Sepratron rockets

[-RanZ-]

Anyone have issues with sepratron motors? I have a rocket that has 3 orange tanks in the first stage, 1 in the middle and 2 radially. The 2 radial orange tanks have a total of 8 sepratron rockets on them that activate during staging and they work fine if I test them at really low altitude (<5000m) but this stage runs out at about 15000m and when I activate the stage the sepratron rockets just rip off the orange tanks and don't really do me any good. I have limited thrust down to 1.6 and the same thing happens. Not sure if this is normal behavior or if I should submit a bug report

[Alshain]

Sounds like the radial decoupler bug. The decouplers are applying a force that induces rotation for some reason and sends the decoupled item into the tank it's decoupled from. This is especially true for long tanks and SRB's because their top rotates inward and impacts the rocket. Sepatrons won't help with that, it's bugged, they just cause the problem to be worse because the added force causes the rotation to be faster. It really is a game breaking bug but we haven't seen a fix for it yet.

However, if you cut engines entirely before staging, they shouldn't have enough relative speed to destroy anything, wait for them to clear before firing the engines again.

[magnemoe]

Its very easy to put the tank off center on the decoupler, this will rotate the tank. In previous versions of KSP struts killed all decopler force and all tanks except the very small was strutted.

Decopler will also rotate tank vertical around its empty center of mass, for long liquid fuel booster this might be above the decopler

Seperatrons will not help with the rotation problem except moving the tank away from core, however the decopler aplies all force at once while the seperatron needs time.

[paul23]

Nah what he describes is even without decouplers true - I experienced it too. Activating too many sepratons at the same time on a low mass simply give s a way too high force/acceleration, and breaks the tanks (which then seems to implode).

[Alshain]

Its very easy to put the tank off center on the decoupler, this will rotate the tank. In previous versions of KSP struts killed all decopler force and all tanks except the very small was strutted.

Decopler will also rotate tank vertical around its empty center of mass, for long liquid fuel booster this might be above the decopler.

That's not how it worked in 23.5. It wouldn't make sense anyway since you can't see the center of mass (or dry center of mass) on a part your attaching. That would just be overly difficult to use.

[-RanZ-]

Sounds like the radial decoupler bug. The decouplers are applying a force that induces rotation for some reason and sends the decoupled item into the tank it's decoupled from. This is especially true for long tanks and SRB's because their top rotates inward and impacts the rocket. Sepatrons won't help with that, it's bugged, they just cause the problem to be worse because the added force causes the rotation to be faster. It really is a game breaking bug but we haven't seen a fix for it yet.

However, if you cut engines entirely before staging, they shouldn't have enough relative speed to destroy anything, wait for them to clear before firing the engines again.

I have noticed everything decoupled does spin inwards also. I guess I could copy the craft to another version, was this a bug introduced in .25? I have a bunch of older versions I can try. This is almost as annoying as the EVA ejection bug. Is Squad aware of the decoupler force bug?

[Alshain]

I have noticed everything decoupled does spin inwards also. I guess I could copy the craft to another version, was this a bug introduced in .25? I have a bunch of older versions I can try. This is almost as annoying as the EVA ejection bug. Is Squad aware of the decoupler force bug?

24.2 I think, they were trying to fix another decoupler bug for x64 clients and ended up breaking them in all clients.

[Heagar]

For me two on the top or the outer tanks - pointing 45 degree up and outbound are enough for stages two orange tanks high.

For the big tanks - expecially when used in conjunction with the engines LFB-KR 1x2 or S3-KS 25x4 (witch came with asteroid redirection) - i suppose:

• To place additionally two sepretons near the bottom pointing 60 degree up and outbound. Their exaust should not touch the core engine on an asparagus design during decopling or it will explode.
  
• Or to mount the core engine slightly higher up than the rest on an asparagus design. This way the rotations will occur under the exaust of the main engine.
  
• Or mount an modular girder segment to the decoupler first to increase the space between the core engine and the outer tanks/engines,
  
• 
  

[tg626]

Get RCS build aid and use it with the booster alone to find the DRY and WET center of mass, then use that to place your seperatons to push the booster sideways away from the core. It's a bit of a pain to dope it all out, but it will work.

With RCS Build Aid, you get this in the VAB:

Note the red circle showing the rotational force that will be applied.

