2C: Advanced Variables

Make sure that your CoDrone Mini is paired before starting the lesson! If you forgot how to do this, make sure to review how to pair to Blockly here.

Quick review: Variables are a way to store information in a program, and they’re used most often to store values. Variables are great if you have a lot of values in your program since you only need to change the variable’s value at the top of the program. 

Using multiple variables in one program might sound intimidating, but we promise it’s not! The first step is to create variables for each value you think you need. For example, if you know you will always have your drone flying for 1 second at 50% power, you can create one variable for time and another for power. You can then set their values at the top of the program, so time’s value would be 1 and power’s variable would be 50.

Try it out now! Set variables for your drone’s time and power, and then use them to have your drone fly forward, yaw to the right, fly forward again, and land. After testing, try changing each variable’s value to see what happens.

You might be looking at your program and thinking, “OK Robolink, that’s great, but what if I want to fly backward or to the left? I need a negative number!” There are two ways you can do that:

1. You can change the value at the top to a negative number. For example, instead of 50 for power, you can have -50 instead. This will change the value for the entire program.
2. In any instance where you need to use a negative number, you can use an equation block to multiply your variable by -1. This will help when you want to change some of your variables to a negative value but not all.

Change two of your power variables in your last program to -50. How is the flight pattern different?

You can also create multiple variables, set their values to integers, and use them throughout your program with the help of math equations. Your math teacher will be so excited to hear this!

Start out by creating four variables and assigning values to each of them. We used 1, 2, 5, and 10, but you can use whatever you like. Next, use them in equations in place of values or variables to have your drone roll to the right for 1 second at 50% power and throttle up for 2 seconds, also for 50% power! Again, you will need the flight variables blocks for this. 

Buried deep in the math menu is the random integer block. When this block is used, it will generate a random number from the range that you set. However, this doesn’t mean too much if you don’t know what that number is! To see the number, attach the gray print block from the bottom of the logic menu to the random integer block. Generate three random numbers!

Check the console to see the output.

A random integer can be stored in a variable! To do this, create a variable with a name you’ll remember (ours is x), and then drag the set variable to block to your workspace. Next, attach the random integer block and make sure the values are set to what you want. To see what the selected random integer is when you run the code, attach a print block to the bottom of your code, and then attach a get variable block to that.

What you can do now is add this to a program that will have your drone fly in a certain direction depending on the integer! In this program, there are three variables set to different random variables. The range is from -100 to 100 because power can be a positive or negative value. Run the code and guess what the values were! Hint: Add some print statements for each value to see if you were right.

Challenge: Variable Square

Program your drone to fly in a square, but there is a catch: you have to do it all with variables! 

Rules:

• You cannot use any numbers in your program except for setting up your variables at the top of your program.
• If you need to change the value of a variable, you can do it at the top of the program, use the change by block in the variables menu, or use a math equation.

Hints:

• One of the variables should be 0 for when you reset your flight directions. 
• Another should be -1 for when you need to go left, backward, or down.