How is "Stabilizer.thrust" calculated?

[WoodyloveBo]

Hello. I attempted to log the thrust based on motor rotation using the code provided in cflib:

https://github.com/bitcraze/crazyflie-lib-python/blob/master/examples/motors/ramp.py

However, upon running the code, I noticed that the entire thrust was logged, despite confirming that the rotation between the four motors was unbalanced.

KakaoTalk_20240425_174619805.mp4

I'm interested in knowing the thrust (possibly PWM) of each motor when they rotate in the same way. I believe this thrust corresponds to the input from "Stabilizer.thrust." I'm curious about how this "Stabilizer.thrust" value is calculated from the PWM of each motor.

Thank you.

[ataffanel]

The variable stabilizer.thrust is the thrust to be applied globally to the platform expressed in a unit-less 0-65636 (0-100%): https://github.com/bitcraze/crazyflie-firmware/blob/d9ee34a78cecf2eaf8b05e0b54487cff0c7b4590/src/modules/src/stabilizer.c#L520-L523.

It is then passed, together with roll/pitch/yaw control to the power distribution to generate actual PWM for each motors. The motor log group allows you to get the control on the motors: https://github.com/bitcraze/crazyflie-firmware/blob/d9ee34a78cecf2eaf8b05e0b54487cff0c7b4590/src/modules/src/stabilizer.c#L818-L843

[WoodyloveBo]

https://github.com/bitcraze/crazyflie-firmware/blob/master/src/modules/src/controller/controller_pid.c

The control->thrust mentioned in the link seems to be the result of multiplying Acc.z by thrustScale in the positionController and then adding the feedforward term. Is that correct?

https://github.com/bitcraze/crazyflie-firmware/blob/master/src/modules/src/controller/position_controller_pid.c#L257

If so, it does not match the architecture shown in the diagram below.

I thought this was the thrust value obtained after calculating Attitude PID Control and Attitude Rate Control. Is it correct to say that the thrust value is the acceleration value converted to Thrust based solely on position and velocity?

[gemenerik]

The control->thrust mentioned in the link seems to be the result of multiplying Acc.z by thrustScale in the positionController and then adding the feedforward term. Is that correct?

Yes, this is correct. However, the thrust you are referring to (a single float) does not directly equal the power distribution to the motors. This actually follows from (also) running the attitude and attitude rate PIDs.

[WoodyloveBo]

https://github.com/bitcraze/crazyflie-firmware/blob/master/src/modules/src/controller/position_controller_pid.c#L260

Why is Thrustraw multiplied by Thrust Scale 1000? Thrustraw appears to be the acceleration value with PID gains applied. I want to know exactly what Thrust Scale represents.

[gemenerik]

From what I can tell it represents nothing more than a scaling of the value that comes out of the PID.