orbital construction

[mpace1217]

So I've built a science ship that I was planning on taking to duna after knocking out kerbins muns.I built it in orbit with two modules, it was fairly easy but I cannot steer the completed ship for the life of me. I even downloaded KAS so as I could see if it was the wobble that was getting me, but it wasn't and now I dont know what to do. Every time I accelerate the ship starts spinning everywere. also ive made sure that the other engines are off, and I went through and tried all kinds of combinations of which reaction wheels should be on so those cant be the problem. It does have the prograde and retrograde marker backwards dont know if thats related, anyways I've now built two different designs and have the massive very expensive ships in LKO but am unable to take them anywhere at all. I can give the design if needed but it really simple, its just a poodle with a rocko x200-32 then some expirements and I've got the lander ready to attach but I really want to figure out how to steer the damn thing. any help is appreciated. 

[Alshain]

We won't be able to offer any help without seeing the craft.  Could be any number of things. 

A backward prograde/retrograde marker is usually an upside down probe core or you are controlling from a docking port somewhere instead of your intended module.  Right click on the probe or command module you want to control from and click "control from here".  If that doesn't fix it, the probe may be on upside down.

Edited May 14, 2016 by Alshain

[Venusgate]

Without seeing anything, I have a suspicion your load isn't balanced, and you don't have enough SAS to keep things steady. You saying "it's really simple, just one engine and a tank" AND "i even turned off the other engines" makes need for a picture necessary

[mpace1217]

I'll post a screenshot in a bit but after some reading on other threads I tried locking the gimbal and it stayed fairly true, just a little to the left or right of where I wanted and when I would correct it responded, I don't know if that's a common practice for large ships in space but it helped a ton. 

[Aubri]

I had a similar problem when I built a skycrane for moving structures around on Duna. It turns out the game has some trouble gimbaling "backwards" engines; the down-facing claw on my crane was taking control when it undocked (an artifact of the way I carried it to Duna), which caused the whole thing to spin on its axis when I lit up the radial engines. When I switched control to the up-facing probe core, everything worked fine.

I'd bet that your backwards core is the issue here. Try controlling it from a forward-facing part like a clamp-o-tron (with the gimbal free and all your reaction wheels online) and see if it steadies out.

[mpace1217]

http://imgur.com/aA6Y7la

this is one of the stations the other is very similiar but without the tri coupler and just a single tank up front, I  removed the front tank as i thought that was a big issue. I know its not a great design so go easy on me lol, but what is my catastrophic failure? if locking the gimbal is not a normal solution. 

Edited May 16, 2016 by mpace1217
clarity

[Aubri]

I can't really tell from the picture -- do you have those tri-couplers bolted together with struts? If not, remember that two parts will generally only connect at one point, so those couplers are probably only linked at one corner. That may be the source of your problem, because it will tend to flop around violently under any kind of acceleration. If you zoom in close and carefully increase the throttle, you'll probably see that the two tri-couplers are flexing through one another in flight.

The probe cores are another possible source of oscillation. It's a bit better, since they're centered, but they're also quite small compared to the rest of the stack, so they could also be a culprit. A set of struts bridging the gap might help that, too.

For the record, multi-docking is terribly tricky. If you don't have the alignment perfect, and I mean pixel-perfect, it won't link more than one of the ports. Even if it does, the docking ports get bugged half the time, so be sure you never want to undock again. You're almost always better off just using a Clamp-o-Tron Sr., or even just a regular C-o-T and a gentle hand on the throttle. Of course, there's also Kerbal Joint Reinforcement, which makes your rockets look and feel a lot more like professionally engineered spacecraft.

Edited May 17, 2016 by Aubri