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Trim Idle Only doesn't work correctly with Crossed Trims

Wow I knew Opentx was "Free Form" but this is incredible - I have enough trouble concentrating on the natural trims - can't imagine remembering this capability let alone using it. I dips me lid to those that can.
Cross trims
Posted on July 4, 2014 by John Case

A radio configuration for using a free thumb to adjust trim. For example on a mode 2 radio the right thumb could set rudder trim using the aileron trim switch and the left thumb could adjust aileron trim using the rudder trim switch. Same idea for swapping throttle and elevator trims.

Throttle Trim Idle Only
Posted on July 7, 2014 by John Case

Restricts trim input to only the idle portion of stick throw unlike the usual offset with affects both ends of the throw. Useful in wet fuel set ups to avoid overdriving the throttle servo. Useful for electric power set ups to keep the prop turning at idle throttle without changing how ESC views the upper end of the throttle.

Without testing, am I right in assuming that despite setting a maxim/minimum throw in 'outputs' the conventional trim that's aligned to channel could override that set value? I know that Graupner (MX22) limit throttle trim activation to the lower end of travel but don't know if it can exceed the idle set value.

These forums are meant to be educational - this episode has been good for me in that regard.

Thanks
 
One of the workarounds I use is via a curve that stays at 0 for 25% of it's length, then goes right to 100 for all the other points. With the E trim Weight of 25% and offset 25%, the curve acts as a filter to block the trim from adding to the stick input when the stick moves above 25% of its throw.

As noted, my old Ace Micropro's did it directly, with cross trims, and that was 29 years ago...shouldn't be too hard of a fix, we just need to get their attention.

Hmmm..but that reminds me of another Ace feature - using the sticks to "slew" the Min throttle endpoint when everything is running. Not subtrim, actually changing the endpoint value using the stick. Get the engine running, and then set the endpoint for best low idle....sounds like a fun little thing to work on replicating when it is -10 outside, like today!
 
IRW2411 said:
Wow I knew Opentx was "Free Form" but this is incredible - I have enough trouble concentrating on the natural trims - can't imagine remembering this capability let alone using it. I dips me lid to those that can.
Click to expand...

While "natural trims" might have the appearance of looking natural, from a practical standpoint they are very unnatural and cumbersome to use during flight, especially with an out-of-trim aircraft. For mode 2 flyers, crossed trims allow the pilot to make elevator and aileron trim adjustments with the free left hand while maintaining full time control of the aileron and elevator stick without ever needing to let go of the stick. This is why crossed trims work far better than "natural trims" during test flights, and also why crossed trims work far better than "natural trims" when very minor trim adjustments are needed. If you ever gave crossed trims a serious try, then you'd never go back to "natural trims".


IRW2411 said:
Without testing, am I right in assuming that despite setting a maxim/minimum throw in 'outputs' the conventional trim that's aligned to channel could override that set value? I know that Graupner (MX22) limit throttle trim activation to the lower end of travel but don't know if it can exceed the idle set value.

These forums are meant to be educational - this episode has been good for me in that regard.

Thanks
Click to expand...

I just ran some tests on my Taranis running 2.1.8.

With the Trim Idle Only disabled, and the throttle trim in the center, the throttle stick movement reaches the full maximum output, and also the full minimum (idle) output as set in the OUTPUTS screen. Raising the throttle trim position does not cause the output to exceed the maximum at full throttle stick, but it no longer lets the output reach the minimum setting with the stick position at idle. So in this case raising the throttle trim has no effect on the full throttle speed, it only increases the idle speed. On the other hand lowering the throttle trim position below center won't let the output reach the maximum at full throttle stick, but has no effect on the output at the full idle stick position. So in this case lowering the throttle trim has no effect on the idle speed, it only decreases the full throttle speed.

This causes a problem if the throttle linkage is initially setup with the carb not quite closing far enough at the full idle stick position. The idle speed will be too high, but the throttle trim won't be able to lower the idle speed since the output is already at the minimum programmed output.

Or if you happen to get the throttle linkage set so the engine idles at the correct speed with the throttle stick at full idle, and the throttle trim in the center, then the throttle cut switch won't work since it can't lower the throttle output any farther than the minimum output setting.

With the Trim Idle Only enabled, the throttle trim position has no effect on the output when the throttle stick is at full power. Full power throttle stick position always outputs the maximum output value as set in the OUTPUTS screen. This is true whether the throttle trim is centered, raised, or lowered. So once the carb linkage is setup to mechanically achieve wide open throttle, changing the throttle trim has absolutely no effect on the output at full throttle, which is why this setting is called Trim Idle Only.

With the Trim Idle Only enabled, moving the throttle stick to the full idle position does not let the output reach the minimum programmed output until the throttle trim is also at the fully lowered position. This minimum output position should also be low enough to kill the engine. This allows the throttle trim to utilize the full range of motion to set the desired idle speed, with the minimum output set low enough to use a switch activated engine kill. The Trim Idle Only function just makes setting up a carb for a glow/gas engine a lot easier and simpler without the need to go back and tinker with linkages or the radio settings.
 
My workaround has been to use the software to cross the aileron and rudder trims, but I installed jumper cable extensions to physically cross connect the wiring of the elevator and throttle trims. This way the elevator and throttle trims function as crossed even though the software does not have them crossed. Since the elevator and throttle trims are not crossed in the software, the Trim Idle Only function works perfectly.

But the real solution is to fix the bug.
 
This has been fixed:)
https://github.com/opentx/opentx/pull/5664 Is merged and closed whuch means the fix/changes were applied and are now in the nightly builds and will be in the next release. Download the Companion nightly and test :) Don't install the nightly firmware as it it not for flying with.
 
