help me wrap my head around RCS and docking

[putnamto]

ok so i have this 



im trying to dock these together at point 1 and point 2 in the picture, but for the life of me i cannot wrap my head around RCS controls, when i switch to docking mode i cant select the ROT.
when im not in docking mode WASD controls my rotation and IJKL does nothing, when in docking mode both WASD and IJKL do translation

please explain rcs controls to an infant. 

EDIT:

after watching this scott manley video i think i have a better idea now, but around the 13:40 ish mark he does rotation withought using rcs and my craft will not do that at all.
https://www.youtube.com/watch?v=srsiLZLPiv0

im tired, i think i know the problem but i cant remember the name of the part that i might have forgotten on my ships, the one that helps with control, its a little disk that uses electricity.

 

Edited February 10, 2018 by putnamto

[The Aziz]

59 minutes ago, putnamto said:

im tired, i think i know the problem but i cant remember the name of the part that i might have forgotten on my ships, the one that helps with control, its a little disk that uses electricity.

You mean SAS? I can see you have it.

About docking though. I personally changed the RCS controls to numpad (7/1 for moving up and down on let's call it z axis, 4/6 for x axis, 8/2 for y axis) it's much easier. I can see you have MechJeb, so you chould have something called SmartA.S.S. There you have a button called TGT, then underneath is PAR-. That should set you parallel to your target. Make sure that you set "control from here" on the docking port you want to use first. Everything you do now is using 4/6/8/2/7/1 controls to set yourself in front of your target and push a little to meet the other docking port. All that without docking mode.

Edited February 10, 2018 by The Aziz

[putnamto]

Thanks.

When  you  say  you  mapped  it  to  your  keypad  where  did  you  go  to  change  your  keybindings?

[swjr-swis]

47 minutes ago, putnamto said:

im tired, i think i know the problem but i cant remember the name of the part that i might have forgotten on my ships, the one that helps with control, its a little disk that uses electricity.

The part you're referring to is a reaction wheel.

It's a bit hard to tell, but I think I see both craft have RCS thruster blocks and monoprop tanks, and they both seem to have a 1.25m reaction wheel as well (craft 1 directly below the marked docking port, craft 2 on the opposite side of the marked docking port).

Assuming you still have monoprop left for RCS, or EC for the reaction wheels, you should be able to rotate your craft with either one (or both) of them. I can't tell from the pic if you have monoprop left, but since your SAS is on and not greyed out, you should still have EC. Have you checked if the reaction wheels are 'running'?

Rotation with WASDEQ and translation with HNIIJKL should work in the default mode when RCS is enabled, you don't need 'docking mode' for that (I never ever use it).

[The Aziz]

17 minutes ago, putnamto said:

Thanks.

When  you  say  you  mapped  it  to  your  keypad  where  did  you  go  to  change  your  keybindings?

Not sure how accurate the screenshot is (found it somewhere) but there, under translation controls.

[radonek]

1. Forget about docking mode, AFAIK nobody really uses that.
2. Switch camera to "locked" and set control to docking port you use ("control from here" context menu). This is important - you can't expect to get handle on controls if your sense of left and right keep changing.
3. It is much easier to practice docking with smaller vehicles. Seriously. Launch two docked capsules, undock and play around.
4. Take your time. Once you get this close, anything over about 1.5m/s is too fast, less then 0.4 m/s is best during final approach. If your alignment is not perfect, it is better to slow down prograde and slowly drift your axes then overcompensate. This is especially true when handling  big ships or nonaligned RCS. 
5. Placing RCS ports at CoM is not as good idea as it seems, it only works well  if your dry and wet CoM is aligned. It is better to place RCS  in pairs at extreme ends (to give them better leverage). Fine mode (caps-lock) will automatically balance them out if possible. When building larger ships, RCS build aid mod is indispensable.
6. Low orbits have noticable drift in orbital plane due to subtle differences  in orbits of both crafts, it is easier to dock in north-sourth axis. If your inclination is close to zero (which it should if you launch from KSC), you can just use planar/antiplanar mark on navball to align both crafts.
7. Since north-south trick is not always usable, get some mod that can display relative alignment.  Note that this hinges on setting point of control ("control from here"). If you have alignment right, final approach can be made solely on translation controls (IJKL). Navball docking alignment indicator is my personal pick.

[Superfluous J]

19 minutes ago, radonek said:

1. Forget about docking mode, AFAIK nobody really uses that.

Just now, 5thHorseman said:

21 minutes ago, radonek said:

1. Forget about docking mode, AFAIK nobody really uses that.

I hate this forum's mobile interface.

I wanted to reiterate this point, and also to point out that docking is a skill. You are not going to get it right away and are going to screw up a lot while learning.

