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rcbarend

How-to use a free gamecontroller axis as ElevatorTrim

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Frequently there are questions in this forum whether a spare controller axis can be used as ElevatorTrim axis.This question becomes even more relevant with the current availability of products like the CH Throttle Quadrant, which, depending on the used aircraft/type&number of engines, offers you a spare axis/lever; either on such a throttle quadrant itself or because the "throttle" level on your yoke/joystick now becomes available when using such a device.Short answer: YES, although with limitations (depending on the quality of the controller).This post describes how you can do this.First of all, as usual :-), there's more than one way of doing it.Although many gamecontrollers have related SW products called "Control Managers" or alike, I personally don't like them (just MY opinion). So I can only describe this ElevatorTrim feature using the standard FS functions; with the adavantage however, that this described method will work for ANY free controller axis. The basic method:- In FS, assign the free axis to the ElevatorTrim axis, via menu Options-Controls-Assignments.- Via menu Options-Control-Sensitivities, set Sentitivity for this axis to MAX, and the NullZone to MIN.And behold, it works :-)Of course this "poormans" ElevatorTrim is too sensitive compared to a real trimwheel, since the whole trim range is now controlled by a relatively narrow control range of the axis lever/wheel, compared to a real trimwheel which usually uses several revolutions to control the whole range. Another problem can be if you use the axis via a socalled gameport-USB convertor, which normally only has 32-64 discrete steps over the whole range, which is very low for a trim axis.A very annoying problem creeps up when you engage the Autopilot ALtHold, which also commands ElevatorTrim. Now your new axis and the autopilot will interfere, which may result in an erratic ElevatorTrim behaviour. Because FS tries to follow both the AP commands AND your ElevatorTrim axis; which obviously conficts.Of course you temporarally disable the ElevatorTrim axis (or even the joystick completely), but this is very awkward.However, you can (mis-??)use a feature of FS to avoid this: FS only "sees" an axis, if it's value changes.In other words: if you don't move the ElevatorTrim lever AND the axis doesnot "jitter", the axis value doesnot change and therefore doesn't interfere with the Autopilot Trim commands.Unfortunately, most controller axis (not only gameport controllers, but also most USB controllers) DO "jitter" a bit (maybe even unnoticeable), so this poses a problem.The remedy for this "jitter" is simple: increase the Nullzone a bit (which creates a small deadzone around the center position of the axis), and, with active AP AltHold, place the ElevatorTrim axis lever in this position.You may want to increase this NullZone a bit more, since most axis levers have no visible detente to mark the center position; so it's difficult to position the lever exactly at the center position.One way to get the optimal NullZone:- Start FS, load the default B747-400 and open the Throttle Quadrant window.- Place the mouse cursor on the ElevatorTrim gauge (make sure the FS Tooltips function is enabled)- Move the ElevatorTrim lever, and observe where the tooltip indicates 0 degrees trim.- On your controller, mark this position of the lever.- To get a more confortable NullZOne (so it's easier to place the lever in this dead/nullzone), increase the NullZone a bit. Not too much, because a large NullZone will limit the max. trimvalue you can set (although this can be compensated by editing the fs9.cfg file, and manually increase the value of AXIS_SCALE= .. to a value higher then 127).I realise that this description is far from perfect&complete, and that it is just a "poor-mans" trimwheel, but IMO it beats the cumbersome way of using TrimUp/Down command via the keyboard or joystick/yoke buttons if you cannot afford to buy a controller with a real trimwheel (or cannot build one yourself).Since I have my own (home-built) throttle quadrant, I now use the spare "throttle lever" on my CH Yoke LE as Trimwheel.For some aircraft I use a Logitech Wingman Force, and then I use its "throttle wheel" as Trimwheel. Cheers, Rob Barendregt PS-1:Just to avoid misunderstandings: sometimes discussions pop up, whether the "Wheel" on the front of the CH Product Yoke (-LE) is a TrimWheel or not; although CH Product may have intended it as such (again, I don't know !), my personal opinion is that it is way too sensitive to act as a TrimWheel and can easily cause miscalibration of the Yoke especially if the wheel is not centered when you calibrate the yoke. But whoever disagrees, it just MY opinion :-) PS-2:The above explanation above, about "when FS sees a controller axis or not", also explains why it is possible to use the F2 key (decrement thrust) to obtain ReverseThrust (which, in FS, is a negative value of the throttle axis).With the Throttle axis at Idle (= value 0 if well-calibrated) FS doesnot see the axis anymore untill you either "move" it out of the idle position or it "jitters" itselfs out of idle. Which causes FS to "listen" to the axis again, thereby disabling the ReverseThrust.PS-3:Of course it's possible (and even more flexible) to use the Controller calibration functions of FSUIPC for the above, but then you need the registered (payware) version of FSUIPC. And PLEASE PLEASE, DON'T HYJACK THIS THREAD to create yet another pro/con discussion about FSUIPC, or the pro's/con's of ControlManagers :-)

