Anth12

What issues have people been having with SAS?

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I was browsing Suggestions & Development Discussion and saw remarks by players who have been playing KSP for longer than a year about problems with SAS

What issues? 

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I've not had any. No clue what issues others are having. Maybe ask them on those threads?

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In most cases I feel it works fine, but in some cases SAS does not seem to go too well with certain (aircraft) designs. For instance, SAS can induce some wobble in an aircraft if the Center of Lift is way behind the Center of Mass, noticeable especially at very high speeds. SAS input is just too coarse and therefore always overcompensates, leading to a pitching up and down cycle. But in such cases the craft is usually perfectly stable on its own at high velocities, so SAS is not really needed for flying it anyhow.

There are however some other long-standing behaviours that make certain wing configurations really not viable. They are related to the internal craft control scheme, i.e. the code that decides, which control surface has to move in which direction on which input (or flight vector). By extension those inconsistencies also affect SAS, which means using SAS to fly such crafts will inevitably lead to rapid, though somewhat scheduled disassembly. An example includes this issue on the bug tracker: Bug #20847

Over the years there definitely were some substantial improvements added to the system, so in general I think it works rather well, considering that it has to handle the vast amount of combinations that parts can be assembled into crafts.

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I have noticed it misbehaves when I have RCS on and lower the reaction wheels authority on my capsules.

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SAS struggles to keep stability with engines with high gimbal range - AKA Vectors. This isn't a problem on extra-large crafts, but with small lifters (ab)using the Vector, SAS can induce very large wobbling as it continually uses the full gimbal range to correct craft - rather than using part of its gimbal range and decreasing the limiters as it gets closer to its intended position. Its fixable by reducing the gimbal range, but I wish to see this corrected.

Another issue with SAS creating wobbling is when to crafts face each other, set to Target lock. A small wobble in either of them creates a larger wobble in the other craft, which is then mirrored by the original craft, creating a sustained wobble. This is more of a nuisance than anything, but it can interfere in docking.

Other than that, I wish SAS would only grey out prograde/retrograde vector lock below 0.1 m/s or some low value. The current 1 m/s is too fast for my liking.

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SAS is not as effective at holding the roll axis as it used to be a few versions back. 

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@Vycma That bug report was interesting, but I am not sure that was SAS related. Seemed like the control surfaces were an issue. Also im not sure what the ceiling was for the panthers, that might have also been something to do with it.

Designs of a plane/craft will affect SAS at times just because that design isn't really optimal.

I have created one SSTO in 3 years of playing KSP. It wants to slowly pitch up because SAS, reaction wheels and engine gimble just arent strong enough to keep it facing the right direction.

@Challyss Reaction Wheels the last time I looked at them wont work well at anything less than 100% (they act more like pre 1.2) and I did post a bug report to the bug tracker about it

@Xurkitree The vectors issue I have seen, that can be compensated by reducing the gimble range.

Yeah there is something weird happening when two craft have target locked each other sometimes.

I agree that 1m/s is too high. Would be nice to be able to have some sort of slider setting to change it maybe

@Vanamonde Yeah that roll issue is something that has been in the game since 1.2. Its as if when it was overhauled in 1.2 that the roll was a kind of oversight. It can be compensated for by toggling the SAS when the rolling gets to the point where its about to turn the other way

Thanks for the input everyone.

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7 hours ago, Xurkitree said:

SAS struggles to keep stability with engines with high gimbal range - AKA Vectors.

I don't think this is a SAS problem, more of the vectors create such a huge offset thrust when gimballed, it would be unreasonable to expect some reaction wheels to be able to hold it. 

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Worth knowing SAS also obeys fine control mode (caps lock), as far as I know, which can reduce a lot of wobbles or wasted RCS fuel on some craft.

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@Anth12 You are right, I think my examples show in general, that ones individual standpoint influences, whether you would attribute such problems to the design of a craft, or the functioning of SAS, or if you see both as subsystems that are intrinsically linked to form a super-system.

