"Wobble" free space stations?

[strider3]

I need to build a larger refueling station in Kerbin orbit. My current one does not have the fuel capacity I would like. One problem I have with the current station is what I'll call progressive "wobble". Orbiting by itself the station was fine, but after docking other ships to it and especially transferring fuel, LoX, etc., it sometimes starts to wobble, which seems to have connection points as the "weak" areas. This will get progressively worse until parts start flying off (tanks, large antennas) or it simply explodes. I asked a few questions in a previous post but thought I would start one dedicated to the problem.

Some points:

Autostruts: I was using stock EAS-4 struts during construction and KAS CS-R2 portable struts during assembly of modules in orbit. These did not seem to really solidify the structure as I would have thought...or prevent the issue. Part of the earlier discussion was about autostruts (I was not using them) and how to use them (Grandparent, Root, Heaviest part). I'm not sure a consensus was reached on the "how" but Grandparent seemed to be more in favor. I would ask for more information on autostruts from the expert builders here...where to use them and how.

Rigid attachment; sounds straightforward but what is it, really, and would it help stabilize and solidify my station?

Attaching station modules in orbit: AFAICT, the only way to attach station modules in orbit is using docking ports, which seem to me to be the weak link in the "wobble" issue. Is this the only way?

Some other points that were brought up: turning off reaction wheels on docked ships and turning off SAS on docking ships before docking with station. These confuse me as, once docked, shouldn't the entire thing act as one ship, with reaction wheels and SAS (no matter where) acting in harmony to control orientation? I do, however, go to the command part of the station (cupola, etc.) and set "control from here" after each docking.

Any other tips and tricks from the experts on reducing or eliminating the wobble, whether through construction techniques, operations, etc. would be greatly appreciated.

Vic "who turned on the darn Wobbulator??"

[4x4cheesecake]

Even though I'm far away from being a expert, but I like to share my experience anyway ^^

After building several stations, the most stable design was always a huge tank used as core module and placing everything else around it, at least if the station is used to refuel other vessels. Everytime I've used multiple tanks radial attached, the station starts to wobble at some point.

Autostruts (Grandparent) seem to be useful whenever a part is surface attached, especially if the part angle is not 90°. The best explanation I can find for this is: Everytime you dock a vessel to your station, the station and the vessel are combined to one vessel which need to be recalculated by the game. At the end of this recalculation, the physics 'kicks' in and may cause a little impulse which causes your (angled) parts to wobble.

Personally, I don't like rigid attachment. It is more like surpressing the wobble instead of preventing it which causes the station to become more brittle and things are more likly to explode instantly instead of wobble around (btw. you can stop the wobble with a quick "on-rails" time warp)

Docking is indeed the only way to build things in space. Maybe some mods like KIS/KAS have some other possibilities, but I don't use them so nothing I can tell you about. An alternative would be to build and launch your whole station at once but this requires some symetrical design and a massiv (expensive) lifter.

So the best advice I have to you: Try to find a design with no long "arms", use the biggest available docking ports as often as possible, use autostruts on surface attached parts and if you use EAS-4 struts, you might want to take a look at this mod:

It allows you to place struts perfectly symetrical and I got the feeling, that symetrical struts are more stable after the physics 'kick'.

[strider3]

15 minutes ago, 4x4cheesecake said:

Even though I'm far away from being a expert, but I like to share my experience anyway ^^

After building several stations, the most stable design was always a huge tank used as core module and placing everything else around it, at least if the station is used to refuel other vessels. Everytime I've used multiple tanks radial attached, the station starts to wobble at some point.

Autostruts (Grandparent) seem to be useful whenever a part is surface attached, especially if the part angle is not 90°. The best explanation I can find for this is: Everytime you dock a vessel to your station, the station and the vessel are combined to one vessel which need to be recalculated by the game. At the end of this recalculation, the physics 'kicks' in and may cause a little impulse which causes your (angled) parts to wobble.

