How do I drop Kickback SRBs?

[Morgan927]

I have four Kickback SRBs strapped of the side of a liquid stage.  I have tried attaching with TT-38K, TT-70, and the hydralic decouplers....when I stage to the liquid engine, the SRBs do not drop off and there are a lot of explosions as I ascend.  How best should I couple/decouple a long SRB?

Edited March 17, 2017 by Morgan927
typo

[Allocthonous]

I find that the basic decoupler works just fine, but there are some caveats. It needs to be located at least 3/4ths of the way towards the top of the kickback. The bottom of the engine also needs to be about level with the bottom of your central stack, or lower. When you decouple, this will kick the top of the booster away from your rocket safely.

[WanderingKid]

My guess is you didn't center the kickbacks onto the staging component.    So, they're probably actually attached to the liquid tanks directly.

One of the things I've found is you have to make sure where you've grabbed the SRB (where your mouse is) you need to make sure it's on top of the decoupler.  The way to really make sure it's attached is once you've hooked the SRB on, grab the decoupler, and if they both come off at once, you're hooked up right and you just need to make sure the staging is straight.  If you only get a decoupler on your mouse key, you're not hooked on right.

So, check your model in the hangar, and then if you're still having trouble, can you post a screenshot with your staging?

[Eklykti]

Best way to attach side boosters and have them fall away cleanly is to make sure than a decoupler is slightly above the booster's center of mass. This can be achieved by using the offset tool to move the booster downwards after attachment.

This way, when you decouple, upper point of the booster will go away first, and then the aerodynamics will help it separate.

But, also make sure that the attachment point is not too far up, because then when you decouple, it will rotate around it's center of mass and it's bottom point may collide with the rest of your rocket.

[Vive_moi]

Time to time (when I have central engine's fins really close to the SRB), I make the above suggestion and I decouple the boosters about 1s before the SRB entire burn. This way, the decoupler will incline the SRB slightly outward and its motor will push it away. But, be careful, you must not have anything in front of the SRB as it will go away with very high TWR. (Don't work with LFO engines that will stop immediatly.)

(In real life, the boosters are decoupled before their entire burn (but also for some other reason.))

See you,

Vive_moi

Edited March 17, 2017 by Vive_moi

[Kryxal]

I tend to make a subassembly consisting of the spaced decoupler, the kickback, a rounded nose cap, and a seperatron attached to the nose cap so it thrusts up and slightly in.  Attach that to whatever, one strut to steady it, and it works just fine.

[Morgan927]

6 hours ago, Eklykti said:

Best way to attach side boosters and have them fall away cleanly is to make sure than a decoupler is slightly above the booster's center of mass. This can be achieved by using the offset tool to move the booster downwards after attachment.

This way, when you decouple, upper point of the booster will go away first, and then the aerodynamics will help it separate.

But, also make sure that the attachment point is not too far up, because then when you decouple, it will rotate around it's center of mass and it's bottom point may collide with the rest of your rocket.

The next stage's CoM or the whole rocket?  I will not be able to put it that high.....bummer.

[Nicias]

Just the kickback's CoM.

[Eklykti]

3 minutes ago, Morgan927 said:

The next stage's CoM or the whole rocket?  I will not be able to put it that high.....bummer.

CoM of the stage you are trying to drop away

Edited March 17, 2017 by Eklykti

[Morgan927]

1 hour ago, Kryxal said:

I tend to make a subassembly consisting of the spaced decoupler, the kickback, a rounded nose cap, and a seperatron attached to the nose cap so it thrusts up and slightly in.  Attach that to whatever, one strut to steady it, and it works just fine.

I have no idea what a seperatron is.....

[Eklykti]

5 hours ago, Vive_moi said:

In real life, the boosters are decoupled before their entire burn (but also for some other reason.)

IRL the SRB thrust is not cut out instantly, because there are some leftover chunks of fuel, but at some point it's thrust becomes so low that it can't accelerate own weight, and usually it's dropped at this point while still burning.

[Aegolius13]

24 minutes ago, Morgan927 said:

I have no idea what a seperatron is.....

The Sepratron is a tiny little rocket motor that burns for just a couple seconds.  It can be useful for helping separate stages where a decoupler does not supply enough force.  

