How do I Autostrut?

[Pacca]

After having the beginnings of my first space station wobble into my own personal Kessler Syndrome, I've decided to look at other options to keep my creations stable. I previously only used EAS-4 Strut connectors, and they did just fine for keeping rockets and landers together. But my space station, having been composed entirely of Sr. docking ports and pieces which are entirely stable on their own, did not have this option. My searches suggest that Autostrutting may be the answer to my problem, but I'm having trouble getting clear info on it;

1. Does Autostrutting dynamically change what an object is "attached" too depending on circumstance (docking/undocking, decoupling, explosive spontaneous deconstruction, etc.)?
2. If not, what happens when the object strutted to is disconnected or destroyed?
3. What do the various options do, and when are they best used? "disabled" is obvious of course, but the rest confuse me, especially since I'm not sure about the above two questions...
4. Should Autostrutting be used to replace EAS-4 Strut connectors or supplement them?
5. How effective is it at keeping space stations and other large docked up structures from destabilizing and damaging or destroying themselves?

I've heard people sing it's praises, and I'd like to know why, but I'm just not sure how to make use of the feature, or even where to get good info on it. Also, I'm trying to go vanilla for now, so I'm avoiding mods; I've only just started, so simple things like bringing one-way payloads to planets and moons are still a real struggle to me. I'd like to really get to know the game before I mod it...

[bewing]

KSP is based on a game engine called Unity. But "joints" in unity have some problems/bugs. They are too flexible, and vibrations do not ever damp down. So the devs gave us all a temporary kludge of these autostrut things until unity gets fixed.

Autostruts are struts that are zero cost, massless, dragless, and are really easy to connect. They have one drawback related to your points 1&2.

1 & 2: Yes, all the autostruts on your craft dynamically recalculate/change their endpoints in flight whenever the make-up of your craft changes through docking, damage, fuel use, or decoupling. However, the disconnect/reconnect process on an autostrut is a very forceful and violent process. So you want to prevent this from happening to your autostruts if at all possible. You prevent it from happening by turning off most/all of your autostruts before you dock/decouple/or when the "heaviest" part on your craft is about to change. Then you turn them back on again once the event is over.

3: Just as you would expect, "Root" creates a strut between the CoM of your current part to the Root part (usually the first part that you placed) of your craft. Heaviest does ditto with the currently most massive part on your craft. If you have a bunch of parts that are equally massive, it just picks one randomly. Root and Heaviest autostruts can be very long, and these long autostruts can either be a godsend or a fatal flaw in your craft. You have to know what you are doing. The "grandparent" part is basically two parts toward the root from your current part. Grandparent autostruts tend to be quite short and they never disconnect/reconnect, and for that reason they are very safe to use. In the Debug menu (Physics tab, iirc), there is a button you can activate: "visualize autostruts" -- it draws lines between each of the parts that are connected by autostruts. So if you'd rather see the autostruts instead of reading a bunch of words, try that.

4. Replace. Grandparent autostruts are better than EAS struts in almost every way. Someday, in some future version, the devs may get rid of them -- but for now they are a nice gift to the players. The only time an EAS strut is better is when you want to connect your current part to someplace really strange.

5. Very effective. Space stations, extremely long rockets, and big surface bases tend to build up large destructive oscillations -- especially if you have reaction wheels active and you turn on SAS. Using a lot of grandparent autostruts can easily rigidize any of these craft in space or on a CB. Just follow two main rules: Be very careful with your autostruts before doing any docking or decoupling, and minimize the number of really long autostruts (let's say a maximum of 5 long ones per craft).

 

[OHara]

1.  Autostrutting makes no change to the tree of parts attached to other parts (similarly to EAS-4 struts).
Struts and autostruts make their attached parts move together as one rigid body, without changing the logical connections use for purposes of un-docking.

2. If the strutted-to part is detached, the autostrut releases (similarly to EAS-4 struts) and then attaches to some other part depending on the setting

3. The setting sets the rule for which part the autostrut should attach to.  I think you know the idea of a 'root' part to which some 'children' are attached and so forth.  Setting to 'grandparant' makes the part automatically set an invisible strut past or through its parent, to attach to its parent's parent.

4. A single EAS-4 strut or single autostrut will do the same job to keep two parts from moving relative to one another, so one cannot supplement the other.   EAS-4 struts are for when you want to see exactly which parts are being held in place.  Autostruts are for when you cannot set an EAS-4 strut between things that you want to be held in place -- most useful between parts that are docked together.

5. If the problem of a space station is the docking attachment points being wobbly, then an autostrut from one side of the weak link to the other will stop the wobbling.   If the physics simulation is working reasonably, maybe simulating a feedback oscillation between reaction wheels and SAS through a wobbly connection,  a wisely placed autostrut will probably help.
Conversely, multiple autostruts holding parts rigidly in place relative to each other can cause large forces between these parts and the rest of the craft, and that can make the physics simulation get jittery.