Trouble with radial attachments.

[strider3]

I have been having an ongoing issue with radial decouplers. Longer engines don't seem to be physically attached at all points? In the picture attached is an example. Notice the 3 SRB's are not being held parallel to the main body...the lower attachments are separated and the SRB's are angled into the main body at the top. I try to make sure everything is perfectly aligned during construction but this issue keeps cropping up in various "builds"? Any illumination is appreciated.

[Superfluous J]

Spaceships in KSP are tree-like structures. Everything is attached to the root part via a line of other parts, ONE part at a time. So, your radially-mounted SRBs are not coming unattached from those other 2 radial decouplers, they were never attached to them in the first place! Also, there is no (good) way to make them be attached.

The good news is, there's the Strut. Throw away those useless extra radial decouplers and replace them with struts. They'll hold the boosters in place and vanish when you decouple.

[Snark]

Just to be clear, when 5thHorseman says "strut", he means this part.

[Kerbin vonKerbal]

My very science-based and complex engineering-based answer is this: 

 

MOAR STRUTS

[strider3]

Just to be sure I understand, in the above picture I would use 1 radial decoupler per SRB (3 total and I'm guessing in the middle?) and then add a strut, top and bottom, for a total of 6 struts?

And thanks for the help with this!

Vic the Newbal

[N_Danger]

Yes. you maybe able just to use one strut at top of the boosters. Try to place the booster such that the radial attachment is slightly above the center of the booster to kick the top(of the booster) away from the body of your center core.

15 minutes ago, Victor3 said:

Just to be sure I understand, in the above picture I would use 1 radial decoupler per SRB (3 total and I'm guessing in the middle?) and then add a strut, top and bottom, for a total of 6 struts?

And thanks for the help with this!

Vic the Newbal

 

Edited April 8, 2016 by N_Danger

[FancyMouse]

14 minutes ago, Victor3 said:

Just to be sure I understand, in the above picture I would use 1 radial decoupler per SRB (3 total and I'm guessing in the middle?) and then add a strut, top and bottom, for a total of 6 struts?

Roughly yes. Although I usually find the bottom strut not needed if it's just one kickback.

[strider3]

I seem to be having an impossible time placing these EAS-4 struts? Trying to center them, perpendicular to the SRB, on the central core is tedious (they are tiny, at this point) but almost doable. But, trying to attach the other end to the SRB is making no sense, so far. They refuse to attach where I think they should on the SRB? They want to attach to some completely wrong looking spot (like the top of the nose cone).There appears to be only a few places on the SRB that they want to attach to...and none make sense? Let me take another pic of what I'm trying to do...stand by ;-)

Edited April 8, 2016 by strider3

[strider3]

OK...maybe this will help explain...I want to remove the upper and lower sets of TT-70 radial decouplers  and add EAS-4 struts instead. Where and how would you place the necessary struts?

Thanks gang!

 

[Superfluous J]

25 minutes ago, Victor3 said:

OK...maybe this will help explain...I want to remove the upper and lower sets of TT-70 radial decouplers  and add EAS-4 struts instead. Where and how would you place the necessary struts?

Yes to removing those two circled decouplers. Place a strut somewhere near the top one, strutting inward to the central tank. It's essentially filling the role that you thought the unattached decouplers were filling: It'll give that booster an extra connection point to the central stack.

[FullMetalMachinist]

@Victor3 this is a pretty important concept:

17 minutes ago, 5thHorseman said:

Place a strut somewhere near the top one, strutting inward to the central tank.

The struts add their mass and drag values to whichever part they were placed on first and the second half is just a connection point. 

That means that when you stage away the boosters, the struts go with them. If you went from the central stack out, then the weight and drag of the struts would stay with you after dropping the boosters. 

