Seeking stock octagon construction advice; parts are not attaching/connecting.

[Particle]

I am currently attempting to build a basic orbital refueling station. I've been watching a few tutorials, mostly those of Matt Lowne and Scott Manley, and they have been very helpful. In my current attempt, I am trying to more or less copy part of a  station that Matt Lowne demonstrated in this video. The part that I'm copying starts at about the 2:10 mark. I don't know if it makes a difference, but I'm using fuel tanks instead of crew quarters. The shape of the parts is the same.  Also, I'm just doing the octagon, not trying to make it rotate. It looks fine in the VAB, but once I move to the launch pad and the physics kick in,  it's obvious that I'm missing some aspect of the construction.

I made a short video if it helps.  It all just starts flopping around.

As long as this game has been out, I'm guessing that this has been addressed somewhere. I did look around a bit for a solution but couldn't find one. It won't look as cool, but if all else fails I'll just go rectangular.

 

[Caerfinon]

Do you have auto strut turned on? that may help with the flopping around;

You need to have advanced tweakables option in the settings turned on to enable the function

Failing that you could just use regular struts between the fuel tanks (really close to the connections to make them less visible).

[AHHans]

My first suggestion is to use regular struts to connect the fuel tanks that touch each other but aren't actually connected to each other. (I.e. the second tank in one arm to the first tank in the next arm.) With a little bit of fiddling you can probably fit that in the gap between the two tanks. That's probably the single biggest improvement for this craft.

The next suggestion is as @Caerfinon said: activate autostruts. I personally use autostruts to "Grantparent" on nearly all parts.

And finally: a station in space does not have to deal with strong forces / accelerations, so the mechanical structure can be fairly weak. - Once it is in orbit! The same cannot be said on the launchpad - where it has to deal with 1 g acceleration - or during launch - where the forces a even higher! So I would add some more struts to the craft to keep it stable during launch. I often add some radial decouplers to the craft and then draw struts from the decoupler to the part I want stabilized. That way I can fire the decoupler and the strut and the connection pieces will stay on the decoupled part. (And will deorbit if you do it right.) If every tank is strutted to a part on the central stack well above and below it, then that will make the whole craft a lot more sturdy and will also reduce the "floppyness" of the waist where the ring is connected.

3 hours ago, Particle said:

I don't know if it makes a difference, but I'm using fuel tanks instead of crew quarters.

It does make some difference because fully fueled tanks are heavier than the crew quarters. But that difference is not significant here!

[Edit:] Example of how to place the struts:

Edited December 4, 2020 by AHHans

[Particle]

Thank you both for the suggestions. I was assuming that since the parts were touching they should meld together, so to speak. I've actually somehow not even heard of auto strut until now, and advanced tweakables was also unchecked. So many cool little things to discover in this game. I'll add some struts in the cracks between the tanks (I like that they're not that visible), and that decoupler method looks pretty cool (and thanks for the visual aid too I'm not sure I would have understood what you meant).  I'll give these a shot and see how it goes. Thanks!

[Particle]

Success! Thank you both again for taking the time to show me this.  Auto strut is insane. I did end up using "grandparent" on almost all of the parts. Now I see how some of these ridiculously large builds get pushed into space. I couldn't help but start laughing as I watched my station get into orbit; it seemed both comical and awesome at the same time. 

[Caerfinon]

16 minutes ago, Particle said:

I couldn't help but start laughing as I watched my station get into orbit; it seemed both comical and awesome at the same time. 

Huzzah! Peak Kerbal success!

[Echo__3]

You can do more than just 8 way symmetry. 
Let's Discuss the Secrets of Symmetry - YouTube

[HansAcker]

11 hours ago, Echo__3 said:

You can do more than just 8 way symmetry. 
Let's Discuss the Secrets of Symmetry - YouTube

To be honest, I think the last one is more of a bug and it's been annoying me at times because you cannot adjust parts anymore after removing one from symmetry.
You can do (almost) any-way symmetry with the Editor Extensions mod.

(yeah, probably off-topic for the question at hand, sorry :)

[Particle]

Echo_3: Thanks for sharing that's pretty awesome. Not sure why but the first time I tried to emulate the cubic strut 3 way part (before you select the parent part and go 4 way) all three parts were embedded in the parent. I couldn't get them to attach on the outside. Alt key didn't change it. I scrapped it, opened a new build and that time it worked immediately. In any case really cool.