Made an engine which can produce its own propellant while thrusting !

[Justin Kerbice]

Hi,

This is another magic of the buggy float curves use more or less the same way for stock engines (and many mods' engines I guess):

with this config:

mass = 0.2
dragModelType = default
maximum_drag = 0.18
minimum_drag = 0.05
angularDrag = 1
crashTolerance = 12
maxTemp = 1200

MODULE
{
	name = ModuleEngines
	thrustVectorTransformName = thrustTransform
	exhaustDamage = False
	ignitionThreshold = 0.1
	minThrust = 0
	maxThrust = 30
	heatProduction = 80
	useEngineResponseTime = False
	//engineAccelerationSpeed = 0.24
	//engineDecelerationSpeed = 0.42
	useVelocityCurve = True

	PROPELLANT
	{
		name = LiquidFuel
		ratio = 1
		DrawGauge = True
	}
	PROPELLANT
	{
		name = IntakeAir
		ratio = 8
	}
	atmosphereCurve
	{
		key = 0 0
		key = 0.68 0
		key = 0.7 10
		key = 0.9 1000
		key = 1 2000
	}
	velocityCurve
	{
		key = 400 0 0 0
		key = 300 0.05 0 0
		key = 0 1 0 0
	}
}

What I was looking for was to make a low performance enigne which can't works over a "fair" altitude (~ 6000 feet), I made this atmo curve as a first trial, as I'm not sure 0.68 match about 2000m, and can't go too fast.

But what I got is this magic engine which have a negative Isp and refuel itself instead WHILE keeping pushing up !

Take a look here for more detail.

As I wrote in this same thread: all stock engines in KSP are most probably messy and can have very weird behaviour under some conditions QA team may are fully unaware of.

EDIT: to Squad devs: Isp may (should) be reset to 0 if it's become negative in ModuleEngines* code, it doesn't make any sense to have a negative Isp, unless Isp in KSP means something a bit different than I assume.

Edited November 23, 2014 by Justin Kerbice

[nli2work]

awesome! I supesct Stock curves are not as bad as this. Most of the curves are only 3 keys, not much chance of getting extreme overshoots like you could with 5 or 6 keys.

[Justin Kerbice]

awesome! I supesct Stock curves are not as bad as this. Most of the curves are only 3 keys, not much chance of getting extreme overshoots like you could with 5 or 6 keys.

Not sure, it's possible less keys means bigger bad tangent points, like a big zig zag when a smooth down/up curve was expected.

[nli2work]

overshoots typically happen when the deltas between two out of 3 keys are large and the keys follow each other close together. Squad's curves are typically 3 to 4 keys, spaced out more or less evenly, with either automatic or flat tangents. that means mostly staircase curves with little or no overshoots.

it would be impossible to unintentionally get bad tangets with a two key curve; and almost impossible with a 3 key curve.

keys from 0.68/0 to 7/10 to 9 1000 is almost guanranteed to generate extreme overshoots without manually specifying in/out tangents at each key.

great case demonstrating the importance of knowing exactly what the curves are doing and what you want them to do.

[TinfoilChef]

Hmm... you could take this one step farther and make it a Bussard ramscoop. It would require power, a crap ton of power, and create an magnetic field to capture interstellar hydrogen to fuel a fusion drive. Late game kind of tech.