I'm trying to get to grips with the PID tuning stuff using X-Plane
Using various GA aircraft, they would all snake when going from Waypoint 1 to Waypoint 2 and back again. I could get them to "stabilize" without too much oscillation, but the aircraft would roll oscillate in trying to follow a track.
When I load up the "Radio Control" example plane - a Great Planes 60 trainer with "stable trainer like handling" all the nav course following snaking goes away immediately, no PID tuning required, same values as the ones troubling for the GA aircraft.
Why would that be?
How do I find search for smooth autopilot settings for General Aviation craft, even the very simple one like the StinsonL5 (high wing trainer)?
The nav tuning guide is in the manual here.
You changed Nav_Roll I, Nav_Roll P and Crosstrack gain and it did nothing? Really?
It did lots of things, for sure, it changed the snakiness, and the aggressiveness of corrections.
But I could not locate values that showed much overall improvement, and worse if I looked at the "servo outputs" especially if you started to add some "D", there started to be big instantaneous spikes in those as well.
Also, APM would only show updates to nav_roll once per second so I was never sure about what was going on at 50hz on the board.
BTW you can see this just with the default values, and any X-plane general aviation demo aircraft. I think.
What exactly is Xtrack Gain (degrees per cm)?
Is there an explanation of why it would be necessary to adjust this and what direction and how much to adjust it by?
but changing the XTRACK setting was dramatic. I did a lot of experiments sitting here watching the x-plane fly around Innsbruck :)
I am pretty sure that setting has critical dependance on the flying speed of the model: small RC planes: 100 is ok. Big fast planes (or RC jets etc), must be much smaller. Perhaps you can ask him that? It is easy to see, you just get the plane (in x-plane) travelling between two waypoints and change dynamically the xtrack value, watch the snaking vanish with low numbers. And get really bad with 100 or above numbers (if the plane is ~80 knot + type plane).
I realize fixing the servo PID is necessary first, and nav roll pid next, BUT decent control is pretty forgiving of mistakes there: it'll fly the plane in windless situations without any drama with all kinds of values.