On Friday 26 August 2005 23:19, Steve Knoblock wrote: > > My attempts so far have left me with some questions. > > Is there a complete and comprehensive list of properties that are > built-in to the FG system (not those created by a particular > instrument)?
I think the best way to explore all the properties is to use the property browser from the file menu. As a rule of thumb you can assume that properties that update in real-time and when you click the . (for current directory) are what you might call built-in. > Do I understand correctly that properties in the instrumentation/ > hierarchy are built-in values, that come from the system and are not > produced by a custom instrument or script? The majority of them are. In addition these are the properties that should be the most interesting to you as autopilot designer. Don't be tempted to use the properties from position/ or velocities/ ! Those are "perfect" values that would not be accessible in real-life. > I do understand that you can bring a property into existence by naming > it and it appears that the properties in autopilot/ hierarchy are > somehow part of the standard autopilot. I believe this means I should > create my own set of properties, such as autopilot/digitrak/settings > etc. Is that correct? I thought that was a good idea too, so that's what I did with the KAP140. > I tried adapting the controller, the cascading one for Heading Bug, > but it will not track. It just spins around. I can see it hit a "bump" > when it equals the setting. The original HDG controller uses the > heading bug error as an input. But I need to input the difference > between the orientation of the a/c and the GPS track into the > controller. I tried making the orientation in roll axis the input and > the GPS track the reference, but that does not seem to work. An autopilot needs to control the roll axis. Either by roll angle as input or turn rate as input. From browsing through the installation guide it looks to me that the _only_ flight data input (ignoring the internal magnetic system for a moment) is from the GPS. It would be difficult to derive the roll angle from the data that the GPS can provide, but it should be quite possible to derive the turn rate. You simply take the time derivative of the track. This can be done in nasal. It might be a bit tricky handling the 360 <-> 0 wrap. Now another controller can be used to set the reference for the pitch axis controller. This will normally be another PID controller, but it could also be you, the pilot, setting the reference to say 3 degrees-per-second turn rate. > Also, I do not really understand the GPS system in FGFS. I need to > take the heading value from the GPS ground track. The Digitrak in its > NAV mode follows a GPS track and ground speed from the GPS. That is > all it needs to function. It has various other modes as well, but that > is the one I want to get working first. There is a tracking bug and a tracking bug error values in the GPS system. I think that eventually you will find that they will come in handy. I find this autopilot interresting seeing that it only uses GPS data for it's input. It's quite different from the traditional designs that use the turn coordinator or the attitude indicator to control the roll axis. Are you using version 0.9.8 or CVS? -- Roy Vegard Ovesen _______________________________________________ Flightgear-devel mailing list [email protected] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
