I seem to recall Erik commited a change to the autopilot code in the
last week or so. Does that fix something? Did that introduce a new
problem? This is pretty subtle, complex code so people shouldn't be
messing with it too much unless they are really sure they know what's
going on with it.
Curt.
Hans-Georg Wunder wrote:
Hello Jeff,
I found the same bug some days ago and I reported it here on the
lists. Your solution was also my first approach, but it did not work
for the Integrator-part. The value ep_n is wrong for the next cycle.
But after a looooooooooot of testing I found this solution:
// Integrator anti-windup logic:
if ( delta_u_n > (u_max - u_n_1) ) {
// We have to add the maxium, which is posibble and then
// to reduce the input value for the next cylcle accordingly
ep_n = (ep_n * u_max )/(delta_u_n+ u_n_1 );
if ( Td > 0.0 ) edf_n = (edf_n * u_max ) / ( delta_u_n +
u_n_1 );
delta_u_n =u_max - u_n_1 ;
// delta_u_n = u_max - u_n_1;
// ep_n = delta_u_n / Kp;
//ep_n =- u_max/Kp;
if ( debug ) cout << "Max saturation " << " New delta_u_n
= " << delta_u_n << " New ep_n = "<< ep_n << " ew edf_n = " << edf_n
<< endl;
} else if ( delta_u_n < (u_min - u_n_1) ) {
// We have to add the maxium, which is posibble and then
// to reduce the input value for the next cylcle accordingly
ep_n = (ep_n * u_min )/( delta_u_n + u_n_1 );
if ( Td > 0.0 ) edf_n = (edf_n * u_min ) /(delta_u_n +
u_n_1 ) ;
delta_u_n =u_min - u_n_1 ;
// delta_u_n = u_min - u_n_1;
// ep_n = delta_u_n / Kp;
//ep_n =- u_min/Kp;
if ( debug ) cout << "Min saturation " << " New delta_u_n
= " << delta_u_n << " New ep_n = "<< ep_n << " New edf_n = " << edf_n
<< endl;
}
I tested it for a P and a PI-controller. I haven't tested yet the
D-part, but I hope, it will work too
It would be nice, if you also could test this solution.
Feed back is welcome
Kind regards
Hans-Georg
Jeff McBride wrote:
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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--
Curtis Olson http://www.flightgear.org/~curt
HumanFIRST Program http://www.humanfirst.umn.edu/
FlightGear Project http://www.flightgear.org
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