S3 KS-25 Vector roll issues.

[DC Zhor]

Has anyone else noticed how much this engine wobbles? Especially after leaving the atmosphere?

I've recently tried using this engine as a testbed, to see if it is worth using on a number of situations. Decided to use it in a similar fashion to the Space Shuttle (3 engines, triangular shape vectoring).
My conclusion is that this engine can only really be used in small bursts of a few seconds, reducing the amount of engines to 1 seems to reduce the wobble considerably, but I can't shake the feeling that this engine needs a lot of tweaks. I mean, what is the point of adding it and the engine mount, that has been added, it seems, specifically for it, if they can't really be combined together. Really need some feedback from other people here...

[andylaugel]

Yup. That said, my Tylo/Laythe rover uses them to land and return to orbit. Once in orbit, another vehicle can move it between the moons.
http://steamcommunity.com/sharedfiles/filedetails/?id=795924099
http://steamcommunity.com/sharedfiles/filedetails/?id=795924166
http://steamcommunity.com/sharedfiles/filedetails/?id=797889095
One way of bringing vectors under control is to limit the gimbals. There is a slider there for a reason.

[DC Zhor]

Interesting. But I feel like they advertised the engine's huge gimbal vector range as a feature, nevertheless... RCS is more reliable anyway. I guess I'll play with the action groups, see if I can set something for Atmospheric/Vacuum flight.

[andylaugel]

The large gimbal range is a feature if do build something like the space shuttle. The center of mass starts out below the glider, and moves up as the solid rockets and main tank get expended. Your center of thrust should be on the center of mass, or your ship will generate torque and flip out.

[DC Zhor]

I accounted for that. Pitch is not a problem, roll is.

[SievertChaser]

Excessive gimball causes oversteering, especially if you're using stock SAS. One of the Stock Plus modules for 1.1.3 grants the ability to lock out gimbals along certain axes, e.g. roll.

[maj.solo]

I use them when no other engine works. They are for heavy lifting.
These days I prefer using poodles and nervs.
If I use vectors I use them like this
1) immediately set gimbal limit to 50% on all engines if the ship is going to do land and take-off acrobatics
2) set gimbal to 0% on engines near the center
3) if the ship is only going to be in space ... I probably rethink and try another type of engine. I can always use more reaction wheels and use Alt-. for x4 time acceleration while burning the engines.
4) while doing course corrections low throttle setting like < 25%
5) while on course only throttle so you get TWR 1 - 2
6) but it is nice to know it have so much power that you can call on if needed.

[DC Zhor]

Originally posted by RoofCatA:

I switch off all engine gimbal right in the factory.
Because it wobbles.
Because it wastes fuel.

Every fuel spent at a thrust vector different than prograde, wastes some fuel. Gimbal endless wobble burns "opposite" all over the place - which is even worse. The larger the gimbal degree limit on engine, the worse.


You may consider to switch it on temporary for bad ships in hard conditions. Like launching a house into space from Kerbin. Just on some engines, at limited gimbal, for a short time.


Build better ships.
Add extra small engines just for gimbal. They still waste fuel, but at least won't tear ship apart.
Use gyros (reaction wheels) for steering. Electricity is wasteless solar or free from engines in some cases.

I do high level testing, part editing, fuel is a non-issue. As for ship designs... I did a shuttle with only 10 parts to test this, making sure that the design is perfectly aligned, accounting for center of mass, lift and thrust. Locking the gimbal works best, however the testing I'm doing is for a SSTO with an analogue fusion rocket equivalent. I thought about editing the KS-25 instead of the KS-25X4, but... as I can attest now, better stick with the big one. I wanted the KS25 for its maneuverability, but it seems I can only really use that in-atmo... who knows, maybe I can salvage the SSTO designs I made so far with it.

[DC Zhor]

Originally posted by dennis.danilov:

Excessive gimball causes oversteering, especially if you're using stock SAS. One of the Stock Plus modules for 1.1.3 grants the ability to lock out gimbals along certain axes, e.g. roll.

With modding I prefer doing it myself... especially considering how slowly they are updating the mods now.

[DC Zhor]

Originally posted by maj.solo:

I use them when no other engine works. They are for heavy lifting.
These days I prefer using poodles and nervs.
If I use vectors I use them like this
1) immediately set gimbal limit to 50% on all engines if the ship is going to do land and take-off acrobatics
2) set gimbal to 0% on engines near the center
3) if the ship is only going to be in space ... I probably rethink and try another type of engine. I can always use more reaction wheels and use Alt-. for x4 time acceleration while burning the engines.
4) while doing course corrections low throttle setting like < 25%
5) while on course only throttle so you get TWR 1 - 2
6) but it is nice to know it have so much power that you can call on if needed.

Hey I didn't know that trick with Alt... over 500 hours on it and still learning, hah!

[George Kerman]

Originally posted by Erendelil Bakun:

Hey I didn't know that trick with Alt... over 500 hours on it and still learning, hah!

