Modified 2020-09-11 by Dev Ramesh
Student version (unknown ref duckiesky_high_school_student/sac3-imu-intro)
Requires:
Hardware -
Basestation with Cleanflight
Build Parts 1, 2, and 3 completed
Previous Lesson
Result:
Knowledge -
Learn the definition and purpose of the IMU
Be able to point out the location of the IMU on the drone
Be able to explain how the IMU works
Skills - N/A
Modified 2020-08-12 by unknown
Modified 2020-04-16 by Garrett Warren
Modified 2020-09-03 by Garrett Warren
By the end of this lesson, students should be able to explain the basic functioning of the IMU and the laws of physics that go behind it.
Modified 2020-09-03 by Garrett Warren
10 min: Watch a short video.
20 min: Give a lecture on the physics of the IMU.
10 min: See the effects in Cleanflight
Modified 2020-04-16 by Garrett Warren
Modified 2020-08-12 by unknown
Teacher Materials
Place to play a video, basestation with Cleanflight, and drone.
Classroom Setup
Teachers can write a DO NOW on the board for students to set up their basestations and Cleanflight
Modified 2020-04-16 by Garrett Warren
Modified 2020-09-03 by Garrett Warren
10 minutes
While watching, pause to emphasize the following:
Where the IMU is located
The two sensors in the IMU: Gyroscope and Accelerometer, that measure angular velocity and acceleration respectively.
Optional: How the Micro-Electro-Mechanical (MEM) System works -
Gyroscope: gyros rotate -> vibration -> voltage -> ADCs
Accelerometer: measure displacement, and then differentiate to get acceleration
They measure without interacting with the rest of the world! E.g. what a spacecraft would have to use. The downside of this is that it does not have long-term accuracy.
Modified 2020-07-28 by Peyton Strong
20 minutes
First Law describes Inertia: Object’s tendency to resist the change of motion.
If we want the object to move, we have to exert eternal forces, and the second law tells us the effect of this.
Newton’s Second Law of Motion: F = ma (The force on an object produces acceleration)
F: Force on object
m: Mass of the object
the acceleration of the object, which is explained here
In short: Displacement is the change in position. Velocity is the rate of change of displacement. Acceleration is the rate of change of velocity.
The accelerometer measures the position changes and calculates all the way down to acceleration (accumulating errors along the way).
What causes an object to have a circular motion? Newton’s Second Law tells us there must be a force exerted on the object. What is the direction of the force?
Centripetal Force! Pointing to the center of the circular path.
Example: The gravitational pull from the earth to the moon is the centripetal force causing the moon to move around the earth.
For circular motion, we also care about how fast the object’s orientation is changing.
Angular velocity, which measures the rate of change of the object’s orientation
Teacher might refer to the first few paragraphs of this page
Similarly, angular acceleration is the rate of change of angular velocity.
The gyroscope measures rotation and calculates all the way down to angular acceleration (accumulating errors along the way).
Note: The analogy between [displacement, velocity, acceleration] and [Orientation, angular velocity, angular acceleration].
One student sits in a chair with eyes closed and another student spins the chair. The student in the chair guesses their orientation based on the feeling of the spin. Note that the student’s accuracy declines over time, which is similar to the accelerometer and gyroscope accumulates errors.
Modified 2020-09-03 by Garrett Warren
10 minutes
How do we account for the errors in the long term?
Pause for group discussion and presentation.
We need sensors that interact with the outside world, such as GPS, to know the location.
Useful Resources and References
Between times 0:21 and 5:00 of this video.