smarter RCS controls

[Laie]

The need to set up a perfectly balanced RCS is starting to get on my nerves. My gripe isn't with balance as such, but that it needs to be perfect. CoM does shift after all, and once you dock two vessels all bets are off. Would it be possible to have a smart RCS controller that tries to utilize the available thrusters in such a way that you get rotation without translation and vice versa?

We already have something along these lines if we try to translate with SAS on. What I'm asking for is a solution that a) tries to minimize the forces before the PID controller even comes into play, and b) also works when rotating. The latter is probably not very important when you have strong reaction wheels, but hey.

[pandaman]

Maybe this could be a feature for higher level probe cores or more experienced pilots?  Or perhaps an extra 'Smart RCS controller' part, though I'd rather it be integrated into existing parts personally.

I believe the CTRL+Shift 'fine control' mode does this to a degree, but I find that it lacks enough 'welly' a lot of the time.

[eddiew]

I would like to see a better algorithm used here too. If I put ports at the front and back of the ship, then the game could calculate the CoM and automatically reduce the thrust of one of them so that a balanced translation happens. 

(Doesn't MechJeb have an RCS balancer? I feel like it's not actually that hard a problem...)

[RoboRay]

Doesn't Fine Controls already do exactly this?   You still have to build a ship that's reasonably balanced, though, since there's a limit on how low they can reduce the thrust and still accomplish anything.

Edited September 21, 2016 by RoboRay

[Alshain]

1 hour ago, RoboRay said:

Doesn't Fine Controls already do exactly this?   You still have to build a ship that's reasonably balanced, though, since there's a limit on how low they can reduce the thrust and still accomplish anything.

No, what Laie is suggesting is a form of throttle controlled balance.  If your pod would yaw to the right during translation left, then the force of the rear right jet would decrease and the force of the front right would increase to maintain translation balance.

I'm kinda back and forth on this myself.  On the one hand I like the challenge, but on the other hand it is translation controls so you would think it would translate and not yaw, pitch, and roll.

Maybe if it were a late tech tree part that was more intelligent than the early tier RCS it could work.

But it inherits a lot of complication.  What if there aren't two jets on any one side?

Edited September 21, 2016 by Alshain

[RoboRay]

3 hours ago, Alshain said:

No, what Laie is suggesting is a form of throttle controlled balance.  If your pod would yaw to the right during translation left, then the force of the rear right jet would decrease and the force of the front right would increase to maintain translation balance.

 

Yes, that's exactly what I'm talking about.  It does.  They added this RCS thruster-reduction for balancing a couple of years ago.  It doesn't do it in coarse control mode, but in fine it does.  Or, it used to, anyway, if it doesn't work anymore.  I balance my craft with RCS Build Aid, so I don't really notice.  And I usually do a single set of thrusters amidships instead of fore-and-aft thrusters, anyway, on smaller craft.

There was a huge fiasco on the forums when  they implemented RCS balancing, because they did it in coarse and fine controls both and it made the coarse controls much weaker.  So they changed it to just balance the thrust in fine.

But maybe that function got lost somewhere along the way.

Edited September 21, 2016 by RoboRay

[Alshain]

31 minutes ago, RoboRay said:

Yes, that's exactly what I'm talking about.  It does.  They added this RCS thruster-reduction for balancing a couple of years ago.  It doesn't do it in coarse control mode, but in fine it does.  Or, it used to, anyway, if it doesn't work anymore.  I balance my craft with RCS Build Aid, so I don't really notice.  And I usually do a single set of thrusters amidships instead of fore-and-aft thrusters, anyway, on smaller craft.

There was a huge fiasco on the forums when  they implemented RCS balancing, because they did it in coarse and fine controls both and it made the coarse controls much weaker.  So they changed it to just balance the thrust in fine.

But maybe that function got lost somewhere along the way.

Must have, I just tried and it's not working.

[RoboRay]

In that case, I wholeheartedly agree that a self-compensating RCS balancing system should be implemented.  Maybe require a pilot?

Better yet, since engineers are under-employed, make it require an engineer to be aboard, so they can calculate the proper settings based on the current mass distribution throughout the ship.

Make the minimum thruster setting like 50%, though.    Much less than that, you may as well not even have a thruster over there.

Edited September 22, 2016 by RoboRay

[Laie]

More often than not, you don't need smart RCS: just translate away and let SAS deal with the fallout.

The use case I have in mind is comparatively long vessels with docking ports at the far ends. Here it would be better if rotation could be avoided to begin with, as even slight oscillations shift the docking port far out of alignment. For all I care the algorithm need not be very smart, just combine translation&rotation into a single action that minimizes one or the other as desired. I don't see me use it very often, but when I need it I really do.

I don't like the idea of tying it to personnel -- unmanned tugs are where I'd need it the most. Better to have it tied to SAS level X. It should be a distinct mode of operation (cycle RCS off-white-blue-off?)

[StahnAileron]

So I just looked at the 1.2 Pre-release to see what RCS offers now... I guess this is an advanced tweakable, but there's an option after hitting "Show actuation Toggles" called "Always full action". Haven't tested it yet, but maybe that's the toggle for smart/compensated RCS thrust? (I have advanced tweakable on by default, so not sure off-hand, but it sure sounds like an advanced option/configuration.)

[eddiew]

14 hours ago, Alshain said:

But it inherits a lot of complication.  What if there aren't two jets on any one side?

Problem for the players rather than the code, imho. The game just needs to see if there is a relevant+enabled thruster on each side of the CoM - if not, you're going to spin no matter what it does so don't try.  

Arguably you could end up with a thruster at the nose, and one just slightly ahead of the CoM in which case the algorithm could disable the nose... but that's probably more advanced than it needs to be. A building guide that says "put RCS on each side of the CoM" is fairly easy to understand  

[Laie]

3 hours ago, eddiew said:

The game just needs to see if there is a relevant+enabled thruster on each side of the CoM - if not, you're going to spin no matter what it does so don't try.

 

Figure 1, how a craft with unbalanced RCS can both translate and fight rotation at the same time.

In a nutshell: as long as you can translate and rotate in all directions, it is possible to get one without the other. On a very unbalanced vessel it becomes utterly impractical, of course -- but not impossible.

[eddiew]

Ok so I was mostly considering outward-facing thrusters ^^;  But yeah, I see where you're coming from on that. Why can't the game identify when the translation key will produce a torque and apply a counter-torque with either reaction wheels, or other thrusters, we might ask...

(Tbh I'm not sure why we even use RCS for rotation in KSP. With free torque provided by infinite reaction wheels, they're redundant outside of self-imposed difficulty.)

[Racescort666]

RCS does not auto balance in fine control mode. Fine control mode only reduces RCS thrust. I can't really speak to versions older than 0.90 because that's the earliest version I've tested but I can say that such behavior is not present in 1.0 through 1.1.3.

[Tyko]

I started a similar suggestion thread a few months ago titled Smart RCS Thrusters   In that thread, @Snark and @Rocket In My Pocket both said that fine control mode also included some measure of thrust balancing. This may have changed with 1.2-Pre.

I dropped the subject, but would still like to see something like what's being discussed here that offers more thrust.