I got 1500+ hours and there are still plenty of things to learn. Especially if you take into account things like the Realistic mods.
As for Vectors, they're the most playful engines in the game. I love to play with them ( but usually they're not needed, bummer :( ). And how else would you take off vertically (fully rocket style) from Eve without Vectors?

[AoD_lexandro]

Tbh gimbals are completely pointless, and just a waste of mass. Ive modded several engines in my install to remove the gimbals completely, because they just cause problems with control and waste fuel. The only time I have actually found a usage for them is trying to hover-fly over the surface Mun/Minmus when Im out of RCS for control. And thats only because I have no wheels to drive around with yet.

[DC Zhor]

Well it is official. I just took 11 S3 KS-25 with their gimbals unchanged to Eve, for testing. As I landed (tricky bit of work that was), I noticed, that even with the breaks engaged and with the ship COMPLETELY still, the flaps AND the engines behaved as if the ship was moving.

Essencially I've isolated the variables and determined the problem isn't AT ALL in the engine, but rather, in the SAS/pilots themselves. The only reason I managed to fly to Eve, was that I had enough monopropellant to constantly correct mistakes. It's not even the ship design itself (which, again I found that they didn't really make drag any better outside of wings). Now, the pilots themselves are not level 5, but they are between level 3 and 4... that's the last variable to iron out. If pilot experience affects their performance, then I should see this ship behaving MUCH better than what it did now.

http://steamcommunity.com/sharedfiles/filedetails/?id=809759285
http://steamcommunity.com/sharedfiles/filedetails/?id=809759200
http://steamcommunity.com/sharedfiles/filedetails/?id=809759118
Inactive SAS.
http://steamcommunity.com/sharedfiles/filedetails/?id=809758766
Active SAS after reactivation and 30 - 45 seconds wait.
http://steamcommunity.com/sharedfiles/filedetails/?id=809758812

There the matter is... nothing to do with the engine.

[DC Zhor]

Originally posted by RoofCatA:

pilot levels just make more SAS options available. Up to lvl 3. Then it's game over. No new skills after that.

If so, they need to overhaul the SAS and autopilot systems in the next update. As well as improving drag for non-wing parts (seriously if I knew I'd record the ship's behavior for all to see... on Eve, 12 km above the surface, wobbling and turning like crazy... I literally flew a brick to the ground, WITHOUT MONOPROPELLANT! lucky I managed it).

[George Kerman]

Originally posted by Erendelil Bakun:

Originally posted by RoofCatA:

pilot levels just make more SAS options available. Up to lvl 3. Then it's game over. No new skills after that.

If so, they need to overhaul the SAS and autopilot systems in the next update. As well as improving drag for non-wing parts (seriously if I knew I'd record the ship's behavior for all to see... on Eve, 12 km above the surface, wobbling and turning like crazy... I literally flew a brick to the ground, WITHOUT MONOPROPELLANT! lucky I managed it).

Idk how you're landing on Mun, Minmus and wherever, but I do it at very low speeds because usually I play on hard and I can't afford mistakes and have someone die (or send rescue missions). In that case, when I'm at around my desired velocity ( 2m/s or so ), the retro hold wobbles so much more than the pre 1.2 SAS that I have to switch off the retro hold and pilot manually. So yeah, there's gotta be some update to this 1.2 SAS, I agree with you.

[DC Zhor]

Originally posted by George van Doorn:

Originally posted by Erendelil Bakun:

If so, they need to overhaul the SAS and autopilot systems in the next update. As well as improving drag for non-wing parts (seriously if I knew I'd record the ship's behavior for all to see... on Eve, 12 km above the surface, wobbling and turning like crazy... I literally flew a brick to the ground, WITHOUT MONOPROPELLANT! lucky I managed it).

Idk how you're landing on Mun, Minmus and wherever, but I do it at very low speeds because usually I play on hard and I can't afford mistakes and have someone die (or send rescue missions). In that case, when I'm at around my desired velocity ( 2m/s or so ), the retro hold wobbles so much more than the pre 1.2 SAS that I have to switch off the retro hold and pilot manually. So yeah, there's gotta be some update to this 1.2 SAS, I agree with you.

Indeed, I just finished refining that design. Had to use Ballast Tanks. I ABHORE the idea of using it, because it is useless weight I'm hauling, but there's no avoiding it. Science parts are not heavy enough, and few other parts fill the role. Made them to be out of ore, so at least I can refuel with the equipment I bring onboard... Is there any mod related to assisted flight? I even tried using an old flightsim joystick I have sitting around... no use, even worse during low-atmo flight in fact.

About Non-atmospheric landings: I usually do the same as you; I use the Apollo configuration: Mothership + Lander, I mostly only use SSTOs for atmospheric landing, it makes things so much easier. Unless you're in Laythe. ♥♥♥♥♥♥♥ that place had virtually no safe place to land until they made water a viable landing area. Had more than a few VTOL SSTOs just for Laythe, as you can see in my profile's screenshots.