, it is difficult for the real robot to drive exactly straight ahead and turn exactly at a right angle. This corresponds to reality, because no car will ever drive exactly straight ahead if the wheel position is fixed, i.e. the steering is locked. This is why robots are equipped with sensors that help them to correct these inaccuracies. So don't spend too much time teaching the robot to drive exactly square.

Example 2: Repeating commands endlessly In many situations, a robot carries out certain activities ‘endlessly’, or until it is switched off or the programme is aborted. For example, if it constantly has to report back sensor data. A repeat loop without a number of repetitions is used for this. In your example, the robot visits four locations endlessly, which are on paths that are at right angles to each other, and returns to the starting point each time.

Program: [► WebTigerPython]

from callibot import *
            
repeat: 
    forward()
    delay(2000)
    backward()
    delay(2000)
    left()
    delay(550)

It is useful to know how to cancel a running programme: The easiest way is to press the blue button at the back of the chassis.

Example 3: Structuring programmes with your own functions
With named programme blocks, called functions in Python, you can structure your programmes better. It is an important programming technique because more complex programmes can be broken down into smaller, easily programmable sub-programmes with the help of functions. Functions are also used to advantage when a programme block is used several times.

A function definition always begins with the keyword def, followed by a function name, a parameter bracket and a colon. The instructions in the function body are indented. The function is called in the main programme.

In your example, you define a blink(), function that causes the red LED to light up once. In the main programme, the robot first moves forwards for 200 ms and then backwards for 2000 ms. While travelling backwards, it flashes both LEDs twice. It repeats this movement twice.

from callibot import *

def blink():
    setLED(1)
    delay(500)
    setLED(0)
    delay(500)

repeat 2:
    forward()
    delay(2000)
    backward()
    blink()
    blink()
    stop()

REMEMBER ...

To repeat a programme block n times, use a repeat loop:

repeat n: Instructions

To repeat a programme block endlessly, use an infinite loop:

repeatn: 
    Instructions 
        

The indented lines are repeated until the programme is aborted by closing the terminal window.

You can use functions to structure your programmes better and avoid code duplication. You must distinguish between the function definition and the function call.

def name(): 
    Instructions 
        

name()

TO SOLVE BY YOURSELF