Do Sr docking ports have more wobble than the old kind?

[Dunbaratu]

Okay, so I made a rather heavy base/rover payload vehicle for a Duna mission, with the idea that I'd have to rendezvous with my space station and pick up a fuel tank there to take with me - rather than trying to lift the fuel in one shot from Kerbin. This is what it looked like when docked with the space station:

See the bit of "debris" in that shot? That's not debris, it's my main engine. I detached it on purpose so that I could pick up a fuel tank, disconnect from the station, and then using RCS only (since I don't have my engine), connect the engine up again to the end of the fuel tank, and thus now have my craft with a heavy amount of fuel to take my heavy payload to Duna.

But then I encountered a problem. The sr docking port is really weak at resisting twisting. It doesn't have much rigidity and so when I would try to rotate my assembled-in-space vessel, it would almost break off the fuel tank as in this screenshot below:

That's just from trying to rotate with capsule torque wheels that's it. When I tried to rotate with RCS, figuring that the RCS thrusters on the tank would help a bit by rotating capsule and tank together... Nope that didn't help either.

After any attempt to rotate at all, the craft would oscillate a LOT, making it nearly impossible to line up a maneuver.

Has anyone had success with assembling a ship in orbit from parts with docking rings? The problem I'm having is that normally you'd fix this sort of wobble with struts, but of course you can't do that when you're docking the parts together in space.

[AustralianFries]

I've noticed they remove almost all wobble, and I build fairly big stations.

[Dunbaratu]

I've noticed they remove almost all wobble, and I build fairly big stations.

It works fine when making stations for me too - but not for making ships out if them.

[Wjolcz]

It's because you put a Sr Docking POrt on that small rcs tank you dum dum

[Jm419]

I can't dock these for the life of me, and I think I'm pretty good at docking.

[DerekL1963]

It's because you put a Sr Docking POrt on that small rcs tank you dum dum

That was my thought too... .0000000001 seconds spent looking at the picture shows it's the Sr-to-tank joint wobbling, not the Sr-to-Sr joint.

[Sma]

Agreed with Veeltch. It looks to me like the sr port - sr port connection is fine. It's the rcs tank (or is it the 6way station core?) between the docking port and rover/lander that could be the problem.

[strongest_2hu]

It's because you put a Sr Docking POrt on that small rcs tank you dum dum

It looks like the port is attached to an adapter, actually, which is then attached to the yellow 6-way structural connector. I think the problem might be the adapter, I've had trouble with them being really wobbly and clipping right through other parts under load in the past. It looks like in the second picture that the two ports are doing just fine but the adapter is dug about 5 degrees into the docking port. I think you should try something similar minus the adapter.

[Wjolcz]

Oh so it's an adapter not rcs tank o.o oops

[CleverClothe]

It looks like the port is attached to an adapter, actually, which is then attached to the yellow 6-way structural connector. I think the problem might be the adapter, I've had trouble with them being really wobbly and clipping right through other parts under load in the past. It looks like in the second picture that the two ports are doing just fine but the adapter is dug about 5 degrees into the docking port. I think you should try something similar minus the adapter.

I agree with your analysis of the problem. But I would suggest just moving the strut connections from the adapter to the docking port. Right now you are transferring all the stress of the lander to the connection between the adapter and the port, rather than between the two ports.

[Dunbaratu]

That was my thought too... .0000000001 seconds spent looking at the picture shows it's the Sr-to-tank joint wobbling, not the Sr-to-Sr joint.

Incorrect. Zoom in on the picture. There is a thin adaptor between the RCS tank and the Sr docking port, and the bend is not happening at the skinny end of the adaptor, but at the "fat" end of that adaptor.

[Dunbaratu]

I agree with your analysis of the problem. But I would suggest just moving the strut connections from the adapter to the docking port. Right now you are transferring all the stress of the lander to the connection between the adapter and the port, rather than between the two ports.

The description DID say that I connected together these parts IN space. Strutting between the two halves of the Sr port connector is not an option because that's the connection that is made by docking in orbit.

