Multi-point Docking

[PTNLemay]

I've noticed that most people (namely, everyone I've seen) seem to create their space stations with 1-to-1 docks. Meaning each constituent of a space station is connected to another via no more than 1 dock. They can dock to multiple modules, but between two there is only ever 1 connection. This is annoying because the docks don't seem to have any angle locks (the kind of locks you can use when building your rocket so that the pieces line up in nice clean 90 degree angles). I find this tends to make your space station core look like a spindly tree with random branches sticking out of it in all sorts of directions. Even if one is very careful when docking, it inevitably happens.

So I wanted to try using this 4-point docking configuration, to ensure that the core of my space station would be a big solid (and most importantly, consistent) square. Basically it would be lots of square cross-sections stacked on top of one another forming the "spine" of the station. Additional modules could be connected to the sides using 2-point connections. I wanted to do a ground test first. I was quite unable to get them to line up one on top of the other, so I decided to try with this side-to-side docking first, and... it won't connect. Is the game just being difficult with me, or are these sort of multi-point connections just not possible at the moment?

Edited July 2, 2013 by PTNLemay

[DMagic]

Lots of people make multi-port connections. You just have to be very careful when docking. Getting all of the ports to actually dock requires everything to be lined up correctly at the same time. There are some additional tricks to getting bi- and tri-couplers to work correctly with multiple ports, but there is a good tutorial video about that which can be found on just about every post on this subject.

Testing out docking on the ground works, but you have to be very careful about lining everything up correctly. If your ports are off by even a little they won't connect. And since you're only really working with 2 degrees of freedom it can be difficult to line everything up right, even with two identical crafts.

[boa3532]

Man, if I tried to built that, my computer would just laugh at me and shut down....

[PTNLemay]

@ DMagic

Okay, so it is possible. Good... I was worried that it was one of those features they might be working on but that we'll never see.

Thanks for the prompt reply.

@ boa

I have a GTX 670 running the show. Best 400$ I've ever spent. lol

[DMagic]

That GTX 670 isn't really going to make a difference here. The choke point is the CPU, not the GPU. And Boa has a good point, if you aren't careful with how big your station is and how efficiently you use parts you will run into some performance issues.

[DChurchill]

Correct me if I'm wrong, but it's one parent one child part, isn't it? It may look like those are both connected, but they're not. Somewhere in that loop is a disconnect. Which is why the stations you see are all one to one.

[ddavis425]

Is that screenshot from the test you did? I really hope you know that there are no docking ports on those ships...

[DMagic]

Nope, it should work fine, if you get them positioned right you can dock as many ports as you want (there might be some upper limit, but not that I'm aware of).

This was docked in space. I'm not sure how easy this is to read, but both ports connected fine and show the 'undock' option, meaning they are connected.

Edited July 2, 2013 by DMagic

[zzz]

Correct me if I'm wrong, but it's one parent one child part, isn't it?

It is, but it's work by some way.(Has dispute on this issue proving that it works)

(both connected\ undock right\ undock left )

(left is connected by two docks\ right only by one(pieces still same but one of docks is inverted and not connects) )

And one of my old stations

Edited July 2, 2013 by zzz

[PTNLemay]

That GTX 670 isn't really going to make a difference here. The choke point is the CPU, not the GPU. And Boa has a good point, if you aren't careful with how big your station is and how efficiently you use parts you will run into some performance issues.

Even so, I'd like to give it a try, I'll reduce the graphics quality if I have to to pull it off.

Correct me if I'm wrong, but it's one parent one child part, isn't it? It may look like those are both connected, but they're not. Somewhere in that loop is a disconnect. Which is why the stations you see are all one to one.

I'm aware that they're not connected, that's the problem. I'm just making sure that this sort of setup CAN connect.

Is that screenshot from the test you did? I really hope you know that there are no docking ports on those ships...

What do you mean? Aren't those six-sided nodes docking ports?

This was docked in space. I'm not sure how easy this is to read, but both ports connected fine and show the 'undock' option, meaning they are connected.

Oh, umm... actually that's not the kind of dock I was thinking of. The one you have there is just 2 x 1-point connections. The one I'm trying to do is more of a loop (like this).

@ZZZ

Yes! Just like that. 2 entities, connected by 2 distinct points, thank you.

[DMagic]

Based on your diagram I have exactly what you labeled 'possible?'. Two crafts, both with two docking ports, all four connecting at the same time.

And no, the 6-way node is a not a docking port, you need to add ports to each face of the node that you want docked.

[olex]

Multiple docking is possible. It was implemented at tester's request during the experimental phase for v0.18 when docking was first introduce. The way it works is, one pair of docking ports establishes an actual docking and joins the part trees of both craft as usual, and the other pairs only connect up with a physical link, like struts.

