Am I the only one stuck with wet noodle rockets in 1.0.5?

[SlabGizor117]

I'm having bad problems with joints on 2.5m rockets. SAS modules, Probe cores, docking ports, and improvised decouplers(for multi 1.25m engine upper stages) all bend like crazy. Am I the only one??

EDIT: It seems to be an over-correction on the SSME gimbal, but I don't want to disable it. Even if it has that much gimbal, there's no reason we can't have more rigid joints. Wat do? Edited November 24, 2015 by SlabGizor117

[Xkay7]

Disable gimbal on the engine?

Use struts?

Replace the engine with a weaker engine?

Install Kerbal Joint Reinforcement mod?

[Superfluous J]

Put your probe core or command pod as close to the engine as possible, so the rocket knows the direction it's GOING, instead of the direction the probe core is FACING. Also, struts.

The problem isn't (totally) the wobbliness of the rocket. It's that the game thinks you're heading in the direction the probe core is facing.

[Guest]

[quote name='5thHorseman']Put your probe core or command pod as close to the engine as possible, so the rocket knows the direction it's GOING, instead of the direction the probe core is FACING. Also, struts.

The problem isn't (totally) the wobbliness of the rocket. It's that the game thinks you're heading in the direction the probe core is facing.[/QUOTE]
Once again, your advice has come through.

[SlabGizor117]

I agree that this will help but I promise the joints between those parts are ridiculously unstable and I know that's the main problem. KJR won't completely eliminate that problem though.. Will it?

[fourfa]

The amount of gimbal on the Vector is absurd. For fun, try putting ten of them on an asparagus-staged launcher, it's hilarious.

Many other engines in the game do just great with 2 degrees of gimbal. Try reducing your gimbal to 10-20% (rather than disabling it entirely) and see what happens.

[jhousen]

too much gimbal causes this, with all the mods I run I have a lot of high gimbal engines, best results I've found so far (for me, anyway) is 1-2 degrees of gimbal at take off and only increase to 3 or 4 degrees if you absolutely need it, any more than that results in severe wobble

[Snark]

Yah, the Vector gimbal is ludicrous. Exacerbating the problem is the fact that in addition to having a huge range, it also has a slow gimbal response speed, which the rudimentary SAS system in KSP doesn't know how to handle.

Basically, you're running up against the fact that Squad envisioned the Vector as a space shuttle engine, and designed it in an ultra-specialized fashion so that (unlike every other engine in KSP), it's useful for that one very narrowly defined purpose and nothing else.

Using it in anything that's not shaped and flown like a shuttle tends to lead to problems. I gotta say that the Vector bugs me-- it's so narrow-purpose that it doesn't really seem to fit into the Lego-like philosophy of most of the game.

If you'd rather repurpose it as something more general-purpose that is useful for conventional rockets, here's a little mod l wrote that you may find useful.

[MarvinKitFox]

[quote name='SlabGizor117']I agree that this will help but I promise the joints between those parts are ridiculously unstable and [COLOR="#FF0000"]I know that's the main problem[/COLOR]. KJR won't completely eliminate that problem though.. Will it?[/QUOTE]

I've highlighted your mistake for you.

The problem is not weak rocket body, the problem is excessive applied bending forces.

Fix the way you design and fly the rocket, and you will find that the rockets are miraculously "stronger"

[Warzouz]

[quote name='SlabGizor117']I agree that this will help but I promise the joints between those parts are ridiculously unstable and I know that's the main problem. KJR won't completely eliminate that problem though.. Will it?[/QUOTE]
KJR does solve ridiculous wobbliness. But docking rings plugged to parts will still bend, you'll need struts.

[cantab]

Try and avoid extraneous parts in the stack. For example instead of using the 2.5m reaction wheel which is a notorious wobbler, radially attached a nosecone or two and mount smaller reaction wheels that way.

[Jouni]

[quote name='Warzouz']KJR does solve ridiculous wobbliness. But docking rings plugged to parts will still bend, you'll need struts.[/QUOTE]

KJR replaces ridiculous wobbliness with ridiculous rigidity.

