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Bug #5257

In symmetrically placed stacks fantom fuel lines sometimes appear

Added by Alchemist almost 9 years ago. Updated over 7 years ago.

Status:
Closed
Severity:
Normal
Assignee:
-
Category:
Gameplay
Target version:
-
Start date:
07/22/2015
% Done:

100%

Version:
1.0.4
Platform:
Any
Expansion:
Language:
English (US)
Mod Related:
No
Votes:
Arrow u r green
Arrow d r red

Description

Platform: found on Win7x64, but most likely platform-independent (please test)
Category: Resources/Fuel drain logic (source most likely in the VAB/editor)
Reproduceability: happens only in some (random?) cases, can be neutralized just by reattaching the stacks

Basic description: with multiple symmetrically attached stacks (found on 8x symmetry, but may be on others as well) there's a chance that one of the stacks will behave as if there was a fuel line to it from the root (?) of another stack (another option - fuel line behaviour spontaneously appearing in a random part attached to the symmetrical stacks)

Video demonstration:
https://youtu.be/HpJe4suWono

Files (full stock):
N1-L3 bug report - full original vehicle (high part count, no need to test. during its development the bug appeared and disappeared several times)
N1-L3 bug report first stage - first stage only
N1-L3 bug report first stage lite - narrowed down to only the significant parts (test on the pad, it spins in flight)
N1-L3 bug report first stage lite 1a - even more narrowed down - lower parts of the stacks replaced (test on the pad, it spins in flight)

Notes:

Replacing bottom parts of the affected stacks doesn't change the bug
If you remove the SAS modules from affected stacks, the glitch seems to disappear... putting them back there may return the bug, but not always. Note: those had been placed on already installed stacks using the symmetry mode
Saving-reloading the craft, detaching-reattaching the affected subassembly, reverting to launch don't fix the bug

Yeah, what's the better bug catcher than the first stage of N1 ;)

N1bugreport.zip (70.3 KB) N1bugreport.zip Alchemist, 07/22/2015 12:04 PM
brokencraft.doc (31 KB) brokencraft.doc Alchemist, 07/26/2015 08:08 PM

History

#1 Updated by Alchemist almost 9 years ago

Looks like adding reaction wheels to the side stacks (the two offset groups of stacks, but not those directly on the axis) of first stage of the attached N1-L3 results in this bug with high degree of reproducibility.

#2 Updated by Squelch almost 9 years ago

  • Category changed from 35 to 81
  • Status changed from New to Need More Info

I am able to confirm this behaviour with the supplied craft, and it has been witnessed elsewhere. However, attempts to replicate from a fresh craft have proved difficult, so we need to find the cause. I do suspect that parts that have been rotated, and are clipped into others are a significant factor. There is also a possibility that these parts are rotating very slightly between the editor and the craft being unpacked. (seen as differences between the .craft file and the same craft in the savefile) This might be a rounding issue, and totally coincidental, but worth mentioning.

I have marked this as needing more information in the hope that we can find some more examples, and work on being able to replicate the issue from a new minimal parts craft.

#3 Updated by Alchemist almost 9 years ago

I've run some analysis of the craft file and here's the finding (the lines seemingly relevant to the issue)
It's in the attached word file. The parts with problems are highlighted each in different color:

One of the reaction wheels (red) is listed as attached to the top node of one fuel tank (green) but refers another tank (blue) as connected to its bottom node. The link reference for the (red) reaction wheel is also listed with the wrong (blue) tank.

Looks like a subcase of broken symmetry bug (or one of its manifestations). Just this time the affected part has right coordinates, but considers itself linked to wrong part (sometimes, when attaching to symmetrical parts, some of the new parts are also visually appearing in the wrong places, overlapping with other new parts)

Unfortunately, it seems that these symmetry bugs appear mostly at high part counts and are rather unreliable (but these reaction wheels have been removed and reattached several times and the bug surfaced in most if not all of them.

P.S. I've also seen another case of symmetry bug when working on this craft - that time attempt to attach something (that were the nesting motors of the lander) to a pair of symmetrically placed parts resulted in symmetrical attachment to the same part, as if it didn't have symmetry counterpart.

#4 Updated by Squelch almost 9 years ago

Your observations are very interesting, and I did notice that one of the reaction wheels had incorrect node assignments. This can actually be seen in the editor if you are able to pick the correct part up. The node it was attached to will be seen to disappear, and only a save of the craft and a reload will fix it. Doing this and adding the reaction wheels back seemed to fix the problem.

I agree it is likely a subcase of the various symmetry bugs. Unfortunately, they are not always reproducible from scratch. Although we have plenty of examples of craft that show the problems, we still don't know what has triggered them in the first place. However, enough good evidential reports such as this, will always be useful in identifying the cause.

#5 Updated by Squelch almost 9 years ago

Not everyone is able to view a word document, so I have taken the liberty of adding an inline formatted version to the comment

#6 Updated by TriggerAu almost 8 years ago

  • Status changed from Need More Info to Needs Clarification

#7 Updated by TriggerAu over 7 years ago

  • Status changed from Needs Clarification to Closed
  • % Done changed from 0 to 100

Closing this report out for now. If you find it is still occuring in the latest version of KSP please open a new report (and this one can be linked to it.) For best results, the wiki contains really useful info for when creating a report http://bugs.kerbalspaceprogram.com/projects/ksp/wiki.

You can also ask questions about the bug cleanup in the forum here: http://forum.kerbalspaceprogram.com/index.php?/topic/143980-time-to-clean-up-the-bug-tracker/ and tag @TriggerAu to get my attention

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