PX4 Firmware to control the speed of each motor

What I’m trying to do is I’m flying fine with QGC offboard mode, but I only want to inject the fault into one motor. I would like to control each motor for failure I would say. For example, when I have a quadcopter, the first of the four propellers has a speed of 0, and what I am trying to do is to reach the target position with propellers 2, 3, and 4.

Here’s my question.

  1. What values go into each motor in px4 iris? My word is, there are too many mixer related files and I can’t find any value that ultimately goes into each motor through the mixer. please tell me.
    And finally, please tell me the location and name of the mixer file that sends the value to motor.
    And is there a topic that contains information about the value that goes into each motor? Please let me know if you have any similar topics.

  2. When I look at uORB, there is actuator_test, but is this implemented?
    If you turn on failure gps off, you can see the gps disappear, and you can also see it shaking on QGC and Gazebo.
    However, actuator_test does not stop motor 1 on gazebo even if you enter the command actuator_test set -m 1 -v 0 like this. Is it correct to type the command like this? If I’m wrong, ask for some examples and elaborate.
    And does uORB work offboard? Or does it work in QGC position mode?

  3. The method I found is from 4000 in the .sdf file
    Changing it to 0 will tell you how to stop the motor. However, this cannot be changed in real time. Maybe you can also tell me how to change the speed of the motor like this in real time.