Shaky navballs!

[demian_travis]

I am trying to dock in a station on the mün. The orbit is not perfectly circular... and the navball goes EVERYWHERE. It is impossible - AT ALL - to have 0 m/s of speed between the targets. It is annoyingly bad! when I time warp the nav ball stops and acts like it should, but I am starting to punch my monitor in frustration....

Edited April 29, 2014 by Vanamonde
Watch the language, please.

[Tex]

Is the craft flipping or shaking at all? If not, you could always eyeball it, using the target you're trying to dock to as a reference.

[FenrirWolf]

I'm afraid I don't understand the issue. The shape of the target orbit doesn't matter except to the extent that you match shapes with it.

Are your ships shaking and/or wobbly? Do you have the other ship targeted and is the Navball actually in Target mode instead of Orbit or Surface? Are you attempting to cancel your relative velocity with the pink marker instead of the yellow one like you should be?

EDIT: Oooh, another biggie: Are you selecting Control From Here on the port you're planning on docking with the other ship?

Edited April 29, 2014 by FenrirWolf

[demian_travis]

The ships are really sturdy and simetrical. I used the exact same ships on an orbit around Minnimus with no trouble at all - managed to send my lander up and down a few times. I am selecting the control from here. I am trying to cancel the velocity with the yellow marker, but... it goes everywhere. In fact, when I managed to make the docking ports "kiss" my lander was flinged into oblivion, smashing a few solar panels from the station. If you guys want I can try to record this issue... But I need a screen recorder for a mac.

Here is a picture of the station (with docked lander), happily orbiting Minnimus:

[FenrirWolf]

OK, so you get the flinging of the navball when controlling the station or the lander? One possibility is that you might be dealing with phantom forces brought on by part clipping or something else wonky about the design.

[kenbobo]

video- get bandicam and e-mail/PM me at [email protected]

[demian_travis]

FenrirWolf - Both. I switch between ships and all of a sudden I get 1.6 m/s speed variations.

Kenbob5588 - Will download it and record what is happening. Give me a few minutes :3

[robogungt8]

I too have this issue sometimes. For me though, it mostly happens when my orbits are very near circular (<100m difference between Ap and Pe). Also happens when I'm making very minute changes in a circular orbit. I think it's the physics engine getting confused calculating direction vectors with very similar number, although I can only speculate. The was I see it, it means the thing have virtually no relative velocity (0.1m/s). I wouldn't worry about it if possible.

[FenrirWolf]

Also, you're not referring to the way the prograde marker jumps around when close to zero relative velocity, right? If so, then you really ought to be more specific than saying the "Navball" is jumping around, because that can be taken many ways.

The relative prograde marker losing precision at low speeds is just a consequence of trying to derive information about your heading when you don't really have one anymore. The best way to work around that issue is to not concern yourself with stopping all relative motion. Once you're in the general neighborhood of your target, a little drifting doesn't matter. Not to mention the goal is to drift into your target anyway, and the marker performs its job quite fine when you're going at the 0.3-1.0m/s speeds expected from a docking maneuver.

Either way I'll have a peek at the video once it's up to have a better idea of what's going on.

[demian_travis]

Fenrir, Sorry. Is the prograde marker that jumps all around. Robogungt8, Yes, I also have this issue when I have really circular orbits.

Uploaded the video:

Still processing, will be ready on a few minutes!

[FenrirWolf]

The reasons for the prograde marker going wonky plus the Ap/Pe markers acting up in circular orbits are pretty similar.

Think of it this way: how is prograde defined? It's the direction you're moving, right? So what does prograde mean when you are not moving? That's where the navball indicator starts having trouble. You see, when you are at rest or nearly so, every direction is prograde.

Same goes for circular orbits. When every point is the same distance from the planet, every point in the orbit becomes the periapsis and apoapsis at the same time.

[FenrirWolf]

As for how to dock when dealing with the finicky cursor? You need to change up your methods. Once your ship has a clear line of site to the target docking port, line yourself up to the purple marker such that you are facing the target.

Now, RCS forward a bit. The prograde marker will get a bit more towards the center of the screen, but chances are it will still be slightly off. Don't move your ship away from the purple marker, instead use RCS translation to shift the the yellow prograde marker to overlap the purple marker, all while keeping your vessel pointed right at them too.

