Stack Decoupler breaks off engine.

[BechMeister]

Hello! I have a noob question. Sorry i tried to google my issue, but i couldn't find a clear answer.

I have this rocket were my 2nd stage is a 3 engine plate with aero spike engines - I have put 1 stack seperator on each engine.. but i cant decouple it without breaking 2/3 engines of. I tried to strut them to the vehicle but it still happens:
Image for reference:


Vab View:

[Wetzelrad]

My understanding is that, when placing a part, it will only attach to the one part you place it on. So you can place C on top of B on top of A, but you can't stick B in the middle of A and C and expect all three to be connected.

The bottom half of your assembly is attached to the top of the assembly only through that one Dart. It would appear from your comments that the other two Darts are attached to the bottom half. So while they may be touching the engine plate they are not connected to it. To fix this, you would need to pick up those Darts and place them on the engine plate by hand. Then they would be connected to the engine plate but not to the stack separators, or not to the three-way adapter.

That is, assuming it's not a bug.

[BechMeister]

Ill try things around, maybe i could also try attack the decouplers th other way around? so the explosive force goes the other way?

[BechMeister]

@Wetzelrad I tried what you suggested - it yielded the same result. How ever, when i flipped the decouplers it didnt break the engines off. There are how ever a few other bugs that i needed to work around. 


If you look at the little black triangle, that indicates what way it blows. - Now i have 2 bugs i need to resolve some how. When i seperate.. for some reason i dont follow the 2nd stage.. but have to press [ to go to it.

Second bug is that the stack decouplers pass over to the second stage, and when you press space, it turns off the engines. I made a new "stage" and moved the engines infront of the stacks again, and then when i pressed space, they flew off and the engines worked.

But my craft works! 

[Wetzelrad]

Sounds like you have it handled. Normally you want the decoupler triangle to be pointing away from the engine so it doesn't stay attached to the engine.

With tri-couplers, in the way that you used them, only one of the three branches is being used structurally. The other two branches are hanging on by their top node. And in fact you only need one decoupler there, because the other two decouplers are not attached in full. Am I making sense? If you hover over with your mouse, you should be able to see by the green outline which parts are connected.

So with that type of design, the critical issue is build order.  It's very easy to attach parts in the reverse order such that they end up on the wrong side of the decoupler. This is not so much a bug as it is a design quirk carried over from KSP1.

Frankly it's much easier to use the engine plate instead.

[BechMeister]

I tried to use the engine plate first.. but the large decoupler did not want to go to the fuel tank beyond the engines.. but instead to 1/3 engines.. and it made the vehicle very wobly understandable

[Scrufdog]

I had a similar issue last night. I had a medium decoupler surrounding 6 engines. On decouple it would randomly knock off 1 or 2 engines. To solve I just turned down the decouple force from the default in the hundreds, down to 5 kN. Seems like the force of the decoupler was too much.

[BechMeister]

I have yet to find out how you make a medium decoupler cover multiple stacks.. I always have it make a cone to 1/x engiens - that was the first i tried with that design, 1 medium decoupler covering all 3 engines

How ever.. I have  lately tried what @Wetzelrad suggested. By having symmetry set to 3, and then placed 3 engines at the same time, then decouplers, and then add the top and move that entire assembly on to the rocket has removed the problem.

Because the first thing i tried was to make the force "zero" and it would still break off. But... yeah, by building it in one go and putting it on the stack seems to work for me x)