RCS Tips?

[Choctofliatrio2.0]

So I did my first orbital rendezvous the other day, with two unmanned probes. I had many RCS thrusters on each. However, when I tried to select one of the icons to the right of the navball (Prograde, target, etc), the probe would use lots of monopropellant making RCS jets in all directions just to hold the ship in place.

Essentially, I couldn't use RCS for anything except stability assist, without wasting a bunch. Is this normal? It it just how probes work, or was I doing something wrong?

Furthermore, what are some tips for placing RCS thrusters so they work well?

[Rocket In My Pocket]

It's hard to say without seeing a picture of the probe in question.

Generally you want them to be symmetrical though, and equidistant from the COM for best effect.

RCS combined with SAS can sometimes produce a constant wobble or over compensation, especially with smaller crafts in my experience.

Edited December 16, 2015 by Rocket In My Pocket

[Hupf]

It may be bad practice to suggest mods for problems, but have a look at RCS Build Aid, be it just for better understanding what is happening.

[Choctofliatrio2.0]

Sorry, I didn't get photos of the probe. So would it be wise to disable reaction wheels when using RCS?

[Rocket In My Pocket]

9 minutes ago, Choctofliatrio2.0 said:

Sorry, I didn't get photos of the probe. So would it be wise to disable reaction wheels when using RCS?

Well SAS is going to try to stabilize the ship with whatever means it has at hand, so turning off the reaction wheels isn't going to stop it.

Once again, without seeing the ship in question I can't really tell you if the reaction torque is hurting or helping the situation, it really depends on where it is, as well as where the RCS nozzles are in relation to it etc...

Do you still have the craft file? You could load it up in the VAB and take a screenshot of it? Or just upload the file itself so someone could look at it.

[Qwarkk]

6 minutes ago, Choctofliatrio2.0 said:

Sorry, I didn't get photos of the probe. So would it be wise to disable reaction wheels when using RCS?

No they should work together, so no need to disable one.

As for the position of your RCS, It needs to be on or equidistant from the COM as Rocket In My Pocket said earlier. Remember that as you burn fuel and use mono-propellant, the COM will move. So take this into account when positioning your RCS thrusters.

Easiest way to do this is to change the fuel/mono levels and watch the COM move, then figure out its 'average' position and place RCS thrusts on or equidistant from this point.

As Hupf said, RCS Build Aid will do this for you - its a terrific mod.

[Choctofliatrio2.0]

8 minutes ago, Rocket In My Pocket said:

Well SAS is going to try to stabilize the ship with whatever means it has at hand, so turning off the reaction wheels isn't going to stop it.

Once again, without seeing the ship in question I can't really tell you if the reaction torque is hurting or helping the situation, it really depends on where it is, as well as where the RCS nozzles are in relation to it etc...

Do you still have the craft file? You could load it up in the VAB and take a screenshot of it? Or just upload the file itself so someone could look at it.

I can get a photo of it up later today, assuming I can figure that out. Essentially, it had three sets of four RCS thrusters, four on the COM, four to the left of it, and four to the right. Not positive if they were equidistant.

 

When I put one in orbit and docked a manned vessel to it. On the manned ship, I only had one set of thrusters, on the COM, and it worked very well.

 

As for mods, I don't really do mods. I've tried them before, and broke my computer XD

Edited December 16, 2015 by Choctofliatrio2.0

[Plusck]

I avoid using anything but stability assist with RCS, unless it's a very small ship. The "pilot" isn't very intelligent, overshoots what he was aiming for and then corrects back. The bigger the ship, the more insane the overshooting/correction gets because the pilot doesn't take momentum into account. This very quickly uses up all of the monopropellant.

[Rocket In My Pocket]

I don't use mods either and I've never had a problem with RCS control, you should be able to figure everything out by trial and error, sounds like you already are!

If you want to upload a pic or the craft file later myself or someone else can show you how to do that, you'll find everyone here is very helpful.

Best of luck!

 

[Choctofliatrio2.0]

1 minute ago, Rocket In My Pocket said:

I don't use mods either and I've never had a problem with RCS control, you should be able to figure everything out by trial and error, sounds like you already are!

If you want to upload a pic or the craft file later myself or someone else can show you how to do that, you'll find everyone here is very helpful.

Best of luck!

