I have been playing around with the autopilot this evening, and
noticed something that seems to me to be broken.
I ran into a problem where I would see a really large change in output
(delta_u_n) but the output would not change (yes, this probably also
means my gains need some adjusting), e.g.:
----- From debug output -------
Updating Yaw Stabilization
input = 119.876 ref = 0.000610361
ep_n = -119.875 ep_n_1 = -118.088 e_n = -119.875 ed_n = -119.876 delta_u_n =
-2.96522
P:-0.268029 I:-2.69719 D:0
min saturation
output = 0.982904
-------------------------------------------
So I checked the code in xmlauto.cxx and found that yes, these lines
were responsible for zeroing delta_u_n:
----------------- From xmlauto.cxx ----------------
// Integrator anti-windup logic:
if ( delta_u_n > (u_max - u_n_1) ) {
delta_u_n = 0;
if ( debug ) cout << " max saturation " << endl;
} else if ( delta_u_n < (u_min - u_n_1) ) {
delta_u_n = 0;
if ( debug ) cout << " min saturation " << endl;
}
-------------------------------------------------------------
Perhaps I am not understanding this correctly (this PID controller is
not like any I have seen before), but it seems to me that it should
read:
// Integrator anti-windup logic:
if ( delta_u_n > (u_max - u_n_1) ) {
delta_u_n = u_max - u_n_1; // <--- CHANGED
if ( debug ) cout << " max saturation " << endl;
} else if ( delta_u_n < (u_min - u_n_1) ) {
delta_u_n = u_min - u_n_1 // <-- CHANGED
if ( debug ) cout << " min saturation " << endl;
}
-Jeff
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