Tri-coupler and center of mass

[gadams99]

Hi all,

I'm new to KSP and am loving my education into space flight. Great stuff and looking forward to more!

Right now, I'm running the latest version along with a variety of add-on's such as Deadly Reentry and the whole Renaissance Compilation. The beginner science tutorial here is great, but I've run into an issue (I think) for my Minmus craft. It essentially starts to side slip to starboard and becomes unstable 5-10km up. Through trial and error, it looks like there is something wonky with the tri-coupler that is used as part of the craft.

With just a capsule and tri-coupler as seen here:

the center of mass looks like from a top-down view:

Then, when I add 3 x FL-T400 tanks, as such:

The center of mass shifts like so in this top-down view:

I can't tell if the CoM ball is off due to camera angles or not, but the craft does start to drift in that direction.

Has anyone seen issues with the tri-coupler and CoM? Are there any plugin's that would show numeric values for the center of lift/mass/thrust while in the VAB? I'd like to get Marvin Kerbal to Minmus....

Thanks!

[SRV Ron]

Tri coupler designs need braces at the base or they get wobbly and go off course. As far as such a design placing Marvin on Minmus and return, easy to do.

Less fuel reserve but still got the job done.

On Minmus with lots of fuel left to return.

Over half a tank left as the return trip comes to an end.

[Claw]

Hmm. I've not noticed this before, but I also haven't been looking for it.

I can't check it out at the moment, but I will say that the top down picture with the FL-T400s looks off center. The thickness of the tri-coupler on top looks wider than on the bottom right, and the bottom right looks ever so slightly wider than the bottom left. (I can also see it on the sides of the Mk1 pod.) That offset is consistent with the CoM displacement shown.

Having a lower CoM magnifies any small offsets from directly overhead. Maybe try centering the ball on top of the Mk1 pod, then see if the craft looks symmetric.

I'm not saying there isn't unwanted offset buried in there, but it's hard to tell because the picture looks tilted.

By the way, welcome to the forums!

-Claw

Edited July 17, 2014 by Claw

[Laie]

Try to bring up one more point, like centor of lift or thrust. That makes it much easier to see whether things line up.

[xcorps]

Off topic, but worth knowing about:

If you use the multistack (especially the tri and quad) couplers in radial symmetry you face the possibility of some nasty bugs. Parts under the coupler get duplicated in weird ways, you can break symmetry, and generally wreck KSP, including corrupting your save file.

[Oafman]

I had a weird thing once where I was trying to fit 4 tanks to a quad adaptor with symmetry. They all showed as green when I clipped, and let me continue building beneath them. But when I launched the rocket I found that only 3 of them were attached, and it soon lost control.

Could something similar be happening here? If you zoom in very close you might be able to see a slight difference in the position of one of the tanks. Or actually, based on your aerial view showing CoM, cold it be that only one of the 3 tanks is actually attached to the adaptor?