How can I transfer my manipulator arm from the cargo shuttle to the station itself?

[kendfrey]

I have this arm docked to the space station, and I'd like to undock it from the shuttle it was launched in, but unfortunately, the way KSP's part tree works means that when I disconnect the arm from the shuttle, it disconnects the other end from the station as well. Is there a mod (or maybe even something in stock) that will let me do this?

The logical part tree goes station <-> shuttle <-> arm, so KSP can't disconnect the shuttle while leaving the other two connected.

[Alshain]

You need to send up a separate arm attached to a base payload and dock that to your station.  Attach it to some component like a structural fuselage or a girder and have docking ports on that.  Just don't put docking ports on the moving parts.

Edited June 27, 2016 by Alshain

[kendfrey]

6 minutes ago, Alshain said:

You need to send up a separate arm attached to a base payload and dock that to your station.

I'm having trouble visualizing this. I don't understand how adding another piece will let me rearrange the pieces of my station. Can you provide a picture or sketch of some kind, illustrating what you mean?

[Alshain]

The video on the IR thread shows you an example.  The arm must be attached to one of the station modules when it is deployed.  Of course, that module can't be attached by the arm, but every module after that can.  HOWEVER, as  I said, you can not grab modules with docking ports, ever.  As I understand itm any part that is put in motion by the arm or any other IR part can not have a docking port on it (though the station itself can having docking ports).  You notice in the video the station does have docking ports, but none of the other vehicles used do, the escape pod, the spaceplane, the rover, the artificial gravity segment of the station, etc all use the IR connector things.  This means if you want to move station modules then you want to build your station without docking ports.  I notice in your picture above you are grabbing the station which has a docking port, that isn't a good idea.  It says it right there on the IR thread....

Do not attach docking ports directly (or indirectly) to IR parts. It will make your life miserable. You have been warned!

 

Edited June 27, 2016 by Alshain

[bewing]

I think a klaw would work better on the end of that arm than a docking port? A klaw won't detach until you tell it to!

[kendfrey]

1 hour ago, Alshain said:

It says it right there on the IR thread....

Do not attach docking ports directly (or indirectly) to IR parts. It will make your life miserable. You have been warned!

Well now I understand why that warning is there. I had assumed it was some sort of kraken or bug, not a limitation of KSP itself.

Too bad the IR/KAS parts aren't sufficient for a manipulator arm of the sort I'm looking for. They don't actually merge the vessels, so I won't be able to transfer crew/resources if using them for docking, and I won't be able to control the arm if it is attached by them.

59 minutes ago, bewing said:

I think a klaw would work better on the end of that arm than a docking port? A klaw won't detach until you tell it to!

I tested this, and they yield the same results as docking ports. They detach when the part tree is broken.

I take it the answer is "No, you simply can't do that." I guess I'll have to bring my arm back home and redesign it with these constraints in mind. Ah, science!

[bewing]

Can't you put a stock part between the IR arm and the docking port/klaw? Just one little girder? That should make the whole thing work, you know!

Because that is exactly how I use klaws in stock. I grab some piece of space junk with a space tug wielding a klaw. Drag it over to a "deorbiter". Attach the junk part to a klaw on the deorbiter. Let go with the tug's klaw. Decouple the deorbiter's klaw with the junk part attached -- and it stays attached!

 

[kendfrey]

5 minutes ago, bewing said:

Can't you put a stock part between the IR arm and the docking port/klaw? Just one little girder? That should make the whole thing work, you know!

Because that is exactly how I use klaws in stock. I grab some piece of space junk with a space tug wielding a klaw. Drag it over to a "deorbiter". Attach the junk part to a klaw on the deorbiter. Let go with the tug's klaw. Decouple the deorbiter's klaw with the junk part attached -- and it stays attached!

The difference there is that the tug and the deorbiter are not already connected. If they were, the part tree would form a loop when you attach the second klaw to the junk. In a space station, it's important that everything is connected to everything else at every moment in time, otherwise you have two smaller stations, which will become permanent if you don't react quickly.

[bewing]

OK, you are right, I wasn't paying enough attention to the potential for loops. But if you get everything ready, undock the MPL from the nose of the shuttle, then let it dock with the docking port on the end of the arm, then decouple from the shuttle, then redock to the nose of the shuttle -- it seems like the docking magnets should make that process fairly easy ....

