How to stop the wobble in larger ships

[workerbee]

Any tips from vets on how to stop the wobble effect you get in larger ships? I can't really turn SAS or RCS on because it just makes it worse and can even break apart the vessel. While thrusting, will turning SAS on or make the wobble worse? It's affecting the efficiency of my burns...

Edited December 18, 2014 by workerbee

[The_Rocketeer]

If you're experiencing oscillation in vacuum (outside an atmosphere) try switching to warp mode and back before you start the burn - this will reset the parts to their default positions and eliminate any wobble.

Otherwise, the obvious answer is to use struts and add more rigidity at the design stage.

SAS will ultimately make the wobble worse because it's a retro-active correction, and tends to amplify oscillations rather than dampen them.

[michaelsteele3]

Use the struts from the parts section. It looks like this:

http://wiki.kerbalspaceprogram.com/wiki/EAS-4_Strut_Connector

Just attach the two ends to parts of the ships, and it should be very stable.

Have fun!

[Crashy_McSplodey]

If this is the problem I have came across with multiple sets of ailerons along the length of a rocket, then there are 2 ways of combatting this wobble.

1) Build your stack symmetrically to improve the balance of the design, reducing or removing the need for SAS/RCS in the early flight where the atmosphere is thicker and this wobble is more easily introduced.

2) Reduce the amount that the ailerons can deflect by when building in the VAB using the settings window.

SAS will ultimately make the wobble worse because it's a retro-active correction, and tends to amplify oscillations rather than dampen them.

^^ So much this ^^

Edited December 18, 2014 by Crashy_McSplodey
Added a quote

[workerbee]

Use the struts from the parts section. It looks like this:

http://wiki.kerbalspaceprogram.com/wiki/EAS-4_Strut_Connector

Just attach the two ends to parts of the ships, and it should be very stable.

Have fun!

I guess I should have mentioned I am not a complete idiot. LOL. This question is more in regards to larger ships that are built in LKO. My current beast is over 900 tons and carries 60K fuel...so yeah...kinda hard to keep it from wobbling

[The_Rocketeer]

I guess I should have mentioned I am not a complete idiot. LOL. This question is more in regards to larger ships that are built in LKO. My current beast is over 900 tons and carries 60K fuel...so yeah...kinda hard to keep it from wobbling

That is quite illustrative to this problem. Perhaps if you submit more help requests in future you should remind us of this!

The best advice I can give is cut back on your throttle and accelerate more gently. Oscillations start because the centre stack get a big shove from the engines and the outlying parts only get that force transmitted through the part joints. Gentler thrusting takes longer but costs no more fuel and gives the force more time to transmit and even itself out through the craft.

[Liowen]

If it is a matter of it shifting after it has been docked you might have one SAS unit, or many, that are 180 degrees, or less, out of alignment; basically up is down to that section so you are fighting motion. Navyfish's docking adapter helps with this, but you could disable different SAS modules to see if it helps. a few degrees off is not bad, but 30 or more seems to be where the problem starts. What I would like to see is maybe a mod that realigns the SAS modules so they are all in line once docked.

[Crashy_McSplodey]

I guess I should have mentioned I am not a complete idiot. LOL. This question is more in regards to larger ships that are built in LKO. My current beast is over 900 tons and carries 60K fuel...so yeah...kinda hard to keep it from wobbling

Ah well in this case then I would reccomend you look at the mod Kerbal Joint Reinforcement: http://forum.kerbalspaceprogram.com/threads/55657

[workerbee]

That is quite illustrative to this problem. Perhaps if you submit more help requests in future you should remind us of this!

The best advice I can give is cut back on your throttle and accelerate more gently. Oscillations start because the centre stack get a big shove from the engines and the outlying parts only get that force transmitted through the part joints. Gentler thrusting takes longer but costs no more fuel and gives the force more time to transmit and even itself out through the craft.

Ahhh, you're right. I apologize. It wasn't a fair question and I can totally see where I come off sounding like a noob. For the record, I've logged 400 hours...new to the forums, not the game ...your advice here is quite helpful. I will give it a go and report back. Thanks!

[workerbee]

Ah well in this case then I would reccomend you look at the mod Kerbal Joint Reinforcement: http://forum.kerbalspaceprogram.com/threads/55657

This. Will do...thanks for the great advice and reminders everyone! Sorry I didn't mention that this question was in reference to larger ships...I sometimes forget there are people who don't know what a strut is

[OhioBob]

I just made an observation that might be helpful regarding wobble, though the particular case that I observed was not a large ship. When I set the SAS to maintain orientation to one of the direction indicators, such as prograde, this induced a wobble. However, when I set it to "Stability Assist" the wobble immediately went away. With stability assist the ship is simply holding its current attitude. However, when you set it to one of the direction indicators, the ship is constantly making minute corrections as it orbits the planet, which produces the wobble. It appears the SAS needs a bigger deadband to eliminate the rapid oscillations. My advise would be to use the directions for initial alignment and then switch to stability assist.

[panzer1b]

Even a single strut between any 2 fuel tansk makes the connection exponentially more rigid.

They also add very little extra processing power (theyre physicsless more or less), so adding 20 struts to a craft atop the normal part count adds little if ANY lag. My view is that when in doubt (and you arent hard limited by the VAB/SPH's level in career), add extra struts, makes it strurdier, less likely to wobble, and less likely to overstress when you come in a tad too fast when docking another craft.

[cantab]

I guess I should have mentioned I am not a complete idiot. LOL. This question is more in regards to larger ships that are built in LKO. My current beast is over 900 tons and carries 60K fuel...so yeah...kinda hard to keep it from wobbling

Ensure you are controlling from a part in a good location. SAS responds to the movement of the controlling part, so you want that somewhere nice and stable, like near your main fuel tanks and/or engines. That way the front end of the ship or whatever can sway around but the SAS will ignore that rather than making it worse.

[Laie]

Docking ports are quite wobbly by design (possibly have to be -- it might make it easier for the connection to come together), but every connection has some flexibility. The more connections you line up, the more your vessel approaches a wet noodle. The solution is to seek inspiration from truss bridges.

There's six struts in the nuclear drive section, and a whole nine holding together the hitchhikers. This vessel turned out to be insanely rigid, it handles like a tiny four-part vessel. Not a small feat when you consider that ordinarily, a stack of six hitchhikers would already bend noticably.

For multi-docking, it's not necessary to use more than three ports (the good old three-legged stool), but rigidity improves with the width of the base. Three ports on a tricoupler are no better than a single senior port; three ports spread over the width of a kerbodyne tank are a noticable improvement, but will still bend a lot if you have more than two such connections in a ship. But the spacing you see in the picture allows for really really long vessels; proportions on the order of 2001's Discovery would be totally possible.