[Bug?] Wobble of Death Destroys My Vehicle

[IamJimmy]

So I made this vehicle to explore the  Jool system, landing on all Jool's moons except Tylo and come back. It consists of two parts, Laythe Descent & Ascent Vehicle  (LDAV) and Jool System Transfer  Stage (JSTS).

The vehicle enters Laythe SOI with the help of a Tylo gravity assist. The Laythe insertion burn depletes the JSTS' bottom stage (the one with 6 Nervs) and it is decoupled and left to burn up in Laythe's atmosphere. After getting into an orbit 70km above Laythe's surface, LDAV is undocked and glided down to land on Laythe. It is then launched into Laythe orbit and docked with JSTS . After getting rid of LDAV's wings and fuel tanks the whole vehicle is then transferred to Vall.

The problem is, when I try to decouple JSTS' bottom stage, its two Mk1 tanks on small hardpoints starts to wobble and blow up in a few seconds. If I go back to space center at the moment it starts to wobble and come back, it stops wobbling. But as soon as I move the vehicle (including changing pitch, roll, yaw; firing engines; etc.), it starts to wobble and then explodes.

I tried to recreate this issue by getting JSTS into orbit around Kerbin using cheat menu. It seems fairly stable on its own. I then tried to get JSTS with a docked dummy LDAV into orbit, but it also doesn't wobble. 

It seems that only a real LDAV docked with the JSTS causes the wobble, and it only happens when JSTS' bottom stage is decoupled. I'm guessing that mirrored small hardpoints on both LDAV and JSTS somehow amplifies the wobble and cause the vehicle to explode.

Here are my questions:

1) What is causing the problem?

2) How to avoid it in the future?

3) Any way I can fix this and continue my Jool exploration? (I know a few struts might be the only thing needed to solve the problem, but I have already spent a few hours refueling and sending the vehicle to the Jool system. I really don't want to do it again.)

[4x4cheesecake]

1 hour ago, IamJimmy said:

1) What is causing the problem?

2) How to avoid it in the future?

1) Probably auto-struts, if you use them

2) Sacrefice your firstborn to the mighty kraken If you use auto-struts, set them to 'Grandparent' (this can be done in flight). Other settings like root or heaviest will cause the auto-struts to switch the connecting parts everytime you dock a vessel. This will initiate the wobble. I would also recommend to turn off SAS/RCS a second before you actually dock the vessels. These systems try to compensate every slightly wobble but usually they fail and even intesify the wobbling.

Oh, and you can always do an 'emergency wobbling stop' with a quick on-rails time warp.

Edited July 8, 2018 by 4x4cheesecake

[Laie]

1) this happens sometimes, it's not all that uncommon, and the true reason is not known.

2) unknown reasons are hard to avoid.

3) you may try playing around with autostruts, selectively enabling (or disabling) them on a few parts and see what happens.

It probably won't be long until someone says that autostruts are the cause of the problem. They're not. I've had this happening to me long before autostruts even were a thing. However, autostruts allow you to reconfigure how your vessel is held together, during flight -- in the olden days one had to revert to VAB.

I emphatically do *not* say that you should use more autostruts. Disabling or re-targeting an existing autostrut is as likely to fix the problem as enabling a new one.

[4x4cheesecake]

7 minutes ago, Laie said:

It probably won't be long until someone says that autostruts are the cause of the problem. They're not. I've had this happening to me long before autostruts even were a thing.

Already said this
Auto-struts may not be THE reason but they are one possible reason, especially if they are set to 'root' or 'heaviest'.

I had some spacestations and wasn't able to dock any vessel to them without wobbling the whole station to death but I was able to fix this by removing some auto-struts and setting the remaining to 'grandparent'. Auto-struts are definitly one possible reason.

[Gargamel]

Well, looking at that design, Intuition tells me those nacelles should wobble more than a drunken cow on harvest night.    Before we had autostruts, we had these things called struts.  I'd strut the tail end of each of those nacelles back to the main ship.  

But try autostruts first, if you're not using them.  If you are using them, stop using them and use regular struts.    Ignore the knowledgeable naysayers above, and love the autostrut.    

[IamJimmy]

10 hours ago, 4x4cheesecake said:

1) Probably auto-struts, if you use them

2) Sacrefice your firstborn to the mighty kraken If you use auto-struts, set them to 'Grandparent' (this can be done in flight). Other settings like root or heaviest will cause the auto-struts to switch the connecting parts everytime you dock a vessel. This will initiate the wobble. I would also recommend to turn off SAS/RCS a second before you actually dock the vessels. These systems try to compensate every slightly wobble but usually they fail and even intesify the wobbling.

Oh, and you can always do an 'emergency wobbling stop' with a quick on-rails time warp.

 

10 hours ago, Laie said:

1) this happens sometimes, it's not all that uncommon, and the true reason is not known.

2) unknown reasons are hard to avoid.

3) you may try playing around with autostruts, selectively enabling (or disabling) them on a few parts and see what happens.

It probably won't be long until someone says that autostruts are the cause of the problem. They're not. I've had this happening to me long before autostruts even were a thing. However, autostruts allow you to reconfigure how your vessel is held together, during flight -- in the olden days one had to revert to VAB.

I emphatically do *not* say that you should use more autostruts. Disabling or re-targeting an existing autostrut is as likely to fix the problem as enabling a new one.

 

9 hours ago, 4x4cheesecake said:

Already said this
Auto-struts may not be THE reason but they are one possible reason, especially if they are set to 'root' or 'heaviest'.

I had some spacestations and wasn't able to dock any vessel to them without wobbling the whole station to death but I was able to fix this by removing some auto-struts and setting the remaining to 'grandparent'. Auto-struts are definitly one possible reason.

 

6 hours ago, Gargamel said:

Well, looking at that design, Intuition tells me those nacelles should wobble more than a drunken cow on harvest night.    Before we had autostruts, we had these things called struts.  I'd strut the tail end of each of those nacelles back to the main ship.  

But try autostruts first, if you're not using them.  If you are using them, stop using them and use regular struts.    Ignore the knowledgeable naysayers above, and love the autostrut.    

After a bit of testing, I determined the wobble is caused by the combination of two pairs of  nacelles. Getting rid of either pair fix the problem. However it is not an option to decouple the  nacelles for the obvious  reason. I didn't use auto-struts previously. In fact the last time I played KSP was years ago on my friend's computer. It was 0.18 at that time and it was only recently that I decided to pick up the game again. I missed out a lot and had no idea that auto-struts was a thing. For now, enabling auto-struts for both pair of  nacelles seem to fix the problem. Thanks for your wonderful suggestions!