On Sunday 11 Oct 2009 4:30:08 pm Curtis Olson wrote: > > I think that your premise that autopilots need to run at very high frame > > rates is not realistic. > > > > When I first got into autopilots and simulation, back in the 60´s, all of > > our models had as the final element a 0.1 second low pass filter which > > simulated the control surface actuator. This turns out to be a reasonable > > approximation for most actuators and is very simple to implement both in > > a analogue computer (which is all we had then) and in digital ones. > > > > As there is such a filter in the inner loop means that there is no need > > to simulate anything which has a faster response time than this. > > Therefore there is no need to run the autopilot at high frame rates. 10 > > or 20 per second is perfectly adequate. > > > > Many of the outer loops (e.g. the heading mode) of the autopilot can in > > practice be run at much slower frame rates as the response of the > > aircraft is quite slow. > > I think what Lee(e) may be observing is that when you tune an autopilot to > behave well when the update rate is 60hz, and then fly into an area of > complex scenery + effects the frame rate in FlightGear can drop > substantially. In this situation, the autopilot (which is running at the > same update rate as the graphics) can go unstable, leading to wild > oscillations. Presumably this is an entirely different issue than what > Pete is dealing with, and neither of these contradict anything you have > said.
Interesting. I would have imagined that the autopilot logic were synchronized with the FDM and hence slow downs should not cause an issue as they would both slow down together. But it seems that the autopilot logic is synchronized with GUI frame paining code. Is there any literature that lists out the sequence? I'm curious to know how the network IO is synchronized. Not having a common time base reference for the various subsystems can lead to varying performance based on the underlying hardware on which flightgear is run. The PID/Autopilot tuning for a given model should not vary based on the hardware on which flightgear is run. Should it? Or did I get this all wrong? -- Cheers! Kishore ------------------------------------------------------------------------------ Come build with us! The BlackBerry(R) Developer Conference in SF, CA is the only developer event you need to attend this year. Jumpstart your developing skills, take BlackBerry mobile applications to market and stay ahead of the curve. Join us from November 9 - 12, 2009. Register now! http://p.sf.net/sfu/devconference _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
