Quick RCS question: 3-thruster symmetry? Strange rotation?

[User Unrelated]

I am using a mod that includes triangular trusses, and I really love their aesthetics

But... with a tri-truss, you really can't use quad symmetry, which I remember seeing as being recommended for RCS thrusters.

I've noticed that when trying to rotate the craft, I will get strange rotations about the axis of the ship (as if I had hit the Q button to spin like a top)

and I end up having to waste more fuel to stop these rotations that I never get with quad-symmetry thrusters.

Am I just doing something wrong? or is there maybe a mod I could install that would include triangular RCS thrusters?

it isn't a HUGE deal, it still translates fine, and is actually good for docking with lighter craft (like my docking practice satellites, essentially an RCS tank with a dock-o-tron on either end), because the thrust vectors aren't parallel to the desired direction, so a portion of the thrust is bled into canceling out the opposite portion of the thrust coming from the other RCS thruster that is engaged. it makes controls nice and fine.

thanks! If I'm just being dumb, forgive me.

here's a picture of my docking practice satellites

[Stratoroc]

I think it's because two thrusters are used in a rotation. For example in your pic if the nose turns to the right the top and bottom left thrusters fire. However the bottom thrusters are angled so a torque that isn't balanced is created because the bottom thruster fires up and to the left. You need either SAS to counter the torque or rotate the ship such that the active thrusters are symmetrical about the plane on which you are maneuvering.

Really this is a small-ish scale of the same problem due to unbalanced rcs placement for translation that plagues ships during docking.

Hope this helps any.

[User Unrelated]

it isn't that big of a deal when they're all docked together, I realize that if they're all at different angles like that, then it isn't going to work well

but when on the way up, trying to fix orbits, and maneuver that whole tank/booster/satelite combo on the right, it just spins all over the place.

I have an SAS module in there.

I built a station today to go drop some landers on the moon, and scan for kethane, and I solved the problem by just using round parts where I want to put the RCS boosters...

I think this is just something I'm going to have to deal with

[Starwaster]

yeah have to agree. that's not good symmetry, and if the RCS is also unbalanced then you're doubly hosed.

so, first go get RCS balancer so you can get visual feedback on how to balance your RCS in the VAB/SPH. Then do what I did and kick yourself for waiting so long to get it.

but then theres the tri- symmetry.... maybe split the truss with a round part you can mount 4 RCS on. or put two such pieces on the end of the truss to mount on.

but i'm a big fan of using just 4 on the CoM

[lammatt]

because ur control is cartesian style?

ie, x-y-z axis

and having the rcs providing thrust along those three axis makes more sense

[RoboRay]

You need four-way symmetry for smooth, efficient RCS translation. Or, a reasonable approximation of it. On many of my craft, I use two RCS quads and a pair of linear thrusters beside them, like this:

If you do this, with one set on the "horizontal" (to the yaw or Y-axis) flat side of the truss and another on the opposite corner of the truss (and make sure the thrusters are parallel to the opposing side's thrusters), you will have two thrusters pointed down each "cardinal" direction of the X, Y and Z axes. This provides equal thrust in each of your translation directions, with no thrust wasted working against other thrusters.

Edited August 16, 2013 by RoboRay

[Keome]

Your RCS needs to be balanced in all three axis (X Y Z) in order to keep it stable.

[Haze-Zero]

Check out the RLA RCS pack, I can not recall which one but one of them has RCS thrusters in different angles and one has a 5 port RCS thruster which I find immensely more useful than the stock 4 port thruster. It maybe worth looking into.

http://forum.kerbalspaceprogram.com/showthread.php/24593