It's probably not necessary for just a Kickback, though.  I usually use a TT-70 set about 2/3 the way up the SRB, and that's enough to get the spent stage clear. 

[Morgan927]

10 hours ago, WanderingKid said:

My guess is you didn't center the kickbacks onto the staging component.    So, they're probably actually attached to the liquid tanks directly.

One of the things I've found is you have to make sure where you've grabbed the SRB (where your mouse is) you need to make sure it's on top of the decoupler.  The way to really make sure it's attached is once you've hooked the SRB on, grab the decoupler, and if they both come off at once, you're hooked up right and you just need to make sure the staging is straight.  If you only get a decoupler on your mouse key, you're not hooked on right.

So, check your model in the hangar, and then if you're still having trouble, can you post a screenshot with your staging?

Sure enough!  I grabbed the decoupler and it came away by itself......I have fixed it and it works!  Thanks

[Spricigo]

 

Another trick to make the separation cleaner its to put fins, on the radial boosters. The drag of the fins will push the booster behind and, if placed in some ways, case the desired rotation (up side moving away) in the booster.

[bewing]

5 hours ago, Morgan927 said:

I have no idea what a seperatron is.....

It's at the very very top of the tech tree. So if you are in career mode you never have it anyway, so you don't need to worry about it.

 

[Capt. Hunt]

On 3/17/2017 at 3:40 PM, bewing said:

It's at the very very top of the tech tree. So if you are in career mode you never have it anyway, so you don't need to worry about it.

 

No, you should get it towards the middle of the tech tree, it's under precision propulsion.  Sepratrons are tiny solid motors with only 4-5 seconds of burn and 8 units of fuel.  They can be attached radially and can be pointed in any direction, so they are good for kicking a spent booster clear of your stack to prevent it from colliding as it tumbles away.

[Kryxal]

I think it's a dead-end tech tree node, so you might not think to unlock it until late, and it can be considered to be "at the top" (as in vertically, in the propulsion section).  It's a cost-160 node in the tree.

[Spricigo]

20 hours ago, Kryxal said:

I think it's a dead-end tech tree node, so you might not think to unlock it until late, and it can be considered to be "at the top" (as in vertically, in the propulsion section).  It's a cost-160 node in the tree.

Considering it "at the top" will just cause confusion. Using this reasoning I may consider anything I choose to research later at the top, resulting in odd conclusion like "the more advanced engine in the game its the Juno".

That said:

The node Precision Propulsion contain a few small engines and a small fuel tank, also its not required for other nodes. While I see why someone may consider it not so necessary/usefull, my perception its quite the opposite.

[Waxing_Kibbous]

Just to reiterate, make sure the SRB is attached properly to the decoupler, this used to get me too when I first started.

I attach the kickback like this: I put the decoupler with the standoffs, the TT-70, a bit higher up on my first stage and attach the kickback. Then, using the translate tool, move the kickback down the decoupler so that the decoupler is about 25% down from the top of the the SRB. Then I adjust the decoupler position using the translate tool so that the bottom of the SRB is below the first stage engine. Lastly I secure the bottom of the SRB with a strut. I usually top it off with a cheap nosecone as well. If you want I can build one and attach a pic if the above isn't too clear.

Edited March 20, 2017 by Waxing_Kibbous

[Loren Pechtel]

On 3/20/2017 at 1:35 PM, Spricigo said:

Considering it "at the top" will just cause confusion. Using this reasoning I may consider anything I choose to research later at the top, resulting in odd conclusion like "the more advanced engine in the game its the Juno".

That said:

The node Precision Propulsion contain a few small engines and a small fuel tank, also its not required for other nodes. While I see why someone may consider it not so necessary/usefull, my perception its quite the opposite.

The rest of the stuff with it I have almost never touched but for bigger rockets the separatron is basically essential, especially if you play with stage recovery.  (Even if you get clean booster separation they're likely to collide with each other after separation, thus preventing their recovery.  Kicking them away under power avoids this and is well worth the price.)

[bewing]

Nah. A single fin is enough to get you clean separation, and costs you 25 kash. A separatron is just silly overkill.