Personally, I don't like rigid attachment. It is more like surpressing the wobble instead of preventing it which causes the station to become more brittle and things are more likly to explode instantly instead of wobble around (btw. you can stop the wobble with a quick "on-rails" time warp)

Docking is indeed the only way to build things in space. Maybe some mods like KIS/KAS have some other possibilities, but I don't use them so nothing I can tell you about. An alternative would be to build and launch your whole station at once but this requires some symetrical design and a massiv (expensive) lifter.

So the best advice I have to you: Try to find a design with no long "arms", use the biggest available docking ports as often as possible, use autostruts on surface attached parts and if you use EAS-4 struts, you might want to take a look at this mod:

It allows you to place struts perfectly symetrical and I got the feeling, that symetrical struts are more stable after the physics 'kick'.

Thanks 4X4! I have KIS/KAS and I don't believe they have anything that would allow orbital construction without docking ports, AFAIK.

Still looking for definitions of "Grandparent, Root and Heaviest". Heaviest of the entire ship, or the heaviest of the sub-assembly being attached...stuff like that.

Would docking ports be considered "surface attached"? As you can tell, the construction terminology is sorta escaping me? LOL!

[mystifeid]

Hardly an expert but I use autostruts as little as possible because at the least, "heaviest part" is dynamic - ie if you dock a ship with a very heavy part all the auto strut configuration changes which can destabilize/destroy the station. And I turn off the station SAS. If I want to stabilize it I quickly go to 5x warp for a second or two.

The biggest problem I have is a fairly hefty lander which is usually docked at my stations when other ships arrive and they sometimes have a very heavy part. Now the legs on the landers have heaviest part autostruts enabled and this cannot be disabled. I find that if I dock the new ship along the same axis as the lander then the station begins to wobble - very slightly at first but within about 60 seconds it is at the point of tearing itself apart.

However, if I dock at a port that is aligned at right angles to the lander's docking port, everything remains stable.

[CrashyMcCrashFace]

1 hour ago, Victor3 said:

...shouldn't the entire thing act as one ship, with reaction wheels and SAS (no matter where) acting in harmony to control orientation?

The should (in a perfect world) but they don't.  I think it's called oscillation and overshoot in a negative feedback loop. If not maneuvering you need very little SAS reaction wheel to stay stable. Turn off all the wheels except a central one on the heaviest part.

[4x4cheesecake]

Well, to understand the definition of grandparent, root and heaviest, you need to know a bit about the way how the game creates the crafts. You can imagine the structre like a tree:

The very first part you place is your root part. You can change the root part within the editor but to keep it simple, lets say, it is the very first part. Then, you attach the next part on the root part. The root part is now also the parent of the second part. Then, place a third part on the second part. Now, the root part is still the root part + parent of the second part + grandparent of the third part. This will go on until your craft is finished.

So, autostrut (root) will always connect to your very first part.

Autostrut (grandparent) will always connect to the part placed two build steps ahead.

Autostrut (heaviest) will always connect to your heaviest part (guess that obvious, isn't it?^^)

The problem is: the root part will change when docking, because there is only one root part allowd but you will merge to vessels into one. The heaviest part will also change as soon as you transfer fuel or dock a massiv vessel. Grandparent is the best option because most parents and grandparents parts will not switch after docking. And everytime you use heaviest or root autostruts, the struts will move around, depending which part is the new root or heaviest one which will cause some serious wobbel.

 

When I say 'surface attached', I think of structures like this:

Also:

Best way to stabilise these structures is to place an grandparent autostrut on the docked part (fuselage on the right) becaue this autostrut will go through the docking port (left docking port is parent of the right docking port and grandparent for the fuselage)

Edited May 23, 2018 by 4x4cheesecake

[strider3]

Thank you for explaining that, 4X4!

[bewing]

Part of the point of KAS is to allow orbital construction, yes -- but you need an electric screwdriver.

Autostruts hook two parts together so they can't move with respect to each other. Everything between them can move, though. The first few (let's say 5) autostruts you add will reduce the wobbles in your station. But they also add stresses to your station, and there comes a point where each additional autostrut will increase your wobble rather than reducing it. As said above, if you have them turned on at the moment that you dock, they often change connection points -- which is a very forceful process and can cause a lot of wobbles. Often it's best to have them all turned off when you dock -- then turn a few selected ones on to kill the wobble. Then turn on a handful more.

