Why can SAS override gimbal lock?

[Fraktal]

As the title says. As I was doing some experimentation with offset engine thrust, I noticed a strange thing. A design I came up with required my craft's engines to be rotated exactly five degrees outward in order to avoid the thrust hitting the craft itself. If even the slightest amount of gimbal was applied to the engine, it produced no thrust. For that reason, I locked the gimbal on all engines to prevent that from happening... except SAS didn't care: if it decides the craft needs to turn and detects that there's an active engine on the craft with gimbal capabilities, it force-unlocks engine gimbal for the duration of the maneuver and re-locks it afterwards.

Why is this a thing? Shouldn't SAS try to use other means of changing orientation (ie. reaction wheels and RCS) when gimbal is manually locked instead of overriding what the user set?

Edited November 15, 2020 by Fraktal

[Serenity]

Do you have any mods?

I have never noticed that problem, hmmm, is the gimbal locked for sure?

You said you locked gimbal on all engines, maybe its a symmetry problem, try to disable symmetry and test it with locking one by one.

Have you tried to reducing gimbal limit to 0, hmm weird, maybe i missed it but i dont think i encountered this before.

Edited November 15, 2020 by Boyster

[Fraktal]

8 hours ago, Boyster said:

I have never noticed that problem, hmmm, is the gimbal locked for sure?

I locked it myself during flight (ie. not in VAB; I tried locking it in the VAB afterwards but SAS still unlocked it during flight). As SAS is steering, the gimbal button toggles on its own from locked to free, then back.

[Serenity]

3 minutes ago, Fraktal said:

I locked it myself during flight (ie. not in VAB; I tried locking it in the VAB afterwards but SAS still unlocked it during flight). As SAS is steering, the gimbal button toggles on its own from locked to free, then back.

Thats super weird, i did some quick testing and the gimbal stayed true, maybe i am missing something, can you like post a picture of the craft this is happening?

I might play a bit later and check it again but i honestly dont remember this to be a problem.

[Fraktal]

One thing I can think of is that maybe the AECS Motion Suppressor mod is doing it? Because I can see that it's using Module Manager to hook into gimbaled engines.

[AHHans]

Two points: On is that "Gimbal Lock" is usually used to describe another effect.

The other is that I just did a quick&dirty test and I got the same results as @Boyster: locking the gimbals on the engine that I used to test made it not move. No matter if I set that lock in the VAB or on the launchpad.

Another - somewhat far fetched - idea: do you have "toggle gimbal" on an action group somewhere?

[Fraktal]

Nope and I'm aware of the other meaning. I used the term in the context KSP uses it in: locking down engine bell gimbaling to stop thrust vectoring.

[foamyesque]

I know for a fact this doesn't happen in stock. I lock or limit engine gimballing frequently and almost always fly with SAS on in some fashion, and I've never, ever, seen those gimbals move where they shouldn't.  I would put money that the culprit is a mod you have.