What is this "autostrut" of which you speak?

[rynther]

I've seen mention of this, and how to enable it, but not where to find it, or how to use it. I'm still not entirely sure WHY I should use them.

Do these differ from normal struts? do they affect part count? weight? 

I've seen this in several threads, and I'm curious, someone please enlighten me on this.

[Gargamel]

41 minutes ago, rynther said:

but not where to find it,

In the options menu there is a setting to Enable Advanced Tweakables.   Enable this.   It's one of those settings that really shouldn't be a setting, and should be enabled by default.

41 minutes ago, rynther said:

or how to use it. I'm still not entirely sure WHY I should use them.

Their basically a form of reinforcing your craft.   Others will be along to describe their usage in more detail, but go ahead and play with them for now, they're fairly user friendly.   Just right click a part and select autostrut for that part in the PAW. 

 

Be aware though, if you have a vessel that you intend to dock, and it has a "Heaviest Part" autostrut, it might invoke a Kraken attack after docking, as the autostrut jumps from one part to another.    It's usually not a major deal, but something to be aware of. 

[bewing]

Once you enable them, and you have 'struts' unlocked in your tech tree, then autostruts appear in the menu of every single part as you are building your craft in the editor.

They are better than struts in many ways. They are free, massless, dragless, and do not add to partcount. They can (and often do) stretch from the very bottom of your rocket to the very top, unlike struts which only connect parts within 'line of sight'.

The only advantage of regular struts is that you can connect two random parts with them. Autostruts connect the current part to a very limited set of the other parts in your craft.

 

[Guest]

They do have advantages as bewing says but I don't like/use them. I still get some wobbling (probably not set up correctly admittedly) whereas normal struts hold solid. 

[jimmymcgoochie]

Have you ever built a long, tall rocket, launched it and then turned up the time warp only to see the whole thing collapse on itself like an accordion, bend in half and/or tie itself in knots mid flight? Autostruts can fix that.

Autostruts are like regular struts- they add rigid reinforcements between parts to hold everything steady- but unlike normal struts an autostrut is free, weighs nothing and can be connected to three parts- the heaviest part on the vessel (which can change in flight especially docking, so use with care); the root part (tends not to change unless you’re docking so pretty safe for general use) and the part’s grandparent (e.g. an SRB attached to a radial decoupler attached to a fuel tank, the booster’s grandparent part is the fuel tank) which doesn’t tend to change at all and can be used just about everywhere.

When building a launch rocket, I tend to set all the engines to autostrut to the root part to stop the rocket compressing under thrust, radial boosters to grandparent part, most fuel tanks to grandparent part and nose cones on boosters to root part, with the root part itself (usually a probe core or command pod) autostrutted to the heaviest part unless it’s going to dock to something. It’s not a good idea to use autostruts on your payloads if you intend to dock them to something else, unless they’re really floppy; in which case remember to turn them off again before docking. Docking changes the root part and recalculates all part relationships so autostruts can get confused, causing weird vessel warping, parts stuck at odd angles and possibly even a total collapse in the physics system leading to massive disassembly- a.k.a. Kraken attack.

Note that rigid attachment is not the same thing and generally not advised for anything in an atmosphere or expected to accelerate rapidly- attaching parts in a rigid way makes them more prone to snapping under stress than if they’re able to move a bit. There’s a reason trees sway in the wind, and planes with rigid wings often end up losing them when you pull some G-forces, which is usually a bad thing...

[rynther]

I will say after hearing what they are, I have mixed feelings about using them. I do thank you guys for the time explaining them, that's good to know.

I will also say it sounds a lot like cheating.

Meanwhile, I think I know what I'll do in the sandbox, autostrut everything on an orbital station, and dock something heavy and explosive.

[OHara]

11 hours ago, rynther said:

I'm still not entirely sure WHY I should use them.

If you want to hold two parts in place relative to each other, and cannot or don't want to make the craft stronger using regular parts or regular struts.   The debug screen from alt-F12: Physics: 'visualize autostruts' (on console, Konami code instead of altF12) draws autostruts as orange lines.

In KSP version 1.0 five years ago Squad put in 'autostruts' to hold the part at the tip of payload inside a fairing, to the fairing.  Often there is no direct line for a strut from the tip of the payload to the fairing's base, and the game does not allow a regular strut attach to the fairing shell.

Then in version 1.1 wheels got autostruts.  Then in version 1.2 autostruts became available for all parts through the 'advanced tweakables' menu.

Autostruts can take a lot of fun out of the game.  There is a stock craft called the albatross that flies somewhat like an awkward sailplane.  Its wings flex in high-G turns which made the glider pilot in me happy.  Sometime before version 1.7.3 Squad ruined the craft by adding autostruts to the wings.  You can still remove all the autostruts by hand to have the craft fly properly; the wing-flex gives dihedral that makes it more stable in yaw.  As jimmymcgooch says, autostruts stiffen without making the wing more brittle.  They simplify the Physics simulation.

I avoid auto-struts because I like the craft-building aspects of KSP.  Regular struts do add mass to the parent part (there is a patch under 'community patches' to zero that mass if you want) and cost and count against the early-career-mode limits to part-count. Their physics is not simulated, so they won't add to CPU load.  Since version 1.2 four years ago regular struts have zero drag. 

[rynther]

I remember the strut drag in 0.91, it made building bigger asparagus stacks kinda tricky

[Death Engineering]

On 3/28/2021 at 7:45 AM, jimmymcgoochie said:

[autostrut connected to] the heaviest part on the vessel (which can change in flight especially docking, so use with care)

Thank you for confirming that "heaviest part" changes in flight - I always wondered if autostrut just kept being attached to the original 'heaviest' part, regardless if that part's 'heaviest' status got replaced by a heavier part.