3.4: Gyroscope

Goals:

By the end of this lesson, I will be able to:

1. Describe how a gyroscope works
2. Explain how a gyroscope reports movements
3. Explain the difference between displacement and angular rotation
4. Describe how gyroscope values can be used to improve the accuracy of flight movements
5. Create programs that use gyroscope values to control flight movements

Steps to Success:

1. What is a Gyroscope?
2. Angular Rotation and Displacement
3. Getting Gyroscope Angles
4. Put it in a Loop!
5. Turn 90 Degrees
6. Gyro with LED
7. Turn_degree()
8. Challenge 1: A More Perfect Polygon
9. Challenge 2: Plinko

When you think of a gyroscope (gyro), you may be thinking of a mounted, spinning wheel that stays balanced in the same orientation, no matter which direction you turn or flip the gyroscope. How? This can be explained by conservation of momentum. While you may not have heard of this term before, you have experienced this. For example, if you have ever spun around on an office chair, you probably noticed you spin faster when you bring your arms and legs in. Since momentum has to be conserved, your speed increases when you bring your mass (arms and legs) closer to you.

In electronics, gyroscopes don’t look like this. They are tiny chips that also use motion to detect changes in orientation. They use a concept called the Coriolis Effect by vibrating a plate on top of a chip. When the phone or device moves, it causes the vibrating disc to slide. This movement changes the electrical current transmitted to the sensor, which is then translated into a digital value. We know it’s hard to believe, but the tiny microchips you see on the CoDrone EDU have moving parts that are affected by movement!

To learn more about how digital gyroscopes work, check out the video here.

Gyroscopes are necessary to stabilize your drone while flying, since many factors could cause your drone to drift off course. A gyroscope can measure how far and in which direction your drone is tilting or rotating. Using some math and algorithms, a drone can try to correct any unwanted orientations to remain stable.

There are typically two types of movement we are concerned with when navigating our drone:

Angular Rotation — this refers to the movement around the drone’s X, Y, and Z axes. The drone tilting to the left or right, forward or backward are all examples of angular rotation.

Displacement — this refers to the movement of the drone’s position from one location to another. For example, changing height would be changing the drone’s vertical displacement.

There are three orientations that we are concerned with when we are flying a drone for stability: roll, pitch, and yaw. The gyro sensor in your CoDrone will return values from 0 to 180 degrees, positive or negative, that correspond to the degrees the drone rotated in each axis. If you have trouble remembering which way is positive and which way is negative, think of the flight movements!

Did you notice that throttle is not included? When a drone flies straight up or down, the change in position is not an angular (turning) displacement but a vertical displacement. The gyroscope does not measure vertical displacement. That’s a job for the height sensor!

Turn on your drone and place it flat on a table. Since there are three axes, each function will return the degrees that CoDrone EDU is tilting in the roll, pitch, and yaw directions. This is why you are seeing three numbers!

from codrone_edu.drone import *

drone = Drone()
drone.pair()

x_angle  = drone.get_angle_x()
y_angle = drone.get_angle_y()
z_angle = drone.get_angle_z()

print(x_angle)
print(y_angle)
print(z_angle)

drone.close()

It is not helpful to take one snapshot of the angle data because you can’t see how the angles change. Set up a for loop that will read the drone’s angles 900 times. This sounds like a lot, but this will give enough time to rotate the drone in every direction to pick up its angle readings.

Your program should look something like this:

from codrone_edu.drone import * 

drone = Drone()
drone.pair()


for i in range(900):

    x_angle = drone.get_angle_x()
    y_angle = drone.get_angle_y()
    z_angle = drone.get_angle_z()
    print(x_angle)
    print(y_angle)
    print(z_angle)

print("Done")

drone.close()

When you run your code, your drone will not fly so try picking it up and moving it in different directions slowly to see the numbers change. You will notice that sometimes the numbers are positive and sometimes they are negative. Remember that left roll, backward pitch, or left yaw will result in negative degrees. When you turn beyond 180 degrees, the value will switch to -180.