Until you don't need to think about which of the 12 directional keys to hit at any point, you will be very frustrated. But take it slow, have a LOT of patience, and try over and over and you will develop the skill required.

[Human Person]

Thruster placement is very important, especially when you need your thrusters to handle rotation. 

If the thrusters aren‘t placed perfectly equal around the COM (the easiest way of doing this is having just 4 thrusters at the same height on your craft as the COM), a rotation will always induce a translation too. 

When you managed to place your thrusters perfectly, you can rotate freely without any translation. A very useful tool (the most useful mod IMHO (yes, even more useful than MechJeb or KER)) is RCS Build Aid.

Edited February 10, 2018 by Human Person

[Kryxal]

1 hour ago, radonek said:

1. Forget about docking mode, AFAIK nobody really uses that.
2. Switch camera to "locked" and set control to docking port you use ("control from here" context menu). This is important - you can't expect to get handle on controls if your sense of left and right keep changing.
3. It is much easier to practice docking with smaller vehicles. Seriously. Launch two docked capsules, undock and play around.
4. Take your time. Once you get this close, anything over about 1.5m/s is too fast, less then 0.4 m/s is best during final approach. If your alignment is not perfect, it is better to slow down prograde and slowly drift your axes then overcompensate. This is especially true when handling  big ships or nonaligned RCS. 
5. Placing RCS ports at CoM is not as good idea as it seems, it only works well  if your dry and wet CoM is aligned. It is better to place RCS  in pairs at extreme ends (to give them better leverage). Fine mode (caps-lock) will automatically balance them out if possible. When building larger ships, RCS build aid mod is indispensable.
6. Low orbits have noticable drift in orbital plane due to subtle differences  in orbits of both crafts, it is easier to dock in north-sourth axis. If your inclination is close to zero (which it should if you launch from KSC), you can just use planar/antiplanar mark on navball to align both crafts.
7. Since north-south trick is not always usable, get some mod that can display relative alignment.  Note that this hinges on setting point of control ("control from here"). If you have alignment right, final approach can be made solely on translation controls (IJKL). Navball docking alignment indicator is my personal pick.

You suggest using normal/antinormal as an approximation for north/south ... in my opinion, it's the other way around.  Once you get aligned and the ships are pointing normal or antinormal, they stay that way, the only drift will be towards or away from the target.

[bewing]

6 hours ago, putnamto said:

im trying to dock these together at point 1 and point 2 in the picture, but for the life of me i cannot wrap my head around RCS controls

OK, there's a lot to this. Probably too much to remember in one session. But I'll go for it anyway. First, you clearly need to understand something about the navball. When you have a vessel that you want to dock to, and you are close to it, your navball of your docking ship should always be in "target" mode. There is never any reason to be in orbit mode when you are close. In target mode, the navball shows your relative velocity -- and you want to keep that relative velocity very low.

Another point is that you absolutely need to control both ships. You need to get them both pointing at each other. So you have to control one, get it pointing basically correctly -- then flip to the other one, and get that pointing closer than it was before -- then flip back to the first one, and fix it so it points a bit better -- and repeat.

A third thing to understand is the concept of setting target points. You can either target a docking port, or you can target the root part of another ship. Radial docking ports usually need to be targeted specially. For inline dockings (such as you are doing here), the root part is usually good enough.

Fourth: SAS. In general, SAS will hold your ship and the target ship in a specific orientation. But the ships are moving with respect to each other. So sometimes you even want to turn SAS off, and induce a small rotation to keep things aligned. Additionally, there is a special feature of SAS that helps a lot with docking. A second ship in SAS target mode will actually follow a target. That is, there is an SAS mode that can help you here, but you do not have enough tech for it.

Fifth: RCS is a very gentle thing. Probably the reason you think it isn't working is that it's so gentle. This is another reason to be in target mode on your navball. That mode will clearly show small changes in velocity.

Sixth: Control points. One of your docking ports is on the back end of your ship. So if you want to orient that docking port with no tricks, you will have to do all your controls backwards. (Which is hard but doable.) Or, you can select the backwards-facing docking port and click "Control From Here". Then all your controls will be normal instead.

So: to dock these two ships --
Target ship 1 from ship 2 (doubleclick on it).
Switch navball to Target mode.
Maneuver until your relative velocity is zero.
Find the Target icon on your navball and rotate ship 2 using WASD until it's pointing at the icon. Verify visually that the docking port is pointing at the other ship.
Switch focus to ship 1.
Target ship 2 from ship 1 (or maybe specifically target the docking port, your choice).
Find this target icon and rotate to point at it, with SAS on.
Switch focus back to ship 2. It should still be pointing mostly at ship 1's target icon, but you probably need to fix it a little -- do that.
Ship 2 seems to have no engine, so use H (with RCS turned on) to get a little forward velocity (maybe .3 to .5 m/s).
And now you just need to keep the two docking ports facing each other as the ships drift together.
So you keep flipping control back and forth between the two and adjusting the rotation. Moving the camera around can either help you align things, or totally disorient you, depending on your luck and skill level.
If it looks like you are going to totally miss, or crash -- then use N to slow to a stop, reorient everything, and try again.

