Leszek

Is there a Mod that can help me align thrust and mass?

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So here is the deal.  My ships are very functional.  In particular they have science experiments all over the place.  I do my best to line up the thrust and the center of mass and get them as close as I can with that little visual indicator they give you in the game.  However the accuracy of this indicator is such that they are normally off a bit.  This can cause problems, especially with probes being driven by RT where the flaw can be fatal to the mission.

I can do things to mitigate such as setting the throttle limiter but it would be great if I had some more accurate indication.  I can't seem to find any indication like that in KER and I don't even know if there already is some sort of tool for that that I just don't know about.

Anyone have any ideas?

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Mechjeb has a differential throttle setting(in the utilities menu) for use with 2 or more engines. I usually fly spaceplanes with 3-4 engines staggered above and below the CoM aligned so with differential off there is a slight pitch up to help raise the nose off the runway. I then turn differential throttle on when the air gets thin and my planes will fly straight when in space. Of course, this only helps when you have 2 or more engines on different sides of the CoM but, it does continuously adjust for fuel usage.

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Another very useful mod for this is RCS Build Aid. You can use it to adjust the relative positions of RCS units and ship components so that RCS maneuvers are balanced (its original purpose) and you can also use it to balance masses around thrusters either by moving the masses or moving the thrusters.

It gives a real-time display of how a ship might turn while thrusting or attempting to RCS-translate, or how it will translate while attempting to turn. This allows you to tweak your design and see how well balanced everything is.

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Normally the animation of the CoM isn't off. But you are burning fuel by which you are shedding mass as you expel it by using your engines.
Try to drain all of your fuel tanks in the VAB or SPH and see if the CoM moves. If it does and It moves about in unfavourable areas you'll have to re-arrange your fuel tanks.

If that doesn't help you can try this mod...

Do pack some extra thrust for the target body, the mod will limit thrust automatically on one side to compensate for offset thrust. But that also lowers your TWR
So if you pack 1.2 TWR for your intended target I would pack 1.3 or even 1.4 just in case :) 

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1 hour ago, Leszek said:

I can't seem to find any indication like that in KER

This is what the TORQUE column is for. Use the translation tool ('2') in precision mode ('c') to slide your engine around till the torque is 0.

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Thanks to all who answered.  This last post is the ticket for my needs.

Quote

Normally the animation of the CoM isn't off. But you are burning fuel by which you are shedding mass as you expel it by using your engines.

Just to be clear, it is not that it is off, it is that it isn't accurate enough for my needs.  You have to eyeball when they line up and you are usually still off a bit. 0.09 kNm on my last design it turns out.  But the CoM and the line of thrust are not near each other and visually they look lined up perfectly.

Quote

This is what the TORQUE column is for. Use the translation tool ('2') in precision mode ('c') to slide your engine around till the torque is 0.

That was easy.  Thanks very much.  One of those fun times where in I am glad I was just oblivious.

Edited by Leszek
Clarification.

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45 minutes ago, Leszek said:

That was easy.  Thanks very much.  One of those fun times where in I am glad I was just oblivious.

You're welcome. Note that this can also be used to balance far more asymmetrical designs, but it's still a good idea to keep the fuel symmetrical around the CoM:

?interpolation=lanczos-none&output-forma

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1 hour ago, HebaruSan said:

This is what the TORQUE column is for. Use the translation tool ('2') in precision mode ('c') to slide your engine around till the torque is 0.

Didn't knew this myself. I'll keep learning everyday, thanks :) 

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1 hour ago, softweir said:

Another very useful mod for this is RCS Build Aid.

I 2nd RCS Build Aid, which doesn't sound like it'll do what you want, but it does. The visual representation of torque on the screen is much easier for me to relate to than a number.

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10 hours ago, 5thHorseman said:

I 2nd RCS Build Aid, which doesn't sound like it'll do what you want, but it does. The visual representation of torque on the screen is much easier for me to relate to than a number.

I have just gone and had a look at a YouTube demo of that Mod and I think I will have to give that a try as well.  Thanks to both of you for suggesting it.

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I've never been able to use RCS Build Aid, just doesn't click with my brain. Is there a mod that just extends the COM and thrust markers into proper screen-wide crosses and removes the big obscuring spheres? Thrust marker would be much more useful if it was screen-wide and the COM marker is so large and hard to align as to be useless.

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14 minutes ago, regex said:

I've never been able to use RCS Build Aid, just doesn't click with my brain. Is there a mod that just extends the COM and thrust markers into proper screen-wide crosses and removes the big obscuring spheres? Thrust marker would be much more useful if it was screen-wide and the COM marker is so large and hard to align as to be useless.

Agreed, never found RCS build aid useful either. I'd also support an option to toggle the big sphere's, they just get in the way.

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There's a slider to change the size of the spheres, but even more useful than the visual indicator is the numerical readout of torques.  Note that it can tell you torque from RCS translation and rotation (the nominal purpose of the mod) in all six axes, but also from engines and parachutes.  As a bonus feature it can tell you how much delta-V your RCS system provides (haven't seen that little nugget in any other commonplace mod yet)

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3 hours ago, Rocket In My Pocket said:

Agreed, never found RCS build aid useful either. I'd also support an option to toggle the big sphere's, they just get in the way.

Open an issue and github. I'll take a look at it, but the slider made to solve the problem for you.

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