Rigid attachment reduces the flexibility of joints between parts. So they bend less with the same force applied. But the joints break more easily.

You can also attach station parts with Klaws. I think they are less bendy than docking ports. But your station won't be nearly so pretty.

 

[Fadly]

8 hours ago, CrashyMcCrashFace said:

The should (in a perfect world) but they don't.  I think it's called oscillation and overshoot in a negative feedback loop. If not maneuvering you need very little SAS reaction wheel to stay stable. Turn off all the wheels except a central one on the heaviest part.

This. Only have ONE reaction wheel, or none at all. this include build in reaction wheel in a probe and capsule.

[Kerbal101]

Hi! As an alternative to docking ports, I recommend "weldable" Docking ports from the Konstruction mod by @RoverDude.
They look like normal Docking ports, but these have a special option "Compress" that explodes the two connected ports ("compression") and permanently connects the parts. It is also part of (larger) MKS package.
The last version is 0.5.0 and supports 1.4.x

 

[blakemw]

The key to a wobble free station is clever use of autostruts. Autostruts are also the key to a station which violently tears itself apart. So getting a wobble free station involves mastering the arcane arts of autostrut mechanics.

When a whole lot of autostruts converge on one part, this creates a concentration of forces which results in the wobble of doom. This will be what tends to happen with root part, and usually heaviest part and in some cases grandparent part, but not in all cases.

The trick is how autostrut combines with symmetry placement. When autostrut targets a part with "symmetry siblings", a strut is created to ALL the symmetry siblings, who knows why, it is just how it works, this works whether the target is "acquired" via grandparent part or heaviest part (and with heaviest part, it doesn't matter if some of the syemmtry siblings are less heavy,  the game first finds the heaviest part, which might be a full fuel tank, and then creates autostruts to it and all it's symmetry siblings, some of which might be empty). This creates a star-like pattern of autostruts which is very strong and wobble resistant. The basic idea then is to make the core of your station a symmetry structure, for example a cross. This can be braced with symmetry autostruts, and whats more when something docks to a symmetry docking port, you can use "grandparent part" on the docked vessel to connect to all the symmetry siblings of the core:

Works well with Heaviest part too:

Understand and abuse this game mechanic and you can have rock solid stations which are pretty resistant to wobble of doom.

Note: In general I would advise bracing the "symmetrical core" with conventional struts. Conventional struts remember their original length and try to restore a vessel to its original VAB shape. Autostruts are re-created every time a vessel docks/undocks or the game is loaded and so autostruts don't remember what a vessel originally was shaped like and distortions can accumulate.

Edited May 24, 2018 by blakemw

[4x4cheesecake]

Wait, symetrie siblings are included when using grandparent autostruts? Thats awsome and really good to know

[strider3]

On ‎5‎/‎23‎/‎2018 at 6:33 PM, bewing said:

Part of the point of KAS is to allow orbital construction, yes -- but you need an electric screwdriver.

Hi bewing. Are you saying that with KAS I can do an EVA with my engineer and tools and attach station modules without using docking ports?

[Xd the great]

There are wielding mods that make new parts out of existing ones. Drastically reduces fiel tank counts.

[Bakkerbaard]

On 5/25/2018 at 4:28 AM, Victor3 said:

Hi bewing. Are you saying that with KAS I can do an EVA with my engineer and tools and attach station modules without using docking ports?

I don't think I am Bewing, but I'm gonna respond to this anyway. In theory that should work, but you'll need both parts close enough that the Kerbal with the screwdriver can reach them. I haven't attempted this with giant station parts yet, but I have been cursing under my breath trying to put fancy caps on ends of my station, which were also too heavy for Bill to carry. The only way I managed it was to float one next to the container it came in, quickly float the magnet over the cap, plug in the magnet, lock on the magnet, turn on the winch the magnet is now attached to which is sitting next to the end I want to put the cap on and wait.

Then when the winch had pulled the cap close enough I had Bill stick it on the end of which ever tube needed capping.

Pro-tip: Don't drag your load through your solar array...