[kendfrey]

2 minutes ago, bewing said:

But if you get everything ready, undock the MPL from the nose of the shuttle, then let it dock with the docking port on the end of the arm, then decouple from the shuttle, then redock to the nose of the shuttle

I considered this, but it wouldn't help for maneuvering uncontrolled space station modules around, which is the whole idea of this robot arm.

I'm starting to think building a self-controlled robotic arm is the way to go, rather than having it be controlled by (and docked to) the parent ship. More thought required though...

[Alshain]

3 hours ago, bewing said:

I think a klaw would work better on the end of that arm than a docking port? A klaw won't detach until you tell it to!

Nonono, the claw is a docking port in code.  KSP doesn't see them as much different.  Do not put it on an IR part.

1 hour ago, bewing said:

Can't you put a stock part between the IR arm and the docking port/klaw? Just one little girder? That should make the whole thing work, you know!

 

Nope, it said do not attach directly or indirectly.   If I'm not mistaken, in the tree, the IR parts can not separate the root part from the docking port.

So this works:

Docking Port <---- Root Part -----> IR Parts

But not this:

Root Part -----> IR Parts -----> Any other parts ------> Docking Port.

 

At the end of the video you see the user dock together a base module, that's ok though because the docking port is not directly attached to the legs in any way, it's attached to the craft, and does not have to go 'through' the IR  Parts to get back to the root part.

Edited June 28, 2016 by Alshain

[kendfrey]

9 hours ago, Alshain said:

in the tree, the IR parts can not separate the root part from the docking port.

This is a gross and misleading oversimplification of the problem. As I understand it, there's nothing wrong with using docking ports on the end of an arm. The trouble only comes when a ship interacts with itself.

[Kerbart]

35 minutes ago, kendfrey said:

This is a gross and misleading oversimplification of the problem. As I understand it, there's nothing wrong with using docking ports on the end of an arm. The trouble only comes when a ship interacts with itself.

What I remember from watching a @DasValdez session (the one with the BEAM module) is that it's exactly this problem (docking ports connecting onto "themselves" so to speak) that results in the IR warning to not put docking ports on moving parts.

I also remember (I'm not an IR player though) that he used "magnets" to bypass that problem. Magnets are like docking ports but they don't actually dock, and are intended for these kind of purposes.

Don't flame me if I got it wrong, please. It's all from memory and I'm only trying to help

[kendfrey]

Mmm, magnets. I actually played with those first (can you spot one in the screenshot?) but they're too power-hungry to be useful for me.

It's the never-ending tradeoff between practicality and realism. Magnets are impractical due to power consumption. Docking ports are impractical due to the part tree. The non-magnetic grabber thingie isn't realistic due to being able to grab onto any part, even smooth fuel tanks.

[Alshain]

2 hours ago, kendfrey said:

This is a gross and misleading oversimplification of the problem. As I understand it, there's nothing wrong with using docking ports on the end of an arm. The trouble only comes when a ship interacts with itself.

Yes, but that will always happen.  You grab a craft and pull it in close for a dock, what else would you use it for?  What other reason could there possibly be for having a docking port on the other side of an IR RMS?   You grab an incoming craft, and dock it to your station and that means it is interacting with itself.  My explanation was correct, the only clarification I could have added was it only applies when actually docking, so grabbing a craft that happens to have a docking port won't be a problem, as long as you don't dock it.  I guess I figured that was implied, as otherwise it is just a part like any other.

Edited June 28, 2016 by Alshain

[kendfrey]

Just now, Alshain said:

Yes, but that will always happen.  You grab a craft and pull it in close for a dock, what else would you use it for?

There are plenty of situations in which you only want to dock to the IR end. For example, a docking washer, or a temporarily berthed spacecraft. A real-life example is the Hubble Space Telescope. It was never docked to the main docking port of the shuttle.

[Alshain]

21 minutes ago, kendfrey said:

There are plenty of situations in which you only want to dock to the IR end. For example, a docking washer, or a temporarily berthed spacecraft. A real-life example is the Hubble Space Telescope. It was never docked to the main docking port of the shuttle.

The Hubble required maintenance on Spacewalk.  Nothing in KSP does, that's apples and oranges.