Stop wiggling of light crafts / satellites when using reaction wheels

[Cairol]

This is not something serious, but I'd like to figure out if there is a solution:

When building very light crafts or satellites, when turning on SAS in stability mode those crafts / sats begin to wiggle a bit around their current orientation

as if the controller of the SAS overcompensates continuously, which is slightly annoying.

Heavier crafts are held steady by the SAS.

I mostly get this problem with light satellites (about 1t mass) with for example an HECS core with the integrated pretty weak 0.5 kNm reaction wheels.

Changing those three control values for the integrated reaction wheels did not help at all. Are those actually mappable to the common Kp, Ki and Kd parameters?

Is there a way to prevent this wiggling?

Edited September 20, 2015 by Cairol

[GoSlash27]

Cairol,

If there's a way, I don't know about it.

I think reaction wheel torque and control surface deflection range should be tweakable like we do with gimbals.

Best,

-Slashy

[InterCity]

Is there a way to prevent this wiggling?

Simply use smaller SAS. I think the HECS built-in SAS is enough.

[Cairol]

Like I said, I use the build-in reaction wheels and it's wiggling with those in the above mentioned example. (HECS core + 1t satellite)

[Superfluous J]

To stop the wiggling, I turn off SAS and hit time warp, stopping all rotation. Then I turn off time warp and rotation remains arrested, hopefully roughly where I wanted to point

But yeah, it's annoying that they wiggle like that.

[Cairol]

I normally keep SAS active when leaving the craft. Especially when it's a space station or a satellite that was optimally turned towards the sun.

I know KSP stops movement when a craft is not active, but it's just my paranoia...

The control values I mentioned in my first post are from the Stock Bug Fix Modules Mod. Didn't realize that until now.

Now that I know what they do, I'll play with them a bit more.

[moogoob]

There are settings in Mechjeb (if you're using that) where you can customize the amount of damping that the stability assist uses.

[Cairol]

There are settings in Mechjeb (if you're using that) where you can customize the amount of damping that the stability assist uses.

I only know MechJebs stability assist as part of the ascent guidance module and the one for rovers.

Is there another one that can be activated instead of SAS during manual space flight?

None of my satellites has MJ installed and I'd like to avoid this anyway.

I use MJ sometimes for automatic ascents or for precision landings.

[Kryxal]

Maybe turn some wheels off when you're station-keeping?

[moogoob]

I only know MechJebs stability assist as part of the ascent guidance module and the one for rovers.

Is there another one that can be activated instead of SAS during manual space flight?

None of my satellites has MJ installed and I'd like to avoid this anyway.

I use MJ sometimes for automatic ascents or for precision landings.

I forget where exactly in, but there a bunch of options to specify exactly how MJ does SAS. You can even have it use the default stock one. One of the options fixed this wobble for me in light spacecraft when mechjeb's SAS was freaking out but stock wasn't.

[Ripper2900]

Mechjeb has SMARTASS. That's it's version of stability. As some of the others mentioned, it can also be tweaked, but I've never had the need to do that.

The non-modded sas attitude hold is also much better at holding the direction stable then the specific modes like prograde, normal or target. Not sure why. Maybe it's got something to do with not adjusting to a continually changing setpoint?

[Cairol]

New findings:

The wiggling increases when being away from Kerbin.

At Mun or Minmus for example, it wiggles considerably, while in LKO it's perfectly stable with stock SAS.

So it seems it has to do with math errors the farther away from the mathematical center a craft is.

Feels similar like my "fluctuating orbital period" discovery at bodies outside Kerbin SOI.

Smart A.S.S. does a better job, but it also can't overcome the games inaccuricies in position/orientation calculation.

So I guess I have to live with it for ligther crafts. Heavier crafts are inert enough to not show this behavior.

Anyway. Thanks for your input, guys.

[TrooperCooper]

That might have something to do with the known phantom forces kicking in at low orbital speeds.

Slightly unrelated, but regarding permanent craft orientation towards sun or surface etc, I think you might like the persistent rotation mod, Cairol: http://forum.kerbalspaceprogram.com/threads/113507-1-0-x-PersistentRotation-1-0-0