Michael Selig writes: > I have noticed that in many fgfs joystick property files some axes > are "squared". This makes the stick-position to control-surface > mapping nonlinear (squared) rather than one to one (linear). I > think real airplanes w/ "reversible" controls are closer to being > linear rather than squared.
Yes, that is correct; however, real controls are also heavily loaded (either naturally, or in the case of fly-by-wire, artificially), so that they naturally hold their trimmed position and require a fair bit of force to budge. Linear control input on a regular spring-loaded joystick or yoke tends to make a plane feel very jittery because of the lack of control loading -- it requires almost negligible pressure to pitch the nose up or down several degrees, for example, and seems (to the user) as if the plane is insufficiently damped. Squaring the axis requires more physical input (rather than pressure) from the user, but after a lot of experimentation, I find it's the closest I can get to the feel of a real plane without building a force-feedback system with big servos to load the controls. The problem shows up especially when flying IFR -- even the slightest jitter of the stick or yoke sends you flying outside IFR tolerances without squaring the axes. > To model small nonlinearities that can occur w/ push rods and control > horns, I think an exponent smaller than 2 would be more appropriate, if > used at all. Instead of "squared", I suggest we add an exponent tag: > > <exponent type="double">1.2</exponent> > > which would lead to the effect: We already have that, except that it's called "power". Take a look at Input/Joysticks/CH/pro-yoke-usb.xml for an example: <axis n="0"> <desc>Aileron</desc> <binding> <command>property-scale</command> <property>/controls/aileron</property> <power>2.0</power> </binding> </axis> The "squared" element is still supported for legacy purposes. Actually, to be most realistic, we'd add an ability to vary the value of <power> based on the calibrated airspeed -- the lower the airspeed, the sloppier the controls. All the best, David -- David Megginson, [EMAIL PROTECTED], http://www.megginson.com/ _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
