Massless parts

[Kasuha]

I think it might be better for parts with PhysicsSignificance set to 1 to have their mass added to the mass of the parent part instead of just ignored. This would avoid the worst of the imbalance issues (assuming you attach stuff to something whose COM is already aligned with the whole vessel COM) without adding more issues by the parts being massless...

Adding their mass to their parent has two problems.

First, their parent might be massless, too.

Second, it may lead to balance problems with ladders on staged landers. You need just one ladder and you may still need to place it on part which is placed in symmetry.

That's why I think the additional mass should be distributed evenly over "massy" parts of the ship.

[Claw]

I think I agree about massless RCS ports feeling cheaty.

- Having all of the extremely minor parts being massless certainly seems like no big deal, and I could definitely live with it. Although I'm also a fan of making incredibly small probes. As such, having all the really small parts being completely massless makes small probes much less challenging. Now I can slap on anything I want.

- The idea of applying the mass directly to the parent part sounds like a good idea at first (and I sort of like it), but I also thought that it might introduce too many buggy "features" by creating special cases in the code that handles the part tree. (Like Kasuha pointed out.)

- Spreading out the mass over the whole ship seems like a workable thing too. Although I imagine it's implementation being a lot more straight forward (and less buggy) if it was just applied directly to the total mass of the ship. (I'm thinking game code here.) I guess what I'm thinking is that instead of peanut-butter spreading the mass over the whole ship, simply apply the total "insignificant" mass as a single "extra weight" at the end of the mass calculations instead of as a moment arm on the ship. So the parts wouldn't effect inertia calculations, but they effect the overall mass. (And subsequently the delta-v, acceleration, etc...)

I think that would still make small probes challenging without having to deal too much with the very sensitive parts balance issues for things like ladders, etc.

Edited April 12, 2014 by Claw

[stupid_chris]

MJ only started doing it correctly a few days ago and KER (the test development version) did the same.

You shouldn't need to change RealChutes as the fix was purely for the VAB rather than in flight (or do you do in VAB calculations?).

I do in VAB calculations to calculate the needed diameter of the parachutes (EditorLogic.SortedShipList.Where(p => p.physicalSignificance != Part.PhysicalSignificance.NONE).Sum(p => p.mass + p.GetResourceMass())

[Streetwind]

So how does one go about to make parts physicsless, or remove that property from parts?

[cantab]

PhysicsSignificance = 1 in the configuration file.

[Padishar]

I do in VAB calculations to calculate the needed diameter of the parachutes (EditorLogic.SortedShipList.Where(p => p.physicalSignificance != Part.PhysicalSignificance.NONE).Sum(p => p.mass + p.GetResourceMass())

In the VAB the parts may not have that property set correctly. You may need to check p.PhysicsSignificance (i.e. directly check the .cfg value) instead (or as well). This is what sarbian and myself have fixed in MJ and KER in the last few days...

As for the massless parts, there are basically 2 classes of part that have been made massless; ones that don't affect the "performance" of the craft and ones that do. The former includes ladders, lights, science parts etc. The ones that do include the RCS thrusters, batteries and the solar panel. I don't think these should be made massless at all, it isn't that hard to balance a ship.

Adding mass to either the parent part or to the COM of the vessel will both require some special code in the core game to deal with changes to the craft, e.g. it needs to recalculate correctly when the craft is staged, undocked, a part explodes etc. However, I don't think this code would be particularly difficult to write whichever mechanism is used.

As kasuha said earlier, the most important thing is that parts with no physics significance seem quite prone to attracting the attention of the kraken and making more parts like this may greatly increase the number of problems people see.

Edited April 12, 2014 by Padishar

[Hurry- Starfish!]

I don't understand why there are massless parts at all. Is it a concession to some shortcoming of the engine?

Performance reasons?

[NERVAfan]

Ah, I'm glad to know this, I've been putting ladders on both sides of my Mun landers....

[Streetwind]

So how does one go about to make parts physicsless, or remove that property from parts?

PhysicsSignificance = 1 in the configuration file.

