Docked ships and station start to wiggle until destroyed?

[strider3]

I have a station in orbit around Kerbin at 300 km orbit. It is a refueling station for ships "heading out" after getting to orbit. For some reason, as I dock ships with it (I'm docking 4, at this point), the entire thing starts "wiggling" until docking points come apart and the entire thing destroys itself and pieces come apart and fly off into space.

Here's a pic of the result. At this point I have been away from the station for several hours as I approach with the last ship to dock. You can see that all my Jumbo64 tanks, which are permanent and strutted parts of the station have been thrown off. Eventually all docked ships will be thrown off or destroyed as the "wiggle" get worse.

Edited April 28, 2018 by strider3

[bewing]

Generally, this is an autostrut problem. Do you use autostrutting?

When you dock a new ship onto a station, the new ship's root part changes. Also the heaviest part changes. If you have those kinds of autostruts on your ship, then they have to disconnect from their old location and reconnect to a new distant one. This is a very energetic, forceful, and sometimes violent process. Not good for station integrity. Additionally, of course, the physical docking process adds its own torques to the station.

Autostruts that already exist on the station will try to absorb the shocks, but will end up causing those sorts of vibrations.

It's best to minimize the total number of autostruts on a fully assembled station. It's also often best to limit the length of the ones that you keep by converting them to "grandparent" autostruts. Sometimes, it's a very good idea to look at your ship that's about to dock and turn off every autostrut on it.

If I've guessed wrong about there being autostruts involved, I can try another guess. Or someone who uses your mods can try loading a savegame of yours to look at it.

 

Edited April 28, 2018 by bewing

[Gordon Fecyk]

I'm with bewing on this one; it does sound like a problem caused by the Autostrut feature.

I often turn SAS off on the craft I have focus of just before the docking ports connect, to give the two craft a chance to settle on their own. This is something I noticed a lot when constructing complex craft in orbit. It might also be helpful to turn off unneeded reaction wheels on both craft; you'll still need something enabled to hold target, but the fewer reaction wheels needed the better.

Instead of autostrutting, I've taken to use DMagic's EVA Struts to strengthen the hold of docked craft; it's a simpler mod compared to Kerbal Attachment System.

 

[blakemw]

Definitely autostrut.

Bear in mind that landing gears and wheels have built-in un-disableable autostruts to "heaviest part", so even if you don't "use autostrut", if you use wheels/gears you are using autostruts. It's important that larger stations not have parts with gears/wheels. I often use ad-hoc landing gears (girders, engine bells or whatever) to avoid the issues that forced autostruts bring when docking to other vessels/stations.

Edited April 28, 2018 by blakemw

[strider3]

The station itself has several autostruts to hold the jumbo 64 tanks. They are strutted top and bottom to the central core and side to side to each other. The struts were placed during EVA, after tanks were attached. The docking ships have none, but have much more mass than the station itself. I've tried turning off the reaction wheels on the docked ships but it didn't seem to help. I was hoping to keep the large ships docked until my Duna launch window comes around...may have to rethink that.

[Serenity]

I learned by streams that having a large full fuel tank in the station makes it that all the heavy auto struts get directed to it and the station becomes structurally very strong.

Its literally like having an anchor, helps a lot to stabilize it.(The ''anchor'' must be the heaviest part of the station)

I use it to my latest designs and i haven't had any major problems.

Of course as the others said, keeping the auto struts to minimum helps the most.

Edited April 28, 2018 by Boyster

[strider3]

Just to be sure, I used a backup of the game and tried again, turning off all reaction wheels except the station's cupola. As I was coming up on the rendezvous with my last ship to dock (#5) I suddenly had station debris appear...the Jumbo 64's again (S-I-G-H). The fact that the autostrutted parts are the first to "fly off" would seem to validate your thoughts on the problem. I should note that the station, by itself, holds together just fine and the same if I have one ship docked vertically on the bottom of the station. Seems all that mass hanging out perpendicular causes the issue...even with reaction wheels disabled. Hopefully I have a backup save that I can load and undock the 3 large ships before things get "shaky" again.

This station sufficed for Kerbin, Mun and Minmus missions but does not have the fuel capacity to really be useful for interplanetary missions so...look for a new thread on building a bigger station with more stability in the future (after all the Duna and Ike landings are done).

Thanks gang!

[bewing]

5 hours ago, Victor3 said:

The station itself has several autostruts to hold the jumbo 64 tanks. They are strutted top and bottom to the central core and side to side to each other. The struts were placed during EVA, after tanks were attached.

Sorry, but those aren't autostruts. Those are from a mod. Whichever mod it is, I think you need to update it. Autostruts do not need any EVA.

[Serenity]

Just remember to F5 before rendervouz/docking with big stations/vessels and if you want to play it ever more safe, split the station roles, make one fuel depot, one science station etc.

