I-Term Lock for Fixed Wing

[DzikuVx]

The I-Term Lock aims to solve the I-term accumulation and ultimately a bounceback on Fixed Wing platforms. Functionally, it's a counterpart of Multirotor I-Term Relax but more suited for Fixed Wings.

I-Term Lock is a hybrid approach to a fixed wing stbilization problem: sabilized + manual depending on current situation.

When pilot is not moving roll and pitch sticks, INAV attempts to stabilize the airplane with a standard PIDFF controller.

When pilot moves the sticks, following happens:

1. P-Term and D-Term are attenuated with a bell curve: no attenuation at stick-center and full attenuation at approximately 50% of rate target
2. I-Term is atenuated in a similar way for as long as error (setpoint - gyro) is low
3. When target reached a threshold (20% of max rate) and error is above 10% of max rate, I-Term is completely attenuated until error is low again.
4. FF-term is never attenuated

As a result, UAV feels like fully stablized near stick center and like in Manual mode when executing fast maneuvers.

https://www.youtube.com/watch?v=lQqi4Ovrw80