Flight SAS Control Surface Oscillation in Atmosphere

[G33k]

The flight controls pretty much snap to their maximum authority, this leads to excessive stress on the aircraft and oscillations with SAS enabled. 
The control surfaces need to move more gradually, ideally this would also be tweakable by the player. In the FAR mod for KSP you can enable a feature that adjusts the maximum deflection based on the vehicles speed, like a real aircraft FCS would. Also would be a good improvement.

Edited January 11 by DibzNr

[ShmackedSloth]

The SAS appears to be miss aligned and it takes Roll inputs and produces a Yaw output and then takes Yaw inputs and produces a Roll output. I compared control surface movement to the SAS reaction while in orbit (so control surfaces had no authority) and that was the result I found. 

[ShmackedSloth]

I suspect this is also why aircraft go crazy with SAS on. The control surfaces get it right but the SAS is twisted.

[Sea_Kerman]

KSP 0.1.1.0.21572

Windows 10

Ryzen 7 5800H

RTX 3060 Laptop

SAS seems to be very twitchy and overcorrect with aircraft control surfaces, leading to underdamped oscillations if the aircraft has high control surface authority.

I had to reduce the control surface deflections on this aircraft for SAS to not freak out constantly, and it still enters roll oscillations at high speeds.

[GMorPC]

Reported Version: v0.1.3 (latest) | Mods: none | Can replicate without mods? Yes 
OS: Win 11 | CPU: Intel Core i-10400 | GPU: GTX 1660 Super | RAM: 16

 

When control surfaces are turned on/installed on any craft that is moving through Kerbin atmosphere, above a certain speed (dependent upon craft,  usually >200 m/s) when direction is changed or any input is put into the controlls with the SAS enabled, the craft starts oscillating in all directions. If this situation is left alone after it begins, the craft will eventually destroy itself.

CPU: Intel Core i5-10400
RAM: 16 GB
GPU: Nvidia GTX 1660 Super
OS: Windows 11

 

Included Attachments:

Edited June 29, 2023 by Anth12

[Anth]

Merged some bug reports.

[Anonymous Bug Reporter]

Reported Version: v0.2.0 (latest) | Mods: none | Can replicate without mods? Yes 
OS: windows 11 | CPU: intel i9 | GPU: nvidia RTX 4070 | RAM: 16gb

When flying a plane and having SAS on it seems to over correct itself trying to stabilize so it ends up just wobbling itself to almost crashing. its not planes are very stable when SAS not active and flying but as soon as it goes on it wobbles itself out

Included Attachments:

[jcheung9941]

Reported Version: v0.2.0 (latest) | Mods: none | Can replicate without mods? Yes 
OS: windows | CPU: ryzen 5 3600 | GPU: radeon 5700xt | RAM: 32gb 3200mhz

 

severity: moderate

 

frequency: high

 

description:

uncommanded roll oscillation occurs with SAS enabled and thrust is applied. most noticable out of atmosphere, where no atmospheric effects need to be compensated for, or dampen out oscillation with dran.

can manually null out roll, but it comes back (see attached video, major roll commands are manual input) fairly quickly.

 

 

technically out of atmosphere, but i feel like is related

Edited January 1 by jcheung9941

[Anonymous Bug Reporter]

Reported Version: v0.2.0 (latest) | Mods: none | Can replicate without mods? Yes 
OS: Windows 11 | CPU: AMD 7700 | GPU: AMD RX7900XT | RAM: 32 GB

Nearly every aero and space plane will "wobble" in flight at speed when using the SAS stability control. This makes it difficult to fly in a straight line, much less try to land. RCS also seems to have a similar issue where, without moving and using SAS, the thrusters will continuously fire, making it difficult to dock in orbit.

Included Attachments:

[The MEKanic]

Reported Version: v0.2.0 (latest) | Mods: none | Can replicate without mods? Yes 
OS: Windows 11 | CPU: AMD Ryzen 5 5600X 6-Core | GPU: Nvidia GeForce RTX 3060 Ti | RAM: 16 GB

Anytime I fly a plane, its wings, stabilizers, and/or control surfaces will flap up and down violently, causing the craft to shake. It has made flying an airplane in this game very difficult. The only workaround I found is to enter timewarp, which I thought would worsen the situation. 

Included Attachments:

[boriz]

Could you post a picture of your plane, in the SPH with CofG and CofL on?

[sgt_flyer]

I guess one of the problems is that in KSP1 the control surfaces did not deflect instantly to maximum deflection during micro inputs - they had an actuator maximum speed, contrary to KSP2, so short inputs from keypresses or SAS would only move the control surface slightly.

I guess it's a problem with the current KSP2 procedural wings - you would likely need to vary the actuator speed depending on the mass of the control surface itself.

Edited January 11 by sgt_flyer

[SolarAdmiral]

I've noticed this happens more often with larger control surfaces. 

So a current workaround that I find often works when I have a craft that does this, is to make the control surfaces smaller, (Smaller Cannards/Control Surface Wings, shorter Control Surfaces on Wings/Stabilizers). For example, if I see my plane is oscillating badly, generally by halfing the length or height of the Stabilizers on the main wings, it will stop the behavior, or lessen it to the point the plane is flyable. Of course this will only work if you still have good control authority with the reduced control surface area. Maybe there needs to be a bit of a scaling dampening factor, for larger surfaces, craft that oscillate.

[Jeq]

Can we have manual curve multiplier for sas controls? SAS is too agressive controlling vessels and thats why this happens.  This is problem with RCS trhusters rotating vessels too, farewell monopropellant. With curve (or turn time) multiplier we would get couple problems fixed.

 

I mentioned turntime multiplier in brackets, its another idea for sas controls. Where you input time in seconds, and SAS tries to do any rotational maneuver to its target orientation within that time, this should be cool too especially with rcs thrusters.  Atmosphere flight it feels curve option might be better.

 

To get this further, SAS could even try to avoid going over predefined G forces, this could be cool at every vessel, including rovers where you must remain inside of G to have grip into surface. (Something that braking should do too.)