1.3 SAS "wobbling"

[Tyko]

Since I shifted to 1.3 I've noticed that ships with SAS wobble frequently. It seems like SAS keeps over compensating and then trying to correct only to overcompensate the other direction. Sometimes the oscillations keep getting larger 

late others seeing this?

[Benjamin Kerman]

I belive that this problem was mostly fixed with the introduction of 1.2. If your rockets are still wobbling around, i suggest the usual: MOAR STRUTS!!!

 

[swjr-swis]

29 minutes ago, Tyko said:

Since I shifted to 1.3 I've noticed that ships with SAS wobble frequently. It seems like SAS keeps over compensating and then trying to correct only to overcompensate the other direction. Sometimes the oscillations keep getting larger 

late others seeing this?

This has existed since they made some changes to the SAS code for 1.2.x. I've not noticed it any worse in 1.3.0... but it's not any better either.

It seems to happen especially frequently in atmospheric flight when you switch from 'stability hold' to 'follow prograde' while pointing slightly outside the prograde marker - workaround: make sure to manually point more accurately at prograde first before switching SAS mode to avoid it from happening, or if you are already in it, switch back to stability hold to kill the oscillation first.

There's another more mild version of it that manifests itself like a continuous trembling of the control surfaces (you may need to zoom in to the control surfaces to see it), which basically makes the craft slowly move away from where it should be holding, be it stability or one of the markers. I have yet to figure out how to reproduce that one reliably, so no idea how to avoid or circumvent it.

[Tex_NL]

1 hour ago, Benjamin Kerman said:

i suggest the usual: MOAR STRUTS!!!

Yes, and no!
Struts in the right places can cure almost any oscillations. Over-strutting, and especially with autostruts, can actually CAUSE oscillations.

[Spricigo]

13 minutes ago, Tex_NL said:

Yes, and no!
Struts in the right places can cure almost any oscillations. Over-strutting, and especially with autostruts, can actually CAUSE oscillations.

Also, it often is a cure to an avoidable problem. Better to understood why the ship is wobbling (aerodynamic instability, control conflicts, weak joints) and avoid it in the first place.

Edited June 29, 2017 by Spricigo

[John FX]

As a workaround I just toggle SAS on and off until it settles down. Turn on, see some change in movement, turn off, wait until heading is nearly at desired point, repeat.

[bewing]

A partial cure for it may have been found by diomedea, but it probably can't be implemented in time for the next patch release.

 

[swjr-swis]

22 minutes ago, bewing said:

A partial cure for it may have been found by diomedea, but it probably can't be implemented in time for the next patch release.

Woot, 1.3.2 confirmed!

I'll be on the lookout, it'll be very welcome.

[Tyko]

3 hours ago, Benjamin Kerman said:

I belive that this problem was mostly fixed with the introduction of 1.2. If your rockets are still wobbling around, i suggest the usual: MOAR STRUTS!!!

 

Thanks, but it's not the rocket wobbling along its length I'm familiar with what that looks like. It's a rocket that's correctly auto-strutted that would have behaved just fine in 1.2.x which is oscillating in its course. It's not a large rocket either I'm seeing it in rockets comprised of a mk1 capsule, small sustainer stage and a single tank booster stage. Not long enough or big enough for the need for moar struts  

Ive been using the exact same autostrut layout for several releases and this behavior is new  

thanks for the input though 

1 hour ago, Spricigo said:

Also, it often is a cure to an avoidable problem. Better to understood why the ship is wobbling (aerodynamic instability, control conflicts, weak joints) and avoid it in the first place.

Yep. If it was a complex rocket I'd agree. I'm seeing this on the most basic of "mercury/atlas" style rockets. 

I also noticed that reducing gimbal down to 5-15% max helps a lot. This points to an issue with how SAS is using control authority rather than structural issues

[Spricigo]

 

BTW: how about some pictures?craft file?

[Tyko]

11 minutes ago, Spricigo said:

 

BTW: how about some pictures?craft file?

I'll have to de-mod a ship to send...running Ven's, Procedural Parts, etc. here are some pix

 

[Spricigo]

On top of my mind:

Disable roll control on the engines.

Maybe CoM a bit low. Compartmentalizing the fuel tank and setting higher priority on lower tanks may help to swift CoM forward faster.

[evileye.x]

Reduce gimbaling range on studs

[John FX]

AFAIK if you have advanced tweakables you can turn down the strength of your reaction wheels which sounds like the root of your issue. Your craft is too small for the torque and so you get wobble.

[Foxster]

In the last release or so there has been something jittery introduced when in level or prograde flight i.e. when little or no attitude or roll control is needed. 

It seems as though SAS is hunting and over-correcting for small deviations. 