 

Quote

 

when i switch to docking mode i cant select the ROT.

You can always select Rotation mode by clicking on the ROT button with the mouse.

Quote

when im not in docking mode WASD controls my rotation and IJKL does nothing, when in docking mode both WASD and IJKL do translation

IJKL never does nothing, unless your RCS is turned off or you are out of Monoprop fuel or you forgot to attach any RCS thrusters.

Quote

after watching this scott manley video i think i have a better idea now, but around the 13:40 ish mark he does rotation withought using rcs and my craft will not do that at all.
 

When you rotate, the system will also try using RCS to "help" the rotation, unless you turn RCS rotation off (which is a really smart thing to do). You do that by turning on Advanced Tweakables, and turning the Roll, Pitch, Yaw controls on the RCS off.

 

Edited February 10, 2018 by bewing

[putnamto]

OK, this  a lot  to  take  in, before  I  load  the  game  later  tonight  I  got  one  question.

 

Are  those  ships  dockable  the  way  they  are  built? Both  ships  have 2 full  roundified  monoprop  tanks  and  four  rcs  thrusters  around  the  com(when  they  were  wet.) Ship  2 has  no  thrust(itchy  space  bar  finger) and  ship  one  has  roughly  half  its  fuel  left, but  its  all  stored  in  the  smaller  tanks  below  the  struts, the  top  half  is  completely  empty.

 

Is  this  doable  or  should  I  scrap  them  and  go  back  to  the  vab  and  do  some  tweeks.

[swjr-swis]

4 minutes ago, putnamto said:

Are  those  ships  dockable  the  way  they  are  built? Both  ships  have 2 full  roundified  monoprop  tanks  and  four  rcs  thrusters  around  the  com(when  they  were  wet.) Ship  2 has  no  thrust(itchy  space  bar  finger) and  ship  one  has  roughly  half  its  fuel  left, but  its  all  stored  in  the  smaller  tanks  below  the  struts, the  top  half  is  completely  empty.

Is  this  doable  or  should  I  scrap  them  and  go  back  to  the  vab  and  do  some  tweeks.

Based on the picture and on what you mention here, I see no impediment for the ships to dock. It might not be the easiest to start with, but technically you seem to have all you need to make it happen.

One suggestion to simplify things a bit, which was mentioned before in this thread but is worth emphasizing: rightclick the RCS thrusters (you'll need to do this individually), select 'Show Actuation Toggles', then set the first three options to 'Off' (Yaw, Pitch, Roll).  This will disable RCS for rotations (the reaction wheels work better for that) and use it for translation only (which the reaction wheels cannot do). RCS tends to be too wasteful and twitchy for rotational use, except for very massive craft.

Ok maybe one more suggestion: make a save before you start your attempt to dock. That way you can return and redo if things go haywire. There's no better way to get to grips with docking than to rinse and repeat.

Let us know how it went.

[putnamto]

Rcs  controls  are  relative  to  the  ship? Or  to  the  camera  angle?

Like  say  my  ship  is  upside  down  would  rcs  up  become  down  and  vice  versa?

[swjr-swis]

44 minutes ago, putnamto said:

Rcs  controls  are  relative  to  the  ship? Or  to  the  camera  angle?

Like  say  my  ship  is  upside  down  would  rcs  up  become  down  and  vice  versa?

Craft controls in KSP (including RCS) are always interpreted relative to the part that the game considers to be the 'control' part. Normally this is either a cockpit, command pod, seat, or probe core, and root parts get priority.

You can also make docking ports and the claw be the control part by rightclicking them and selecting 'Control from here'. You can do the same thing to switch to a different control part, for example to return control to the pod after having docked.

Note that all this means that the exact orientation of the chosen control part is important. Spend a bit of time in the VAB/SPH looking at the different parts as they are placed by default, so you can recognize what is front/back, up/down, and left/right once you are in flight. For some parts it's a bit difficult to make out (notably probe cores), and other parts can be misleading (eg. the 'front' texture of the Jr docking port is actually upside down, which could confuse you about which way is up/down or left/right).

[putnamto]

14 minutes ago, swjr-swis said:

Craft controls in KSP (including RCS) are always interpreted relative to the part that the game considers to be the 'control' part. Normally this is either a cockpit, command pod, seat, or probe core, and root parts get priority.

You can also make docking ports and the claw be the control part by rightclicking them and selecting 'Control from here'. You can do the same thing to switch to a different control part, for example to return control to the pod after having docked.