[IMG]http://jltsiren.kapsi.fi/ksp/1.0/kjr.jpeg[/IMG]

That's a 0.625 m decoupler between the lower stage and the upper stage.

[Kurld]

Sure, maybe KJR is OP, but your example shows building something silly that shouldn't work but does, instead of what is arguably a far worse problem: building something that should work but doesn't, which is why we have KJR to begin with.

[Jouni]

[quote name='Kurld']Sure, maybe KJR is OP, but your example shows building something silly that shouldn't work but does, instead of what is arguably a far worse problem: building something that should work but doesn't, which is why we have KJR to begin with.[/QUOTE]

The real issue is that individual parts don't bend and break. Unless we want to make the game silly and unbelievable by having large rigid structures, a rocket stack must bend under stress. That can only happen at joints.

Due to whatever technical reason, the rigidity of a joint seems to depend only on node size. If you have many joints close to each other in the middle of a heavy stack, the rocket behaves like a nunchaku. On the other hand, if you know what's going on and avoid poor design choices, bendy rockets become extremely rare. At least as long as you're using stock parts. With 5 m and larger parts, the joint system starts breaking down, and KJR eventually becomes necessary.

[SlabGizor117]

Ok so I'll try all of that but my main point is that those parts are so bendy in the first place. It's nothing precarious like Jouni posted, all the parts are 2.5m. So why, if all the joints lie flat against each other, they shouldn't be bending. I understand that the joints aren't perfect and engines like the Vector make it worse but why are these parts so wobbly in the first place? If parts like those have to have such bad joints, at least make them brittle instead of flopping around into an L before it breaks..

[Seajay]

It's not hard to reinforce your rocket, 4 girders sticking radially out near the joint strutted to the tanks well above and below the joint will do it. Of course that comes with a drag penalty and I enjoy finding more subtle ways of achieving the aim. If you don't enjoy that, KJR is the answer.

However, don't imagine that KJR fixes a problem with KSP. It's a decision to leave out another aspect of reality for more fun, of course we're all doing that to some extent or we'd be playing orbiter (or building rockets in a shed).

[More Boosters]

Install KJR, never used a strut since.

[Jouni]

[quote name='SlabGizor117']Ok so I'll try all of that but my main point is that those parts are so bendy in the first place. It's nothing precarious like Jouni posted, all the parts are 2.5m. So why, if all the joints lie flat against each other, they shouldn't be bending. I understand that the joints aren't perfect and engines like the Vector make it worse but why are these parts so wobbly in the first place? If parts like those have to have such bad joints, at least make them brittle instead of flopping around into an L before it breaks..[/QUOTE]

KSP doesn't handle stacks with many joints correctly. It treats all joints individually, instead of determining their bendiness by the dimensions and the mass of the stack. A stack of 24 X200-8 fuel tanks bends much more than a stack of three orange tanks, even though both stacks should be the same. The best workaround is to avoid stacks with many small parts in the middle. If you need probe cores, batteries, reaction wheels, and similar parts, place them inside a service bay.

[Threadsinger]

[quote name='5thHorseman']Put your probe core or command pod as close to the engine as possible, so the rocket knows the direction it's GOING, instead of the direction the probe core is FACING. Also, struts.

The problem isn't (totally) the wobbliness of the rocket. It's that the game thinks you're heading in the direction the probe core is facing.[/QUOTE]

Wow, I never considered that myself. Thanks for the imparted wisdom - so many launch troubles now make way more sense.

[BenCushwa]

[quote name='Threadsinger']Wow, I never considered that myself. Thanks for the imparted wisdom - so many launch troubles now make way more sense.[/QUOTE]

Yup, any amount of bend in a joint between your active pod and a gimbaling engine translates to your SAS commands being off. This can set up some nasty resonating states that will tear an otherwise reasonably stable rocket completely apart. This is one more strike against really tall rockets: they're much harder to keep perfectly straight.

On a few occasions, I've manually limited the gimbal range of my lowest stages and this also helped.

