SAS makes the craft shake

[Sokar408]

I don't know why this has all of the sudden become a problem, but for some reason whenever I turn on SAS now, the craft will start to shake from side to side, more and more violently. It'll get to a point where it isn't increasing the shaking anymore, but its like swinging 45 degrees from one side to the other at that point. Anyone know why this is happening, and how to fix it?

I am not using FAR, nor DRE (Both seems very buggy atm)

Edited May 17, 2015 by Sokar408

[Snark]

They did something to the control parameters for SAS in 1.0, not sure exactly what.

I've noticed that the problems seem to pop up if you have "too much" SAS torque authority.

For example, my standard craft for rescuing a kerbal from LKO is a Mk1 command pod with a hex probe core perched on top (so I can launch it unmanned). For reentry, it ditches tank + engine, so it's basically just the pod, probe core, and chute coming down.

The command pod has 5 units of torque, which appears to be way too much for 1.0 SAS, I get weird effects. But if I disable the command pod's torque and just use the probe core's (which is only 0.5) then it's fine.

I really wish they'd make reaction wheel torque tweakable, like they did for engine gimbal in 1.0. Right now, you can only set it to enabled or disabled, which is inconveniently constrained.

[JTpopcorn]

Disable reation wheels the sas is overcompensating itself to destruction.

[Nutter]

If you have a thrust vectoring engine and a high thrust-weight ratio, clamping down on the gimbal range also seems to work.

[Sokar408]

Disable reation wheels the sas is overcompensating itself to destruction.

Even with the Mk1 Command Pod's torque disabled, it does the exact same thing. The rocket goes completely straight without SAS, but swings itself out of control with it on.

If you have a thrust vectoring engine and a high thrust-weight ratio, clamping down on the gimbal range also seems to work.

What do you mean?

EDIT: If you meant limiting the gimbal on the engines themselves, then doing this, going down to 50% gimbal, lets the rocket fly a bit further, but the end result is the same :/

Whats really funny is, this wasn't a problem a few days ago, so and all I have done since, is install and uninstall FAR and DRE. I also did a complete reinstall after that, so that shouldn't have anything to do with it.

Edited May 17, 2015 by Sokar408

[DeMatt]

Does your rocket have any other sources of control? Steerable fins, RCS jets? Does it happen just after you've staged off a piece?

A pic of your craft would be helpful.

[Sokar408]

Does your rocket have any other sources of control? Steerable fins, RCS jets? Does it happen just after you've staged off a piece?

A pic of your craft would be helpful.

It happens more or less straight off the bat. There is no RCS, no fins, its early hard career, so I can't afford the part count.

The thing is, this probably occured as well, with a completely linær pod, fuel tank, LV 909, rocket. its like something is messing with the SAS. I have no MJ modules on the crafts, and I reset the trim several times, so no trim.

EDIT: I tried to remove the side rockets, and just let it fly as a linear rocket. It starts swinging out of control at 120 m/s

Edited May 17, 2015 by Sokar408

[Aerindel]

Yep. Its been this way ever since 1.0 Reducing engine gimbal to 30% seem to help. It also helps to only use SAS to hold a heading and not actually use any of the other features like prograde tracking.

Just item 10057 that was broken in 1.0.

[Sokar408]

Yep. Its been this way ever since 1.0 Reducing engine gimbal to 30% seem to help. It also helps to only use SAS to hold a heading and not actually use any of the other features like prograde tracking.

Just item 10057 that was broken in 1.0.

Holding heading, gimbal at 30%, completely linear craft: Pod, Tank, Engine. Cheated into orbit. Swings out of control after engine has been on for 10 secs.

[DeMatt]

It happens more or less straight off the bat. There is no RCS, no fins, its early hard career, so I can't afford the part count.

The thing is, this probably occured as well, with a completely linær pod, fuel tank, LV 909, rocket. its like something is messing with the SAS. I have no MJ modules on the crafts, and I reset the trim several times, so no trim.

EDIT: I tried to remove the side rockets, and just let it fly as a linear rocket. It starts swinging out of control at 120 m/s

I have to say, I'm not seeing any of this in a stock install. A replica of your center stack (with the service bay empty) flew perfectly straight with SAS on, right through to burnout of the first stage (didn't bother testing further). I could steer the stack without problem within the atmosphere, so long as I didn't get more than about 15 degrees off of prograde. If I oversteered, then SAS was unable to stabilize the rocket until the airspeed dropped.

Holding heading, gimbal at 30%, completely linear craft: Pod, Tank, Engine. Cheated into orbit. Swings out of control after engine has been on for 10 secs.

Tried that, only way I could force SAS to not hold a good heading was by asking it to aim at a wildly changing target, e.g. a maneuver node with only a small maneuver to perform.

Could you be mistaking "camera shake" for "rocket shake"?

[Sokar408]

I have to say, I'm not seeing any of this in a stock install. A replica of your center stack (with the service bay empty) flew perfectly straight with SAS on, right through to burnout of the first stage (didn't bother testing further). I could steer the stack without problem within the atmosphere, so long as I didn't get more than about 15 degrees off of prograde. If I oversteered, then SAS was unable to stabilize the rocket until the airspeed dropped.

Tried that, only way I could force SAS to not hold a good heading was by asking it to aim at a wildly changing target, e.g. a maneuver node with only a small maneuver to perform.

Could you be mistaking "camera shake" for "rocket shake"?

Yes in a completely stock install, this isn't happening. I'm atm trying to isolate what mod, or combination of mods, that are causing it.

- - - Updated - - -

I found it. The problem is with the "http://forum.kerbalspaceprogram.com/threads/97285-KSP-v1-0-2-Stock-Bug-Fix-Modules-%28Release-v1-0-2d-2-14-May-15%29"

Whenever these are added, the SAS stops working right. I suspect its the gimbalfix. I'll report back

- - - Updated - - -

It was indeed the GimbalFix. With this removed, SAS works probably again

Edited May 17, 2015 by Sokar408