Cross Trims - works now. Noticed that the trim centre does not work as expected. When cross trimmed the trimT does not have a trim centre (remember this has been crossed so actually is ELE trim)

Also the TrimE, which is now THR trim has a centre when it probably should not... Tried this on the latest companion nightly....
 
YIPPEE!
I think they finally fixed it in 2.2.2!

I just tested the nightly build from 12-Feb-2018 07:27 on Companion and it seems to work perfectly with the trims crossed and the Trim Idle Only activated, with the exception of no center beep for the throttle trim.

RCdiy is correct. If the Trim Idle Only is activated, the center beep doesn't work on the assigned throttle trim. This is true whether the trims are crossed or in a normal configuration. Unfortunately it's nothing new and has always worked this way. The lack of a center beep has always been an annoyance, but it never caused an operational problem, so I've just been ignoring it. Fixing the center beep problem will probably take opening another github issue to get it resolved.

THANK YOU TO EVERYBODY who took the time to comment on this issue in github! I really appreciate your help!

And a special thanks to Wayne for starting this forum that generated enough additional activity over on the github issues forum to convince the OpenTx developers to finally fix this long standing issue.
 
They closed that issue.
What I reported was a bit different from the way the issue was worded.

Now that trimT is ELE trim should it not have trim centre?
Now that TrimE is THR trim should not the centre beep be removed?

That issue is reporting trim centre not occurring.
I'm reporting an asymmetric behaviour.

Before cross trimming there is no centre beep on the THR trim.
After cross trimming there now a centre beep on the cross THR trim which should not be there. Because it is centre beeping at I think -75 which has no meaning really unlike regular trim beeps at 0.
 
I just checked on Companion and you are correct. The Trim Idle Only selection removes the faint chirp at trim center from the TrmT button, regardless of whether or not the trims are crossed in the software.

So with crossed trims the active elevator trim (TrmT) does not have a faint center chirp, which it definitely should.

And with crossed trims the active throttle trim (TrmE) retains the faint chirp at center trim. I would like to see this center chirp remain active, but I can live without it if it's that important to the opentx team to keep it silenced.

My mistake was assuming the center beep selection boxes were referring to the center trim positions. I didn't realize the selection boxes were referring to the stick positions instead, which is an entirely different sounding beep tone. Stick center produces a loud beep, whereas the trim center produces a faint chirp.
 
I just checked the nightly builds for OpenTx 2.2.2.
In the one dated March 7, 2018 the center trim chirp (apparently calling it a beep causes massive confusion on github) now works correctly for the elevator channel trim with the trims crossed and the Trim Idle Only selected.

So with the trims crossed in the software, and the Trim Idle Only selected:
* The TrmT button controls the elevator channel trim, works correctly, and now has a center chirp.
* The TrmE button controls the throttle channel trim, works correctly, and does not have a center chirp.
* The Trim Idle Only function works correctly.

Bandaid solutions will no longer be required once version 2.2.2 is released!

A big thank you to everybody in this thread for getting the attention of the OpenTx team to finally fix this long standing issue!
 
Dave - in a earlier post you said I should try crossed trims - you couldn't see, but my eyebrows were raised. Recently had need to test fly a friends model which was wildly out of trim. I mostly fly with a tray so can use my left hand to effect trim changes if necessary - however I was using the friends Tx without tray - well, I was much like a one armed paper hanger - finally got it trimmed sufficiently to land safely. Recalled your comment and yes, it would have been advantageous on the day. Not a convert yet but considering!!.
Cheers
 
That test flight of a severely out of trim plane is the best case for using crossed trims. If that doesn't convince you to try them, nothing will.

The next best case is that crossed trims allow you to keep making fine trim adjustments until the stick feels absolutely centered. It's MUCH easier to feel the absolutely centered stick position if your fingers/thumb continuously stays on the stick.
 
Disappointing news. Apparently the Trim Idle Only with crossed trims bug fix that was scheduled for 2.2.2 apparently caused some other issues, so the fix was removed from 2.2.2 and rescheduled for opentx 2.3. So after nearly 5 years of waiting to get this bug fixed, it looks like we will have to wait even longer. I really don't understand why this bug is such a complex thing to fix.
 
UPDATE: Great news! After 7 years the issue of using the Trim Idle Only (TIO) function AND crossed trims at the same time has finally been solved in the official release of OpenTx 2.3.10.

If using Companion, a new selection box has been added to the SETUP screen called "Throttle Trim Switch". For mode 2 crossed trims the default selection of TrmT needs to be changed to TrmE.
Then TrmE also needs to be selected under INPUTS as the trim for the throttle channel. This is done by changing the "Include Trim" selection box from the default YES to TrmE.

If programming directly on a Taranis (and maybe others), under MODEL SETUP the "Trim Switch" selection box needs to be changed from Thr to Ele. Then go to the INPUTS screen and edit the throttle channel "Trim" selection box from the default ON to Ele.
 
Careful using this new fix....I was converting my models that used a work-around, and stumbled across....

If using the TTrim lever to control Elevator trim, and pick the option in Outputs to apply Trim→Subtrim, the subtrim does change correctly. But, the TTrm lever is not reset to 0, like it is for all the other trims when using the option. You have to move it back to center manually, otherwise you have double the amount of trim you intended.
Trim→Subtrim does work correctly with cross trims in older versions...but then, of course, Trim Idle Only and Instatrim doesn't.

Haven't yet tried using TTrm for some other variation of cross trims, but would assume it has the same issue with Trim→Subtrim.

(BTW - with the new fix, Instatrim is deliberately disabled if you have cross trims set up, so at least you can't get deep into trouble that way!)

Case opened over on Github.

--Yep, I'm cross posting this, just so people that are interested are aware!
 
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