autopilot - how does FS Force work with AP engaged

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PICuS
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autopilot - how does FS Force work with AP engaged

Post by PICuS » Wed Aug 12, 2009 9:26 pm

This sounds like a great software addressing a huge problem that is rarely discussed let alone attacked.

I see how FFB works and the need to abandon MSFS' trim function. However, if one is not flying mannually, how would auto-trim in an autopilot work with FS-Force? Ignoring the mechanical modifications needed to move the trim-wheel, how would MSFS "know" about the position of the trim tab given that its built-in trim function is disabled?

RussDirks
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Post by RussDirks » Wed Aug 12, 2009 11:50 pm

With the autopilot dis-engaged, all user trim commands are intercepted by FS Force and prevented from reaching MSFS. This continues to be the case when the autopilot is engaged, but also at this time MSFS begins to manipulate the trim wheel "internally", in a way that FS Force in unable to block. Thus the autopilot is able to do it's job.

If you try the demo, you can see this in action. When you're in the air and make trim adjustments, the trim wheel on the aircraft control panel will not move, because MSFS is not receiving those commands. However, when you engage the autopilot, then you will see the trim wheel start to move. This is being done by MSFS.

When FS Force detects that the autopilot is on, it slowly moves the FF centering force to the physical center of the joystick travel, so that when the autopilot is disengaged, there will not be a sudden lurching in pitch attitude.
Russel Dirks
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PICuS
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Post by PICuS » Thu Aug 13, 2009 2:06 am

Thanks for replying so quickly.

So, when AP is engaged, everything will behave as if FS Force was not there, right? The yoke's neutral point would be its original default position (or whatever its last position was before engaging AP) and the same would be true for the real trim wheel.

If I want to have another set of servos to take the readings from MSFS' autopilot auto-trim so that I could physically pull or push the yoke to the correct position as well as rotate the trim wheel (a real one rather than the pictorial one inside MSFS), is there a way to "inject" such readings into FS Force?

What I am trying to accomplish is that if AP is disengaged say in the middle of a climb, I would like to have the yoke's neutral point already shifted backwards and the physical trim indicator showing a nose high trim, and I would not need to do anything. Without that, the lack of awareness between MSFS and FS Force could really mess up the controls and feedback, right?

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Post by RussDirks » Thu Aug 13, 2009 8:58 am

PICuS wrote: What I am trying to accomplish is that if AP is disengaged say in the middle of a climb, I would like to have the yoke's neutral point already shifted backwards ...
If you disenage the AP with the yoke shifted backwards, the plane will pitch up violently. I don't know if real planes do that, but MSFS ones do. The yoke needs to be in the center of it's physical travel in order to have a smooth AP disengage.
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PICuS
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Post by PICuS » Thu Aug 13, 2009 11:18 am

Thanks Russel.

I gave up using MSFS because of difficulties in the way it handles trim, amongst other anomalies. In a real flight, the AP will physically move the yoke and trim wheel. So, in a climb, the yoke's neutral point would be shifted back and trim would be on the nose up side.

One should engage and disenage AP only in level flight then when using FS Force?

Am I right in saying that there is no way of doing a reverse feedback from FS Force to MSFS for autopilot operation? Are FS Force variables to the yoke exportable?

PS: just realised you are in Chilliwack - great pies at the airport cafe!

crim3d
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Post by crim3d » Thu Aug 13, 2009 2:15 pm

MSFS is a simulator that tends to ignore or simplify what they know most people will not notice. And the trim function is one of them.

Anyway, the proportion of FF joysticks is very low. And the proportion of people with a FF joystick that knows what it should be doing beyond funny vibrations when firing cannons is also small. FF is often described as a rumble feature on news, blogs, reviews (also!), etc.

That's why almost none cares about implementing realistic trimming in their simulators and here comes your difficulties with MSFS.

If I understand correctly, when the AP is disengaged FS Force has had time to bring the stick to the center. But what disturbs my dreams :) is that it means that the MSFS trim should be centered also at the same or the virtual axis travel and the real one will no longer match.

The best solution would be to disable the stick input when AP is enganged, read MSFS trim position and move the stick center accordingly (that won't interfere with aircraft control as it's been disabled). When AP is disengaged the stick input is re-enabled and both the virtual and real stick match.

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