New version ejection force

[Knyght]

So after messing around with this for a while I decided to buy it because it is awesome and such.

With the new version having much lower ejection forces on the radial decouplers I\'m not sure how to design my rockets any more. My previous designs worked just nicely, but now all my boosters scrape down the side of my rocket and usually take out the central engines when they\'re ejected.

Since I prefer to use the stock parts for everything, I\'m not sure how to design stuff now such that my boosters and other objects are cleanly ejected.

So what is a good way of doing this without modding or having to work by trial and error all the time just for a simple orbiter?

[Corax]

So after messing around with this for a while I decided to buy it because it is awesome and such.

With the new version having much lower ejection forces on the radial decouplers I\'m not sure how to design my rockets any more. My previous designs worked just nicely, but now all my boosters scrape down the side of my rocket and usually take out the central engines when they\'re ejected.

Since I prefer to use the stock parts for everything, I\'m not sure how to design stuff now such that my boosters and other objects are cleanly ejected.

So what is a good way of doing this without modding or having to work by trial and error all the time just for a simple orbiter?

One way might be to experiment with the centre of mass of the stages you want to eject - try to put the radial decoupler at a higher or lower point of the stack than where it is now, and optionally an additional strut at the top or bottom; this may help with how the ejected stage clears the stack.

Another thing that may help is to experiment with throttle and delay; instead of decoupling under full thrust, try throttling down a bit before staging, and/or wait a second or two.

It may also be worth considering to reduce the amount of overall radial staging - try to time the engines of a stage so they run out of fuel at the same time, and separate from the whole bundle at once.

[sal_vager]

Hi Knyght, I haven\'t had much trouble with the lower ejection forces, most of my boosters are attached either in the middle with a strut or 2 for strength,or only at the top with a strut at the bottom.

With the radial decoupler half way up the boosters seem to fall fairly evenly, and with them at the top they seem to kick away just enough not to hit my rocket, I think if they are mounted too low the top of the booster would hit me when the bottom gets kicked outwards.

How do you have yours set up?

[BillWiskins]

It won\'t help your thrust-weight ratio much, but if you cannot find any more efficient way around it you could try mounting the decouplers on decouplers. Never been an issue with me, but it could give you the extra clearance you\'re after.

[Knyght]

Hmm well my setup is similar to the basic design on the wiki. A rocket with capsule, SAS, thrusters+fuel, some fuel and a liquid engine on the bottom. Then a tri-coupler with three 5-high stacks of fuel with liquid engines on the bottom of each. Then there\'s boosters strapped to the fuel with radial decouplers. This is the bit that seems to be failing. The setup here is currently that each booster is held with it\'s own decoupler, in three rows of 6. When the bottom 6 burn out, they are decoupled (and often here the engines get taken out). This repeats in turn. Often the entire thing explodes on the second or third decouple.

I\'m using SAS from pre-liftoff so everything is nicely vertical when things fall off. I\'ve also tried using less boosters.

[sal_vager]

Ok it\'s hard to picture your rocket in my mind

Something I find when I use the tricoupler is the 3 stacks of tanks try to move around a lot, and they need bracing round the bottom with struts, their movements can often be enough to hit your boosters when they drop, especially as the load on those 3 stacks changes when the boosters expire.

[Knyght]

Yeah I have struts on the tanks already.

I\'ve attached the craft. It\'s actually a bit overpowered for just an orbiter but I want to expand on it for other stuff. Also the placement of stuff is a bit whacky buecasue I\'ve been experimenting the the placement of boosters on the struts to no avail.

[sal_vager]

Ok I see the issue, you only have 1 strut at the bottom, if there were meant to be more they didn\'t \'take\'

This is allowing your central 3-stack to drift around a lot, it\'s only the SAS at the top of each that\'s preventing the rocket disintegrating for so long.

I added struts and successfully dropped the second ring of solids but the 3rd set still took the engines off, they were held at the top and they spun slightly as they fell away.

They fall past a lot of rocket before they get clear, so I think your best option is to mount them lower down, you can put solids on other solids, just make sure they are kept under control with a strut to each.

Update: I fixed it I think, I have changed your ship as little as possible so you can see how close you were to a successful design

[Knyght]

asdfasdfasdf. Those struts randomly seem to either dissapear or detatch. But yes, even with the strust back on properly, I get the same thing.

I suppose mounting the boosters lower down will fix it, hopefully it won\'t mess up the balance.

[Knyght]

Mmm, even moving the boosters as low as I could the second set wiped out two of the engines

[sal_vager]

I uploaded what I tried to fix your rocket above, can you give it a go and see how it differs from your own fixes?

[BillWiskins]

Gah, beaten to it. Anyway, I am not the most qualified rocket engineer around here, but I toook the liberty of reconfiguring your Orbiter a little so that it can make orbit without SRBs... if you can\'t solve a problem, best to just avoid it, I say

I don\'t know if it\'s helpful, but here\'s what I have:

[sal_vager]

Hi Knyght, I have been playing with your rocket some more and found it has a love of doing cartwheels, this was very easily fixed with 3 wings fitted to the bottom between the solid boosters.