One test is to launch vertically a simple rocket that has rear tail fins to prevent flipping and it will sometimes spin unnecessarily after lift-off. Disable roll on the rear fins and the issue disappears. 

[Tyko]

4 hours ago, Foxster said:

In the last release or so there has been something jittery introduced when in level or prograde flight i.e. when little or no attitude or roll control is needed. 

It seems as though SAS is hunting and over-correcting for small deviations. 

One test is to launch vertically a simple rocket that has rear tail fins to prevent flipping and it will sometimes spin unnecessarily after lift-off. Disable roll on the rear fins and the issue disappears. 

Yep. This is a good explanation of what I'm seeing. Reducing gimballing, SAS and roll control all are good fixes, but it sure seems like the sensitivity is higher in 1.3 because I've flown the same ship designs in 1.2.2 and didn't see this 

thx!

[Red Iron Crown]

On 6/29/2017 at 4:50 PM, Tex_NL said:

Yes, and no!
Struts in the right places can cure almost any oscillations. Over-strutting, and especially with autostruts, can actually CAUSE oscillations.

How do superfluous struts cause wobble? Must be some effect of which I'm unaware. 

[Tex_NL]

1 hour ago, Red Iron Crown said:

How do superfluous struts cause wobble? Must be some effect of which I'm unaware. 

HOW they cause it I don't know. But I do know they CAN. I've had it happen to my own game and about half a year ago it was mentioned and discussed several times on the forum.

In order to shore up a rather flexible station I applied a generous amount of autostruts. At first everything was solid as a rock but over time it started vibrating WITHOUT any SAS or control input. Slowly but surely the oscillations build up to a level where the station shook itself apart. Only by removing all autostruts I was able to prevent it from happening again.
I've seen very similar stories by others. A station, nice and steady. Never had a problem with it. Now the player docks a lander to it and suddenly it starts shaking itself apart. Turned out the autostruts from the lander legs auto connected to the heaviest part all the way on the other side of the station causing some kind of tension.

"Autostruts are evil! They are the spawn of the devil and should only be applied with extreme caution!"
The thought behind autostruts is just. But the need for them should be eliminated/fixed ASAP!

[Spricigo]

2 hours ago, Tex_NL said:

"Autostruts are evil! They are the spawn of the devil and should only be applied with extreme caution!"

The thought behind autostruts is just. But the need for them should be eliminated/fixed ASAP!

There is a issue(or issues) ,  but not nearly as cataclysmic as you want to imply. 

Autostruts induce oscillation and SAS induced oscillation are very similar.  Both generate a "restorative force"  that push the part/vessel through the "point of equilibrium"  and  do it all again and again. 

 

[KerBlam]

If I have more than one reaction wheel setup on my craft, usually some in command pod and another set of reaction wheels near the CoM of my third stage.

I usually set the larger one to 'SAS only' during launch and that usually gets rid of all the wobble during launch. Once I'm out of atmo I turn it back to 'Normal'.

It seriously helps.

 

[kermand]

I have this problem with my smaller probes, it i set SAS to prograde, the probe oscillates around prograde but never stabilizes.

I tound that having my center of mass far from the reaction wheel (or far from the command pod if it has a wheel) solves the problem.

 

[Spricigo]

7 hours ago, kermand said:

I tound that having my center of mass far from the reaction wheel (or far from the command pod if it has a wheel) solves the problem.

 

Odd.  For me is the opposite. 

[Tex_NL]

2 minutes ago, Spricigo said:

Odd.  For me is the opposite. 

And for a lot of people/designs it does not freaking matter. And that's exactly my point: There is no ONE solution!

Throwing more struts at a problem might help in some situations but may make others worse. Changing which reaction wheels to use (or not to use) could help but it might also do nothing or worse. The required solution is as unique as the individual problem . People should REALLY need to stop regurgitating the same old BS every time as if it is the hole grail.
There's nothing wrong with suggesting to add more struts or switching reaction wheels. But do NOT claim it to be THE solution. Because it isn't!

[Red Iron Crown]

8 hours ago, kermand said:

I have this problem with my smaller probes, it i set SAS to prograde, the probe oscillates around prograde but never stabilizes.

In my experience this is a result of having too much torque per unit mass. Try toning down the reaction wheel torque and see if it helps.

[Spricigo]

2 hours ago, Tex_NL said:

... exactly my point... 

I'd try to put it more politely,  but frankly don't think is worth so much effort of my part. 

You may or may not have a point. In any case,  the way up put it make me,  and I suppose lots of people,  simple don't care what it may be. 

Stepping in a civilised discussion and angrily call what other people said as 'BS being constantly regurgitated'  make you looks not like someone that can bring something valuable to the talk,  rather you stand out as the idiot that should be ignored. 

Hopefully forum etiquette are equal to game mechanics in two points:

1. It can be learned 
2. There is lots of people in this forum to teach.