It's all gone a bit wobbly

[bigcalm]

As a consequence of the 1.04 upgrades to solid boosters, my craft suddenly had lots of fuel spare after doing what they needed to do in low kerbin orbit.

Instead of redesigning them all, I've started rendezvousing the spares into a fuel dump which I'm sure will come in useful later on (currently 23k liquid fuel + appropriate oxidiser). But it's all gone a bit wobbly - every time I try to dock something with it, it flollops about all over the place and is getting a little difficult to dock anything more to.

Would welcome some suggestions in terms of constructing a less wobbly fuel dump but not sure quite how to go about it - more docking ports? more compact? Can I use struts somehow? (Stock + MechJeb)

Edited July 20, 2015 by bigcalm

[Hcube]

Hi ! it seems to me that your refueling station is getting huge... and that is Kraken bait. The simple fact that it is pretty big and has a lot of docking ports and joints might be responsible for the wobbling. Also the fact that you have many huge structures connected by reltively small docking ports !

maybe try building something more "compact", that would have more than 1 connection per module (try attaching the cylindrixal tanks together with 2 docking ports on each side, those are pretty sturdy.

Or, if your part count is OK, you could install KIS and space tape the hell out of this.

[HoloYolo]

KJR is great for wobbling issues. If you don't want mods, just turn off SAS.

[Foxster]

If they are lots of part-filled tanks, how about draining them into the big centre tanks and ejecting the empty tanks? Else create two+ stations?

[rofltehcat]

The culprits are the 4 reaction wheels at the end of the four fuel tanks sticking out. Disable two on them (180° from each other) and maybe even use "control from here" on one of the docking ports next to one you didn't deactivate. If that doesn't help, deactivate all four of them. I can't see if there are more reaction wheels in the main shaft but that is really where you want the reaction wheels to be for such a huge station. It'll takes ages to turn the station, so just keeping it stable and flying around it to dock is usually best.

[Warzouz]

I had an auto-wobbeling station around Mun. Even with all SAS deactivated, it could wobble, sometime slowly, sometime ino explosive wobbling.

I trashed the station and built a new one. It was very hard to dock to it because of the random rotations.

So deactivate everything, if it wobbles, your station is doomed.

[Wolfox]

Turning off SAS helps, you can stabilize it with brief pushing x2 time warp. If it wobbles without any control input, thats bad, means that there are parts colliding. In normal state, with no part clipping and out of atmosphere, things should hold still indefinitely, since there is no natural force source. Of course, until you reach dangerous part counts and therefore invite Kraken into your bedroom...

[Superfluous J]

I have a lot more luck with a dedicated fuel station made solidly. I like taking one of the largest fuel tanks (Usually an orange tank or that huge SLS tank) and then putting 6 of the same tank on it radially. Then attach Sr docking ports to both ends of the first tank, and regular and Jr docking ports radially to the radially attached tanks. Finally, tuck a few big RCS tanks somewhere as well. Don't bother making the fuel depot a station, though if you really want you can toss a probe core on it somewhere and some reaction wheels.

That right there is a station that won't shake a bit when you dock to it.

[Sharpy]

Remember enabling time wrap (normal, not phys-) for a moment smooths out any wobbling and rotation... until it wakes again, or unless you're denied the wrap because "ship is under acceleration" (from all the wobbling).

[bigcalm]

> just turn off SAS.

Never turned it on :-) (though obviously MechJeb is doing stuff).

> The culprits are the 4 reaction wheels at the end of the four fuel tanks sticking out.

Ok that's pretty good - disabling some of the outer reaction wheels has helped. It's still wobbling but not nearly as badly as before (and yes it does have a lot of reaction wheels - it's largely because it's a space station made from many different vessels all of which came with at least one reaction wheel).

> how about draining them into the big centre tanks and ejecting the empty tanks?

It's actually pretty full already -- (my general strategy has been to dock, shift the fuel around and then undock and delete the empty craft).

> Else create two+ stations?

I'm rapidly coming to this conclusion. It's simply too big (352 tons) and has too many docking ports. It's a shame because it's not currently laggy (part count hard to estimate but I'd guesstimate at 200).

> I like taking one of the largest fuel tanks (Usually an orange tank or that huge SLS tank) and then putting 6 of the same tank on it radially

The station currently contains enough fuel to fill eight and a bit orange tanks (and currently has space for about another ~3 + 4 big liquid fuel only tanks).

> you can stabilize it with brief pushing x2 time warp

Yes, this helps! Bit fiddly to do whilst docking and I do occasionally get the "cannot warp whilst under acceleration" but all good.

Thanks all!

Edited July 20, 2015 by bigcalm

[pincushionman]

Break it apart and take different parts to different places. Instead of one refueling station, have one in equatorial LKO, one at Mun, one at Minmus, etc…

[Targa]

Kerbal Joint Reinforcement will solve those issues.

[ajburges]

I also prefer a network of fuel containers. There is always one near phase to dump/take fuel. This is handy because at a 100 km orbit, fuel is always just 50 m/s away, but phase correction can take a while. My tugs can handle the logistics of transferring fuel between them. By keeping the part counts low, I can also comfortably do 4 craft rendevous at them which is handy for operations and some missions.

My fuel resouvouir will be a custom built station at 250 km optimised for part count so it can incorporate a 70 part habitat ring. I am still trying to design a launcher for the ring. My Mainsail based one makes my system cry and has little margin for error with even 6 km/s!

Edited July 21, 2015 by ajburges

[Edax]

My experience with docking fuel tanks was to use a tri-coupler with 3 docking ports and both ends of an orange tank, and that no more then 3 orange tanks could be strung together length wise before the wobbling got to be worrying. The culprit is the docking ports, they bend under stress. The more docking points in the ship, the more "floppy" it gets. Probably the most you can get away with is a 3 orange tank by 3 orange tank configuration centered around the hubmax. It'll sway a little, but so long as your not firing off a Mainsail engine on the station, it should all hold together.