[Whackjob]

What do you mean? Aren't those six-sided nodes docking ports?

Nope! They're purely structural. You have to add docking ports to each node. Select the standard size or junior docking port, use WASD to flip them around to the correct orientation, then add them to the six sided die piece. One docking port per side of the die.

[DMagic]

Nope! They're purely structural. You have to add docking ports to each node. Select the standard size or junior docking port, use WASD to flip them around to the correct orientation, then add them to the six sided die piece. One docking port per side of the die.

And if you're interested, there is a mod which adds a really good, large 6-way node that can be used with the big docking ports. It adds a lot of other really nice station parts, too.

http://forum.kerbalspaceprogram.com/showthread.php/32179-WIP-Large-Structural-Components-for-KSP-20-Image-Heavy

[PTNLemay]

Based on your diagram I have exactly what you labeled 'possible?'. Two crafts, both with two docking ports, all four connecting at the same time.

Yeah, I see it now. I thought you just strapped two separate engines to the bottom.

And no, the 6-way node is a not a docking port, you need to add ports to each face of the node that you want docked.

I see I see... that'd explain why I'm having so much trouble getting them to click. lol

Thanks again guys. You were all of great help.

[Mazlem]

I made the KSS Vincible with two docking nodes on each section:

Also made this delivery ship using two nodes per side, and the modules it was delivering had nodes on their sides too - they actually docked together in addition to docking with the delivery ship. Once I got there and undocked one node for one module, both of that module's nodes undocked. Interesting but I'd hoped to send them both down in one piece.

[Vanamonde]

I see people saying that they can get links between assemblies through 2 or more sets of rings, but in my own game I only ever see one solid link and one rubbery link that parts under stress. In this failed design, for example, you can see that the docking rings at the front of the tanks, even though they claim to be docked, are not holding under acceleration.

[M5000]

Correct me if I'm wrong, but it's one parent one child part, isn't it? It may look like those are both connected, but they're not. Somewhere in that loop is a disconnect. Which is why the stations you see are all one to one.

Yes, in the editor it absolutely is, well actually, I think your wording is a bit off..

A part can have as many CHILDREN as it wants, but it cannot refer to itself as one of its own children, or one of its children's children, or so on and so on, that's why you can't have things attach at any more than one point between two pieces.

The only things that may break this rule are struts, as they essentially are (I believe) two physical parts (seen as one) that are both children of some part on a vessel, and are "linked" by a non-modeled, 2-D "line" of metal. Fuel lines are the same thing.

So, when you build docking ports in the editor, they're not connected but at one point. However, when the physics world kicks in, you can attach as many points to as many points as you'd like till the cows come home. It's no longer a parent/child relationship, they're just attachment points at this point. If you build a craft where it may look like the docking ports are connected, but they are not, so long as they are very close, upon physics enable, they will automatically couple together.

[soranno]

I tried at first with a 4 port assembly, and it failed every time. I could never get all 4 to dock, after even dozens of attempts on all manner of ships.

Then I switched to a 3 port assembly... and have a 100% first time every time docking rate. 3 port docking at least is flawless.

[Starwaster]

Also wanted to weigh in, it's definitely possible to do things through docking that can't be done in the editor. Another way to describe what happens in the editor is that you can have multiple branches off of a part but they can't all reconnect later. For instance if you use a three way coupler (tri-coupler? I forget) to branch down into three parts and then try to attach an inverted tri-coupler, only one connection will be sound. The craft format can't describe a situation where all three children merge back into one; only one path can continue and the others have to terminate. Making it structurally unsound and in need of strutting.

But the format is different in the persistence files. (the save files). From what I can interpret of it, it doesn't depend on a root or parent/child system.

[PTNLemay]

I found another problem while experimenting with docks. I'm trying to see what surfaces the actual docks will fit on.

In my contraption I'm trying to drop a module with a dock on it's bottom onto the rig that has a dock waiting right underneath the module. The problem is that the top part just stays gray when I place it in the editor, and when I launch it... disappears. See my included pics to see what I mean.

(Test Rig 1)

(Test Rig 2)

Edit:

Same with this approach. I feel like I'm missing something painfully obvious about the game here... are there some ways in which parts just don't want to click into place? How do I get these greyed out parts to join with my construction?

(Test Rig 3)

Edited July 3, 2013 by PTNLemay

[Flixxbeatz]

Lots of people make multi-port connections. You just have to be very careful when docking. Getting all of the ports to actually dock requires everything to be lined up correctly at the same time. There are some additional tricks to getting bi- and tri-couplers to work correctly with multiple ports, but there is a good tutorial video about that which can be found on just about every post on this subject.

