Mass Solutiobn

[JimmyAgent007]

Just a quick idea on the subject of ladders and other parts that dont have mass. The reason as i understand it is that if they did then we would get some lopsided flights because you might only have a ladder on a single side of the ship. So my idea is that the parts have mass but they are added to the part they connect with rather than the part in question. For example, the command pod of choice has a mass of x, then the ladder has the mass of y. You attach the ladder to the pod, so then the pod has the mass of x+y. So you can have a realistic mass of your rocket without making the flight wobbly by having some mass off to the side. Unless im totally missing something.

[Red Iron Crown]

The reasons for massless parts haven't been officially revealed as far as I know, but one of the speculations about it is it makes it easy to balance a ship with asymmetric part placement (ladders are often placed on only one side, for example). If the parent part of the ladder is not along the center of mass' axis, your solution would not eliminate such a balance problem.

That said, I like where you're going with this idea, there shouldn't be such a thing as a massless part.

[Vaporo]

...there shouldn't be such a thing as a massless part.

Yep. I think this has been suggested a couple of times, and I totally agree with it. I'm not sure about the oft-suggested thing where you just add to the center of mass of the parent part, though. Realistically, the center of mass of the parent part should shift as well. I'm just not comfortable with the idea that I could add fifty solar panels onto one side of a structural beam without unbalancing it.

Also, I think that the official reason that this was done was to reduce the load on the physics engine of having to account for all of those insignificant little parts hanging off the side of rockets. Don't take my word on that, though.

Edited June 4, 2014 by Vaporo

[JimmyAgent007]

Perhaps then adding the mass to the overall centre of mass of the ship. The centre of mass starting at 0 mass but adding each time you add something that is normally without mass. Treating it as a single object for the purposes of processing. Just a quick recalculation each time the part count changes either from stage separation or docking. Then, like with most things in KSP, let the players control themselves with regards to abusing the rules.

[the_bT]

Its probably the physics engine load thing. The proposed solution is good. Add to the mass of the parent part though. Masses at abstract points on your craft is asking for trouble I think.

What happens when such parts get torn off your craft? If you only add mass to parent part you need to change only the mass of that part. Should be doable, fuel tanks do that all the time. If you also shifted the center of mass than you need to shift it back. I don't know if the center of gravity of a part can be shifted during a flight or indeed at all.

[JimmyAgent007]

Doesnt the engine always calculate the centre of mass after each stage or docking... or crashing and breaking off fuel tanks? I agree it shouldnt be abstract anyways but assuming adding it to the parent part isnt an option i figure it to be a plan B

[Red Iron Crown]

I'm not sure it calculates the CoM outside the VAB/SPH. Ships are a close-flying formation of individual parts as near as I can tell.

[the_bT]

I think the physics engine comes up with a center of mass from the combined centers of mass of all the parts in combination with the joints that connect them.

Basically there is no such thing as the center of mass of the whole craft, just parts and joints. That way no special calculations are needed when a joint breaks. Of course you get in trouble if you connect a lot of parts with a lot of joints. Physics engines have mostly been made to blow stuff up, not keep them together. They also frequently treat moving the center of mass as something that is not necessary telling you to move the visible and collision geometry instead.

[rtxoff]

How is this problem solved in real life equipment?

[JimmyAgent007]

I would think counterweights are the real life solution, or other parts that do other things that balance out in the end.

I would think in KSP that you could just add the mass to the command pod, but some ships have several so it might not work even then. Adding it to the parent part seems like the only workable solution for now with how things are currently done. Not perfect but at least then things would have mass.

[rtxoff]

It's not only mass, also drag that is missing.