Edited April 28, 2018 by Boyster

[strider3]

10 minutes ago, Boyster said:

I learned by streams that having a large full fuel tank in the station makes it that all the heavy auto struts get directed to it and the station becomes structurally very strong.

Its literally like having an anchor, helps a lot to stabilize it.(The ''anchor'' must be the heaviest part of the station)

I use it to my latest designs and i haven't had any major problems.

Of course as the others said, keeping the auto struts to minimum helps the most.

The funny part is I've never seen the auto struts actually move? Stuff just starts wobbling until it disconnects and wanders off. I'll have to ask for advice from the group when I build my next, much bigger station somewhere in the future.

Thanks Boyster!

[Serenity]

30 minutes ago, Victor3 said:

The funny part is I've never seen the auto struts actually move? Stuff just starts wobbling until it disconnects and wanders off. I'll have to ask for advice from the group when I build my next, much bigger station somewhere in the future.

Thanks Boyster!

Read what bewing said, you cant see autostruts like the ones you have(that helps a ton cause they dont add in part count).

You can see where they attach when you change their target.

You need to turn them on the advanced tweakables on settings then right click to a part to autostrut(you can autostrut even after the launch).

Um except if you meant the debug option to visualize autostruts.

Edited April 28, 2018 by Boyster

[strider3]

3 minutes ago, bewing said:

Sorry, but those aren't autostruts. Those are from a mod. Whichever mod it is, I think you need to update it. Autostruts do not need any EVA.

They're from the KAS mod (CS-R2 Portable Strut) and were placed during construction of the various parts in the VAB . Once all the parts had been launched and connected, my engineer EVA'd from the station and built the struts between the CS-R2 units.

[blakemw]

Note that ALL the issues from autostruts CAN be replicated by normal struts, it's just that autostruts make it really easy thanks to limitless range and symmetry. But when you have heavy stuff on wobbly arms struted to other stuff, that is when the wobble-of-death can happening. Note that (perhaps surprisingly) moar struts helps with this because suppressing the wobbling prevents the problem, but it also means there is more pent-up energy in the station which can cause other kinds of kraken attacks, no struts has a tendency to be most safe against kraken attacks, with lots of struts being better than few struts. (unless those few struts are carefully placed - it mainly is heavy weights on wobbly arms that cause the wobble-of-death, so for example autostruts running the length of the vessel from the probe core to the engine can be safe because there is no leverage).

Edited April 28, 2018 by blakemw

[Serenity]

4 minutes ago, blakemw said:

Note that ALL the issues from autostruts CAN be replicated by normal struts, it's just that autostruts make it really easy thanks to limitless range and symmetry. But when you have heavy stuff on wobbly arms struted to other stuff, that is when the wobble-of-death can happening. Note that (perhaps surprisingly) moar struts helps with this because suppressing the wobbling prevents the problem, but it also means there is more pent-up energy in the station which can cause other kinds of kraken attacks, no struts has a tendency to be most safe against kraken attacks, with lots of struts being better than few struts. (unless those few struts are carefully placed - it mainly is heavy weights on wobbly arms that cause the wobble-of-death).

The no struts design make the crafts way too unrealistic, they wobble so so much .

I 100% believe the best way is what you said about few carefully placed struts plus a heavy ''anchor'' part.

Edited April 28, 2018 by Boyster

[strider3]

OK gang, I think I'm confused. Apparently I have no idea what "auto-struts" are? The only "struts" I've knowingly (LOL) used are the portable ones mentioned above or the EAS-4 stock ones during construction.

[Serenity]

7 minutes ago, Victor3 said:

OK gang, I think I'm confused. Apparently I have no idea what "auto-struts" are? The only "struts" I've knowingly (LOL) used are the portable ones mentioned above or the EAS-4 stock ones during construction.

https://forum.kerbalspaceprogram.com/index.php?/topic/148015-auto-struts/

You right click to a part at anytime and select where it will ''strut''.

They work the same way as the struts except at least four things,

1) You can change where they attach at any point, even after launch

2) You cant see them visually(except when you change where they attach or enable from debug menu the autostrut visualization)

3) They dont add to part count

4) And finnally you have limited options to where they attach.

Edited April 28, 2018 by Boyster

[strider3]

15 minutes ago, Boyster said:

https://forum.kerbalspaceprogram.com/index.php?/topic/148015-auto-struts/

Alrighty then. I do have Advanced Tweakables enabled (have for quite awhile as I use the Fuel Flow to set up and verify my asparagus set-ups) but have never really played with the auto struts. I Right clicked all my CS-R2 struts on the station and they were are all set to "Autostrut Disabled". So, do you think autostruts are still the issue or is the basic construction of the station (when large mass stuff is docked) just not stable? Here's a pic of the station, after (thankfully) undocking the "heavy" side hangers, to show you how I set up the portable struts.

