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, you may be thinking of a mounted, spinning wheel that stays balanced in the same orientation, no matter which direction you turn or flip it. 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!

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 and correct any unwanted displacements to remain stable. Displacement is a movement from one position to another position.

There are three orientations that we are concerned with when we are flying a drone for stability: roll, pitch, and yaw. The gyroscope 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!

You may notice there are two blocks related to the gyroscope. For this example, use the function get_angle() in the “Sensors” menu.

In a 3-axis gyroscope, you have access to all 3 axes. Add three blocks and use the dropdown menu to select the axes. Finally, connect a print block to each one.

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 100 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.

Enclose the code you wrote in a repeat block.

Sometimes, it can help to format the output of your code so that it is easier for a human to read and interpret the data. In the “Input/Output” menu, use the create text with block with print statements to format the output.

Finally, print the X, Y, and Z angles with a label. Add a space before and after the letter so you can read your output clearly.

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. Tilting to the left, backward, or turning to the right will return negative angles. When you turn beyond 180 degrees, the value will switch to -180. What else do you notice?

Your mission is to program the CoDrone EDU to change its LED colors based on its turning direction. Each quadrant of the circle will be represented by a different color: Red for 0-90 degrees, Yellow for 90-180 degrees, Green for -180 to -90 degrees, and Blue for -90 to 0 degrees.

Here are the steps to help you get started.

• Create a loop that repeats 100 times
• Inside the loop, read the z-angle and store it in a variable
• Add an if statement with 3 else-if conditions
• In the first condition, change the color to red if the angle >= 0 and angle < 90.
• Repeat for the other 4 quadrants.

Note: this program doesn’t include any takeoff, landing, or flight commands! Place your drone flat and turn it with your hand. As a challenge, add in flight commands and have the LEDs change color while flying.

We provide a function that allows the drone to turn to a given angle, turn_degree().  This function turns the drone right or left with absolute reference frame to drone’s initial heading. The drone’s initial heading is defined (set to 0 degrees) by the drone’s heading after takeoff or when drone pairs to the controller after powering on.

Using turn_degree(45) will turn the drone 45 degrees to the left, and using turn_degree(-45) will turn the drone 45 degrees to the right.

What happens if you run the code below?

You will notice that using turn_degree(45) consecutively will turn the drone 45 degrees to the left, relative to the drone’s initial heading, once and then do nothing after. Why? This is because, after the drone turns +45 degrees for the first time, the drone is already +45 degrees relative to the drone’s initial heading! Therefore, the drone does not have to turn again.

Run this code to become familiar with the turn_degree() function:

Note: This function only accepts angles from -180 to 180 degrees.

Remember when you flew CoDrone EDU in different shapes? Now, let’s put that knowledge to use with the gyroscope! Create programs that turn just the right amount of degrees for each shape. Here’s a tip: use turn_degree().

• Triangle
• Square
• Pentagon
• Hexagon
• Octagon