3E: Timers

Timers are everywhere so they might not seem like a big deal, but being able to use a timer in your program is an incredibly useful and powerful skill! This can help you keep better track of your flights and the movements within them.

With CoDrone Mini, time is stored in variables. For this lesson, you will be storing the start time in one variable, the end time in another, and then subtracting the two to get the total elapsed time.

For this activity, you will be programming a timer to keep track of your CoDrone Mini’s total flight, starting at takeoff and finishing with landing.

After importing the CoDrone Mini and time libraries, creating the drone object, and pairing, create a variable to store the drone’s starting time (we called ours  start_time ). Have your drone take off and land, and then create another variable to store the drone’s ending time (we called ours  end_time ).

To get the total time of your drone’s flight, create a variable that will subtract start_time from end_time. We called ours  elapsed_time . Finally, use a print command to have your program print the elapsed time in seconds.

Once you have tried this out, add hovering and then some flight movements into your program. What changes do you notice?

Your code should look something like this:

import CoDrone_mini

import time


drone = CoDrone_mini.CoDrone()

drone.pair()

start_time = time.time()

drone.takeoff()

drone.land()

end_time = time.time()


elapsed_time = end_time - start_time

print(elapsed_time)

What if you wanted to check how long one section in your program took, like how long your drone takes to fly in one square, or if pitching forward for 2 seconds actually takes 2 seconds? There’s a way to do that, and it just involves moving some timers around in your program!

After importing the CoDrone Mini and time libraries, creating the drone object, and pairing, have your drone take off, and then set pitch to 40. Next, create a variable to store the drone’s starting time, and then have your drone move for 2 seconds. It is very important to start the timer in this location! Starting it before setting pitch will add extra time, and starting it after the drone moves will skip over what you’re trying to time.

After the drone’s move command, create another variable to store the drone’s ending time, and then have the drone land. Create another variable that will subtract  start_time from  end_time , and use a print command to have your program print the elapsed time in seconds.

After trying it out, use a timer and see if the move command actually takes the amount of time you put in the parameters. If there is extra time, where do you think it’s coming from? Move the timers around, add more flight movement, and see what happens!

Your code should look something like this:

import CoDrone_mini

import time


drone = CoDrone_mini.CoDrone()

drone.pair()


drone.takeoff()

drone.set_pitch(40)

start_time = time.time()

drone.move(2)

end_time = time.time()

drone.land()


elapsed_time = end_time - start_time

print(elapsed_time)

Creating multiple variables to time one thing can be a lot. In cases when you want to time one movement, you can create a function instead! This will run a timer for the  move() function for however many seconds you put in the parameters.

After importing the CoDrone Mini and time libraries, creating the drone object, and pairing, define a function (we called ours  fly() ) and put seconds in the parameters. Next, create a variable to store the drone’s starting time. Create a while loop so that if the time minus the start time is less than the seconds in the parameters, the drone will move.

Next, have your drone take off and set the pitch to 30. Include the fly() function and set the parameters to 2 seconds, and then have the drone land.

Play around with the time in the parameters. What happens? Does increasing or decreasing the pitch have an impact on the time?

Your code should look something like this:

import CoDrone_mini

import time


drone = CoDrone_mini.CoDrone()

drone.pair()


# -------- function definition ---------

def fly(seconds):

   start_time = time.time()

   while time.time() - start_time < seconds:

       drone.move()

# --------------------------------------


drone.takeoff()

drone.set_pitch(30)

fly(2)

drone.land()

Challenge: One Minute Code

Fit as much flight movement as you can into one minute exactly (according to the  elapsed_time variable in your program)!

Rules:

• You must include at least one pitch, one throttle, one yaw, and one roll.
• Any flight movement, including hovering or delaying, can only last for 3 seconds.
• The same movement cannot be used in consecutive order, whether that is one after the other or in a loop (so don’t loop pitching forward for 3 seconds 20 times).
• Takeoff and landing are included in the one minute.