totm feb 2024 Rendez-vous help?

[Mister Spock]

3 hours ago, HebaruSan said:

Those worked fine, but the lateral thrusters placed on the decoupler at the COM never worked, and I was not able to figure out why.

Thank you so much for posting those screenshots. That's exactly what I was thinking of trying. Maybe I won't now, lol. I guess I'll try again with the four-directional thrusters, placed better.

[boolybooly]

4 hours ago, HebaruSan said:

the lateral thrusters placed on the decoupler at the COM never worked

did you check fuel pass through on the decoupler and any intervening structures was enabled?

I think there is monopropellant in the capsule so you might be using that for the forward thrusters

Edited January 14 by boolybooly

[HebaruSan]

14 hours ago, boolybooly said:

did you check fuel pass through on the decoupler and any intervening structures was enabled?

I think there is monopropellant in the capsule so you might be using that for the forward thrusters

The aft thrusters are also attached below the decoupler (and work), so I think that possibility can be ruled out.

Edited January 14 by HebaruSan

[Mister Spock]

Docking success! For me, this is one of the most satisfying things to do in KSP, or in all of gaming for that matter. 

The rendez-vous is now easy for me, thanks to this thread's advice on using target mode and burning retrograde to the target once you're close. Docking itself also went smoothly; it took about 5 minutes, and I didn't really need the docking alignment mod at all.

But first I had to rebuild my satellite and use two sets of 4-way RCS thrusters, one at the bottom, one at the top. With this configuration, when I ordered the ship to translate left, the right thrusters (only) fired, as expected, and vice-versa. For whatever reason, when I was using only one bank of 4-way thrusters, if I ordered the ship to translate left, a different thruster on each thruster block would fire, resulting in chaos -- something other than translation left, maybe a roll. Only fore-and-aft thrusters fired in unison. Why is one bank of 4-way thrusters behaving like that? 

Edited January 14 by Mister Spock
Edited for clarity.

[Bej Kerman]

18 minutes ago, Mister Spock said:

For whatever reason, when I was using only one bank of 4-way thrusters, if I ordered the ship to translate left, a different thruster on each thruster block would fire, resulting in chaos -- something other than translation left, maybe a roll. Only fore-and-aft thrusters fired in unison. Why is one bank of 4-way thrusters behaving like that? 

Can you send a recording of this behaviour?

[Mister Spock]

9 minutes ago, Bej Kerman said:

Can you send a recording of this behaviour?

Sure. I'll try to do it tomorrow. Thanks for your interest. Should I just post it in this thread, or PM you?

[Bej Kerman]

4 minutes ago, Mister Spock said:

Sure. I'll try to do it tomorrow. Thanks for your interest. Should I just post it in this thread, or PM you?

You're free to put it here if you're comfortable with that, cheers

[Mister Spock]

4 hours ago, Bej Kerman said:

You're free to put it here if you're comfortable with that, cheers

Hmm, I don't have a YouTube or Twitch channel. I suppose I could make one? How do people typically upload videos here?

[steveman0]

The 4-way RCS will activate multiple ports if necessary to achieve the direction by your input. This will happen if your placement isn't perfectly aligned on the axes such that only the one port aligns with the direction. For most cases, multiple ports firing should work fine as the overall thrust vector should still match your input direction, but I could imagine for some imbalanced scenarios that this leads to worse performance. For best results, you should always place them so their ports are aligned with the ship axes.

[Mister Spock]

36 minutes ago, steveman0 said:

For best results, you should always place them so their ports are aligned with the ship axes.

Thanks for your reply. I see -- so when I was telling RCS to translate left, it had no single set of ports that could do that, so it fired more than one. Hmm, maybe that's what was going on. Often, however, it seemed like all four ports would fire at once, all working against one another.

Maybe I could have cured it by rolling the ship so that the ports were aligned straight left, right, up and down as I looked at them from behind. I assume that's what you mean by my ship axes?

Incidentally, I found it easier to dock without using docking mode. I used WASD to pitch and roll the ship, and IKJLHN to translate. I think that's muscle-memory from KSP1 -- I rarely used docking mode there, either.

