1.1: First Flight

By the end of this lesson, you should be able to:

• Use the print() function and describe its value in debugging (finding and fixing errors) in your code
• Add comments to your code and understand the importance of well documented code
• Pair with your drone using the drone.pair() function
• Understand how to use the drone.takeoff()and drone.land() functions

In this lesson, you will complete the following steps. Make sure that you demonstrate your completed code to your instructor after each step:

1. Hello World! (Using the print() function)
2. Using Comments
3. Pairing and Printing
4. Takeoff! (Your First Flight Test)

It’s time to write your first Python program! This program will use the print()function. You’re not printing with ink and paper, but you’ll print to the screen so you can see any output from the program. Programmers use print statements to track the order in which a computer runs lines of code, which helps them debug (find errors in) the code. They also use the print()function to check the values of variables (containers that store values) as the program progresses. 

Make a new Python file called helloworld.py and run this line of code:

print("Hello, world!")

When you use a print statement, the output will appear in the console. The console is a tool in most IDEs (Integrated Development Environments) that allows you to see specific commands and information about the program as it runs. Most console windows will appear at the bottom of your screen. Here’s what it looks like in “Python for Robolink”.

The “Hello World” program has been used to introduce beginner programmers to a new programming language since the 1970s. Welcome to Python!

Comments are ignored by the computer when running your code, so you can write words and sentences as you would in a normal document.  You can add comments to your code by beginning the line with a hash symbol (#). These are for single-line only comments, which means that when you start a new line, the program goes back to normal code.

Comments can also be used by programmers to debug by “turning off” parts of the code by commenting them so they are ignored. This way they can test specific parts of a program to narrow down what the problem may be.

Try it out with the code below!

# print("The computer is ignoring this")

print("The computer is printing this!")

What do you see?

If you want to write a longer comment, insert the block of code between two sets of triple quotation marks or triple apostrophes. The first set of triple apostrophes is the beginning of the comment, and the second set is the end of the comment. Everything in between will be ignored by the computer. Try it out with the code below:

'''
This is a longer comment that the computer will not read:
I
Love
Programming
Drones!
'''

In this step, we will learn how to make the drone take off and land. Since the drone will be flying, please make sure you follow all safety precautions and make sure you place your CoDrone EDU away from other objects on the floor.

The takeoff() function

Follow the steps below to prepare a new file for this step:

1. Create a file called flight_test.py (note we use an underscore, you could also use a dash)
2. In this new file, add a drone object (you can call it drone or give it a name of your choosing)
3. Tell the drone object to pair

We use an underscore or dash to make the file name readable. It is possible to use a space, but is not good programming practice, as not all interpreters will be able to understand or use file names with spaces. If you are having trouble with these steps, please go back and review the previous step and code.

Now we are ready to write our flight test! Write the drone.takeoff() command, which will allow your CoDrone EDU will take off and hover. Note that the takeoff command does not take in any parameters, so the parenthesis should be empty. This is because drone.takeoff() goes through the steps of starting the motors and flying the drone to a preset height. Add the following code to your flight_test.py:

drone.takeoff()
print("taking off")

The land() function

Much like the takeoff() function, the land() function follows a preset routine that will land the drone safely on the ground.

There are two ways a drone can land. The first is with the drone.land()command, which will gently bring your CoDrone EDU to the ground. 

drone.land()

The second is with the drone.emergency_stop()command. This immediately turns off all the motors, which will crash your CoDrone EDU to the ground. Ideally, this should only be used in emergency situations, and you can program your keyboard’s space bar to act as an emergency stop if it’s hit. For now, we will stick with a simple land command. Below you will find an example of the code with print statements included.

from codrone_edu.drone import *

drone = Drone()
drone.pair()
print("Paired!")
drone.takeoff()
print("In the air!")
print("Landing")
drone.land()
drone.close()
print("Program complete")

If you want your CoDrone EDU to hover for more time before landing, you can use the hover() function after calling takeoff().

drone.hover()

Don’t forget to type, inside the parentheses, the amount of time in seconds that you would like your CoDrone EDU to hover.

Sample code that includes the drone.hover() function is provided below.

from codrone_edu.drone import *

drone = Drone()
drone.pair()
print("Paired!")
drone.takeoff()
print("In the air!")
print("Hovering for 5 seconds")
drone.hover(5)
print("Landing")
drone.land()
drone.close()
print("Program complete")

Using the hover() function is one way to make your program pause for a duration of seconds. You can also use a sleep() function:

#The following code will cause the program to wait for 5 seconds.
time.sleep(5)

This function will pause your program. No other commands will be sent until the delay finishes. Enter a number of seconds inside the parentheses to establish the timing of the delay.

The time.sleep() function comes from Python’s time library. To use the function, add the following import statement to the top of your program:

import time

While running the program provided in this lesson’s previous step, replace the drone.hover() with a time.sleep(). What do you observe?

In this lesson, you learned about how to take off, hover, and land your drone just by using code! In the next lesson, we will learn additional flight movements.