Fixing wobbliness on very large parts?

[Absolution]

I'm working on some very large parts (~30m long). KSP handles them fine until the physics engine gets a hold of them. They are not heavy parts (3 tonnes) but their size is causing quite a large moment on the single attach nodes that put them together. I've been around the block a few times so I know that "wobbly rockets" was an issue in the earlier days but they seemed to have resolved the worst offenders. I was wondering if there was some config trick I can use to prevent the parts from wobbling so much?

I don't want to use struts and I'd prefer not to break up my parts into smaller chunks if I can help it.

Ideas?

[CaptainKipard]

Have you tried the Kerbal Joint Reinforcement mod?

I don't think there's anything you as a modder can do other than strongly suggest that the users of your mod also install that mod.

...except make sure your stack node sizes are large enough. Size 2 for 2.5m parts and size 3 for everything larger.

Edited September 19, 2014 by Cpt. Kipard

[nli2work]

if you don't have KJR; node size affects joint strength, to what extent I don't know. if you do have KJR, node size no longer applies; supposedly KJR calculates joint strength based on the surface area. Ferram4 explains it little more here

I suggest grabbing the invisible struts from B9 in conjunction with KJR

[SpannerMonkey(smce)]

Hiya, been there had the wobbles, my fix was to double up the nodes and in some cases triple them laying them out in a triangular pattern, simple fix perfect results, i always do this now with larger the stock parts.

[CaptainKipard]

Hiya, been there had the wobbles, my fix was to double up the nodes and in some cases triple them laying them out in a triangular pattern, simple fix perfect results, i always do this now with larger the stock parts.

What you're describing seems to be joint loops and I thought those were impossible. Am I missing something?

[SpannerMonkey(smce)]

Nobody ever told me you couldn't do it , is it really a loop? I see at as 3 separate nodes attaching to 3 other nodes, on the opposite part or whatever arrangement

[nli2work]

gave it a test. it doesn't appear to hurt anything, but doesn't seem to add anything either. Non-KJR install.

I arranged the stack nodes for the largest NASA mission fuel tank. attached them together and tested size1, 2 and 3 nodes. 1xNode attach versus 3xNode attach flexes equally, presumably the game only selects one of the nodes when creating the joint, whichever one snapped together first in VAB.

node_stack_top2 = 0.0, 3.74, 0.0, 0.0, 1.0, 0.0, 3
node_stack_bottom2 = 0.0, -3.74, 0.0, 0.0, 1.0, 0.0, 3

node_stack_top1 = 1, 3.74, 0.0, 0.0, 1.0, 0.0, 3
node_stack_bottom1 = 1, -3.74, 0.0, 0.0, 1.0, 0.0, 3

node_stack_top3 = -1, 3.74, 0.0, 0.0, 1.0, 0.0, 3
node_stack_bottom3 = -1.0, -3.74, 0.0, 0.0, 1.0, 0.0, 3

top to bottom: size1, size2, size3 nodes

with KJR, node size doesn't make a differece. the part size determines joint stiffness. 1.25m and up appears to be roughly equal in stiffness. 0.625m joint is very weak.

Edited September 19, 2014 by nli2work

[CaptainKipard]

Maybe Monkey is confusing this with docking nodes, which DO actually allow you to do multiple connections between two parts. That's another topic though.

[SpannerMonkey(smce)]

No i'm not confused.

While i appreciate your findings, I can only say that it seems to work in reducing bend and wobble on my colossal parts, which are considerably larger than anything in the stock game or nasa packs, Although i will check my results and parts to see if this is just wishful thinking on my part.

[nli2work]

not unreasonable to think multiple nodes would add to joint strength/stiffness. I started testing because I really wanted to see how much I can benefit from it. results were unexpected to me. I just tested again with the same large tank scaled up 3x (that's about all the VAB can handle without extension plugin). holding 10x fuel. each tank weighs 720t. with 3 tanks and using node sizes 1, 2, and 3, same attach arrangement as before. Results were about the same. considerable rubber banding for size 1 node; negligible for size 2 and 3. Node size can go up quite high, 1000 or so. I think most benefit is from increased node size rather than number of nodes. and biggest beneficiary would be surface attach nodes since there's no green ball to block visibility. All assuming you are not using KJR of course.

Edited September 19, 2014 by nli2work

[CaptainKipard]

Nobody ever told me you couldn't do it , is it really a loop?

Sure. I think. Afaik KSP vehicles are essentially trees made out of parts, and you can't make a branch loop back on its parent. Afaik.