[Plusck]

6 hours ago, Victor3 said:

I seem to be having an impossible time placing these EAS-4 struts? Trying to center them, perpendicular to the SRB, on the central core is tedious (they are tiny, at this point) but almost doable. But, trying to attach the other end to the SRB is making no sense, so far. They refuse to attach where I think they should on the SRB? They want to attach to some completely wrong looking spot (like the top of the nose cone).There appears to be only a few places on the SRB that they want to attach to...and none make sense? Let me take another pic of what I'm trying to do...stand by ;-)

You should never need more than one strut per SRB, even the biggest ones.

To be sure that the SRB peels off cleanly, place the decoupler slightly higher than where the SRB's centre of mass will lie. Then place the SRB, then use the offset tool to drag it down a bit to the desired height. Then strut at the bottom of the SRB, from its centre (as others have said, it is important to start on the SRB since the strut's mass stays with the part it is first attached to) in to the core.

Struts are so rigid that it really doesn't matter if it is perfectly aligned on the core. I've only noticed a problem if you are placing huge parts (such as 2.5m LF boosters, with SRB's on the outside of those...) and even then you have to be quite far off centre before it starts being a concern.

Those SRBs also have a compounding problem in that you can't actually see where the strut connects to it (the texture for the SRB appears to be slightly outside its "real" surface), so you just have to aim as well as you can and hope for the best anyway.

Edited April 8, 2016 by Plusck

[Snark]

6 hours ago, Plusck said:

You should never need more than one strut per SRB, even the biggest ones.

+1 to this, at least in stock.  (If you're running a parts pack that has monster-huge parts in it, like SpaceY, then you may need more than one strut).

 

[strider3]

16 hours ago, Plusck said:

Those SRBs also have a compounding problem in that you can't actually see where the strut connects to it (the texture for the SRB appears to be slightly outside its "real" surface), so you just have to aim as well as you can and hope for the best anyway.

This may be what was throwing me off on the "weird" looking placement. I don't always "see" the small attachment "pad" when placing the strut on the SRB. Your explanation may account for some of that.

OK, I'll take all the great advice and try again...let you know how it goes.

[max_creative]

Answer: STRUTS!!!

[Foxster]

I always attach SRBs and any other radially attached boosters at the top like this...

This ensures that the explosive force of the decoupler pushes the top away from the rest of the craft and it will cleanly peel away without damaging anything. You do this by placing the decoupler, then attach the SRBs and then use the move/offset tool to shift them down. 

One pair of struts at the bottom is then all it needs. It is a good idea to have the struts at the bottom for another reason: They have more drag than the decouplers (odd but true). This helps in a small way to keep the craft stable during your gravity turn to orbit. 

Edited April 9, 2016 by Foxster

[strider3]

HMMmm...apparently it IS rocket science, LOL. SOooo, attempting step one (attach SRB's to a single decoupler above the center mass of the SRB). Not having much luck. I can only get the SRB to attach at one elevation relative to the central core, and this appears to be well below the center mass of SRB? (see pic 1):

ANY other attempt at moving the SRB's down, to attach to the decouplers above center mass, results in the SRB's attaching to central core, instead (see pic 2):

Just to verify this was not the graphics issue mentioned by Plusk, I tried a quick launch and decouple with the SRB's attached as in pic 2...BOOM! The SRB's decoupled...by exploding! LOL!

So gang, what the heck am I doing wrong? Why can't I get the SRB's to attach to the decouplers where I need them for clean separation (or, more interestingly, anywhere I want within reason)? Keep in mind that the positioning of pic 1 was the only position that the SRB's would attach to the decouplers and not the central core itself...no amount of upward or downward movement of the SRB's resulted in an attachment to the decouplers beyond that one position. S-I-G-H!

