M700 Survey Scanner and SAS Weirdness

[Srpadget]

I am finally starting to experiment with the resource system, and am seeing some odd behavior. I took one of my veteran off-the-shelf standardized probe/satellite designs, popped an M700 Survey Scanner on top of it, launched it, and ... noticed some seriously odd behavior with SAS.

If I set SAS to its default "attitude hold" mode, it behaves as expected for a small probe with more gyros than it needs: a brief transient of electrical, rocket nozzle, and attitude-rate activity while the SAS engages and locks down, followed by a rock-solid platform that requires basically no control input. So I know there's plenty of control authority available. However, if I set SAS to align with a maneuver mode, the satellite behaves ... unexpectedly. There is an ongoing "jitter" of large control inputs (power consumption presumably from reaction wheels, attitude rates all up and down the axes, and the poor little Terrier is quivering like an overexcited puppy), while the probe's alignment lazily drifts around a position about 5-10 degrees right-and-down from the maneuver node.

This behavior survives quit-and-restart of KSP. So it's presumably either something buggy in the .craft file or in my save as a whole.

Now, I can work with it just fine; as long as I've got the ability to hold attitude, I can just point the vehicle manually like back in the days before "point at maneuver node" was a thing. But I would rather prefer to have "lazy mode" be an option...and more importantly, it's a bit unsettling to watch my satellite drift off-attitude like an incipient dead hulk.

So, is this a known bug/issue with the M700? Or with SAS in certain vehicle configuations that I've just never run across before? Or did I just get (un)lucky with this design? (The probe is pretty basic and straightforward

Craft and save files on Dropbox:

https://dl.dropboxusercontent.com/u/36651676/Resource_Scanner_SAS_Problem/Resource%20Scanner%20Sat.craft

https://dl.dropboxusercontent.com/u/36651676/Resource_Scanner_SAS_Problem/ResourceScannerSatBorked.sfs

I would add a screenshot, but other than the attitude offset the behavior is kind of dynamic; I doubt a still image would really communicate it. I'll add that if anyone thinks it'd be helpful.

Edited September 15, 2015 by Srpadget

[Geschosskopf]

The "point in a specific direction" SAS things have always been bugged. I have this same problem with or without the M700, so I never bother using these commands. Most of my time in the game is from before these functions existed so I'm quite used to doing this myself. I tried using the "new" pointing functions when they 1st appeared to see if they saved me any trouble and they didn't, so I haven't used them since.

[Vegetal]

They are bugged for small craft, but they work fine for larger ones. Not necessarily large, kerbaled ships usually are large enough for it to work properly.

[Srpadget]

I generally only use attitude hold and maneuver-node pointing myself. And in career, the latter is only available with late-game cores. And by then I'm not usually doing much with small probes. So if they're bugged for small craft, that would explain why I haven't seen it before: I generally only bother with sandbox-mode "simulations" for larger, kerballed craft.

So this may well be the first time I've ever done anything particularly prolonged/involved with a small probe in sandbox mode...and hence the first time I've ever tried to use that SAS function on a small craft.

Which in turn means its highly unlikely that I'll ever see this effect "for real" (i.e., in a career save). Good to know.

[nothingSpecial]

You know, limiting torque fixes this problem. Helps me a lot.

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Well, not sure about complete fix, but oscilations become so miniscule that I can ignore them.

Edited September 15, 2015 by nothingSpecial