But if you fiddle with the Sepratrons a bit, you get NO circle:

Which means when you launch, you get this:

I also have Tweakable everything installed and usually use it to max out the ejection force. (however, that's stock ejection force in the GIF above)

Edited October 23, 2014 by tg626

[-RanZ-]

I could deal with the problem by moving sepratrons to counteract the spin but the issue I am having is the spratrons rip off my orange tanks and just spin all over when I stage them

[tg626]

Craft file?

I just made 2 Orange tanks in the middle, and 1 tank on each side with 3 mainsails.

I put 8 sepratrons facing upward on each side tank.

While the side tanks tipped inward and collided with the bottom core tank and destroyed it, the sepratrons stayed attached...

Just did it again, with struts this time (duh)... No sepratron troubles, sep at 29000km

Edited October 23, 2014 by tg626

[Alshain]

Get RCS build aid and use it with the booster alone to find the DRY and WET center of mass, then use that to place your seperatons to push the booster sideways away from the core. It's a bit of a pain to dope it all out, but it will work.

That can't be the solution. Squad can not tell you the only way to make the game work is to download a mod. It's not just an inconvenience, it's show stopper. It makes them useless without the mod.

[justidutch]

I have been separating orange tanks and also the big ole S3-14400 Tanks, using the TT-70 Radial Decouplers and Separatrons with great success. It does take some testing to figure out exactly where to place the Separatrons, but it always works out in the end. Usually just two, one on each side at the top pointing horizontally away from the body of the craft. No pics at the moment (I'm at work) but I can post them later on if it would help to see an example.

[-RanZ-]

https://dl.dropboxusercontent.com/u/10641606/DunaIke%20Mk%20II.craft

fly it about 1/2 - 3/4 throttle until SRBs are spent, stage after outter 2 tanks are empty which is usually around 15000m, the sepratrons will just spin away from the tank

[merendel]

Claw worked up a fix for the decoupler bug in the last day or so. you could try useing that and see if the problem persists. you can find the fixes here http://forum.kerbalspaceprogram.com/threads/97285-0-25-Stock-Bug-Fix-Modules

[Levelord]

I fixed it for you: https://dl.dropboxusercontent.com/u/16683090/KSP/DunaIke%20Mk%20II.craft

The main problem is with the Hydraulic Detachment Manifold.

It's ejection force was so large that it shakes the side boosters apart from its separatrons and main engines. If I'm not mistaken, these large decouplers are meant for the largest tanks like the Kerbodyne S3-14400 Tank.

+ = OK

+ = Bad

However, the other 2 decouplers work fine with the standard orange tanks:

= ok

= ok

[-RanZ-]

seriously? I guess I didn't think of that... I will re-do my craft and give it a try.

[Kerbart]

Note the red circle showing the rotational force that will be applied.

Yeaaahhh, let's from now on call that torque, that'd be great.

[Kerbart]

The main problem is with the Hydraulic Detachment Manifold.

http://wiki.kerbalspaceprogram.com/w/images/thumb/1/1b/TT38K_flat.png/24px-TT38K_flat.png

It's ejection force was so large that it shakes the side boosters apart from its separatrons and main engines. If I'm not mistaken, these large decouplers are meant for the largest tanks like the Kerbodyne S3-14400 Tank.

You're probably on to something... challenge for "old timers" is of course that they are used to using the Hydrolic Detachment Manifold as the radial decoupler of choice for the orange tanks as the small ones weren't strong enough.

[Lheim]

Just use the editor to create an tank + engine combo empty of fuel, and note the height of the center of mass by eyeball. You can place yer seperatrons there in the full build later.

[tg626]

Yeaaahhh, let's from now on call that torque, that'd be great.

[REDACTED]

I fixed it for you: https://dl.dropboxusercontent.com/u/16683090/KSP/DunaIke%20Mk%20II.craft

The main problem is with the Hydraulic Detachment Manifold.

http://wiki.kerbalspaceprogram.com/w/images/thumb/1/1b/TT38K_flat.png/24px-TT38K_flat.png

I learned something new. I took the craft file and used MechJeb (which was already a part of the vessel) to make 2 launches. The one with the Minifold blew the Sepratrons off, the one with the Radial Decoupler didn't.

I'd have never thought of that!

Edited October 24, 2014 by tg626

[SRV Ron]

Something definitely changed in 0.25. No matter how I brace or mount the BAC style SRBs, they continue to rotate inward at the top upon staging in designs that slid off cleanly before. The fix for now will be tweaked sepatrons that just fire long enough to counteract the rotation.

