CoM Balancing

[Xurkitree]

I’m currently planning a big mission, and need to use the External Command Seats. However, one of my landers made with those has extreme control problems. It’s hard to control when landing on tylo and becomes uncontrollable on ascent. I think it is a CoM/CoT issue, so my question is, is there any way I can perfectly align Space Chairs on the CoM? Extra help regarding Command Seats in Service Bays would be a great help, since I can’t get it right

[Bej Kerman]

Try using another object that has the same mass as a kerbal in a seat as a counterweight.

Either that or you can zoom into the bay whilst facing down and place the chair dead bang in the middle of the CoM.

[Hydrothermalventclam]

You could use an engine with a really high gimbal range, like the vector.  That will allow SAS to keep the thrust vector through the CoM. 

If you are not opposed to adding mods, Throttle controlled avionics can automatically thrust limit the engines on your ship to keep the thrust vector through the CoM.

I have not used command seats much, but I would not have expected a small deviation in position of a kerbal on a command chair to render a ship uncontrollable, especially something as big as a Tylo lander.  Kerbals are pretty tiny.  Do you have enough reaction wheels, RCS and vectoring engines on your craft?

[Gaarst]

In stock, other than using symmetry or visually align the gigantic CoM and CoT markers there aren't really ways to exactly balance a spacecraft.

If you are OK with mods, Kerbal Engineer Redux and RCS Build Aid both give you a thrust torque reading to help balance a craft.

Edited November 1, 2018 by Gaarst

[I_Killed_Jeb]

The other thing to make sure is that even CoM and CoT are aligned, if your control point is not in-line with these, then you will fly off-axis. This can happen with command seats as control points because they're usually surface-mounted.

[Snark]

Moving to Gameplay Questions.

On 10/31/2018 at 3:17 AM, Xurkitree said:

I’m currently planning a big mission, and need to use the External Command Seats. However, one of my landers made with those has extreme control problems. It’s hard to control when landing on tylo and becomes uncontrollable on ascent. I think it is a CoM/CoT issue, so my question is, is there any way I can perfectly align Space Chairs on the CoM? Extra help regarding Command Seats in Service Bays would be a great help, since I can’t get it right

Could you post a screenshot of your ship?  Would really help us get a more specific idea of what you're dealing with, and let us give specific suggestions for fixing problems.

Other than potential CoM issues, I could also imagine a potential problem with orientation of control point, depending on how/where the command seat is attached.  The control point of probe cores and crewed command pods points upward, but the control point of a command seat points forward (i.e. in the direction the passenger seat faces).  Depending on how you have the ship set up, it's conceivable that you may have a control point that's oriented differently than you expect, which can make the controls feel like they've gone completely haywire. 

Or maybe that's not your issue at all.  But a screenshot would really help for diagnosing.

[Klapaucius]

It's worth noting as well that while (as far as I know) Kerbals don't add weight to enclosed command modules, they do with command seats.  So your weight will change once your craft is manned, er--Kerbaled.

 

[Xd the great]

Also, a seperate probe core with sas might help. Might. Remember to control the craft from there.