Given that a player has the ability to design one part of this system (the craft), but has very limited influence over the other (controls and by extension SAS), I tend to attribute such issues more to the latter than the former component, especially when a craft by all indications should be perfectly stable and flyable (CoL behind CoM, CoT lined up with CoM and CoL, etc.). In case of the bug, even limiting authority or inverting deployment direction doesn't resolve the issue, since either pitch or roll will be correctly inverted, but not both. Hence, SAS runs on a faulty 'wiring' and therefore fails under certain conditions.

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Many moons ago, when KSP was but a young lad, SAS was a mighty force that would hold a craft straight and true. Then the “moar realism!” crowd started screaming and complaining and SAS eventually got gimped into the weak, pathetic, almost useless feature we have today.

The ironic thing is that most of the people who complained about SAS being “too powerful and not realistic” also use MechJeb to fly their craft for them. So, they never really used SAS in the first place (just substituted MechJeb for it), but they made darn sure to screw it up for everyone else by whining and complaining about it until they got their way.

Yeah, I’m a little bitter. How could you tell? :)

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Other than the over touchy roll issue, which Anth12 touched on above, the only other issue I have had, and only once, was SAS in target mode with the target being a radial docking port. The SAS would not align with the targeted docking port. I "think" I fixed it by opening the craft in the VAB and using the "re-root" tool to make sure my docking port, on the docking ship, was aligned with the root part...

 

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Posted (edited)

Using navball retrograde markers for surface rendezvous it auto-switches between orbit, surface, target/orbit and target/surface in a somewhat unintuitive and uncontrollable way. I still find myself sighting down the rocket body towards the HUD target marker rather than using the navball when doing precision landings on bodies that rotate with any speed.

Edited by ExtremeSquared

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2 hours ago, Johnny Wishbone said:

Many moons ago, when KSP was but a young lad, SAS was a mighty force that would hold a craft straight and true. Then the “moar realism!” crowd started screaming and complaining and SAS eventually got gimped into the weak, pathetic, almost useless feature we have today.

The ironic thing is that most of the people who complained about SAS being “too powerful and not realistic” also use MechJeb to fly their craft for them. So, they never really used SAS in the first place (just substituted MechJeb for it), but they made darn sure to screw it up for everyone else by whining and complaining about it until they got their way.

Yeah, I’m a little bitter. How could you tell? :)

Sign me up as someone who - from the moment they implemented it - likes the "new" SAS better, but does not use MechJeb.

(which is actually more "realistic" than flying manually but hey whatever)

6 minutes ago, ExtremeSquared said:

Using navball retrograde markers for surface rendezvous it auto-switches between orbit, surface, target/orbit and target/surface in a somewhat unintuitive and uncontrollable way. I still find myself sighting down the rocket body towards the HUD target marker rather than using the navball when doing precision landings on bodies that rotate with any speed.

I don't think I've ever had it auto-switch after I manually set the mode.

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15 minutes ago, ExtremeSquared said:

Using navball retrograde markers for surface rendezvous it auto-switches between orbit, surface, target/orbit and target/surface in a somewhat unintuitive and uncontrollable way. I still find myself sighting down the rocket body towards the HUD target marker rather than using the navball when doing precision landings on bodies that rotate with any speed.

Huh, I have not figured out how to rendezvous with a surface target other than manual piloting. Using the "anti-target" doesn't get you there...it just points away from the target. I do like you...sight down the landing craft body and manually piloting to as close as I can get. AFAIK there are a few mods (MechJeb being the most used) that will auto-pilot you to a landing at a surface target...but I haven't tried MechJeb. I'm updating to 1.6.1 as we speak and will try that mod for the first time.

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58 minutes ago, Victor3 said:

Huh, I have not figured out how to rendezvous with a surface target other than manual piloting. Using the "anti-target" doesn't get you there...it just points away from the target. I do like you...sight down the landing craft body and manually piloting to as close as I can get. AFAIK there are a few mods (MechJeb being the most used) that will auto-pilot you to a landing at a surface target...but I haven't tried MechJeb. I'm updating to 1.6.1 as we speak and will try that mod for the first time.

MechJeb isn't perfect, I've run into problems with it's "SAS" exciting wobbling in large vessels that flipping over to the stock SAS would damp out. And it's ability to hit a landing target varies a bit depending on your lander design. When I have a surface base I usually have to dial in the coordinates I feed MechJeb for different landers if I want precision. If somewhere within a couple kilometers is good enough, MechJeb is fine.