Vic the Newbal

[Superfluous J]

12 minutes ago, Victor3 said:

HMMmm...apparently it IS rocket science, LOL. SOooo, attempting step one (attach SRB's to a single decoupler above the center mass of the SRB). Not having much luck. I can only get the SRB to attach at one elevation relative to the central core, and this appears to be well below the center mass of SRB? (see pic 1):

ANY other attempt at moving the SRB's down, to attach to the decouplers above center mass, results in the SRB's attaching to central core, instead (see pic 2):

Just to verify this was not the graphics issue mentioned by Plusk, I tried a quick launch and decouple with the SRB's attached as in pic 2...BOOM! The SRB's decoupled...by exploding! LOL!

So gang, what the heck am I doing wrong? Why can't I get the SRB's to attach to the decouplers where I need them for clean separation (or, more interestingly, anywhere I want within reason)? Keep in mind that the positioning of pic 1 was the only position that the SRB's would attach to the decouplers and not the central core itself...no amount of upward or downward movement of the SRB's resulted in an attachment to the decouplers beyond that one position. S-I-G-H!

Vic the Newbal

Translation of the decouplers is buggy. There is no other way to say it. I personally use the mod No Offset Limits to overcome the bug.

However in this case you don't need to offset the DECOUPLER. Place the decoupler at the top like in @Foxster's pic, and then place the SRBs on it in the middle so they're way too high. THEN, drag them down with the offset tool. Don't even TOUCH the decoupler with the offset tool, though, or it'll do what your pic shows.

That said, I almost never offset SRBs on the decouplers. I just place them as high as I can and that puts enough twist on them to keep them from hitting my center stack on liftoff. Your mileage - of course - may vary.

EDIT: I may have misunderstood the question. You may not know how the translate tool works. In your pic, it's the 2nd of the 4 icons floating in the upper left of the main window, just next to the Wheesley. You can also activate it by hitting "2" on your keyboard. That and the rotate tool ("3") are amazing tools that will transform your rocket building experience.

Edited April 9, 2016 by 5thHorseman

[Foxster]

You will only get the SRBs to attach at their centre. What you need to do is place the decouplers higher, then place the SRB on them, then move the SRBs down using the move tool (press 2). 

Edited April 9, 2016 by Foxster

[Plusck]

10 hours ago, Victor3 said:

HMMmm...apparently it IS rocket science, LOL. SOooo, attempting step one (attach SRB's to a single decoupler above the center mass of the SRB). Not having much luck. I can only get the SRB to attach at one elevation relative to the central core, and this appears to be well below the center mass of SRB? (see pic 1):

 

ANY other attempt at moving the SRB's down, to attach to the decouplers above center mass, results in the SRB's attaching to central core, instead (see pic 2):

 

Just to verify this was not the graphics issue mentioned by Plusk, I tried a quick launch and decouple with the SRB's attached as in pic 2...BOOM! The SRB's decoupled...by exploding! LOL!

So gang, what the heck am I doing wrong? Why can't I get the SRB's to attach to the decouplers where I need them for clean separation (or, more interestingly, anywhere I want within reason)? Keep in mind that the positioning of pic 1 was the only position that the SRB's would attach to the decouplers and not the central core itself...no amount of upward or downward movement of the SRB's resulted in an attachment to the decouplers beyond that one position. S-I-G-H!

Vic the Newbal

Sorry - didn't see that my suggestions were causing problems until just now.

Yes, as @Foxster has very clearly shown, you need to place the decouplers normally, but a bit higher than you want the SRBs to end up, then add the SRBs centrally (no other option), then use the offset tool to move them down.

The offset tool will tend to make the SRBs jump in or out a touch (there is some invisible grid that the offset tool seems to follow). You can correct this by deactivating the "snap" function (default key: C) then finalising the offset, to make sure that all the parts are indeed touching.

[strider3]

See, I knew I was missing something. Thanks and I'll let ya know.

Vic the Newbal

[Nich]

Let it be known if you get mysterious rotating forces on your rocket you may want to try double strutting to keep things perfectly straight.

 

[strider3]

Those gizmos work perfectly. I really had no idea what they were for...I do now!

Thanks much, gang!

Vic the Newbal