What the heck is going on!?!

[W. Kerman]

I have a rover, but even with SAS off, SAS is steering it, (in circles). Help?

[Alshain]

Most likely Trim.  Press Alt+X

[W. Kerman]

Fixed, thanks

[Palaceviking]

1 hour ago, Alshain said:

Most likely Trim.  Press Alt+X

Please elaborate, this trim thing has always evaded my understanding. 

Yet somehow I have been able to get ssto etc nearly everywhere 

Edited October 2, 2016 by Palaceviking
Addition

[FullMetalMachinist]

1 hour ago, Palaceviking said:

Please elaborate, this trim thing has always evaded my understanding. 

If you're flying a plane that is naturally stable and has a slight nose-down tendency, you can use trim to keep it level instead of SAS. In that case, you would hold Alt-s until it keeps level without you having to keep tapping the 's' key. The longer you hold it, the more trim gets set. You can see this by sitting still on the runway and holding Alt-s and watching the pitch indicator in the bottom left of the screen. Reset by pressing Alt-x. 

The problem is it's fairly easy to set a little trim by accident and not know that it's set, so it seems like there are phantom forces or a bug. Seems like every few weeks there's someone asking a similar question as the OP, and usually the answer is Alt-x. 

Another thing to note about trim is that SAS will override/ignore it, so don't try to use both at the same time. 

[Plusck]

1 hour ago, Palaceviking said:

Please elaborate, this trim thing has always evaded my understanding. 

Yet somehow I have been able to get ssto etc nearly everywhere 

Trim is only really meaningful for aero control surfaces: it adjusts the "dead stick" point so that it corresponds to a given angle of the control surface in question. When flying, this means you adjust trim so that the aircraft flies level without you having to apply any effort to the stick. The amount of trim you need to apply will vary depending on speed, whether flaps are up or down, etc.

In KSP, you apply trim with alt-WASDQE so that your aircraft flies level without having to touch the controls and without SAS. If SAS is activated, the SAS control inputs will override trim completely. If you normally fly using SAS, you've probably never had any need for trim at all.

However, in KSP all control authority (torque wheels, aero control surfaces, and apparently wheels too) seem to operate from the same basic "control input". So if you apply trim while flying, the craft will start tumbling once you're out of the atmosphere. And it seems it applies to wheels too.

[Palaceviking]

I have a bizarre collection of kas related junkships on and around duna from semi failed rescue missions so this may help with the kind of uneven thrust issues you get with hand-made rockets thanks for the replies guy, still the most awesome forum i know.