For docking with SAS no matter what you use, never set both vessels to target the other. It always leads to oscillations. Set the target vessel to a fixed reference like prograde/retrograde and only have the vessel you are maneuvering use target mode.

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30 minutes ago, Tonka Crash said:

MechJeb isn't perfect, I've run into problems with it's "SAS" exciting wobbling in large vessels that flipping over to the stock SAS would damp out. And it's ability to hit a landing target varies a bit depending on your lander design. When I have a surface base I usually have to dial in the coordinates I feed MechJeb for different landers if I want precision. If somewhere within a couple kilometers is good enough, MechJeb is fine.

For docking with SAS no matter what you use, never set both vessels to target the other. It always leads to oscillations. Set the target vessel to a fixed reference like prograde/retrograde and only have the vessel you are maneuvering use target mode.

Well, to start the upgrade to 1.6.1 is a non-starter...my Dres mining base is apparently no longer usable as the part changes from 1.4.3 are too much. So I guess I won't be updating at all for quite some time...I have a mining base on Dres that NEEDS to work for my entire Jool system exploration mission to work? S-I-G-H! I wish upgrading would just automatically replace older parts so that my hours and hours of hard work could continue...but I get it.

Back to the point. I always leave the craft to be docked to (usually a refueling "station") in Normal or Anti-normal mode and follow the rules as you stated them above. Landing near a target is simply...manual piloting, at this point. This isn't a "bad" thing...we could all use some piloting skills practice, me thinks.

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40 minutes ago, Tonka Crash said:

MechJeb isn't perfect, I've run into problems with it's "SAS" exciting wobbling in large vessels that flipping over to the stock SAS would damp out. And it's ability to hit a landing target varies a bit depending on your lander design. When I have a surface base I usually have to dial in the coordinates I feed MechJeb for different landers if I want precision. If somewhere within a couple kilometers is good enough, MechJeb is fine.

Somewhere within a "couple of kilometers" would be completely out of the realm of acceptable, when you consider that linking 2 ships with the CC-R2 connection ports has a max range of 40 meters? I may get rid of the MechJeb mod and just go back to my old dependable KER.

More to another point, and very disappointing, is that I must continue my exploration of Jool system and Eeloo using 1.4.3. I have spent way too much time and energy to just start all over to make 1.6.1 work? Not sure what parts on my mining base are the issue in upgrading to 1.6.1 but it really doesn't matter...I refuse to start all over again.

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@Victor3 I'm not saying MechJeb can't do precise landings, it's just that on my mining sites I would have to do multiple landings to figure out what coordinates worked to put a lander down where I wanted. Once dialed it it was repeatable to the same spot on the ground within a couple meters. But the coordinates needed were unique for each lander design. I keep a scratchpad next to my keyboard with a list of MechJeb coordinates for each lander and what phase angle it needed for a station rendezvous. I've also use MechJeb to hover taxi around a base to better position things on the ground. KER and Mechjeb do different things that to me have little overlap, I'd keep both. KER is my HUD, MechJeb is my autopilot.

I would guess your biggest problem updating is KAS. The KAS version in use for 1.4.3 has parts that have been completely dropped in KAS 1.2, they're still there in KAS 1.1, but labelled as Legacy. KAS 1.2 has a save file updater that is supposed to replace old parts with the equivalent current part. But you need to read the KAS wiki to know what to expect. Whatever you do research it first and keep backups. Also don't try KAS 1.2 in 1.7, it's broke for now, but works in 1.6.1. KIS has a debug mode that you can spawn parts directly to a Kerbal inventory to fix whatever's ends up broken.

 

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3 minutes ago, Tonka Crash said:

@Victor3 I'm not saying MechJeb can't do precise landings, it's just that on my mining sites I would have to do multiple landings to figure out what coordinates worked to put a lander down where I wanted. Once dialed it it was repeatable to the same spot on the ground within a couple meters. But the coordinates needed were unique for each lander design. I keep a scratchpad next to my keyboard with a list of MechJeb coordinates for each lander and what phase angle it needed for a station rendezvous. I've also use MechJeb to hover taxi around a base to better position things on the ground. KER and Mechjeb do different things that to me have little overlap, I'd keep both. KER is my HUD, MechJeb is my autopilot.

