Spinning out, no idea why

[Loren Pechtel]

I've been on vacation and was playing on my laptop.  I copied everything back onto my main machine (synchronized the whole directory structure, everything should be identical) and launched a rocket that I had flown successfully many times.

On my main machine as soon as the SRBs come off it starts to wobble then spins out.  MechJeb is flying it in both cases.

I will agree that it's near the stability limit.  It's using the reaction wheel of the probe core that guides it, but it does have 4 fins that let it fly reliably to orbit.  (After retrofire it has exactly the same number of m/s every time, if it were wobbling I would not expect that.)

What could possibly make it fly on one machine and not on another?  I do not recall loading any updates with CKAN while I was away and if I had they would have been mirrored to this machine during the sync anyway.

 

Edit:  It took 2 3.75' reaction wheels to get this bird to fly and it still wobbles.  The heavier weight also caused the engine to blow up on re-entry but I also don't have the fuel dialed in perfectly, that added weight, also.

How can my two computers be so different when I copied everything over??  (And I rechecked the sync--nothing different except the config files that got updated when I ran the game.)

Edited June 2, 2017 by Loren Pechtel

[Streetwind]

I'd ask for a craft file, but you're using mods, so it'll probably be near impossible to load without replicating your whole install.

How about some screenshots instead?

[Loren Pechtel]

8 hours ago, Streetwind said:

I'd ask for a craft file, but you're using mods, so it'll probably be near impossible to load without replicating your whole install.

How about some screenshots instead?

Unfortunately I only have the now-fixed version.

I forget exactly what was on the nose, not much, then a probe core tweaked to 2.5m, 2.5m->Mk3 fuel tank, 3x 16 passenger compartment, 3x Mk3 fuel tanks, I forget the engine but it was a 2.5m tweaked up to 3.75m.  My memory was wrong, the original had a 2.5m reaction wheel.  To get it to fly the modified one needed 2x 3.75m wheel (tweaked).  LET chutes along one side so it would tip upon landing rather than fall over after the chutes cut.

2 hours ago, llanthas said:

I'm guessing you have FAR installed on one of them... 

 

The thing is both machines are running absolutely the same mods.  I synchronized the entire SteamApps\Common structure between the machines.

[Snark]

33 minutes ago, Loren Pechtel said:

Unfortunately I only have the now-fixed version.

Fair 'nuff, but honestly, any "why is this ship not aerodynamically stable?" is going to need a screenshot for anyone to be able to give meaningful advice.

(Ideally a screenshot in the SPH with the CoM indicator turned on.)

[Loren Pechtel]

27 minutes ago, Snark said:

Fair 'nuff, but honestly, any "why is this ship not aerodynamically stable?" is going to need a screenshot for anyone to be able to give meaningful advice.

(Ideally a screenshot in the SPH with the CoM indicator turned on.)

The thing is my question is why is my ship unstable only on my desktop machine.  I'm trying to understand the difference.

[Snark]

11 minutes ago, Loren Pechtel said:

The thing is my question is why is my ship unstable only on my desktop machine.  I'm trying to understand the difference.

Yes, and without a screenshot, nobody is going to have the slightest clue what might be wrong with your ship.

Without any idea what might be wrong wtih the ship at all, it's pretty hard to advise what might be causing a difference between platforms.

1 hour ago, Loren Pechtel said:

The thing is both machines are running absolutely the same mods.

in the absence of a screenshot, can speak only in generalities:

1. make sure that they really are the same mods
2. ...with the same versions
3. ...with the same config
4. ...with the same settings
5. ....with the same KSP options & settings
6. etc.

[Spricigo]

1 hour ago, Loren Pechtel said:

 I'm trying to understand the difference.

For whatever reason, there is a difference in how (or what parameters are used by) the machines are computing the situation, it can be as small as a single binary digit being copied wrong while synchronizing. Also, Its not that rare for a application to only have problems running with a particular processor/memory/operational system/whatever.

Given the fact that a slight change in the craft design solved the problem: If is not broken, don't fix.

[bewing]

I'm going to guess that the difference is the SSE support level for the two CPUs in your two machines.

 

[Loren Pechtel]

2 hours ago, bewing said:

I'm going to guess that the difference is the SSE support level for the two CPUs in your two machines.

 

Ah, that makes sense!  It's probably a tiny precision difference that lets it fly acceptably on the laptop.