RE: Lag filter implementation

> I am implementing a RC UAV in FlightGear and need a little help with
> the control system...
>
> The control system is fly-by-wire, with a receiver and standard RC servos.
> The servo response is similar to a first order lag, so I am using a
> lag-filter with C1 = 600.
>
> This is the elevator command system:
>
> <COMPONENT NAME="Pitch Trim Sum" TYPE="SUMMER">
>        INPUT        fcs/elevator-cmd-norm
>        INPUT        fcs/pitch-trim-cmd-norm
>        CLIPTO       -1 1
> </COMPONENT>
> <COMPONENT NAME="Elevator Control" TYPE="AEROSURFACE_SCALE">
>        INPUT       fcs/pitch-trim-sum
>        MIN          -20
>        MAX          20
>        GAIN         0.01745
> </COMPONENT>
> <COMPONENT NAME="Elevator Actuator" TYPE="LAG_FILTER">
>        INPUT      ................
>        C1            600
>        OUTPUT    fcs/elevator-pos-rad
> </COMPONENT>
>
>
>
> What should the input be for the lag filter?

The component can be addressed by the use of a property, whose name is created by using
the name of the component, making it all lower-case, and replacing spaces with a "-". So.
the "Elevator Control" component would be referenced by the property: "elevator-control".
This would be the input of your elevator actuator (after being prefixed with "fcs/"):

<COMPONENT NAME="Elevator Actuator" TYPE="LAG_FILTER">
       INPUT      fcs/elevator-control
       C1            600
       OUTPUT    fcs/elevator-pos-rad
</COMPONENT>

> Should there be an output from the elevator control?

No. There should only be one output specification, and it should be from the last
component in the chain of components. In your case, above, the elevator-pos-rad would be
set each pass to the correct value. So, I would expect that somewhere in your aerodynamic
specification you would have a reference to the property "fcs/elevator-pos-rad".

I hope this helps!

Jon


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