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Use TRIM instead of pitch/rudder controls for SAS. Why? Read here!


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Do you hate it when your craft is tugging along on SAS and you want to correct the course a bit? You touch pitch controls and it gets all wobbly.

 

There is a simple solution to your problem: SAS should not control the control input, but work via the TRIM settings. You control input would be combined with the TRIM and you would have perfect controls even with SAS activated.

 

Better yet: Allow the TRIM settings to be kept when leaving SAS (maybe with a modifier key or so) and move your craft from SAS to full manual control without even the slightest bump.

 

Why we should do this? Because usually it is done like that. Your input is combined with stabilisation/trim.

 

If it is still unclear what I mean exactly, move down three posts. User OHARA does explain it better!

Edited by dr.phees
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No. I mean I want to be able to fly an SAS stabilised craft without the sudden jerks back and forth when I touch the controls. IF SAS used TRIM instead of the direct input, that would be the case.

Also it would be good to keep SAS's input when turning it off, basically making SAS input the trim when disabling it. You could disable SAS and have butter smooth flight. Without having to immediately compensate for it recentering the controls.

 

An example: The autopilot settings in FlightGear do exactly that. You let your plane for example hold a course and turn off the autopilot. The trim stays, so the plane doesn't turn a bit in that moment and you take over a perfectly balanced and stable craft from the autopilot.

Edited by dr.phees
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The specifics of your suggestion are a slightly unclear among the mentions its desired effect.

It seems like a good idea to have SAS do its job by adjusting the same trim setting that we adjust with alt-WASDQE.  Then our WASDQE-or-joystick inputs move the controls from the SAS starting points, just as they move from the trimmed point today.  Then as I understand you, releasing SAS would leave trim, and the control positions, in whatever off-centered position was last used by SAS.  The second paragraph of an old suggestion is very similar.

Probably SAS should leave the trim fixed while user-inputs are active, so that SAS does not fight the pilot.  

The current system, where user input causes SAS to restart from zero control-inputs, is very awkward, but probably the improved system should keep an option to revert to current behavior.

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as well as trim, flaps should be added

9 hours ago, dr.phees said:

Do you hate it when your craft is tugging along on SAS and you want to correct the course a bit? You touch pitch controls and it gets all wobbly.

 

There is a simple solution to your problem: SAS should not control the control input, but work via the TRIM settings. You control input would be combined with the TRIM and you would have perfect controls even with SAS activated.

 

Better yet: Allow the TRIM settings to be kept when leaving SAS (maybe with a modifier key or so) and move your craft from SAS to full manual control without even the slightest bump.

 

Why we should do this? Because usually it is done like that. Your input is combined with stabilisation/trim.

 

used to press yaw control buttons to correct small errors when it comes to landing on the runway, however whole plane wobbles and literally f*cks up. Nice idea there dr.phees!

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I hope this will be done at some point. I am currently trying to find out if there is some way to do this via an addon. The problem is, that the autopilot input would have to be re-routed to the trim. Does anyone know if that is theoretically possible at all?

With kOS it should be quite easy to do, I would guess.

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How does the current SAS system work? What causes it to mess up your attitude when you try to correct it? If anyone could post the code that would be nice since I don't have access to KSP (I'm not a programmer and have limited knowledge of it, I just want a basic idea).

Does it just correct your attitude every X amount of time?

Could it instead correct your rotation/trim based on rotation?

This feature could be useful while accelerating with misaligned CoM/CoT, like maybe with a mothership with long ion burns

Edited by Skylon
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Just to let you know, if you use Atmosphere Autopilot, it fixes one problem with the SAS system in stock: it unlinks the axes from each other.

My biggest gripe about the stock SAS is that with it engaged, ANY player input overrides ALL the SAS commands. So SAS can be holding pitch for you. Your craft can be rolled a bit and you want to level out. You inputting roll-only commands for some reason turns off the current SAS hold-pitch inputs. So now you're rolling manually while pitching down unless you input some pitch as well. You may or may not have to add yaw input as well. It's an absurd system that made fine-tuning attitude nearly impossible without mods to compensate (Pilot Assistant being the primary one I used until I found AA; using both now.)

Anyway, isolating the axes for SAS goes a way to solving the wobble-after-input problem. (It's be only one axis you need to fight, not possibly all three.) Another thing that may help is limiting max control surface deflection (or deflection speed?) based on dynamic pressure. (Dynamic Deflection does the former.)

I would still find the method mentioned here useful as well. It does sound kinda dumb using only an absolute zero-point (no trim control) rather than a relative zero-point (trim-based SAS).