You’ve probably noticed that you can’t program your drone to fly a specific amount of degrees. Up until now, you could only use trial and error with the power and number of seconds. Sometimes this method is great, but for things that need precise angles, like flying in a shape, it doesn’t work well.

Fear not! With your new knowledge about CoDrone EDU’s gyroscope, you can create a function that will have the drone turn a specific number of degrees to the right or left. It uses information from the gyro sensor to make more accurate turns.  

Let’s start with a 90-degree turn (perfect for squares!). Think about how you would write code to keep turning while the angle reading is still less than 90. Hint: You need to use a while loop to check the yaw angle.

from codrone_edu.drone import * 

drone = Drone()
drone.pair() 

drone.takeoff() 
z_angle = drone.get_angle_z() 

while z_angle < 90:
    drone.set_yaw(-20) # Yaw is actually opposite! 
    drone.move() # No parameters since we need to move "forever" 
    z_angle = drone.get_angle_z() # Update the angle 

drone.land() 
print("Done")
drone.close()

Your challenge for this part: write a program that will change CoDrone EDU’s LED colors as the drone turns! You can pick whatever colors you like, but we used:

• Red for 0–90 degrees
• Yellow for 90–180 degrees
• Green for -180 to -90 degrees
• Blue for -90 to 0 degrees

Add a sleep() command for 1 second and reset the drone’s sensors.

Add a for loop that repeats 100 times and will get the drone’s yaw with the  get_angle() function and then store it to a variable called  angle.

Next, write an if statement that will turn the CoDrone EDU’s LED red if the angle is greater than 0 and less than 90. Be careful with this one! Negative numbers are being used in this program, so you do need to include greater than 0 in this conditional.

Do the same for the other three angle settings, but use else if statements instead. Finally, include an else statement that will turn the drone’s LED white.

Include a sleep() command for .05 seconds and then write a print command that will display as “Done!”

Note: this program doesn’t include any takeoff, landing, or flight commands! As a challenge, add those in yourself.

from codrone_edu.drone import *

import time

drone = Drone()

drone.pair()


time.sleep(1)


for i in range(100):

    angle = drone.get_angle_z()

    if angle > 0 and angle < 90:

        drone.LED_color(255,0,0,100) # red

    elif angle > 90 and angle < 180:

        drone.LED_color(255,255,0,100) # yellow

    elif angle > -180 and angle < -90:

        drone.LED_color(0,255,0,100) # green

    elif angle > -90 and angle < 0:

        drone.LED_color(0,0,255,100) # blue

    else:

        drone.LED_color(255,255,255,100) # white

    time.sleep(0.05)

print("Done!")
drone.close()

To fly in shape formations or do autonomous flight missions, you will be using the gyroscope a lot. Instead of having to rewrite the turning code over and over, turn it into a function turn_right_degree(degrees) that will take a parameter of how many degrees you want to turn right. Remember that the gyroscope uses a positive angle for turning left and a negative angle for turning right. This is opposite the flight movements!

def turn_right_degrees(degrees):
    z_angle = drone.get_angle_z()
    while z_angle > -90:
        drone.set_yaw(20)
        drone.move()
        z_angle = drone.get_angle_z()

drone.takeoff()
drone.turn_right(45)
drone.land()
drone.close()

Try changing the parameters for turn_right(). Make sure you stay below 180.

Challenge: Write a function turn_left() all on your own!

Use the gyro and loops to have your drone fly in the shape of your choosing!

• Triangle
• Square
• Pentagon
• Hexagon
• Octagon

You may have seen a plinko board before, if not there is an image example above. A puck is dropped, and it bounces back and forth in a zigzag towards the bottom. For this challenge, you will recreate the downward zigzag motion of a plinko board using the gyroscope.

This program must:

• Start at a specific height
• Drop in a zigzag
• Use a loop
• Use the gyroscope

All motions must be equal (Hint: this will happen if you use the gyroscope)

In this lesson, you learned about the CoDrone EDU’s gyroscope sensor. You learned how a gyroscope works, how it reports the drone’s movements, and how that can be used to control the CoDrone EDU’s flight movements.