RCS Translation not even

[Mazen]

Hey guys, I got a problem trying to dock a new module to my little spacestation.

It looks like this:

I marked my RCS-Thrusters red, in each case there are 4 around the construction. As you can see I choosed the RCS-Block-Thruster (Are they called like that? Whatever, I mean the ones facing in 4 directions )

When I push IJKLHN I expect my ship to go straight in on direktion. Translate forwards or backwards with H and N works fine, but when I want to translate in any other direction the long front end is faster than my Commandpod and I get in some kind of rotation which makes it unpossible for me to dock.

I think it's because the commandpod is heavier than the struts? And then the struts probably works like a long lever strengthen this effect.

How do I compensate that? ASAS would probably work but burns to much RCS Fuel. Is there another option?

[Vanamonde]

Moving the upper set of thrusters down would give them much less leverage. You could also replace the lower sets with the linear thruster variant, which only fires in one direction per thruster, but is stronger. Or, you could add more thrusters at the capsule end, but that's an inelegant solution that would add to part count and burn through your RCS propellant faster. However, it is possible to dock a ship like that, if you are prepared to counter-act the rotation with attitude burns after the translation burns. It's much more work, but can be done.

[capi3101]

You need to put a set in the center of mass of the whole module; I see sets at both ends but none in the middle. It's the middle set that will aid in translation. You've also got more thrusters (and therefore more torque) in the bottom set, so you'll probably need to add a second set near the top to compensate. Widening your module near the top to even out the distance of the thrusters from the axis of motion wouldn't hurt much either.

[ThePsuedoMonkey]

What I like to do is put a set of quads at the center of mass and a set of linear ones as far from it as possible, which will also let you isolate your translation and rotational maneuvers from each other by putting those in different action groups.

[Vanamonde]

Oopsie. Perhaps I should have read ThePsuedoMonkey's post before replying to it. Nevermind.

Edited May 2, 2013 by Vanamonde

[Mazen]

The idea to place another set of thruster on the center of mass seems to be a good idea. But apart from that it's really like trial and error to get the right position and amount of thruster on such an unshaped spaceship?

[Zephram Kerman]

What I like to do is put a set of quads at the center of mass and a set of linear ones as far from it as possible, which will also let you isolate your translation and rotational maneuvers from each other by putting those in different action groups.

That's a lovely idea! It basically makes two action groups into something like the ROT/LIN mode switch.

My technique is to put quads in the middle around of the Center-of-Mass. Since they are at the CoM, the thing is easily balanced and should not rotate during translation. (That is, unless the fuel tank is off-center. You did put the fuel tanks at the CoM, didn't you?)

Urr, also, I noticed a module in MechJeb2 called "RCS Balancer". I haven't messed with it yet though.

Edited May 1, 2013 by Zephram Kerman

[Mazen]

Thanks to all of you. I'll definitly try that out and give feedback

The fact that I can't orientate the dockingport on the station to north/south is making this whole thing even more difficult. I watched a lot of Tutorials but I think I need alot more practise.

[Alistone]

Just eyeballing it, the center of mass seems to be near the command capsule. The "Quick Fix" is to disable the top set of RCS thrusters.

If you still get excessive torque turning your ship when using RCS then disable the very bottom set as well.

With just the 1 remaining set that is closest to the center of mass you should experience less rotation during translation. The imbalance that is present should be small enough (with just the thrusters nearest the center of mass running) that ASAS can balance it out using torque from the command capsule.