Erm, is that all? Most of the parts that are said to be physicsless by default do not have this line anywhere in their configs. I was able to find it on a ladder, for example, but not on landing gear, not on the OX-STAT panels, and not on the small batteries either. Chris said earlier in this thread that "it's in the module", and that he succeeded in removing it himself, but I don't know what he meant with that, so I wanted to ask for clarification.

[Aedile]

I don't know. It doesn't seem so hard for squad to add the mass of the mass-less parts directly to the CoM, and remove it when part is dropped.

Also the whole massless thing is pretty annoying. For those of us who takes care to balance our ships, is very frustrating to figure out that one of the parts has mass and the other is massless, leading to a ship which is supposed to be balanced, not to be.

[John FX]

PhysicsSignificance = 1

This line makes the parts massless. The Z-100 battery also shares this, as well as the ladders. I've changed the behaviour of some parts in the Stock Rebalance project (link in my sig). Some parts like the battery /should/ have a mass, and those who don't have their mass changed to zero so they don't affect the CoM.

Wait, the batteries are massless? That makes no sense. I can understand items you need to fit off centre, like ladders or things that are only on the bottom, like wheels but batteries?

Surely they should be part of the mass/utility balance to avoid spamming them to heck and back?

I have quoted and bolded something that bears repeating...

EDIT : I may have to bite the bullet and get your rebalance...

Edited April 13, 2014 by John FX

[Claw]

Erm, is that all? Most of the parts that are said to be physicsless by default do not have this line anywhere in their configs. I was able to find it on a ladder, for example, but not on landing gear, not on the OX-STAT panels, and not on the small batteries either. Chris said earlier in this thread that "it's in the module", and that he succeeded in removing it himself, but I don't know what he meant with that, so I wanted to ask for clarification.

The small landing gear bay (used on airplanes) used to be massless, but I don't see that line in the gear part anymore. Maybe that's why it was on the list. I was able to find the PhysicsSignificance line in the small battery (Z-100). Chris said he removed this line from his parts. It looks like this if you want to do it.

Go to the corresponding parts.cfg for whichever thing you want to remove the massless physics. The example below is the Z-100 battery pack. Note that the Physics line is lower in this part than typical (I made it bold).

PART
{
// --- general parameters ---
name = batteryPack
module = Part
author = NovaSilisko

// --- asset parameters ---
mesh = model.mu
rescaleFactor = 1

// --- node definitions ---
// definition format is Position X, Position Y, Position Z, Up X, Up Y, Up Z
node_attach = 0.0, 0.0, 0.0, 0.0, 0.0, -1.0

// --- editor parameters ---
TechRequired = scienceTech
entryCost = 800
cost = 80
category = Utility
subcategory = 0
title = Z-100 Rechargeable Battery Pack
manufacturer = Zaltonic Electronics
description = The Z-100 battery pack is the standard model for electrical applications. Holds two (2) AAAA batteries and holds a maximum 100 units of charge.

// attachment rules: stack, srfAttach, allowStack, allowSrfAttach, allowCollision
attachRules = 0,1,0,0,0

// --- standard part parameters ---
mass = 0.005
dragModelType = default
maximum_drag = 0.2
minimum_drag = 0.2
angularDrag = 1
crashTolerance = 8
maxTemp = 3200

[B]PhysicsSignificance = 1[/B]

RESOURCE
{
 name = ElectricCharge
 amount = 100
 maxAmount = 100
}
}

Delete that line, and your part will be as it was in 0.23.0.

I don't know. It doesn't seem so hard for squad to add the mass of the mass-less parts directly to the CoM, and remove it when part is dropped.

Also the whole massless thing is pretty annoying. For those of us who takes care to balance our ships, is very frustrating to figure out that one of the parts has mass and the other is massless, leading to a ship which is supposed to be balanced, not to be.

True (and I agree), but the game is also deeply in development. So I'm sure they are trying out different things along the way. There are quite a few features that "shouldn't be so hard for squad to do," but they're also putting in things that are hard to do. And they make changes like this so that we can give constructive feedback (like this thread).