Re: [Flightgear-devel] autopilot vs joystick

[James T. <zak...@ma...>]

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