How does "Auto-strut" determine which part it is going to attach during flight?

[HeleleMama]

I'm always confused by the way Auto-strut working. 

For example, if I select "heaviest part", parts will be attached to the heaviest part(mostly the largest fuel tank) in factory. However, during flight, when that tank runs out, will Auto-strut attach those parts to something else, like the engines? 

The "Root part" option can be very weird too. For example, what will happen if I dock two ships that both have their own root part respectively? Since two docked ships are consider as a single ship by the game, there should only be one root part. Which root parts will be consider as the new root by  Auto-strut?

I raise this question is because :

1) I find Auto-strut to root part can make large ship very sturdy without any extra reinforcement. 

2) When I dock two large ships that auto-strut every parts to their own root together can sometimes trigger  madly wobbling and explosion. (even when SAS and RCS off)

 

[Foxster]

Can't help with all your questions but it might be helpful for you to turn on the option to Visualize Autostruts. It's on the Alt-F12 menu under Physics. 

[Superfluous J]

Whenever the ship state changes, all autostruts recalculate. So for example "heaviest part" will strut to - say - an asteroid when you grab one. "Root Part" on both vessels that dock together will go to whichever part the game makes the root. "Grandparent" will sometimes reverse direction if the direction to the root part changes.

If the ship state doesn't change, though, the struts will not change. So as you empty fuel tanks, "heaviest part" struts will not re-strut to new parts. Until you stage.

[nightingale]

Turning Free Pivot on/off on the claw also causes it to re-calculate the autostruts (because the struts aren't allowed to cross the free pivot boundary.

[HeleleMama]

1 hour ago, Foxster said:

Can't help with all your questions but it might be helpful for you to turn on the option to Visualize Autostruts. It's on the Alt-F12 menu under Physics. 

Thanks! never know Auto-struts can be visualized... I will test it out.

[HeleleMama]

1 hour ago, 5thHorseman said:

Whenever the ship state changes, all autostruts recalculate. So for example "heaviest part" will strut to - say - an asteroid when you grab one. "Root Part" on both vessels that dock together will go to whichever part the game makes the root. "Grandparent" will sometimes reverse direction if the direction to the root part changes.

If the ship state doesn't change, though, the struts will not change. So as you empty fuel tanks, "heaviest part" struts will not re-strut to new parts. Until you stage.

That sounds very bad. The root change can be quite random and result in struct unstable...

Which makes assembling large space ship by docking multiple sub-parts almost impossible.

Do you know any possible solutions in vanilla game?

[Superfluous J]

4 hours ago, HeleleMama said:

That sounds very bad. The root change can be quite random and result in struct unstable...

Which makes assembling large space ship by docking multiple sub-parts almost impossible.

Do you know any possible solutions in vanilla game?

Don't use auto struts, or don't strut to root.

Though I've never had trouble with them.

[bewing]

14 hours ago, HeleleMama said:

However, during flight, when that tank runs out, will Auto-strut attach those parts to something else, like the engines? 

Yes.

14 hours ago, HeleleMama said:

Which root parts will be consider as the new root by  Auto-strut?

It just picks one.

11 hours ago, HeleleMama said:

Do you know any possible solutions in vanilla game?

When autostruts change their connection point it is a very violent process, and you generally want to avoid doing that. However, you usually know exactly when it's going to happen. So just before you dock two ships together, for example, you turn off all the autostruts on both ships. Then you dock. Then you turn some of them back on again.

 

[HeleleMama]

2 hours ago, bewing said:

Yes.

It just picks one.

When autostruts change their connection point it is a very violent process, and you generally want to avoid doing that. However, you usually know exactly when it's going to happen. So just before you dock two ships together, for example, you turn off all the autostruts on both ships. Then you dock. Then you turn some of them back on again.

 

I'm testing this solution( disable auto-strut before docking) just now. Here are some results.

1) The root change is not completely random. It has something to do with the craft type and how many auto-strut parts each craft has. It seems the "Plane" type has higher root priority over the "Ship" type and the "Ship" is higher than the "Probe". If two craft share the same type, the game will compare which craft holds more auto-strut parts and shift the other ship's root to it. It's quite reasonable, considering this approach can minimize the "changing impact".

2) Base on above fact, there are no need to disable all auto-struts on both crafts before docking. Instead, you need to change the craft type by re-name it and disable all auto-struts on the ship which is not going to be your new root. This gives your more control of the root changing.

3) Un-dock will restore each crafts' original roots.

5) Combining use of different types of auto-strut can be a disaster due to the re-calculating. Using auto-strut to root only.

 I think we can end this discussion here. Thanks for all your help. 

Edited March 25, 2018 by HeleleMama
wrong info