Trim: apply to aero and thrust only

[OHara]

I love trim for aerodynamic control surfaces, and for gimballing thrust on NASA-shuttle-like craft, but trim can be troublesome when used accidentally. (Trim being what we get with Alt-A,S,D,Q,W,E, Alt-X to turn it off)  I suggest that trim should apply only to the 2 steering controls that are physically connected to the torques we typically 'trim out'.

Aerodynamic control surfaces: apply trim, as it balances other aerodynamic forces, and lets us set for a desired AoA
Swiveling thrust: apply trim, as it compensates for the misalignment of the nominal thrust vector with the CoM.
Reaction wheels: ignore trim, any application of which seems to be done as well or better with SAS (true?)
Reaction Control System (the little jets): ignore trim, as this is never desired to be applied continuously (true?)
Rover-wheel Motors: apply trim, as people already use that
Rover-wheel Steering: apply trim, only because it seems to do no harm

For a space-plane with both control surfaces and reaction wheels, the control surfaces would be positioned according to the position of the control-input indicators, but the reaction wheels would torque only according to the difference between control-input (red) and trimmed position (green).

Am I forgetting anything?  
I admit that I have used reaction-wheel trim to wrangle asteroids, but that exploits the unrealistic infinite angular-momentum capacity of KSP wheels, so I would not mind if that were less easy; trimming the thrust gimbals to the CoM, though, seems to be in the spirit of the game. Trimming for takeoff solves the fishtailing problem for me, and of course has all the other usual uses for flight, so I'd like to let more people use trim without worrying about forgetting to turn it off.

This might be considered together with an earlier suggestion for a better UI and SAS-interactions for trim (from which I stole the image above).  I saw discussion about a mod implementing some of this but I cannot find a live mod.

Edited August 14, 2016 by OHara
forgot rovers

[Alshain]

You should simply be able to tweak it on or off on any given control surface, engine, or RCS, or Reaction wheel so you can choose how you want your craft to behave.  Then we can create module manager patches to set the default for that tweakable and everybody is happy.

However, the bigger issue for trim at the moment is it's completely locked to the keyboard.  I have an 8-way hat switch on my flight stick and I would love to use it but instead I get to ignore the fact trim even exists because I'd rather not use it than use it on the keyboard only.  The fact that Mod+Key inputs are not an assignable combination in the control configuration is a big problem.  As far as I'm concerned, any development on the trim system that doesn't include adding it's control assignments to the list is nothing but a waste of development time.

Edited August 12, 2016 by Alshain

[ZooNamedGames]

I'd like a simple set of keys like alt+QEWASD to incrementally increase trim, or simply have a slider bar that I can click/scroll (when hovered over) to increase or decrease the trim for whatever modes.

if you wanted something specific exempt from the trim you could use the fancy lock gimbal function. 

[OHara]

On 8/12/2016 at 7:52 AM, ZooNamedGames said:

I'd like a simple set of keys like alt+QEWASD to incrementally increase trim, or simply have a slider bar that I can click/scroll (when hovered over) to increase or decrease the trim for whatever modes.

Alt-QEWASD are the set of keys to increment trim.  

By "for whatever modes" do you mean that you'd like a way in-flight to selectively apply trim to certain parts?  
Myself, I'm not dexterous enough with a mouse to select a control-surface in flight. (Maybe I have unusual habits as an airplane and sailplane pilot, changing trim very often in flight.)

If you mean you'd like keys/sliders to trim individual parts in vehicle assembly (balancing the craft) we have the rotate-part tools, using either shift-QWEASD or the mouse, to adjust the center-orientations for control surfaces and thrust.  There are suggested ways to improve the rotation tools in general.

Assuming the elevator is rotated in assembly so that neutral elevator gives best rate-of-climb, before takeoff I need to trim nose-up so it doesn't wheelbarrow, in flight I trim-out the tendency to roll right (even Val's designs do this a little)  but I don't need the reaction wheels to help with any of this, and am always surprised when the space-plane rotates faster and faster when out of the atmosphere.

I should have linked to a recent explanation from @Snark about how unexpected trim can confuse people.  I'm suggesting that having reaction wheels ignore trim by default will make everybody happier.

[The Optimist]

But that'll kill off my stock propeller planes, as they run on reaction wheel power.

[Alshain]

2 hours ago, The Optimist said:

But that'll kill off my stock propeller planes, as they run on reaction wheel power.

That's why I said make it a tweakable option.  I knew there would be someone out there that wouldn't want this change.