Re: [Flightgear-devel] autopilot vs joystick

[leee <le...@sp...>]

On Friday 06 Nov 2009, James Turner wrote:
> On 6 Nov 2009, at 14:47, dave perry wrote:
> > It seems to me it should be possible in controls.nas to choose
> > between the two values for aileron and two values for elevator
> > based on an agreed upon autopilot properties.  To do this, one
> > needs to be able to access the joystick axis value.
>
> This is one of the reasons I had to make the autobrakes be C++
> code, and make some other unpleasant changes - we're missing a
> layer of abstraction between 'input system output properties' and
> 'FDM input properties'. I found there's many joystick config
> files that expect full ability to mess with the /controls
> properties - which seems reasonable.
>
> What's not reasonable is that the FDMs read the same properties
> directly, which makes life hard for auto[pilot|brake|etc]
> systems. For YASim, it's bearable, since the 'input' control
> properties are defined in the aircraft XML files (so I redefine
> the YAsim brake inputs to be /
> autopilot/autobrake/left-brake-output instead of
> /controls/left-brake, for example), but for JSBSim I needed to
> change the glue C++ code to stop it reading FGControls directly,
> if the autobrakes are active. (Yuck!)
>
> I'm not sure what the solution is - I think it's to create a tree
> of 'fdm-input' properties analogous to /controls, which is not
> touched by any joystick scripts / external inputs / etc, and
> which by default is simply a copy of the /controls values, but
> which the autopilot (and similar systems) can manipulate.
>
> That's exactly what my C++ autobrake currently does, btw, and
> this was necessary to be able to correctly implement the
> interaction between autobrake input and pilot over-ride inputs;
> namely that any pilot control input automatically disarms the
> autobrake system.
>
> Regards,
> James

One of the things I never got around to was to add an offset value 
to the gain and reciprocal filter types, precisely for this sort of 
job.  As it was, I used PID controllers to control my airbrakes, 
instead of filters, which was easy enough anyway.

LeeE