darshanrai

Additional links:

1. The Story of Self-Repairing Control Systems. https://www.nasa.gov/centers/dryden/pdf/88798main_srfcs.pdf

2. Flight Test Implementation of a Second Generation Intelligent Flight Control System. https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/200502...

3. Flight Test Results from the NF-15B Intelligent Flight Control System (IFCS) Project with Adaptation to a Simulated Stabilator Failure. https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/201000...

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... [2] https://www.controleng.com/single-article/fundamentals-of-ca...

There's also this[1] series of blog posts by Brett Beauregard that speaks of a few improvements for real-world implementations.

[1]: http://brettbeauregard.com/blog/2011/04/improving-the-beginn...