Note that all this means that the exact orientation of the chosen control part is important. Spend a bit of time in the VAB/SPH looking at the different parts as they are placed by default, so you can recognize what is front/back, up/down, and left/right once you are in flight. For some parts it's a bit difficult to make out (notably probe cores), and other parts can be misleading (eg. the 'front' texture of the Jr docking port is actually upside down, which could confuse you about which way is up/down or left/right).

thank you, thats where alot of my confusion was coming from.

basically if i "control from here" the docking port then that means i would base my controls on the navball correct?

[bewing]

The navball reorients itself to point in the same direction as the part you select as the control point. So yes, you always base your controls on the navball display.

 

 

[Superfluous J]

3 hours ago, putnamto said:

thank you, thats where alot of my confusion was coming from.

basically if i "control from here" the docking port then that means i would base my controls on the navball correct?

You should ALWAYS base your input off the navball. It's the only thing on the screen that is guaranteed to show you the proper orientation.

Except in rare cases where you put something on backward.

[putnamto]

39 minutes ago, 5thHorseman said:

You should ALWAYS base your input off the navball. It's the only thing on the screen that is guaranteed to show you the proper orientation.

Except in rare cases where you put something on backward.

i was trying to be funny, i know to always watch the navball(acept for when i forget)

[putnamto]

i think ive done something horribly wrong, i dont know what it is but my two ports just bash into eachother then seperate again.

and im going under .1 m/s it was so close i could taste it, then it all just went bad real quick and suddenly none of my inputs with rcs seemed to matter and the other ship just kept getting farther and farther away.

and somebody said to select rot in docking mode click it with your mouse, its greyed out and clicking it does nothing.

Edited February 11, 2018 by putnamto

[Clipperride]

First thing to remember - Docking is hard to master, but well worth the time.

Just a note on the placement of your RCS thrusters if you don't have any mods installed.

In the VAB, detach anything below the stage(s) that are going to be left when you dock.  Reduce the propellant to approximately the amount you will have remaining when you dock.  Experience helps here, or you can run a "simulated" mission (fly the mission, get the two vessels close together, then hit "revert")

Turn on the overlay, place a ladder as close as possible to the CoM and extend the ladder.  You can now position your first set of thrusters, rotate the ladder through 90° and place the second set the same distance from the CoM, using the ladder as a ruler!  Having a well balanced RCS system reduces the amount of rotation induced from translations.

[bewing]

8 hours ago, putnamto said:

i think ive done something horribly wrong, i dont know what it is but my two ports just bash into each other then separate again.

OK, then something is indeed wrong with the way one of the ships is put together. Maybe one of the docking ports has been attached upside-down or something. It's always a good idea to test out the docking ports on the ground, if at all possible -- before you launch the ships.

8 hours ago, putnamto said:

and im going under .1 m/s it was so close i could taste it

It was indeed! If you got them to touch, you basically have it finished.

8 hours ago, putnamto said:

 then it all just went bad real quick and suddenly none of my inputs with rcs seemed to matter and the other ship just kept getting farther and farther away.

Sounds like you probably ran out of electricity on the ship you were controlling. Either that or you ran out of monoprop fuel.

8 hours ago, putnamto said:

and somebody said to select rot in docking mode click it with your mouse, its greyed out and clicking it does nothing.

The mode you are already in should be greyed out. If you are saying they are both greyed out, then I want to see a picture.

 

[putnamto]

I  have  a  feeling  one  of  the  ports  is  a  Jr.

Going  to  scrap  both  the  ships, go  back  to  the  vab, move the rcs, make sure their all the same size ports and  add  lights  to  the  sides  so  I  can  tell  orientation  better.

Speaking  of  orientation  lights, is  it  green  on  the  left  and  red  on  the  right? Or  vice  versa?

Edited February 11, 2018 by putnamto

[InterplanetJanet]

On 2/11/2018 at 2:05 PM, putnamto said:

Speaking  of  orientation  lights, is  it  green  on  the  left  and  red  on  the  right? Or  vice  versa?

Red on left, green on right.

Also, if you have the Tweakable Everything mod installed... well, I had to remove a piece of it, I think TweakableDocking-something.dll because I also was bouncing docking-port-to-docking-port, for literally hours.

[Capt. Hunt]

The other thing to remember is that you can switch between translation and rotation while in docking mode.  Once you switch to docking mode, you'll get two buttons (as well as a key command) that will allow you to switch back and forth.  Although, I've found it just as easy to switch in and out of docking mode entirely to do rotations.

 

I don't think they're all set by default, but you can change the key commands to allow both trans and rot simultaneously.  I usually have WASD set to one and IJKL to the other in both staging and docking mods.

[Kryxal]

I think you're right, looking closely the port on #2 looks smaller...