7 hours ago, Skylon said:

How does the current SAS system work? What causes it to mess up your attitude when you try to correct it?

As I mentioned, all the axes are "linked": SAS is all or nothing in stock. Either it has full control of your craft or you are in control. So trying to correct just one axis manually (say, yaw) makes SAS disengage completely until there is no more user input. This means if it was holding pitch, it's not anymore.

Second, it's use of control surfaces is also all-or-nothing for the most part. SAS is basically coded to change attitude as quickly as possible, screw efficiency, from what I've experienced. As such, it's pretty aggressive and coarse with adjustments. This can be havoc on controls depending on control surface area, atmospheric density, and speed. Fine Control mode mitigates this a little bit, but it depends on how fine you want your deflection rates to be. (A example situation could be landing a plane: you may want pretty fine controls during the terminal stage just a little before touch-down.)

I'm fine with stock SAS in space (for the most part...), but in atmosphere could use some work. On the other hand, mods have more or less corrected that, both in atmosphere (AA, PA, DD) and in space (MechJeb).

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No idea. I imagine it'd be up to a SQUAD dev to look at a mod's code to see how the functionality is implemented. Other features from plug-in based mods have been incorporated before, so there's a possibility. How easily is another matter.

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Squad should be careful if they choose to examine mod code though. If they don't use 'clean room design', where one person (or team) examines the mod code and documents it and another person reads that documentation and writes the new stock code, then Squad open themselves up to copyright infringement claims by the copyright holder for the mod.

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On 06/04/2017 at 7:34 PM, cantab said:

Squad should be careful if they choose to examine mod code though. If they don't use 'clean room design', where one person (or team) examines the mod code and documents it and another person reads that documentation and writes the new stock code, then Squad open themselves up to copyright infringement claims by the copyright holder for the mod.

In this case squad should be perfectly able to do this without looking at any code. It is a basic thing and already implemented in the stock SAS. It is "just" a bit of rewiring...

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It would also depend on the licensing. Recall that SQUAD requires all mods to declare a license of some sort.

But let's be real: the code is written by a KSP player. Said player is likely part of this community. It's not like SQUAD can't just ASK for a license and/or terms. Or just hire the modder like they've done before on a contract basis and have them work on that aspect of the game directly. Modder gets paid for work and SQUAD gets new integrated code.

Of course this assumes SQUAD is even interested in integrating a feature made possible by a mod. Things are also a little different when you work with a plugin (which has to go through an API) and the core game code itself (far more direct processing).

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1 hour ago, Physics Student said:

What is trim?

Considering your moniker, I'm surprised you ask. But on the assumption you're not trolling us...

Trim is a fine-tuning control adjustment, in KSP adjusted with alt-WSADQE for pitch roll and yaw. It can also be applied to roverwheels throttle (not engine throttle) and RCS translation. On an aeroplane, there are often small versions of the major control surfaces, e.g. a smaller rudder set into a full-size rudder, to make small adjustments or 'trim' how the plane is flying. The point is to accomodate imbalances in forces acting on the craft to maintain a particularle attitude or heading - these could come from differences in engine power, wind direction and force, shifting fuel or payload mass etc.

TL:DR it's fine-tuning for steering controls.

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36 minutes ago, The_Rocketeer said:

TL:DR it's fine-tuning for steering controls.

Another way to think of it is zeroing-out steering controls so that without any input from the pilot, the craft maintains a given relative direction of flight and/or attitude at some given flight profile. It's like SAS's "Hold Attitude", but without the actual SAS.

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On 06/04/2017 at 6:04 PM, StahnAileron said:

Just to let you know, if you use Atmosphere Autopilot, it fixes one problem with the SAS system in stock: it unlinks the axes from each other.

My biggest gripe about the stock SAS is that with it engaged, ANY player input overrides ALL the SAS commands. So SAS can be holding pitch for you. Your craft can be rolled a bit and you want to level out. You inputting roll-only commands for some reason turns off the current SAS hold-pitch inputs. So now you're rolling manually while pitching down unless you input some pitch as well. You may or may not have to add yaw input as well. It's an absurd system that made fine-tuning attitude nearly impossible without mods to compensate (Pilot Assistant being the primary one I used until I found AA; using both now.)

Anyway, isolating the axes for SAS goes a way to solving the wobble-after-input problem. (It's be only one axis you need to fight, not possibly all three.) Another thing that may help is limiting max control surface deflection (or deflection speed?) based on dynamic pressure. (Dynamic Deflection does the former.)

