Stability Assist Problem

[Benasaurus Rex]

Anyone else having problems with the stability assist not working properly
it keeps making my ships roll on launch

[jhendriks87]

what do you mean roll? as in flip?

[Gertjan]

It shouldn't do that.

Try to launch the ship with the stability controls *off*, and see what happens.
If you still roll, it is more a factor of the assist being incapable of keeping the craft stable, there is only so much they can do.

Add winglets/canards for low-atmosphere rolls, SAS modules or RCS ports (and fuel) for higher atmosphere and orbital rolls.

Also: make sure that your mass is distributed properly; one end being heavier makes you hard to control (i did that just today: i packed 2 sattelites, dropped one and changed orbits: it didn't go too well as i flipped; so i send the sat off on its own).

Finally: don't do too fast in thick atmosphere (below 20 km, roughly), if you go too fast, you will simply flip ass-first due to the airodynamics (the same that put you ass-first on reentry), no amount of control mechanisms can save you from a flip due to going mach 3 at 10 km up

[SievertChaser]

Probably rotate along the longitudinal axis. Or the guy has the jargon mixed up.

Are any of the control surfaces skewed? It's pretty difficult to achieve unintended roll.

[sal_vager]

Could be flexing, some struts should help, it's hard to know without a pic though.

[Manwith Noname]

ALT+X

[mreed2]

To be clear: If this is happening, your control systems (reaction wheels, most likely -- one is built into your command capsule, and more can be added) is being overloaded. In that case, it can't maintain the commanded attitude and bad things proceed to occur.

Solutions:

1) If the problem /is/ roll, as you stated in your original post, and you are having the problem almost immediately at launch, then you have one or more engines slightly out of vertical or horizantal alignment. This won't happen as long as you are bulding serially (one engine directly above another), and it won't happen with the first layer of radial (engines side by side, almost certainly with tanks above them) either, as long as you use "symentry" option in the VAB during construction.

But when you start adding a second, radial, layer (one engine in the middle, surrounded by 4 more, each of which has 2 /more/ flanking engines) you'll run into this. You really do need to be pixel perfect when creating designs like this or you'll have contrallability isseus.

2) If the problem is pitch or yaw (a much more common problem). The key question here is "Does the problem not occur if you just let it go 'straight up'?" If so, you are falling victim to areo dynamic forces, for which there are several solutions:

a) Easiest: With the nav ball set to "surface" (it is by default -- it will eventually change automatically to "orbit", but that's a way off into your ascent), make sure that the nose of the ship is always inside the circle component of the prograde marker (circle with cross-hairs -- it is the symbol that appears immediately after you take off). The prograde marker (in surface mode) shows the direction your ship is actually moving -- taking into account the effects of gravity. If your nose isn't pointing directly at the center of this marker, you are holding an "Angle of Attack" (AOA), and the slipstream will try to increase it further (if you are holding the nose 5 degrees above the direction of travel, the airstream will be trying to increase it to 180 degrees).

Note that there is no gurantee that maintaining a low angle of attack will actually result in you making it to /orbit/ -- it /can/, but it depends on a wide variety of factors and is very rare, even if you are atempting to achiee this. In most cases, it won't -- but you'll maintain control on your sub-orbital flight... :)

Also, note that maintain a zero degree angle of attack is the optimal path (lowest fuel consumption) to orbit, as it minimizes drag. But...

b) Next easiest: Add fins -- ideally fins with working control surfaces (which you won't have if you are just starting out in career mode). Place them as low as you can on your rocket, ideally on stages that will be dropped once you get out of most of the atmosphere (say, ~50-60k meters). Fins that have control surfaces will automatically be tied into SAS -- dramatically increasing your control authority. Even without control surfaces, though, fins will add lift and drag forces that will natually oppose the forces generate by changing your AOA (if you mount them below the center of gravity, at least), so they will help even without control surfaces.

c) Hardest: Add additional reaction wheels, positioned as close to the center of gravity of your rocket as possible. Like fins with control surfaces, all reaction wheels will automatically tie into SAS and work in consert to maintain your commanded attitude. In the atmosphere, though, aerodynamic surfaces provide much more stability at a lower cost (both $$$ and in term of weight).

[andylaugel]

Is your command module properly oriented? You should see all blue in the navball when your rocket is on the launch pad. Or the top half blue and the bottom brown when on the runway. If not, your vehicle may not know which way is up. But you do have one or a docking port in the proper orientation, you can left click on that and select "Command From Here."

Example: I need to switch control from the inline cockpit to the cupola module on the launchpad. Otherwise it'll point the wrong way if I tell it to go prograde.

http://steamcommunity.com/sharedfiles/filedetails/?id=589543519

[Benasaurus Rex]

When i said roll i was refuring to the rol in the staging box (bottom Left Of Screen) without sas on i can just manage the normal tweeks you get with pitch and yaw but it doesnt roll unless i try using the sas thought it might of been a glitch with the recent update

[Benasaurus Rex]

Originally posted by andylaugel:

Is your command module properly oriented? You should see all blue in the navball when your rocket is on the launch pad. Or the top half blue and the bottom brown when on the runway. If not, your vehicle may not know which way is up. But you do have one or a docking port in the proper orientation, you can left click on that and select "Command From Here."

Example: I need to switch control from the inline cockpit to the cupola module on the launchpad. Otherwise it'll point the wrong way if I tell it to go prograde.

http://steamcommunity.com/sharedfiles/filedetails/?id=589543519

I did turn the command module upside down to give a better fit on the launcher you think it could be the cause?

[andylaugel]

Originally posted by lawsonpearce:

I did turn the command module upside down to give a better fit on the launcher you think it could be the cause?

If the problem is just roll, and not pitch or yaw, probably not. Putting the command module upside down would just reverse prograde/retrograde and other markers and controls. Stability Assist should be okay though. It's worse on mine though, as the inline cockpit's idea of prograde/retrograde is 90 degrees off from the canopy's idea of those directions. (The inline cockpit is perfectly placed for driving on the ground though.)