0.625m SRB

[DeMatt]

After wishing for the umpteenth time for a SRB bigger than the Seperatron and smaller than the RT-10, I remembered this thread, and how it scaled down an existing model with just a .CFG file.

I can do that, said my brain, and after a few hours of tinkering, produced this:

PART
{
// Kerbal Space Program - Part Config
// RT-5 Mini Solid Fuel Booster
// 

// --- general parameters ---
name = miniSolidBooster
module = Part
author = NovaSilisko/shrunk

// --- asset parameters ---
MODEL    {model = Squad/Parts/Engine/solidBooster/model}
mesh = model.mu
scale = 0.1
rescaleFactor = 0.75


// --- node definitions ---
node_stack_bottom = 0.0, -9.4, 0.0, 0.0, 1.0, 0.0, 0
node_stack_top = 0.0, 7.8, 0.0, 0.0, 1.0, 0.0, 0
node_attach = 0.0, 0.0, -3.3, 0.0, 0.0, 1.0, 0

// --- FX definitions ---

fx_exhaustFlame_yellow_small = 0.0, -5, 0.0, 0.0, 1.0, 0.0, running
fx_exhaustSparks_yellow = 0.0, -5, 0.0, 0.0, 1.0, 0.0, running
// fx_exhaustLight_yellow = 0.0, -5, 0.0, 0.0, 0.0, 1.0, running
fx_smokeTrail_light = 0.0, -5, 0.0, 0.0, 1.0, 0.0, running

// --- Sound FX definition ---


sound_vent_medium = engage
sound_rocket_hard = running
sound_vent_soft = disengage
sound_explosion_low = flameout

// --- editor parameters ---
TechRequired = precisionEngineering
entryCost = 3000
cost = 150
category = Propulsion
subcategory = 0
title = RT-5 Mini Solid Fuel Booster
//manufacturer = Jebediah Kerman's Junkyard and Spaceship Parts Co.
description = While the RT-10 is made out of a full-size trash can, the new RT-5 Mini is made out of a smaller, more handy wastebasket. Good for those times when all you want to move is a trash can.

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

// --- standard part parameters ---
mass = 0.0625
dragModelType = default
maximum_drag = 0.3
minimum_drag = 0.2
angularDrag = 2
crashTolerance = 7
maxTemp = 3600 

// --- solid booster parameters --- 3.75

stagingIcon = SOLID_BOOSTER

MODULE
{
	name = ModuleEngines
	thrustVectorTransformName = thrustTransform
	throttleLocked = True
	exhaustDamage = True
	ignitionThreshold = 0.1
	minThrust = 0
	maxThrust = 60
	heatProduction = 500
	useEngineResponseTime = True
	engineAccelerationSpeed = 10.0
	allowShutdown = False
	fxOffset = 0, 0, 0.12
	PROPELLANT
	{
		name = SolidFuel
        ratio = 1.0
		DrawGauge = True
	}
	atmosphereCurve
 	{
   	 key = 0 230
  	 key = 1 220
 	}

}

MODULE
{
      name = ModuleAnimateHeat
      ThermalAnim = heatAnimation
}



RESOURCE
{
 name = SolidFuel
 amount = 54
 maxAmount = 54
}

MODULE
{
	name = ModuleTestSubject

	// nowhere: 0, srf: 1, ocean: 2, atmo: 4, space: 8
	environments = 15

	useStaging = True
	useEvent = False
}
}

Now, there's a couple things I'm not enthusiastic about:

• The FX definitions. I did find a list of the things on the wiki, but I'm still iffy about whether I A) picked the right ones, or should've been looking for a rescale function of some kind.
  
• The attachment nodes. I eyeballed them in KSP (that's what took the hours), but I'm wondering if I actually did them right.
  

Anybody willing to take a peek?

[Kartoffelkuchen]

I think that if you take an existing model and you rescale it via the config file the nodes become adapted automatically. About fx: You can't rescale fx I think, you probably have to create a new, smaller one, but I'm not completely sure

To find the fx you want you can easily try every engine ingame, and with the engine ewith the fx you want you can easily copy the fx name and Paste it in your cfg.

[NathanKell]

Three things affect scale.

First, does the part use MODEL nodes? Skip to part B.

A (MODEL node not used; instead "mesh = blah" used)

1. "scale = foo" determines how the first three numbers for each attach node line (the X, Y, Z coords of the node) are scaled. It does *not* affect anything else. Default = 1.0 if not present

2. "rescaleFactor = bar" scales both the model (and its transforms) *and* the attach nodes. Default = 1.25 if not present.

B (MODEL node(s) used)

1. Inside the MODEL node, "scale = blahX, blahY, blahZ" determines the scaling of the model and its transforms. Default is 1.0, 1.0, 1.0. It does not affect node positions.

2. Outside the MODEL node, "scale = foo" works as above.

3. Outside the MODEL node, rescaleFactor works as above.

HOWEVER, there is a bug in scaling. For parts with MODEL nodes, rescaleFactor is applied twice to the mu, *unless* (a) the part is the root part of the vessel and ( you've reverted to launch (or perhaps switched in flight? Don't recall). All other times, it is applied twice. What this means is that if you have scale = 1.0, 1.0, 1.0 in the MODEL node (or no scale at all), and rescaleFactor = 1.25, then your mesh will actually be 1.5625 as big, but your nodes will be scaled outwards 1.25.

For this reason, when scaling parts using MODEL nodes, it is suggested to leave scale (outside the MODEL node) and rescaleFactor both at 1.0, and instead both change the scale = x, y, z inside the MODEL node and manually scale the positions of the attach nodes.

In sum, you need to use rescaleFactor = 1.0, and set scale = x, x, x in the MODEL node (where x is the desired scaling factor) and then manually change the first three numbers of each node_whatever to be what_they_originally_were*x

[DeMatt]

...That's some nice, general information...

...But I was really hoping for someone to give the part a try and offer specific criticisms, assuming they had any.

[NathanKell]

And yet in that general information I told you exactly what's wrong, and how to fix it: don't use rescaleFactor of value not-1.0 if you're using MODEL nodes. Instead, use scale in the node, and manually fix the attach nodes.