We actually ended up using this when writing a controller for a quadcopter[1]. Essentially, we have one PID controller operate on the absolute angle (error = de

We actually ended up using this when writing a controller for a quadcopter[1]. Essentially, we have one PID controller operate on the absolute angle (error = desired angle - actual angle). The output of this controller is fed into the second controller as the desired rate of rotation (RoR) (error = desired RoR - actual RoR). The output of the second controller is finally fed to the motors. Apart from being easier to tune, I just found a good article[2] for why this approach works better for problems such as this. For quadcopters, of course, this allows one to easily switch between rate/acro mode and angle mode. [1] https://github.com/ThePinkScareCrow/TheScareCrow/blob/master/controls.cpp#L284-L285 https://github.com/ThePinkScareCrow/TheScareCrow/blob/master... [2] https://www.controleng.com/single-article/fundamentals-of-cascade-control/bcedad6518aec409f583ba6bc9b72854.html https://www.controleng.com/single-article/fundamentals-of-ca...