Rocket flipping?

[ContiX]

Every now and then I end up with a rocket that works exactly once perfectly (ASAS or SAS on, perfectly straight up, orbit, landing, everything), and then stops working for every launch afterwards.

By stops working, I mean between 1000m and 2000m, decides to behave as though the ASAS/SAS were turned off, and start spinning wildly. I don't mean as though I'd held down Q or E, I mean it leans to one direction (generally forward or to the right) with no warning, and is entirely out of my control.

Someone told me it had to do with SAS, and how it's apparently bugged a little in 0.17, but why would it work perfectly once? I've tried restarting the program, going to the VAB instead of "Restart Flight" and then going back out...I've tried removing the SAS modules and flying normally (although I can't pilot worth beans), adding/removing struts, even changing engines. It usually happens with Mainsails, but I've had it happen with every larger-size engine (i.e., not the poodle or the tiny one), including boosters.

I'm at my wit's end here; this happens often enough that it makes me want to stop playing. Any suggestions?

(Oh, and here's a picture of my current rocket: http://i.imgur.com/SHkBC.jpg - Yes, I know I don't need that many struts, but I was desperate for some change))

EDIT: Here's the craft file: http://www./?wwytj2o7d8i8rb7

EDIT 2: Sorry, everyone. Thanks for all of the compliments on my design, and I'm sorry that I was ornery with you.

Edited October 17, 2012 by ContiX

[Vanamonde]

HarvesteR, the main designer of the game, has strongly advised against placing control surfaces at the tops of rockets. He says they're a de-stabilizing influence there, and he should know. That doesn't explain why it might work once, but it probably is at least part of why it doesn't work after that. Also, I don't think those vertically-mounted elevators on the sides of the outer boosters are doing anything but flapping in the breeze. That is one interesting, George Pal-looking ship, though.

On further examination, I have no idea what attaching struts to control surfaces like that might do to the stability of your ship. As the flap moves, it would apply torques to your booster stages. I don't know how much or what kind of effect that would have, but it can't be good.

Edited October 16, 2012 by Vanamonde

[ContiX]

I know the control surfaces on the sides don't do anything; most of what's on there was desperation. As for attaching struts to the flaps, it doesn't seem to move the things at all. The flap moves irrespective of the strut, as though the strut is mounted to something that's invisibly there.

EDIT: Removed the control surfaces and the winglets at the top. Does absolutely nothing.

Edited October 16, 2012 by ContiX

[Qumefox]

struts apparently don't have a physical presence except for the structural effects they have on other objects. I've tried to use a web of struts to catch stuff before, and said objects went right through the 'web' like it wasn't even there.

[TheDarkStar]

Based on the picture, remove all control surfaces and SAS modules. Your gimballing engines are enough, and the ASAS especially will often overcorrect and flip your ship. As long you use struts to hold together the top and bottom sections and between the heavier lifting stages, it should fly fine.

Edit: That RCS tank is really just extra weight, since your gimballing engines will do that for you in flight, and since the ship is smaller, rotating it while in orbit shouldn't be too bad on 2x-3x timewarp.

[NIN3]

and since the ship is smaller, rotating it while in orbit shouldn't be too bad on 2x-3x timewarp.

Um, once in orbit you cant use physics warp?

[Qumefox]

Um, once in orbit you cant use physics warp?

Yes you can.. alt-, and .

[SpeedDaemon]

Another thing you can try for setups like that is make a copy of that 2m engine, and remove the gimbal ability from the copy. Then replace all but the center stage with non-gimballed engines. That reduces the overcorrectiness/wobble of ASAS and MechJeb. Not sure if it'll help in this case, but it's something else you can try.

[ContiX]

Based on the picture, remove all control surfaces and SAS modules. Your gimballing engines are enough, and the ASAS especially will often overcorrect and flip your ship. As long you use struts to hold together the top and bottom sections and between the heavier lifting stages, it should fly fine.

Edit: That RCS tank is really just extra weight, since your gimballing engines will do that for you in flight, and since the ship is smaller, rotating it while in orbit shouldn't be too bad on 2x-3x timewarp.