And, as others have stated, save the hydraulic separators for the big fuel cans. Besides, they have a lot more mass then the others.

[Geschosskopf]

There is a very simple solution to the radial decoupler problem. By "radial decoupler problem", I mean the way that since 0.24.2, radial tanks have tipped inwards at their top ends and collided with the central stack.

The solution is to use 1 pair of Sepratrons facing horizontally outboard at the very top end of the radial stack. That's it, only 2 Sepratrons per radial stack, no matter how wide or tall the radial stack is. These Sepratrons keep the top end of the stack from tipping inboard. This works for all radial decouplers, and also for various amounts of strutting the radial stacks to the central stack.

There are many possible variations to the above general solution that you might find applicable to your particular rocket. For example, you might find that these Sepratrons work too well and cause the opposite problem of the bottom end of the radial stack rotating into the central stack. This is general only a problem if the radial decouplers are mounted high up on the central stack. If the radial decouplers are mounted near the bottom of the central stack, then the bottoms of the radial tanks will usually swing inboard safely below the nozzle of the central rocket. They might hit each other but won't affect the central rocket. But if this bothers you, you can adjust the arrangement of the 2 Sepratrons on the top of the radial stack. Options include:

• Slide the Sepratrons down the a bit from the top end of the radial stack
  
• Reduce the burn time of the Septratrons by tweaking their fuel down (this is usually a better idea than reducing their thrust)
  
• Slide the Sepratrons towards the outboard edge of the radial stack so less of their thrust is directed straight out from the central stack (you generally want to do this anyway to keep the Sepratron flames from hitting the central stack)
  

Personally, I build radial stacks as follows:

1. I always use the TT-70 radial decoupler. The height of this decoupler provides useful standoff distance between the radial and central stacks, to allow some pivoting of the radial stacks without hitting the central stack.

2. I mount the TT-70s as low as possible on the central stack, then build the radial stacks up, down, or both directions from there. Usually I build the radial stacks upwards only.

3. Each radial stack gets 2 and only 2 struts to the central stack, 1 at the top end and 1 at the bottom end. I only strut radial stacks to each other if they extend far below the central stack.

4. Each radial stack gets 2 and only 2 Sepratrons mounted horizontally at its very top end. These are usually 1 or 2 angle snaps outboard from the centerline of the radial stacks, to protect the central stack from their flames. Because of this, I have never yet had to tweak the Sepratrons.

This works so well for me that it's become my automatic standard practice and I have long since ceased to worry about the decoupler bug because this work-around is so simple. Most of the time the radial stacks come off totally clean without even hitting each other below the central stack but if they do collide, I don't care because by that point they're just debris and they don't hurt the central stack. Plus, all launches are better when punctuated by harmless explosions .

[Geschosskopf]

Here's a short video demonstration of how I outlined doing Sepratrons above.

It's something of a worst-case scenario in that the rocket is using the 5m SXT lower stage with the tapered sides so the NASA SRBs are leaning inboard to start with. Plus there are 12 boosters, each of which has 2 Sepratrons at the top, so the central stack is getting hit with 24 jets of flame. This are also 12 tail fins between the boosters and the main engine also flairs out at the bottom, so the SRBs have to be shoved away without hitting any of that.

Anyway, the boosters are attached on TT-70s mounted very low on the central stack, plus 1 strut at the top and 1 at the bottom, with the lower 1/4 or so of the SRBs sticking down below the central engine. The Sepratrons absolutely prevent the tops of the boosters from swinging in and hitting the central stack. They swing the tops away so fast that all 24 can't burn up the central stack (also, they're angled outboard a lot instead of straight into it). The boosters come together can collide under the main engine, but that just adds some entertaining but harmless explosions to the launch. The rocket went on to Eeloo and back no problem, without even losing a tail fin.

https://www.dropbox.com/s/k090kcta21q3p9q/Sepratron%20Demo.mp4?dl=0

[MarvinKitFox]

That can't be the solution. Squad can not tell you the only way to make the game work is to download a mod. It's not just an inconvenience, it's show stopper. It makes them useless without the mod.

It makes them useless unless you have brains to figure out that you want to place the thrust at/neat the center of mass, you mean.

Funny thing, that. If you place a strong thrust on an object, and don't bother placing it at the center of mass, it will rotate. Gosh!