Remedy for rubberbanding on inline structure

[Jestersage]

So right now I am working on an ISS clone, and I notice it has quite a bit rubber band after rotation that does not settle. Not sure what may cause it.

I am, of course, using the standard size ports for connections, and autostruct everything through grandfather. Not sure if teh autostruct cause the problem or not.

If you guys need some pictures, do let me know.

[Tyko]

Autostrutting is risky on large structures - especially on stations with ports as sometimes docking or undocking can cause autostruts to recalculate and break things.

I'm assuming by "rubber band" you're describing how parts of the craft aren't entirely rigid and tend to flex in response to changes in rotation? I've switched from autostrutting everything to use the Kerbal Joint Reinforcement mod. It makes the actual joints stiffer/stronger rather than adding on all the calculations for invisible struts...seems to work better.

Another consideration may be station design. depending on how extensive your station is it might just be too much for 1.25m ports to handle. Here are some ways to reduce flex A) Build smaller stations, B) Launch larger sections so you have less connecting ports, C) Put the heavy stuff in the middle - a full fuel tank way at the edge will be harder to start and stop D) use bigger ports.

Here's an example of why autostrutting is dangerous: Check out the section with the solar panels on the right-hand station and work your way left to the docking port on the nose of the craft. You'll see how autostruts threw a bunch of parts out of whack.

 

 

[Geonovast]

^^^

KJR is magic.  I don't play without it.

Also, if you're having issues at docking ports that are permanent, get Konstruction! and weld those parts together.

 

[Jestersage]

Okay, I am trying to go stock, namely because I want others to be able to share in the glory.

16 minutes ago, Tyko said:

 Here's an example of why autostrutting is dangerous: Check out the section with the solar panels on the right-hand station and work your way left to the docking port on the nose of the craft. You'll see how autostruts threw a bunch of parts out of whack.

 

I am not seeing the issues...

In any case, would it be better to just disable autostructs?

[Tyko]

4 minutes ago, Jestersage said:

Okay, I am trying to go stock, namely because I want others to be able to share in the glory.

I am not seeing the issues...

In any case, would it be better to just disable autostructs?

Sure, but if you aren't using Autostruts nor KJR you're relying only in Stock rigidity and your station will get more bendy during maneuvers.

With regards to seeing issues - it doesn't happen all the time with every station I build, but it happens to at least 1/3 of the stations I've autostrutted and you won't know if a given station is affected until you've gone through the trouble of launching it and docking something to it. I've had to scrap and rebuild enough stations that I'm not willing to take the risk any more.

[Zhetaan]

18 hours ago, Jestersage said:

I am not seeing the issues...

Look at the misalignment at the connecting rings.  The entire central module is rotated out of true with the rest of the station.  Also look at the two arrows on the right side:  they point to two radially attached batteries, and if you look closely, you can see that the lower battery has a gap such that it appears almost disconnected from the module, but the upper battery appears clipped into the module.  There are other places, too, such as the constriction on the left side, where things are misaligned.  This is a situation that practically begs for a rapid unplanned disassembly.

... Or did you mean to say that you were not experiencing the issues yourself beyond the wobble?  If so, then you have my apologies for my misunderstanding.  In that case, I have found that autostrut issues tend to appear most often with parts that change orientation or size, especially in multi-part stations and such.  There are a lot of mod-derived inflatable parts that can trigger the problem, but in stock, I've found that anything with a collider that changes shape can do it.  That means anything with doors, such as cargo and service bays, anything with an extendable collider such as solar and radiator panels or landing gear--though landing gear are rarely a problem because the landing gear are rarely in the way of an autostrut--and airbrakes.  Drills don't usually do it for me because the drill head is cosmetic only; the physical mesh doesn't contact the ground.

Another possibility, since you did say that it occurred after rotating the station, is that the wobble occurs because your station's flexibility is throwing it out of alignment with your target orientation and your reactions wheels or RCS are too powerful for the station joints.  The torque shakes the station, it comes out of alignment with your chosen orientation, SAS comes on to re-orient it, it over-corrects, so it comes on to back-correct, and it creates positive feedback that eventually destroys the station.  In that case, turn off SAS, let the station settle, and press Caps Lock to activate fine control mode before re-orienting again.  Also consider disabling extra reaction wheels.

