TIL: You can dock a vessel to itself to create secondary connections (I made a inching Kanadarm!)

[spudbean]

I've always know you could create double/triple/etc docking connections when docking two craft together. One pair of docking ports will have the real, primary connection, and the other pairs have a secondary "self" docking connection where the parts aren't parented with each other, but there is a fixed physics joint between them.

But I didn't know you could create these secondary docking connections at any point (so long as you can move docking points around, e.g. with Infernal Robotics).

Mods used:
* DROMOMAN robotic arm parts http://forum.kerbalspaceprogram.com/threads/37680-DROMOMAN-modular-arm-parts-for-Damned-Infernal-Robotics
* Infernal Robotics http://forum.kerbalspaceprogram.com/threads/37707-0-90-Magic-Smoke-Industries-Infernal-Robotics-0-19-3

[Zephram Kerman]

Well now, that's pretty cool. With a bit of planning, you could have that arm inching its way all over a large station, carrying a payload from one end to the other.

[katateochi]

Self docking has always worked, but what I'm interested in here is that you've got a docking port on a hinged arm. That has previously been a recipe for problems and infact InfernalRobotics has a big bold notice on the first page saying that doing this will make your life miserable. What normally happens when you dock a port on a hinged arm is that the hinges, pistons etc that sit between the docking port and the crafts root part will get messed up (reset to weird impossible positions or become fixed so they can't move anymore).

In the past I've gone to odd lengths to work around that because having a movable docking port like this is so useful for base assembly, cargo arms etc. Unfortunately the best solution I've had no longer works because it requires a now deprecated functionality from KAS (being able to set a winch to "undocked mode"). That enabled the docking port on the end of the arm to be treated as if it was a separate craft and then docking didn't cause problems to the robotics parts. The other solution is to use the KAS magnet instead of a docking port, but that used to be problematic too. Last time I used that approach the magnet had been improved and it worked fine, but it used to often result in parts being ripped off.

I wonder if because its docking to itself, rather than to another craft, if that is the reason it hasn't caused problems for you. Have you tried using the arm to dock to another craft? If this now works then I'm extremely happy 'cos I can make construction rovers again, yay!

[spudbean]

katateochi: ha, seems like you and I have gone down exactly the same journey with docking ports / IR / KAS / winches / magnets etc.

I *think* my setup is working because there's a small Cubic Octagonal Strut between the hinge joint and the docking port. I've had all sorts of problems if the port and hinge are adjacent parts. Even with my setup, IR is not completely happy, and have to reload the scene to avoid trouble.

I wonder if because its docking to itself, rather than to another craft, if that is the reason it hasn't caused problems for you.

I will experiment with this and report back.

[spudbean]

I wonder if because its docking to itself, rather than to another craft, if that is the reason it hasn't caused problems for you. Have you tried using the arm to dock to another craft? If this now works then I'm extremely happy 'cos I can make construction rovers again, yay!

So this is the result of my experiment (same ship as before with RCS added): http://madbean.com/pub/tmp/2015/ksp-selfdock-2.mp4 (2.6MB)

AFAICT: it's working? From the end of the arm to the root: Docking Port Jr, an octagonal strut, and then two DOROMON rotation joints, then a 2m arm, a rotation joint, a 3m arm, two rotation joints, strut, octagonal docking port.

[RainDreamer]

Well, ports being able to dock with other ports has been around for a while, and is the basis for connecting multiple parts together outside of VAB on launchpad (for example, tricouplers with dock ports and child pieces with dockports facing the ports on tri couplers would helps all pieces connect, despite the tree structure in editor.

[Zephram Kerman]

Yes, but this is a new application of the old idea. Ports on both ends means the thing is no longer required to be physically at its parent object. I wonder if this is related to the new VAB offset tool?

[RainDreamer]

I imagine this would be pretty nice with KAS.

[SpaceHips]

I thought this was common knowledge?

It's an oft-used workaround due to multiple nodes not connecting because of poor logic or something.