Double hydraulic piston lift requires cyclic node connections

[Hotel26]

My question relates to the craft shown in the image below.  It shows a mobile base with an elevated payload connected via twin hydraulic pistons that allow the elevation to be controlled..  In particular the passenger carriage above is lowered onto the base while in transit.

The rear piston is connected above and below.  In the case of the forward piston, I've attempted to connect the lower end of the piston to an octa-strut located on the base, using a strut.  It appears that, in operation, this strut somehow breaks or extends such that the two pistons no longer move in harmony.

(I understand about the tree-like structure of connections from the root node.)

Is there a way to make this connection without using docking ports, or is that the only one?  What is the 'official' way (endorsed by BG Robotics experts) to accomplish this?  I would be most grateful for a workable answer to this!!

 

 

[OHara]

The pistons can 'surface-attach' (as opposed to node-attach) to most parts, so instead of using one cubic-octagonal, I surface-attached both pistons as shown at right.

KSP uses a logical tree structure, for things like picking up a part and having a predictable sub-assembly come with, but allows any physical network of connections through the EAS-4 strut.  Unfortunately they weigh 50kg each.  You can attach the EAS-4 between the moving portion of the piston and its load.

Alternatively to the EAS-4, if you enable 'Advanced-Tweakables' through the in-game Esc-key Settings menu, you can turn on same-craft interactions on (1) the piston that would otherwise need an EAS-4 and (2) its load.

I'm not a Breaking Ground robotics expert, though -- maybe get this moved to the relevant sub-forum?

[Hotel26]

@OHara, I just noticed your kind reply and advice as I came back here to post.  Thank you very much!

I had been hoping to avoid an answer that said, "use docks", but I bit the bullet:

It appears to work although I cannot be sure the rear docks actually docked.  But it works.  The major draw-back is just the space it takes causing the lowest elevation of the claw to be higher than I want, in order to dock with my smallest craft.

It's a bit of tinkering, isn't it?

I will give it some trials and see how it does.  I'd certainly be willing to collaborate with anyone on this project.  https://KerbalX.com/Hotel26/Paxmover

 

Edited July 25, 2020 by Hotel26

[FleshJeb]

12 hours ago, Hotel26 said:

The major draw-back is just the space it takes causing the lowest elevation of the claw to be higher than I want, in order to dock with my smallest craft.

I'd use two hinges and make a Z. I'd collab, but I'm on an even worse machine now, and I hate loading KSP with only 4GB of RAM.

[Hotel26]

29 minutes ago, FleshJeb said:

I'd use two hinges and make a Z. I'd collab, but I'm on an even worse machine now, and I hate loading KSP with only 4GB of RAM.

This was actually the original plan and implementation.  No matter what, when docking, it always shook itself to pieces.  (The big let-down of robotics!)

I originally copied this design: KerbalX.com/Brikoleur/LIFTMECH.

(So good to see you back!)