[Dunbaratu]

It looks like the port is attached to an adapter, actually, which is then attached to the yellow 6-way structural connector. I think the problem might be the adapter, I've had trouble with them being really wobbly and clipping right through other parts under load in the past. It looks like in the second picture that the two ports are doing just fine but the adapter is dug about 5 degrees into the docking port. I think you should try something similar minus the adapter.

It doesn't look that way to me - it looks like I see the two Sr docking port halves 5 degrees off from each other. But I will try using a different size adaptor - the longer cone shaped one. I'll see if that's any better.

[Atanar]

To my experience, they are less wobbly but very likely to break.

[Dunbaratu]

I just tried it again, replacing the "Rockomax Brand Adaptor 02" with a "Rockomax Brand Adaptor" in the design and leaving everything else as it was. The wobble is GREATLY reduced and it's now managable. That seemed to be the culprit.

I looked at the parts files for the two and I can't see any relevant difference in their stats. The only differences seem to be the coordinates for stretching the mesh model.

Edited June 18, 2013 by Steven Mading
typo: "not" -> "now"

[leax256]

It works fine when making stations for me too - but not for making ships out if them.

Meet the Bacon Interplanatary Moho Transport. carries way more fuel that yours and 100% not wobbly.

[DerekL1963]

I just tried it again, replacing the "Rockomax Brand Adaptor 02" with a "Rockomax Brand Adaptor" in the design and leaving everything else as it was. The wobble is GREATLY reduced and it's now managable. That seemed to be the culprit.

In other words - despite your terse replies, before testing, to those pointing out that it wasn't the Sr.-to-Sr. joint failing... actual in flight testing showed them to be correct.

But your problem isn't just the adapter you're using, it's also your strutting. As CleverClothe points out, you really should be strutting directly to the docking port... much of your wobble probably comes from the un-reinforced adapter-to-Sr. connection. In a situation like what you appear to have there, I'd use a Structural Fuselage or two as a spacer (rather than an adapter and a six-way), and then strut directly between the payload and the docking port.

[Tokay Gris]

It works fine when making stations for me too - but not for making ships out if them.

Ehm. What?

Ok, it has a low TWR, but almost no wobble and there are two connections in this vessel.

[Dunbaratu]

In other words - despite your terse replies, before testing, to those pointing out that it wasn't the Sr.-to-Sr. joint failing... actual in flight testing showed them to be correct.

The majority of said replies were demanding I correct things that weren't even true about the design in the first place. It wasn't until the suggestion that it was the type of adapter that any of the suggestions were even remotely related to what I'd actually built. Your snarky tone and use of the word "despite" is undeserved trolling. When someone did suggest that solution - the first one ACTUALLY based on noticing what I'd actually built, I specifically said I'd give that one a try despite the fact that it doesn't look like it's where the flexing is happening, and then I did try it. I still stand by what I said that it doesn't visually LOOK like that's the problem. I'm grateful for the advice because the actual culprit and what LOOKS like the culprit don't match. IT looks like the docking ports are bent 5 degrees from each other, not the rockomax brand adapter and its docking port. But what it looks like and what's actually happening don't match. So I'm glad someone gave that advice - it would never have seemed like the culprit.

But your problem isn't just the adapter you're using, it's also your strutting. As CleverClothe points out, you really should be strutting directly to the docking port... much of your wobble probably comes from the un-reinforced adapter-to-Sr. connection. In a situation like what you appear to have there, I'd use a Structural Fuselage or two as a spacer (rather than an adapter and a six-way), and then strut directly between the payload and the docking port.

The problem went away ENTIRELY based on just changing the type of adapter. Without changing the strutting.

The reason you don't see the 6-way connecter being fully utilized is because of another bug where the attachment point disappeared in the VAB and it refused to allow anything to connect to it, which as it turns out after reporting that bug and reading the replies, is ALSO due to the Rockomax Brand Adapter 02 - that part seems to be very broken - when you attach it to other parts the other parts start acting wrong and it's not visually obvious that it's the adapter that's causing it. The original design would have used the 6-way connecter better but I got tired of fighting with the bug and just left two of the faces of the 6-way unused rather than re-designing everything from scratch.

Edited June 19, 2013 by Steven Mading