They kept the orbiter controllable almost all the way to orbit but they lose traction as the air gets thinner.

So I put 3 RCS thrusters in the gaps beside the wings, they were enough with the upper stage thrusters to give good control when circularizing the orbit, I didn\'t need them at all until after cutting the drive when the Apoapsis hit 80k.

Your booster stage is pretty good, I had to jettison the thing early so it\'d burn up, and it could have easily got me to a high orbit, the upper stage was able to finish the orbit with almost all it\'s fuel remaining.

Edit:

I have your ship in a 3k meter orbit around the Mun with more than enough fuel to get back to Kerbin, you call this a simple orbiter but it\'s so close to being Munar landing capable

[Knyght]

I solved most of my problems by creating a completely new design. I am now working on something with legs and so forth for Munar playing.

Now of course I need to figure out how to get to the Mun. All my orbits of Kerbin seem to be slightly out, they\'re not perfectly horizontal around the equator so it\'s time to do some learning and figure out how to either correct my orbits or orbit better in the first place. Fun times ahead.

Anyway, thanks for the help. I\'m not exactly surprised you managed to get it to the Mun. It\'s pretty overpowered really. But it\'s more down to skill than boosters for me until I figure out these astrofizzix. I\'m still working on my orbiting techniques :x

[sal_vager]

I\'m glad you got it sorted out knyght, we\'ll help if you ask but trial and error is fun.

And thanks for your ship, I can\'t land it on those wings but I have been testing just landing on an engine reinforced with struts, seems to work on Kerbin and it\'ll let me keep your rocket as close to your original design as I can.

Good luck orbiting

[marko dash]

you could always spin your ship up to help radial mounts fling away

[Ydoow]

Hey guys.

Just so we\'re fully informed (I didn\'t see this mentioned before), decoupler forces we\'re actually increased from the last version.

But yes, you are right they 'seem' weaker.

What happened is that Harv incorporated Newtons 3rd law into KSP, opposite and equal forces opposite and equal reaction.

In the demo version decouplers would just shoot backwards, in the paid for version decouplers push against your craft and then shoot backwards, in effect actually pushing your craft upward slightly.

This makes decouplers appear as if they have smaller ejection forces.

Technically, they still had the same data value, however the act of pushing against the craft made them 'distance themselves' from your craft less.

Harv noted this and actually increased the force of them, however many people like you (and me) still feel like they\'re underpowered.

So, that\'s just the fully story behind why and what\'s happening.

You can change this by adjusting the .cfg file (very simple and not game breaking) value to your heart\'s desire.

I definitely had to adjust my craft design when the update came out, a lot of my boosters would clip my craft and take half of it out

[sal_vager]

Ydoow, while that is true, it should have had no affect on radial decouplers that are symmetrically mounted.

Any force felt by the rocket would be canceled out by the equal force on the opposite side, with no where else to go the ejection forces would be transferred into the boosters.

KSP is acting as if the rocket is being moved sideways slightly, but with the equal and opposite force from the other decoupler this shouldn\'t be happening.

This effect might be true if the rocket itself were being crushed as a consequence, but I don\'t think KSP is modeling things to that extent.

[SynMonger]

The issue is very easy to solve. Since none of the parts are balanced yet, it\'s not cheating to go in the part.cfg and edit the ejection force to 500-1000.

This should give you plenty of clearance.

[togfox]

I\'ve ajusted my ejection force to 600 and there is no noticable effect. SRB\'s positioned high up on the stack tumble straight down and take out the bottom half of my rocket.

[sal_vager]

Yeah I have noticed this as well, and another strange thing, try changing the RCS thruster weight, I made mine 10kilos and covered a rocket in them and it made no difference at all.

Maybe those new modules for stock parts override the cfg?

[UmbralRaptor]

Yeah I have noticed this as well, and another strange thing, try changing the RCS thruster weight, I made mine 10kilos and covered a rocket in them and it made no difference at all.

Maybe those new modules for stock parts override the cfg?

In the case of RCS units, struts, and fuel lines, they\'re being (mostly) ignored by PhysX. All of them are effectively massless and dragless.

No idea about decoupler weirdness, though.

[Nibb31]

I\'ve ajusted my ejection force to 600 and there is no noticable effect. SRB\'s positioned high up on the stack tumble straight down and take out the bottom half of my rocket.

I haven\'t got time to experiment right now, but maybe it relates to the mass of the SRBs. A 1 ton SRB might need much more ejectionforce than an empty SRB that is 0.1 ton.

[togfox]

Nah - I worked it out - its the equal and opposite force thing. A 1000 force ejection looks the same as a 5 force ejection when placed on an immovable object (ie a super heavy stack).

I reduced my stack mass and my 1000 force ejection literally blew my craft apart.

[vexx32]

The ejection force should be equally applied to each side of the decoupler -- assuming it\'s in Newtons, 500N to the SRB and the stack itself. The actuall effect on the stack will be negligible, as its inertia and mass are so high that 500N would produce only a slight change, but the SRB itself, having such low mass should by all rights be flung off violently.