I would guess your biggest problem updating is KAS. The KAS version in use for 1.4.3 has parts that have been completely dropped in KAS 1.2, they're still there in KAS 1.1, but labelled as Legacy. KAS 1.2 has a save file updater that is supposed to replace old parts with the equivalent current part. But you need to read the KAS wiki to know what to expect. Whatever you do research it first and keep backups. Also don't try KAS 1.2 in 1.7, it's broke for now, but works in 1.6.1. KIS has a debug mode that you can spawn parts directly to a Kerbal inventory to fix whatever's ends up broken.

 

Thanks, TC! One issue I have is the entire "coordinates" thing? I have no idea how to find them or use them.

I have completely reverted to 1.4.3 and will continue my exploration of the Jool system and Eeloo in this version. I envision this exploration going on for years so...maybe I'll tackle Eve and Moho at a future date...with the latest KSP version?

I would still ask...is there some way to have parts automatically update when updating KSP to a new version? I think I know the answer as the parts in question may be mods, not stock. But...worth the ask.

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@ExtremeSquared Targeting works ok for me most of the time. Sometimes I will be trying to do a rendezvous with another craft in orbit and I will realize its in 'orbit' instead of 'target' but its rare

@Victor3 Yeah that off targeting to a radial docking port is a bug that has been reported.

@5thHorseman For the most part I like how SAS works. definitely compared to pre 1.2, but there are always work arounds. I never use mechjeb after trying it out for a few hours and realizing it made KSP way too easy though it taught me how to get into orbit better

Note that if there are any bugs that have been reported that Squad wants people to upvote/downvote bugs to show their importance from our perspective. Not really happy with that type of system but if any bugs exist and they are

important to anyone, go to the bug tracker and upvote.

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8 hours ago, Victor3 said:

Huh, I have not figured out how to rendezvous with a surface target other than manual piloting. Using the "anti-target" doesn't get you there...it just points away from the target. I do like you...sight down the landing craft body and manually piloting to as close as I can get. AFAIK there are a few mods (MechJeb being the most used) that will auto-pilot you to a landing at a surface target...but I haven't tried MechJeb. I'm updating to 1.6.1 as we speak and will try that mod for the first time.

This is why V(target)(surface relative) and V(target)(orbit relative) should be manually selectable. While the error is barely visible on high-orbit tidally-locked moons, it makes sense for the game to coddle people during landings on Minmus and other non-locked moons.

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13 hours ago, ExtremeSquared said:

This is why V(target)(surface relative) and V(target)(orbit relative) should be manually selectable. While the error is barely visible on high-orbit tidally-locked moons, it makes sense for the game to coddle people during landings on Minmus and other non-locked moons.

For now, until I get a better handle on what Tonka Crash said regarding coordinates, I'm getting pretty good at manually piloting to a "close" landing to my mining base. With my fuel carrying rover having 2 CC-R2 connectors on each side, and a CB1 ground base with 2 CC-R2 connectors, I only need to get within 120 meters of the mining base to connect my fuel hauler...completely doable 99% of the time.

The KAS "migration" wiki page is not very...clear...on exactly how to replace my old parts with new ones. In truth, I've only read through it 7 times so maybe 10 - 12 times will make it understandable to me. I feel like there is a language translation issue with it?

I have 2 choices here, as far as I can see. Continue the Jool and Eeloo exploration with 1.4.3...or start all over after updating to 1.6.1 or 1.7 (and the recalcitrant KAS, causing all the issues). Not sure how I'm going to proceed, at this point. I don't quite get why KSP can be updated and my old stock parts automatically replaced with the new stock parts...but KAS is incapable of doing this?

For now I think I will leave KSP alone and go kill things on my XBox...a good way to get rid of the stress that this attempt at upgrading KSP has caused.

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About that radially attached docking port not lining up correctly (pointing the dock at it's target when control is set to that radially attached port) when tracking a target using the Target function in SAS; I've experienced that too. It works about %80 of the time if I was forced to ballpark a figure.

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