Also, you can't just target one of the ports and control a port from the spacecraft you are docking since they will be the only ports that will connect, leaving others unconnected (and making your spacecraft/ space station unstable). Since 0.20, the only thing that you can do to alleviate this is to place a probe core behind the port assembly to serve as your target, like this:

  -----------------------
  |      SPACECRAFT     |
  -----------------------
  |      PROBE CORE     |
  -----------------------
      /  BI-COUPLER  \
     ------------------
      |PORT|    |PORT|

[ddavis425]

I found another problem while experimenting with docks. I'm trying to see what surfaces the actual docks will fit on.

In my contraption I'm trying to drop a module with a dock on it's bottom onto the rig that has a dock waiting right underneath the module. The problem is that the top part just stays gray when I place it in the editor, and when I launch it... disappears. See my included pics to see what I mean.

(Test Rig 1)

(Test Rig 2)

Edit:

Same with this approach. I feel like I'm missing something painfully obvious about the game here... are there some ways in which parts just don't want to click into place? How do I get these greyed out parts to join with my construction?

(Test Rig 3)

In your first test rig the 6-way node did not attach to the structural beam. In the second test rig the tank won't attach because there's not enough room for it to fit. Keep in mind that even if you could get the tank to attach in the editor it will only be connected to one of those beams, not both.

[DMagic]

Also, you can't just target one of the ports and control a port from the spacecraft you are docking since they will be the only ports that will connect, leaving others unconnected (and making your spacecraft/ space station unstable). Since 0.20, the only thing that you can do to alleviate this is to place a probe core behind the port assembly to serve as your target, like this:

Well, using bi- and tri- couplers is tricky, they don't work like most people think they do, there is a very specific way to set them up. But using the example I showed, two crafts, each having two ports, but not using any bi-couplers, you can control from a port on one craft and target the port of another craft. It worked fine for me at least.

Also wanted to weigh in, it's definitely possible to do things through docking that can't be done in the editor. Another way to describe what happens in the editor is that you can have multiple branches off of a part but they can't all reconnect later. For instance if you use a three way coupler (tri-coupler? I forget) to branch down into three parts and then try to attach an inverted tri-coupler, only one connection will be sound. The craft format can't describe a situation where all three children merge back into one; only one path can continue and the others have to terminate. Making it structurally unsound and in need of strutting.

Like I said above, these have to be setup in a very specific way, but it does work. You can dock and undock all three (and I assume four using the KSPX quad-couplers) ports if you do it right.

I found another problem while experimenting with docks. I'm trying to see what surfaces the actual docks will fit on.

This is an unrelated problem, but it's easy to fix. You just have to rotate the 6-way node to get it connect in examples 1 and 2. Only the top and bottom part of the 6-way nodes can connect to a parent part, just fiddle with the rotation keys 'QWEASD' until you get it rotated correctly and it should connect fine. Once it is connected you can then attach something to the sides like normal.

As for the third example, you should be able to connect the top or the bottom of that fuel tank to the end of that truss piece (though you will need to move one truss to make room for it), but you can't connect it the way you are trying. It's basically the same issue as the 6-way node; you can only connect the top or the bottom to a parent part, then you can attach something to the side.

Edited July 3, 2013 by DMagic

[Tiron]

I built several versions of this a few versions back, before giving up on the design as causing too much (@%( lag.

I found a few interesting things while messing with it. First and foremost: Multidocking is really, really annoying if there's any flex at all between the ports. Once the first port in a multi-dock is locked on the others lose their 'magnetic attraction' capability and only lock if they physically touch. And when they do lock, they lock however they happen to hit...which means they're not necessarily aligned correctly (if you've got flex in the structure between the ports, the changes of getting full alignment are basically zero.) If you disconnect a port, you can reconnect it by moving it far enough away from the port it was connected to (Cue wobbling a tank arm back and forth to reset it trying to get it to align properly).

A useful trick with it is that if two unconnected ports are at least mostly-aligned when a scene load completes, they'll automatically lock on. You can use this fact to build structures that aren't normally allowed right in the VAB: Simply place pairs of ports facing each other, and they'll automatically multi-dock when the ship loads in on the pad. For example:

The fully docked port, connected in the VAB, is the one on the BOTTOM. The strain is pulling the top two apart but they ARE still connected.

At least until I decouple it. The two multidocked ports lose connection at that point, and don't re-lock (presumably that 'has to move far enough away first' restriction is at fault), and the exhaust in the decouplers causes some interesting motions (and explosions). The fully docked bottom stays locked on, however:

So yes. Possible. (But only with docking ports). Extremely useful.