Understanding mc_att_control

Hello !
I am trying to understand the attitude controller for multicopters. I don’t understand the comment mentioned below,

What is the significance of it ?

Thank you!

Additionally, the equations in the code for attitude controller do not comply with equations mentioned in the cited paper :

Mellinger, Daniel, and Vijay Kumar. “Minimum snap trajectory generation and control for quadrotors.” Robotics and Automation (ICRA), 2011 IEEE International Conference on. IEEE, 2011.

Please correct me if I am wrong. How is the P loop implemented ? As per my understsanding,

rates-sp = params.att-p * (attitude_sp - attitude)

In the code rates are calculated as,

rates-sp = params.att-p * e_R

I understand Euler angles are not used for the implementation of the controller. But then how is the P controller implemented ? How is e_R computed ? Please can someone help me regarding this.

Thank you ! I appreciate it !

I found the controller diagram for position control of multi-copters, however I did not find one for attitude controller. I saw few sketches posted by some members on this forum. However I need more detailed sketch to understand the code better. Any help is appreciated.
Thank you !

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