Can we talk about docking ports?

[MidwestB]

Hello, this is my first time posting a thread, so hopefully I don't mess it up.

I just got rendezvousing and docking down a couple weeks ago, and have spent my time making stations around Kerbin, the Mun and Minmus. Now that I've made some simple stations, I wanted to make a "floating city" type of a thing.

Please excuse the *ahem* shape of it currently, I plan to have rings of modules radiating outward from all sides, but that's where this problem arises. I've done searching around the forum and wiki about multiport docking, and actually, the two modules connected to the center tower are connected by 2 ports each that both are docked. However, I wanted to test putting a module between them as a sort of corner, but that requires 4 ports to come together. When I tried it, only the top two ports, near the cupola capsule, docked while the bottom two don't seem to do anything.

I undocked and came back in with the two lower port angled down so they's contact first, and they still didn't seem to recognize the others and when the top ports came down, they docked again. This caused me to rotate the module as seen in the screenshot above, so the capsule was facing the opposite direction, but the same thing appeared to happen, ruling out the ports on the station. Having just the two ports docked makes the other two appear docked because of the alignment, but they still don't grab.

Anyway, I was wondering if anyone has more insight on how docking ports work, maybe code-wise, that could maybe explain this. I know I could install quantum struts to stabilize it, but it would be way cooler to have everything dock properly. I'll try again when I have time, but it doesn't seem to be alignment as much as the ports not recognizing each other. I think it would be a nice feature to be able to right click 2 ports like fuel tanks and tell them to dock if they're close enough, but I don't know how hard it would be to make something like that possible.

Any insight would be appreciated, thanks.

[Pursuedtank]

Two ports are able to be docked together, however they have to be exactly lined up and have to go together at the same time, it is very difficult to do properly and often requires numerous attempts. It is, however possible. Even if one is magnetised slightly before the other that one will connect and the other won't.

[MidwestB]

Yeah, I found that out with the first two modules, but two of the four ports on the third module don't seem to want to dock at all and I'm wondering if it's because of something other than the alignment

Edited May 26, 2013 by MidwestB

[Pursuedtank]

I can't think of anything that would cause it to not dock properly except alignment or not lining it up properly.

[SmallChange]

Multi-port docking is totally doable, but if the ports are slightly off, it might not work. My station is made of triple-docked pieces, and they go together just fine. Never attempted any sideways multiport docking though.

Example of quad-docking:

I know Scott Manley has a video on this topic, too.

[Boffinbox]

it is just the alignment, honestly. when it comes to multi-port docking, it's not as simple as using rcs to send the ship in the general direction of the docking port. you need the two halves to have the same attitude

http://i.imgur.com/bfAT4d4.jpg

it can be done! if only two or three out of four stick, just undock and try again. and again. and again...

[Dictator Dan]

Its a pain, but its doable, often it will take several attempts to get them all to stick, if they dont all latch, just undock, back away a few meters, and come in again, eventually they will all latch, it just takes a lot of patience, and sometimes luck.

[Atanar]

Trying to multi-dock is the best bait for the space-kraken. Try to have few and stable parts between the diffrent docking ports.

Edited May 26, 2013 by Atanar

[Tokay Gris]

I think the main problem is that the ports need to be EXACTLY at the same spots. No tolerance.

This was more a pain because the ports are not on the 90/180/270/360-positions, but at 45/135/225/315.

But after a lot of tedious manouvering all three ports connected without glitch. I didn't touch the ports after the first build, so they all are in exactly the same positions.

Might that be the problem?

[MidwestB]

Okay, got a chance to try again, and it's the same problem. It does NOT appear to be alignment, it's that these two lower ports don't recognize each other. There's no magnetic force between them!

I put the larger picture so you can see the ports easier. You're going to need to take my word that the pair on the other side are lined up as well, sorry.

I was able to press them together, but there still was no magnetic force. I've had them lined up without it, and they still didn't attach. When the front end came down, the top two ports docked just fine.

I don't think the orientation of the ports themselves on the ships matter, but maybe? I don't know what's wrong.

EDIT: The plot thickens, I launched another module, and have found out that the last 3 modules I've launched have all be piloted by Bob Kerman, same orange jump suit and everything. When I went to attach this latest module, I EVA'd the Bob in it and put Jeb in, and got 3 out of the 4 ports docked this time. Wonder if these duplicated Bobs are causing a problem.

Edited May 28, 2013 by MidwestB
Added information

[strongest_2hu]

It's clear that you have a good grasp of multiport docking from your screenshots in the original post which everyone seems to be ignoring. The problem you've caught up with is that docking with multiple ports out of plane with each other is extremely difficult. It seems like no matter how well you nudge them into place one plane will get the magnetism effect first and prevent the docking of the other plane.

However, it can be done: I have a nearly identical setup (2 sets of 4 port symmetry around 4 objects docked up in a square) in orbit right now with all 8 connections showing as docked, which I did by bringing the last piece in extremely slowly and at an angle such that both sets of ports got the magnetism at pretty much exactly the same time. I won't recommend it though, as even though it shows as docked one of the ports is visibly misaligned and separated. I suspect this is the cause of the phantom forces that are slowly making the entire structure rotate faster and faster over time :-).

Your best bet if you really want to go through with construction as planned is to remove the out-of-plane docking problem entirely. In your OP screenshot, I would suggest undocking one of the two existing pieces from the station, docking it with the new piece, then docking the whole assembly back with the station. That will put the four ports in question in the same plane and let you easily dock them with normal multiport precautions. It makes the whole thing pretty tedious, but I don't think there's any other way to avoid the problems you're having.