[steveman0]

Rolling your ship doesn't change their inherent axes relative to how it was constructed.  If you hold two directions at the same time, like left and down, this should correct the offset if you had 45 degree off-axis alignment.  I can't say I've ever seen them all firing at once.  Maybe if I had multiple buttons pressed at once.  I'm not sure if when you have them off-axis whether or not it regulates the thrust to achieve a mathematically aligned thrust vector or not.  I've never explicitly tested and I always try to keep them well aligned.

Edited January 15 by steveman0

[Bej Kerman]

9 hours ago, Mister Spock said:

Hmm, I don't have a YouTube or Twitch channel. I suppose I could make one? How do people typically upload videos here?

YouTube, Google Drive, anything that hosts files and supports videos.

[Bingmao]

I guess your thrusters are not aligned with your center of mass. When you try to make translation, the ship would rotate around it's center. And that would cause the other thrusters fire in the opposite direction, if you have SAS enabled, to keep the orientation.

Either placing the thrusters near the CoM or symmetrically "above" and "below" the CoM would cancel out the rotation.

Sorry for the hand drawing, I'm on my phone right now, but I think you get it. 

 

Edited January 16 by Bingmao
Typo

[jmbailey2000]

10 hours ago, Bingmao said:

I guess your thrusters are not aligned with your center of mass. When you try to make translation, the ship would rotate around it's center. And that would cause the other thrusters fire in the opposite direction, if you have SAS enabled, to keep the orientation.

Either placing the thrusters near the CoM or symmetrically "above" and "below" the CoM would cancel out the rotation.

Sorry for the hand drawing, I'm on my phone right now, but I think you get it. 

 

Not sure it could explain things any better!! Simple is always best!!!! Great job!!!

[Mister Spock]

Thanks for that explanation, @Bingmao! Very helpful, and fun to look at, lol.

[boolybooly]

The reorientation thrust only works if you have RCS enabled so the workaround is to give a little translation thrust and then immediately switch off RCS or give the thrust with SAS disabled when you will see the craft rotate and translate from the same thrust, then switch off RCS, then switch on SAS and realign using reaction wheels only.

Believe me when I say it is doable but not ideal. Best when making the craft to check CoM behaviour with full and low fuel and place thrusters accordingly.

 

On 1/14/2024 at 2:56 PM, HebaruSan said:

The aft thrusters are also attached below the decoupler (and work), so I think that possibility can be ruled out.

Oh sorry, my mistake, I assumed you had a monoprop tank buried in the rear half somewhere.

I tried to recreate your craft from the image and the lateral thrusters worked OK using translation keys (which I have mapped to IJKL) when connected to the TD-12 stack decoupler (even with fuel pass through OFF which really shouldn't happen) or anything else. But I could not identify the tube between the TD-12 and the Explorer pod on yours. It looks like a short section of TOOB-125 but I cant see its base segment, which would be wider than adjoining  structures and cannot be hidden inside them by widgit translation, so is not that, I cannot find an equivalent among stock parts. What is that?

[HebaruSan]

2 minutes ago, boolybooly said:

But I could not identify the tube between the TD-12 and the Explorer pod on yours. It looks like a short section of TOOB-125 but I cant see its base segment, which would be wider than adjoining  structures and cannot be hidden inside them by widgit translation, so is not that, I cannot find an equivalent among stock parts. What is that?

That's a heat shield fairing. (Part of that craft's mission was to test whether 1.25m heat shields can protect that lander can. It successfully demonstrated that they can't.) I can definitely believe that heat shields would obstruct fuel flow, which would leave the mystery of the aft thrusters. This isn't important enough to me to re-run the mission to check whether I'm misremembering about those.

[boolybooly]

1 hour ago, HebaruSan said:

That's a heat shield fairing. (Part of that craft's mission was to test whether 1.25m heat shields can protect that lander can. It successfully demonstrated that they can't.) I can definitely believe that heat shields would obstruct fuel flow, which would leave the mystery of the aft thrusters. This isn't important enough to me to re-run the mission to check whether I'm misremembering about those.

I see, thanks for explaining. I just tried the same configuration and it messed up the thrusters completely just as you describe.  Only one of the four lateral thrusters fired, on key H while its opposing key L fired one of the rear thrusters, which would mess up control completely and has to be a bug.

I will try to simplify the conditions and then report it.

EDIT Done, it is the heat shield, happens with all of them.

Spoiler

 

Edited January 19 by boolybooly