Meanwhile, pay attention to the actual vessel view too. You might be coming in at an angle relative to the port, and it might be necessary to make a few corrections to line up for a successful connection.

Either way, the thing to remember is that on a docking approach, you don't steer your ship to the prograde marker. Instead you steer the prograde marker to your ship.

EDIT: That's the best precision you can get with the default navball markers. If you don't mind a lightweight mod, this one adds a 3rd alignment marker to the navball that makes the process even more straightforward. http://forum.kerbalspaceprogram.com/threads/54303-0-23-5-Navball-docking-alignment-indicator-v2

Edited April 29, 2014 by FenrirWolf

[Sophistry]

From watching the video I think your issues are the slow speed you're going at combined with the fact you're using RCS to turn.

In similar situations I turn RCS off when I rotate my ship, because it can build a slight velocity; the multiple vectors that all the slight RCS spurts create is what is making the prograde indicator go ballistic. My suspicion is reinforced by the RCS set up on the station: that lifter rocket still attached doesn't have RCS thrusters by the looks of it. Without equal placement of RCS on each side of the centre of mass, all your RCS use will change your vector slightly.

Try using RCS only for translation, on the lander, and stick to using reaction wheels on the station until you stage off that large fuel tank: try it and see, at the very least to rule it out

Edited April 29, 2014 by Sophistry

[demian_travis]

Thank you, guys!! I will try those methods... tomorrow. I am too pissed to play this again.

[Superfluous J]

That video looks like most dockings I've ever done. 0.1m/s is not all that fast, so just pretend it's 0. If you're moving almost 0, the direction you're moving isn't that important.

And back away a bit. Get about 20 or so meters away before you rotate your station to the ship, and then come in about a meter per second or so. The shakiness is all due to the fact that you're going slow, and minor oscillations in your craft are enough to confuse the markers.

Edited April 29, 2014 by 5thHorseman

[MockKnizzle]

I think your problem might be between the chair and the keyboard. You thrust forwards before you're properly aligned and inevitably bounce off and go spinning away into space. Be a little more patient when you're lining everything up.

[Heagar]

What i had to notice in your video was that you have the mod for dock align in the upper right corner of the screen after selecting your docking port. And this device was stable in it's behavior. Use this as refrence rather than the navball!

I don't use this mod, but are playing "Orbiter" as well, where a docking instrument is the only reference you can trust in. Even on the dark side of an stellar object! But this device is diffent and seems to be an modified ILS approach instrument (ILS=Instument Landing System). In case there is no documentation for this device:

• The orange dart on top is for rotation.
  
• The green lines are indicators for your attitude relative to the selected dockingport (your flightpath to the middle of the docking port if centered).
  
• The orange double-circle is your alignment with the selected docking port. If it is centered, you are pointing in the same direction as the docking port. In case you can't see it, there is a orange dart from the center of the crosshairs to it's position.
  
• The yellow marker is for your closing speed.
  
• 
  

Digital readings:

• upper right corner seems to be your rotation relative to normal position in degrees.
  
• bottom left corner is your distance (DST) in meters.
  
• bottom right corner is your closing speed (CVEL) in m/s. A positive reading means you are closing in, a negative you are moving away.
  
• 
  

While closing in

• Begin with the rotation. Center the orange dart.
  
• Center the orange double-circle with pitch and yaw.
  
• Then begin to translate up/down and left/right with RCS until the green lines are centered.
  
• 
  

Control all readings, especially if you are shortly about to dock. It may be, that the indicators are in logarithmic scale. In that case they would behave more sensitiv to minor corrections at an closer range.

Edited April 29, 2014 by Heagar

[Yasmy]

Looks like everything is behaving normally and correctly. Your relative velocity really is changing that much.

If you turn off SAS the prograde marker should stop jumping around, but that doesn't solve your problem.

The practical way to solve this problem is:

1) let the two ships drift much further apart along the docking port axes (20-50 meters),

2) line up and approach at a reasonable speed (for example, with 1 to 2 seconds worth of RCS puff).

Having a small but non-zero relative velocity will make the prograde marker stay steady.

3) continue to adjust your relative velocity so that it stays pointed at the target

4) kill most of your relative velocity when you get close (a few meters).

Edit: Oops. I missed an entire page of responses to your video before posting this. Now it's quite redundant.

Edited April 29, 2014 by Yasmy
Didn't see the 2nd page of replies...