[Workable Goblin]

[quote name='Jouni']The real issue is that individual parts don't bend and break. Unless we want to make the game silly and unbelievable by having large rigid structures, a rocket stack must bend under stress. That can only happen at joints.[/QUOTE]
But real rockets [i]are[/i] rigid, unless you're a stress meter (in which case you probably wouldn't be posting) or stresses exceed the strength of the material, in which case they break up. I don't see how it's silly and unbelievable to expect them to fail in a brittle fashion instead of an elastic one.

[Jouni]

[quote name='Workable Goblin']But real rockets [i]are[/i] rigid, unless you're a stress meter (in which case you probably wouldn't be posting) or stresses exceed the strength of the material, in which case they break up. I don't see how it's silly and unbelievable to expect them to fail in a brittle fashion instead of an elastic one.[/QUOTE]

Large structures are never rigid. They're intentionally designed to bend, because otherwise they wouldn't survive storms, earthquakes, large waves, and other everyday forces. The bending is often noticeable, especially if you're inside the structure.

If you like realistic brittle rockets, you can probably configure KJR for that. Just keep joint rigidity the same as in the stock game, but make the joints much more brittle. The end result would probably be a massive increase in launch failures.

Remember that the joints between large parts are already rigid enough. The joints between small parts are the real problem, because KSP (Unity?) models rigidity on a per-joint basis. That's an issue you can't solve adequately by adjusting joint rigidity and brittleness.

[BenCushwa]

[quote name='Jouni']Remember that the joints between large parts are already rigid enough. The joints between small parts are the real problem....[/QUOTE]

This is why I'm more prone to use struts on Mk1-based vessels than I am on pretty much anything else: Mk1 joints are kind of flimsy

[SlabGizor117]

[quote name='Jouni']Large structures are never rigid. They're intentionally designed to bend, because otherwise they wouldn't survive storms, earthquakes, large waves, and other everyday forces. The bending is often noticeable, especially if you're inside the structure.

If you like realistic brittle rockets, you can probably configure KJR for that. Just keep joint rigidity the same as in the stock game, but make the joints much more brittle. The end result would probably be a massive increase in launch failures.


Remember that the joints between large parts are already rigid enough. The joints between small parts are the real problem, because KSP (Unity?) models rigidity on a per-joint basis. That's an issue you can't solve adequately by adjusting joint rigidity and brittleness.[/QUOTE]

Rockets are not skyscrapers. They're not structures, and they're never in storms earthquakes or large waves. If they had no way to make rockets as rigid as they are, they would bend into an L as soon as the engines fired. Skyscrapers and other tall structures are made to bend because it's easier and cheaper to take the path of least resistance and let it have a little bend, rather than just pour a foundation 3 times as big and add twice as much structural rigidity. Rockets are facing millions of pounds of force, and the path of least resistance has to be up, and straight. If they weren't as rigid as possible, the slightest drift off course would bend it in half. Look at the footage from The Martian when the rocket failed. How far did it drift off course before it broke apart? The rocket has to withstand all of that force so that it goes into pushing the rocket [I]up[/I], not [I]sideways[/I]​.

When you have that much force under a rocket, trying to lift so much weight, the path of least resistance, being that it bends over, really[I] is[/I] the least resistance. It takes a lot to overcome that and make the path of least resistance being, again, up and straight. It's so much easier for the rocket to just bend over and break off than for it to fly lift all that weight straight up. When my rocket would bend, and finally break, the top would fall away and the rest of the rocket flew up further, [I]perfectly straight[/I]. It shed that weight, and was free to fly perfectly fine. As soon as the problem was solved by the bending section of the rocket breaking off, the path of least resistance became for the rocket to fly up, because the rest of the rocket was so rigid. Edited November 25, 2015 by SlabGizor117

[A_name]

ITT: A bunch of people saying OP is designing and/or flying his rocket wrong, but not bothering to explain WHY or what would be the "CORRECT" way to do it.

Just install KJR. Edited November 25, 2015 by A_name