I removed everything you said; it did absolutely nothing. 900m or so, and it flies over backwards. As for RCS, I only need it just for rotating the center tanks/engine and the lander; otherwise, it takes forever to do any turning. The lander by itself, sure, normal SAS is good enough.

Also, I feel dumb, but I have no idea what gimbaling means.

[Quasar]

Gimballing (aka. Thrust Vectoring) is when the engines point themselves in different directions to help you steer. Watch the big Rockomax engines when the ASAS is on: you’ll see them jumping about slightly. That’s gimballing. It makes steering that much easier when you’re thrusting, but too much of it can make the ASAS oversteer (it’s not the only thing that can, though. Not by far).

Based on your picture though, I'd guess your rocket is simply too top-heavy, with the thrust spread out too far away from center. Try counter-balancing with more weight in the center (extend the middle column downwards) and add some winglets to it's base (the extra drag will keep the rocket upright).

[AtmaStorm]

...That's a bizarre looking upper stage, I must admit.

Sometimes there is something wrong the design- but I've logged enough hours into this game to say that there times when all you can do is stare in bewilderment as your space ship decides to tumble.

My favorite glitch is when the physics engine doesn't completely register that you're in free fall, and the whole craft just ends up twirling end over end.

It's frustrating, especially when you spend a great deal of time on a rocket, only for it to start misbehaving midflight.

I rebuilt the important bits of the rocket using the picture as reference, and she flies just fine.

Sometimes the best thing to do is wipe the slate clean and rebuild.

[m1xte]

If you got your control surfaces in the top and your rocket tilts out of the steering range of the control surfaces its over.

Think of your rocket flying completely sideways. Drag from control surfaces and fins in the bottom will push bottom down, while control surfaces and fins in front will push the front down.

[TheHengeProphet]

Would you care to post a craft file? I believe a little physical testing might work out the kinks.

Also, can it fly without using A/SAS? I've had many a rocket work fine, but once you use ASAS, or SAS, it all goes to hell.

[ContiX]

Added to the op. I've tried flying without assistance; same thing.

[Qumefox]

I agree. posting the .craft file and us actually playing with it is probably the best way for us to tell you just what's wrong with it.

[nhnifong]

I think it's the wings. Have you ever looked at the center of lift for wings on a vertical rocket? it points sideways! and then if you grab the capsule and rotate it a little bit it changed direction completely. Wings are buggy black magic and should not be mixed with good old fashioned rockets.

[TheHengeProphet]

I seem to have fixed the issue with this craft. The first thing I saw when I looked at this thing in the VAB was... what were you doing with those fuel lines? Feedback loops are a huge no-no... That does some weird stuff. Anyways, two of three sides were not connected to the center stage with fuel lines, meaning your fuel would not drain evenly. That was your problem. I took the liberty of straightening out all of your fuel lines and making all engines burn on liftoff.

With the fixed setup, I got an escape orbit quite easily (almost got to the Mun with your ascent stage alone).

I find the RCS tank to be entirely unneccessary and believe you can get away with one small one, rather than that hunk of unused fuel. Other than that, I was surprised at how easily this thing flew and congratulate you on an impressive and unconventional rocket!

I wouldn't advise landing on anything with an atmosphere, with it, though.

[ContiX]

GAH!

Sorry, getting frustration out. I am 100% I checked the fuel lines because I watch the fuel tanks when I'm switching stages. Apparently at some point during troubleshooting, I disconnected the lines.

I've got the RCS Tank on the top specifically because I suck at piloting and I needed a little extra help reorienting.

EDIT: Sorry, was just feeling sorry for myself. This situtation happens a lot. Is there some way to manually reset the physics engine or something? Have you launched more than once?

Edited October 17, 2012 by ContiX

[TheHengeProphet]

Reset the physics engine? I don't know what you mean.

Yes, I have launched more than once, and aside from a little wobbling, the craft flies beautifully!

[edit]Keep in mind, I only fly manually on ascent. A/SAS in 0.17 is a nightmare with large ships.[/edit]

Edited October 17, 2012 by TheHengeProphet