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Excellent post Rob, especially PS-3. :-) Thanks for taking the time to give us this good information. This might be a good one for Avsim to "pin" at the top of the forum. Right out in the open, all by itself where it is easy to find. I suspect that there will be MANY of us looking to use this info in the very near future. Just a thought!!Tom,Ken-- how about it?? :-)Regards,Paul

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That's a good post. The main problem is that after you select a pitch control mode on the AP, moving the trim axis to zero will cause a pitch excursion, until the AP can compensate. I use a Saitek X45 and it has a zero detent on the rotary so that helps.scott s..

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Hi Scott,Yes, I know. But (at least the default AP) compensates such trimconflict very fast (within a second), so an incidental axis movement (like when setting it to the deadzone) is hardly noticeable.It's just awkward that your have to think of doing it (unless you have a very good (=non-jittering) controller axis of course).Cheers, Rob

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I might be mistaken but I thought I saw a new option in FSUIPC 3.4 (registered) that will break the AP/trim association. Technical-tab maybe? I'm guessing Pete included it to address this very issue...Al

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Hi Al,Yes, you are right.But:1. Then you DO need a registered version of FSUIPC.2. I'm pretty sure that this can ONLY work if the aircraft panel uses the standard FS AP-AltHold function. But some payware aircraft have there own implementation of AltHold (and trim control).Cheers, Rob

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I sure hope nobody out there starts to sneeze too badly when I dust this one off !!!!!

 

Let me set the scene......I'm running FSX Gold.and have had no problems (other than having a crappy old 2.4 CPU) I like flying the default c172 low and slow......but here's the prob.

when I set the A/P for Alt Hld....the trim wheel keeps clicking all over the place,and won't let the plane settle on the proper alt.   I tried searching,but only came up with Rob's solution, In my case I'm using the Saitek Yoke and single Quadrant. I have the middle (blue) lever set for trim, and the values that Rob recommends.....but still the plane is all over the place instead of the set Altitude !!!

 Can this be one of FSX's glitches that you just have to live with ???  Or can I do some editing somewhere....or has someone found another solution ???

Thanks for any help....sorry for the dustoff...".God bless you" !!!

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I sure hope nobody out there starts to sneeze too badly when I dust this one off !!!!!

 

Let me set the scene......I'm running FSX Gold.and have had no problems (other than having a crappy old 2.4 CPU) I like flying the default c172 low and slow......but here's the prob.

when I set the A/P for Alt Hld....the trim wheel keeps clicking all over the place,and won't let the plane settle on the proper alt.   I tried searching,but only came up with Rob's solution, In my case I'm using the Saitek Yoke and single Quadrant. I have the middle (blue) lever set for trim, and the values that Rob recommends.....but still the plane is all over the place instead of the set Altitude !!!

 Can this be one of FSX's glitches that you just have to live with ???  Or can I do some editing somewhere....or has someone found another solution ???

Thanks for any help....sorry for the dustoff...".God bless you" !!!

No problem on the dustoff :)

Allthough I can't remember having written this post ..LoL

 

As to your problem:

This problem of a "jittering" trim controller axis is still actual in FSX; i.e. a slight change in the controller axis value (due to "jittering") will cause the FS trim setting to be reset to that value.

So it's constantly fighting the AP trim setting when AP-AltitudeHold is set.

Which is what probably happens in your case.

Besides using larger null values as described (and setting the controller axis centered), the only way is using the registered version of FSUIPC.

This has an option to disable the trim controller axis when AP-AltHold is On.

See the user manual of FSUIPC (search for "trim").

 

Note that this FSUIPC option only works for aircraft implementation that use the standard FS autopilot AltHold  function (like all default FSX aircraft and most addons).

Because if the standard FSX ALtHold function isn't used, FSUIPC has no way of knowing what the new AltHold variable is. (and doesn't know when to disable the Trim controller axis)

 

Best, Rob

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Thanx for that info. Rob.

Iv'e been toying with the idea of FSUIPC for years, but have existed using the Saitek software which has been ok.

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