I would still find the method mentioned here useful as well. It does sound kinda dumb using only an absolute zero-point (no trim control) rather than a relative zero-point (trim-based SAS).

As I mentioned, all the axes are "linked": SAS is all or nothing in stock. Either it has full control of your craft or you are in control. So trying to correct just one axis manually (say, yaw) makes SAS disengage completely until there is no more user input. This means if it was holding pitch, it's not anymore.

Second, it's use of control surfaces is also all-or-nothing for the most part. SAS is basically coded to change attitude as quickly as possible, screw efficiency, from what I've experienced. As such, it's pretty aggressive and coarse with adjustments. This can be havoc on controls depending on control surface area, atmospheric density, and speed. Fine Control mode mitigates this a little bit, but it depends on how fine you want your deflection rates to be. (A example situation could be landing a plane: you may want pretty fine controls during the terminal stage just a little before touch-down.)

I'm fine with stock SAS in space (for the most part...), but in atmosphere could use some work. On the other hand, mods have more or less corrected that, both in atmosphere (AA, PA, DD) and in space (MechJeb).

The part about overriding pitch if you adjust yaw etc... this is my exact problem with my shuttle designs - I'm sure this problem was made worse after they adjusted SAS for 1.2 (or whenever it was recently). 

I'd never quite understood what the problem was, but this explanation has nailed it for me. So annoying when I try to correct yaw on my MK3 part shuttle only to have attitude change with it - made the craft a complete poodle to fly! Would using a joystick help with this? 

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15 minutes ago, MR L A said:

[...] So annoying when I try to correct yaw on my MK3 part shuttle only to have attitude change with it - made the craft a complete poodle to fly! Would using a joystick help with this? 

Not sure as I don't have any sticks (I don't play enough sims to warrant the investment; not much desk-space either), but I imagine it can since you can input both command types (pitch and yaw) more naturally.

Otherwise, use the AA mod. You will feel like you're cheating with how well it eliminates wobble and unlinks the control axes, giving you independent control of pitch, yaw, and roll. "Fly-by-wire" indeed. Well, I haven't tried it with a shuttle design, but it works wonders for my simple SSTO spaceplane. I had made a pretty responsive design. I don't have to fight AA like I do with stock SAS at times.

I jumped from 1.0.5 to 1.2. SAS is still brute force, but it's not (as) retarded like 1.0.5 and prior with taking really weird rotations to match a SAS command. In space it's not TOO bad. In atmosphere, it's still more or less balls. Although not as bad as letting 2 autopilots control the ship at the same time because you forgot to turn one off and wondering why that maneuver node burn went to complete crap. (Done this too many times with MJ and PA...)

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1 minute ago, StahnAileron said:

Not sure as I don't have any sticks (I don't play enough sims to warrant the investment; not much desk-space either), but I imagine it can since you can input both command types (pitch and yaw) more naturally.

Otherwise, use the AA mod. You will feel like you're cheating with how well it eliminates wobble and unlinks the control axes, giving you independent control of pitch, yaw, and roll. "Fly-by-wire" indeed. Well, I haven't tried it with a shuttle design, but it works wonders for my simple SSTO spaceplane. I had made a pretty responsive design. I don't have to fight AA like I do with stock SAS at times.

I jumped from 1.0.5 to 1.2. SAS is still brute force, but it's not (as) retarded like 1.0.5 and prior with taking really weird rotations to match a SAS command. In space it's not TOO bad. In atmosphere, it's still more or less balls. Although not as bad as letting 2 autopilots control the ship at the same time because you forgot to turn one off and wondering why that maneuver node burn went to complete crap. (Done this too many times with MJ and PA...)

I'll deffo give the mod a go thanks :) I've had a stick lying about for years.. hardly touched the thing lol. I'll give it a go but I think the transition between WASD and a stick might result in more than a few reverts :sticktongue:

hah, yeah I've seen it take ridiculous routes just to do a 180

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The problem with the SAS implementation is that it isn't coordinated along all axes. That and it seems to uses a horizon even in space. (Pitch doesn't seem to be treated as a single full circle, but instead as two half-circles merged. Roll and Yaw/Heading don't seem to be treated that way.) So you can yaw to a heading and while that happens, want to roll for some reason. Because inputs aren't proportional and just drifting the rotation isn't a thing to SAS, you wind up in a spiral-like movement instead.

Honestly, it feels like SAS has little to no 3D spatial awareness. It just tries to zero out all three axes at once at full power without coordination. Even MechJeb does some odd rotations at times, though it's still better than stock SAS. (For one, it's actually proportional control rather than full-power or no-power only.)

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