All the different sections are attached with docking ports. Can this be a problem? Is there a way to attach various sections, in orbit, using a more solid attachment?

Edited April 28, 2018 by strider3

[Serenity]

Looks like your issue might be NOT using autostruts haha .

Turn them on, see how rigid the station will become(speaking of rigid i hope you had it off when you were building it, it usually messes things up).

I am sure the lack of them was the problem.

Remove any struts you have placed from EVA or from building it, except if you like them for the design.

You will also see fps improvement.

Attach them mostly on heaviest part and try avoiding putting them to docking ports or putting too many on.

See how it goes, i am sure you will be surprised from the results.

Grandparent and heaviest part balance is the key when you play with autostruts.

Edited April 28, 2018 by Boyster

[bewing]

1 hour ago, Victor3 said:

I Right clicked all my CS-R2 struts on the station and they were are all set to "Autostrut Disabled".

It's not the struts that use autostrut. It's the parts themselves. Right click on the orange tanks, and see if they have autostruts enabled. Sounds like probably not. You will want them enabled and set to "Grandparent".

It looks like each of your orange tanks has 3 struts attached. That's too many. Moar struts does not help in space -- the more you have, the more likely a deathwobble will occur. You want fewer. As boyster said, you may want to remove all those extra ones you added, and replace them with one autostrut instead.

You may also want to turn on "rigid attachment".

 

 

[strider3]

1 minute ago, bewing said:

It's not the struts that use autostrut. It's the parts themselves. Right click on the orange tanks, and see if they have autostruts enabled. Sounds like probably not. You will want them enabled and set to "Grandparent".

It looks like each of your orange tanks has 3 struts attached. That's too many. Moar struts does not help in space -- the more you have, the more likely a deathwobble will occur. You want fewer. As boyster said, you may want to remove all those extra ones you added, and replace them with one autostrut instead.

You may also want to turn on "rigid attachment".

 

 

Actually, 4 for each tank...2 to the adjacent tanks and 2 to the upper and lower central station "core" parts. I'll send Jesgan out to disassemble the portable struts (never tried undoing anything during EVA before) after adding an autostrut and rigid attachment for each...sound right?

[Serenity]

2 hours ago, bewing said:

It's not the struts that use autostrut. It's the parts themselves. Right click on the orange tanks, and see if they have autostruts enabled. Sounds like probably not. You will want them enabled and set to "Grandparent".

It looks like each of your orange tanks has 3 struts attached. That's too many. Moar struts does not help in space -- the more you have, the more likely a deathwobble will occur. You want fewer. As boyster said, you may want to remove all those extra ones you added, and replace them with one autostrut instead.

You may also want to turn on "rigid attachment".

Ops i misread his post  .

I though rigid attachment makes the craft easier to break the moment force is applied.

I never considered it as a helping addition to the wobbling stations, i have to try it, tnx for the info.

@Victor3 Sounds good, i think it will be a lot better.

Just note that you cant toggle rigid after launching the vessel(If there is a way pls tell).

Also maybe try adding a grandparent one in the connector.The Hubmax in the middle.

Edited April 28, 2018 by Boyster

[bewing]

1 hour ago, Boyster said:

I though rigid attachment makes the craft easier to break the moment force is applied.

It's a tradeoff. It makes a craft (or a section of a craft) stiffer and less wobbly under normal use, with the price of having it be more fragile if you whack it really hard.

1 hour ago, Boyster said:

I never considered it as a helping addition to the wobbling stations, i have to try it, tnx for the info.

Just note that you cant toggle rigid after launching the vessel(If there is a way pls tell).

Woops! You are right. I forgot about that detail. That does make it harder, doesn't it.

1 hour ago, Boyster said:

Also maybe try adding a grandparent one in the connector. The Hubmax in the middle.

Good idea.

[Rauko]

Regarding autostruts problem, is not a good idea to autostrut always to grandparent? I have the impression that "heaviest part" can change easily when docking, leading to woble and explosions, but grandpa is more dificult to change, and is equaly effective making the whole structure stronger. Am I wrong?

[strider3]

7 hours ago, Rauko said:

"... but grandpa is more dificult to change, and is equaly effective making the whole structure stronger. Am I wrong?..."

This Grandpa agrees completely...oh...you meant auto struts...

Sorry, just could not resist.

[Serenity]

7 hours ago, Rauko said:

Regarding autostruts problem, is not a good idea to autostrut always to grandparent? I have the impression that "heaviest part" can change easily when docking, leading to woble and explosions, but grandpa is more dificult to change, and is equaly effective making the whole structure stronger. Am I wrong?

Grandparent is better but if you always go with it you need to be extra thoughtful in the design.

Putting just a few heavy ones might increase the risk of woble and explosions but it will be easier in the long term to keep it stable enough to be realistic.

So yeah, grandparent is the key but i believe some good heavy ones are also important if you building something big.