SAS Can't Handle Steady Error

[natsirt721]

In my experience (1000+ hrs) SAS has always had a really difficult time negating steady-state error.  As I understand it, SAS uses a PID controller to maintain a constant heading, and the wiki confirms this. However, the integral gain must be set to zero (a PD controller), because the system simply does not respond to steady-state error.  You can see this yourself with any spacecraft where the thrust vector doesn't intersect the CoM.  Setting the SAS and engaging the engines causes the craft to slew.  The SAS will stop the slew after a few degrees (depending on the strength of your control schema), but it doesnt even try to get the heading back to the original state, even if the control axes are not pegged.  It seems like the directional holds are slightly better at countering error but this may be blind optimism.  

If anyone has any insight into why this may be it would be greatly appreciated. 

[Azimech]

I agree that the one-size-fits-all solution is a bit unpractical for some. However once Squad would give in to requests for custom SAS setups I think they could start a separate section on the forum. There are multiple mods that allow you to adjust the PID settings yourself. 

One thing I've discovered with the newest SAS is that it all depends on how you build a craft i.e. CoM and lift/drag. Too much control authority doesn't help either. In my case it's a bit different, my engines produce vibrations which often confuse the SAS. I had to implement a stock autopilot solution for that.

[Snark]

Personally, I tend to view this as a feature rather than a bug, i.e. a challenge to either engineer craft that aren't lopsided, or else to develop piloting skills to compensate.

I kinda like that SAS is fairly dumb: if I wanted really smart automation, I'd be running MechJeb (which I don't, for precisely that reason).

What I didn't like about SAS, for the longest time, was its fairly poor PID tuning that kept causing all sorts of problems (jittering, overshooting).  Drove me up the wall.  Now that they've fixed that in 1.2, though, SAS now behaves exactly the way I like it: well-tuned without being overly "smart".

Just my own tastes, though; obviously other folks like different things.

[natsirt721]

I agree that the system is very kerbal in nature.  I was expecting more from the description of SAS than it was providing, and that disconnect was the source of my ire.  Also probably should have seen the 'get a mod' response.