Rocket spinning crazily out of control?

[YourEverydayWaffle]

I just recently made a rocket made to go to Duna, lightly modded. In the top 3 stages, it was IMPOSSIBLE to gain the Delta-V required at the right time to complete a Hohmann transfer with Duna, because the rocket would spin faster and faster upwards in direct relation with the throttle of the mainsail engine I was using. I was far out of the atmosphere at the time, but I had to use <25% throttle in order to keep the stupid thing stable. The main payload was roughly 20 or so tons, which probably didn't outweigh the mass of the fuel tanks (at least 63 tons in S3, 27 tons in S4) so the center of mass was low. I had SAS and RCS, yet that was still not enough to overcome the weird spinning pitch force. There aren't any major model collisions on the ship either. I CAN NOT figure this out. Please help! Thanks!

[aeronaut]

Could you post a picture of your rocket so we can see what you are talking about?

[YourEverydayWaffle]

Could you post a picture of your rocket so we can see what you are talking about?

http://imgur.com/Nee8mmo

The first image is of the second to last stage, and the second image is the first stage (which might not be all that helpful, but I didn't get too many screenshots at the launch)BTW, you may notice that mechjeb WAS equipped, but it was impossible to use that with the spinning. All I had up was Vessel information.

[AletzN1]

How about you put some Reaction wheels (AKA the new purpose of ASAS and SAS) or RCS, or Wings, all of them are sure to help you.

But if your problem is the first stage then put Reaction Wheels on the boosters the big 2.5M ones. the upper stages should be fine as long the craft has a command pod in it. As they have Reaction wheels already in them.

Edited October 20, 2013 by AletzN1

[YourEverydayWaffle]

How about you put some Reaction wheels (AKA the new purpose of ASAS and SAS) or RCS, or Wings, all of them are sure to help you.

Well... Wings don't work on 0 atmosphere, and I DID have reaction wheels and RCS thrusters on it.

[AletzN1]

well try with more reaction wheels and struts, just in case, you never know.

(sorry didnt read the rcs and sas part of the first post)

[AletzN1]

And also mechjeb is NOT the best at autopilot-ing sometimes it can glitch out, try doing it manual.

[lajoswinkler]

Well, how about turning on the SAS function?

With all those mainsails that use SAS, your rocket should keep going straight.

Also you might try actually flying the rocket without MechJeb. Damn thing destroys pilot skills every day.

[zxczxczbfg]

Also, you must ABSOLUTELY ensure that the center of mass is balanced directly over the center of thrust on EVERY stage of your rocket. If the CoT and CoM aren't lined up exactly, the result will be a pitching/yawing rocket.

[SDIR]

There's one thing I've noticed regarding high powered engines in KSP. If you don't strut them properly, sometimes they will actually shift sideways on the fuel tank and screw up your center of thrust (i.e. shift it up, down, left or right). Try strutting your mailsail to the fuel tank and see if that solves your problem.

[Oddible]

Try turning the gimbals off on your outer rockets.

[YourEverydayWaffle]

Well, how about turning on the SAS function?

With all those mainsails that use SAS, your rocket should keep going straight.

Also you might try actually flying the rocket without MechJeb. Damn thing destroys pilot skills every day.

The reason I didn't use SAS on the ascent is because with the really tall, floppy payload, it tends to wobble far out of the control ranges of SAS (which also tends to overcompensate). I see what you mean, but usually it is only the upper stages, not the lower ones that do a kamikaze-flip, when there is just one mainsail. The force of that flip is powerful enough to overcome that of multiple reaction wheels and RCS, which really stumps me... I try not to use autopilots with MechJeb, I just like to use it for maneuver plotting (which I really still haven't gotten the hang of yet. )

[BenHR]

I doubt this is the case for you, but yesterday I had some ships spinning wildly 'cause I left a joystick plugged in that I was using to fly some planes, and because it's old and loose it was giving a very slight leftward input. I thought it was 'cause of all the batteries I had, but nope.

[boomerdog2000]

Could your payload be too tall? If too much mass is out on the end of that rocket the gimbals in the mainsails won't be able to compensate.

[Hodo]

Your rockets Center of Mass (CoM) is to far from your Center of Thrust (CoT). All your weight is at the or near the top of your rocket and all your thrust is at the back of the rocket. Without your SAS on your rocket will tip one way or the other, and with all that weight when it flexes your engines are no longer in line with the CoM and this is what is sending your rocket out of control.

There are two ways you can fix this.

1- Add more struts to your rocket making it a far more ridged structure.

2- move your payload closer to the middle or bottom of your rocket (which isn't always possible)

[LeFudge]

Yeah ive had my Mainsails start jimmying around under the jumbos. I recommend trying a skipper.