Modified 2020-09-11 by Dev Ramesh
Student version (unknown ref duckiesky_high_school_student/sac3-motors-intro)
Hardware -
Basestation
Build Parts 1, 2, and 3 completed
Previous Lesson
Knowledge - How our motors work, what systems are in place to check them
Skills - The ability to utilize Cleanflight and a corresponding Python script interacting with Cleanflight
Modified 2020-07-23 by Peyton Strong
Modified 2020-04-16 by Garrett Warren
Modified 2020-07-29 by Peyton Strong
By the end of this lesson, students should be able to demonstrate their knowledge of the innerworkings of their motors, and should be able to run a Python script to navigate Cleanflight and operate their motors.
Modified 2020-07-29 by Peyton Strong
5 min: Brainstorming discussion about motors
10 min: Brief lecture
45 min: Activity with Python and Cleanflight
Modified 2020-04-16 by Garrett Warren
Modified 2020-07-29 by Peyton Strong
You may want to have the Python script that is already written ready to distribute to students, and to make sure all of the students have their Cleanflight flashed and working.
Materials needed
For Students: Basestation with Cleanflight and drone with Build Parts 1, 2, and 3 completed
For Teachers: Basestation with Cleanflight, drone with propellors detatched, and Python script
Modified 2020-04-16 by Garrett Warren
Modified 2020-07-29 by Peyton Strong
5 minutes
Class discussion:
Have the students spin their motor’s manually and trace the wires back on their drone to see everything the motors are connected to
Have them brainstorm about what each component of the FC -> ESC -> Motor chain could do
Think back to the ethics and safety lessons…Why is smooth motor control so important?
Modified 2020-07-29 by peytonstrong
10 minutes
Motor Lecture:
Motor Explanation-
There is a coil of metal within each of the 3 wires connected to the motor that allow electrons to flow through and create currents that combine to make a magnetic field that pushes and pulls on the motor to make it speed up and slow down.
ESC Explanation-
The ESCs take the input of power from the battery and digital signals from the flight controller, and then sends volts of electricity to the motor through the 3 wires.
It is the interface between the digital signal of the FC and the raw voltage going to the motors.
Accuracy Explanation=
Actuators aren’t completely accurate, just like sensors aren’t always completely accurate, so there is a small sensor inside the ESC that gets feedback from the motor by measuring it’s back current (the voltage that comes back into the 3 wires while it’s spinning). This sensor allows our drone to monitor it’s motor activity mid-flight.
Vocabulary:
3-Phase AC: Stands for 3-Phase Alternating Current and describes how none of the currents from each of the 3 wires leading to the motor align at the same point, which creates the dissonance and the magnetic field.
Back EMF: Back electromotive force, aka counter electromotive force, is the voltage that is emitted in opposition to the change in current of the motors. Each ESC has a small sensor that measures the back EMF and sends that information to the FC in order to monitor the motors as they are spinning.
TODO: Have them point out different things in Cleanflight that go with this lesson, so they can have things that are hands on to look at.
Modified 2020-07-29 by Peyton Strong
45 minutes
Showing motors in action with Cleanflight!
This is the most exciting part of this lesson, so it might be best to leave extra time for it.
Exercise: Use a Python script that sends a constant throttle command that spins the motors at a slow speed. Student tilts the drone to observe the FC corrections. Script prompts the student to input a roll or pitch angle. Students will observe adjacent drone motors spinning up faster. Students will move the drone to the desired angles until the motors return to equal speeds.
This exercise is trying to build intuition for how the motors actuate the drone and how controllers get layered. It also gives an initial hands-on experience with a closed loop controller which they’ll understand better later.
TODO: Put that script or a tutorial to make that script in here?
TODO: Might be best to give another option of an activity that doesn’t involve Python, but just involves Cleanflight, so classes with less coding confidence can still have a hands-on activity.
The following was marked as "todo".
TODO: Might be best to give another option of an activity that doesn’t involve Python, but just involves Cleanflight, so classes with less coding confidence can still have a hands-on activity.
Location not known more precisely.
n/a
in module n/a
.Useful Resources and References
The Actuators video of this edX lecture.
This more advanced explanation of 3-Phase AC motors.