 

Thank you

And thanks everyone else for your suggestions

[Pecan]

1 hour ago, Choctofliatrio2.0 said:

Sorry, I didn't get photos of the probe. So would it be wise to disable reaction wheels when using RCS?

Reaction wheels are good for re-orienting your ship and don't use fuel (although they do need power, of course).
RCS is about the only way you have of accelerating sideways or backwards.
I only use RCS for docking and only add monopropellant tanks to a ship if it's meant to be a tug doing a lot of docking and/or handling awkward loads.  That means most of my ships have very limited fuel for RCS and I don't want it wasted doing the job of reaction wheels.

If I want to rotate - RCS and SAS off, WASDQE and reaction wheels.
If I want to translate - RCS and SAS on, HIJKLN and monopropellant while reaction wheels compensate for any RCS imbalance.

[Corw]

With RCS less is more. Small puffs. Use precision mode (caps locks on), it will try to balance use of RCS so you don't wobble too much.

[Venusgate]

Actually, i think the most immediate thing you can do is turn on precision controls by pressing CAPSLOCK (it will turn the needles in your yaw/roll/pitch dials in the bottom left from orange to blue)
basically, what this does is give your RCS and SAS a longer "accelleration" to get to full, instead of just 0 thrust/full thrust. This should help your wobbles quite a bit.

The wobbles themselves is a continuing bug where the SAS tries to overcompensate itself, especially if there are multiple sources of SAS and if you have any parts that are clipped, it will definitely exacerbate the problem.

As for not being able to use prograde et al, I've run into this too. another bug. not sure howto fix.
 

[Geschosskopf]

3 hours ago, Choctofliatrio2.0 said:

So I did my first orbital rendezvous the other day, with two unmanned probes. I had many RCS thrusters on each. However, when I tried to select one of the icons to the right of the navball (Prograde, target, etc), the probe would use lots of monopropellant making RCS jets in all directions just to hold the ship in place.

Essentially, I couldn't use RCS for anything except stability assist, without wasting a bunch. Is this normal? It it just how probes work, or was I doing something wrong?

Furthermore, what are some tips for placing RCS thrusters so they work well?

First off, the stock autopilot "point in a given direction" thing is pretty poorly done.  I recommend NEVER using it but always orienting your ship by hand.  The stock orientation thing always WAY overshoots the mark then way overshoots it again, gradually oscillating (after a minute or so) onto the desired heading.  This is whether or not you use RCS.  So yes, if you use RCS with the stock orientation thing, you WILL waste MUCH fuel.  If you don't want to aim your ship by hand, use MJ's SmartASS function instead, which shows how such a system should be done 

As to placement of RCS, it depends on what you're using it for.  Do you need it for docking (translation) or added orientation control authority (rotation)/.  These require different strategies, as follows:

For docking, it's very important to have balanced RCS thrust around the ship's CoM so that you get pure translation without any unwanted rotation.  The mod RCS Build Aid is WONDERFUL for doing this and I'm shocked it's never been incorporated into stock.  With small ships, you can usually get by with a single set of 4 RCS 4-way thrusters mounted symmetrically right at the CoM.  For bigger, heavier ships, you usually want multiple thrusters pointing each direction to have more control authority.

For orientation, what you want is to give the RCS thrusters the most leverage as possible and you don't care at all about balance.  You use this sort of RCS for orienting big, long, heavy things like SSTO lifters, motherships, stations, etc.  With lifters, this is pretty easy to do.  Just put 1 set of thrusters all way way at the bottom of the stage.  Because you build rockets with the CoM as far foward as possible for atmospheric stability, having the RCS at the rear end gives the most leverage.  If you've got multiple big stages, put thrusters at the bottom ends of each stage.  And I recommend using the Vernor engines (they burn LFO) instead of RCS for this job.  First, the Vernor engines are strong enough for the job and 2nd you don't have to have RCS fuel tanks in the lower stages.  The Vernors burn insignificant LFO so have no worries about them robbing you of the dV you need to get to space.

You can combine these strategies in the same rocket, too.  Normally, only payload at the top will dock so build it by itself first with balanced RCS for docking.  Then build the lifter under it and add more RCS thrusters or Vernors at the bottom of each lifter stage.

[Carepanda]

13 hours ago, Choctofliatrio2.0 said:

However, when I tried to select one of the icons to the right of the navball (Prograde, target, etc), the probe would use lots of monopropellant making RCS jets in all directions just to hold the ship in place.