 

Edited September 7, 2018 by Zhetaan

[Jestersage]

11 hours ago, Zhetaan said:

Look at the misalignment at the connecting rings.  The entire central module is rotated out of true with the rest of the station.  Also look at the two arrows on the right side:  they point to two radially attached batteries, and if you look closely, you can see that the lower battery has a gap such that it appears almost disconnected from the module, but the upper battery appears clipped into the module.  There are other places, too, such as the constriction on the left side, where things are misaligned.  This is a situation that practically begs for a rapid unplanned disassembly. Or did you mean to say that you were not experiencing the issues yourself beyond the wobble?  

 

Another possibility, since you did say that it occurred after rotating the station, is that the wobble occurs because your station's flexibility is throwing it out of alignment with your target orientation and your reactions wheels or RCS are too powerful for the station joints.  The torque shakes the station, it comes out of alignment with your chosen orientation, SAS comes on to re-orient it, it over-corrects, so it comes on to back-correct, and it creates positive feedback that eventually destroys the station.  In that case, turn off SAS, let the station settle, and press Caps Lock to activate fine control mode before re-orienting again.  Also consider disabling extra reaction wheels.

 

Yeah, didn't see the misalignment.

As for the reaction wheel -- Ooh, that could be the reason -- to mimic the 4 reaction wheel of ISS, I placed 4 large reaction wheels right at center strut...

Considering how many ISS clones are there, how much reaction wheels is actually needed?

Edited September 7, 2018 by Jestersage

[Zhetaan]

1 hour ago, Jestersage said:

Considering how many ISS clones are there, how much reaction wheels is actually needed?

You need one, or perhaps two if you have a lot of mass outside the centre.  KSP reaction wheels are insanely overpowered compared to real-life versions, and that's before considering that they run on alien spacemagic and create momentum from nothing.  Part of it is also that while space stations do occasionally need to rotate, they usually only need to hold an orientation:  they don't need to be quite so responsive as vessels under thrust.

To put it into perspective, four large wheels give a total of 120 kN of torque.  That's along the lines of a mid-sized rocket engine--not quite a first stage, but definitely more powerful than the vacuum engines--whose entire output is dedicated to twisting your station about.

Also note that if you want to mirror the look of the ISS, there's nothing wrong with sending four reaction wheels and disabling three of them.  Then you have extras on hand if it works out that you really do need more.

 

Edited September 7, 2018 by Zhetaan

[Gargamel]

22 hours ago, Jestersage said:

Okay, I am trying to go stock, namely because I want others to be able to share in the glory.

I believe that most ships built under KJR would still be playable as a stock ship.    Yes, it might be a bit wobbly, but should still be usable, but it really depends on the ship itself.   I would think a warning in a download saying it was built with KJR should suffice to warn players when sharing the craft. 

Personally, I consider KJR and a couple other mods to be my version of stock, as they just make the overall game better.   But that's an argument for a different thread....

[Rocket In My Pocket]

Doesn't the stock "rigid attachment" option work similar to KJR?

[Aeroboi]

On 9/9/2018 at 4:06 PM, Rocket In My Pocket said:

Doesn't the stock "rigid attachment" option work similar to KJR?

In stock you have to click buttons, with KJR you don't

Maybe a similar function such as rigid attachment is tugged inside the KJR system but it either can give away slightly so the joint still remains (which means it isn't actually rigid)
Or the joint is just magically held in place by KJR (probably not magical but I don't know how it works) I do know that KJR was scaled for RSS sized vessels and masses so the values to ensure rigidity are massively scaled. Maybe if you scale it up enough there's a barrier where rigidity snaps but I have never reached that limit using KJR.

Suggestion: On very long stations with many more modules I often use 2 docking ports to restrengthen the joints, but then you'll have to rebuild the vessel. And it will not look like the ISS. Also try reaction wheels instead of RCS for rotating.