SAS always on. Use main engines while you far from target(RCS off). Approach to 50-100m, reduce relative speed to 0-1m (still without RCS). Align both vessels docking ports one to one(no RCS yet). Switch mode to stability assist, turn on RCS and start docking. You dont really need prograde or target alignment assist at last stage where you using RCS.

[nosirrbro]

I would recommend, when selecting, say, prograde lock, make it take you there, then go back to stability assist to conserve mono propellent unless you want to install RCS mods.

[Choctofliatrio2.0]

So I've started a space station, and I haven't had too many problems with the wobble, for the most part. I have started the strategy of putting one set of RCS thrusters at the COM. Somewhat slow, but it gets the job done.

But I'm beginning to think the game doesn't want me docking things. With a few of my new designs, I've faced an issue where pressing the Up translate button, for example, a different thruster fires. Essentially, if I try and translate up, two RCS thrusters will fire up, but two others will fire left, sending me off course. Is this normal, thrusters that can't fire in a certain direction instead firing a different way and sending the ship in the wrong direction? 

I haven't managed to reproduce this in all my ships, (Probably 2/4) and I can correct it by pressing two translate keys at the same time.

[TopHeavy11]

Instead of using target lock all through-out, use it when your far away and when your a few meters away. As for RCS placement, that depends on your craft size. With smaller crafts, your RCS  is best placed right on the center of mass. For larger crafts, it's best placed at equal distance above and below the center of mass. Some more protips: RCS blocks are the way to go, and go slow on the docking. It earned it's nickname "space ballet" for a reason. Be patient. After that, your good to go! Happy dockings!

[Plusck]

6 minutes ago, Choctofliatrio2.0 said:

So I've started a space station, and I haven't had too many problems with the wobble, for the most part. I have started the strategy of putting one set of RCS thrusters at the COM. Somewhat slow, but it gets the job done.

But I'm beginning to think the game doesn't want me docking things. With a few of my new designs, I've faced an issue where pressing the Up translate button, for example, a different thruster fires. Essentially, if I try and translate up, two RCS thrusters will fire up, but two others will fire left, sending me off course. Is this normal, thrusters that can't fire in a certain direction instead firing a different way and sending the ship in the wrong direction? 

I haven't managed to reproduce this in all my ships, (Probably 2/4) and I can correct it by pressing two translate keys at the same time.

Sounds like whatever you are using to  'control from here' isn't lined up with your thrusters.

For translation, RCS thrusters never fire except in the direction that the ship thinks is up, down, left or right. However, if no single (or pair) of thrusters is pointing in the right direction, it'll combine two vectors automatically.

[softweir]

3 minutes ago, Plusck said:

Sounds like whatever you are using to  'control from here' isn't lined up with your thrusters.

For translation, RCS thrusters never fire except in the direction that the ship thinks is up, down, left or right. However, if no single (or pair) of thrusters is pointing in the right direction, it'll combine two vectors automatically.

To translate somewhat:- the thrusters facing left would appear to be pointing slightly up as well, and the game therefore thinks they will help with the up movement. You may need to tweak their positioning slightly in the VAB.

What would be nice is if there was a facility to associate thrusters with control axes, so you tell the game that a particular thruster is only meant to be used for Translate Left, for instance.

[radonek]

22 hours ago, Geschosskopf said:

…The mod RCS Build Aid is WONDERFUL…

These words could be set in stone. And RCS Build Aid should be set in stock.

[flyboy67109]

I typically turn off RCS until I'm ready to dock or to a planned transition. Otherwise, I rely on SAS to keep the craft stable.

[TopHeavy11]

45 minutes ago, radonek said:

These words could be set in stone. And RCS Build Aid should be set in stock.

I've never tried RCS Build Aid. Is it good?

[radonek]

15 hours ago, TopHeavy11 said:

I've never tried RCS Build Aid. Is it good?

No, it's not good. Like Gescho said, its wonderfull. I will put it this way - it does not add any parts, nor does it actually control anything and you can remove it anytime, so just give it a try.

[Scarecrow]

Unless I am manoeuvring specifically using RCS, so mostly translation for docking purposes, I turn the RCS off becuse SAS will use up monoprop just trying to keep the ship stable.