RotSpeed

Description:

The RotSpeed property determines a random range of angular speeds that newly emit particles will have. A random angular speed is chosen upon emission, so changing this property will not affect already emit particles. This property, along with ParticleEmitter/Rotation affect the angle of the rendered particle image. This property is a DataType/NumberRange measured in degrees per second.

Below is an animation of two default ParticleEmitters. The right has a nonzero RotSpeed, so its particles rotate as they move through the world.
Two default ParticleEmitters; the right emitter has a RotSpeed applied

Using a spiral as a ParticleEmitter/Texture like the one below, you can create some quite interesting particle effects:
A swirl texture A portal effect using RotSpeed and a Swirl texture

Particles with very high angular speeds can appear to rotate slower or not at all - this is because the angle of rotation is synchronized with the software render speed. In other words, if the particle is rotating at exactly 360 degrees every frame, there will be no apparent change in rotation.

Code Samples

Creating a Particle Emitter from Scratch

This rather lengthy code sample shows how every property of a ParticleEmitter can be set, including DataType/NumberRange, DataType/NumberSequence and DataType/ColorSequence properties. Below is how the ParticleEmitter should after every property is set. Try playing around with the different properties to customize how the effect looks!

The final product

			
			
				Creating a Particle Emitter from Scratch

			
			
			
				Expected Output
			
			
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			local emitter = Instance.new("ParticleEmitter")
-- Number of particles = Rate * Lifetime
emitter.Rate = 5 -- Particles per second
emitter.Lifetime = NumberRange.new(1,1) -- How long the particles should be alive (min, max)
emitter.Enabled = true 

-- Visual properties
emitter.Texture = "rbxassetid://1266170131" -- A transparent image of a white ring
-- For Color, build a ColorSequence using ColorSequenceKeypoint
local colorKeypoints = {
	-- API: ColorSequenceKeypoint.new(time, color)
	ColorSequenceKeypoint.new( 0, Color3.new(1, 1, 1)),  -- At t=0, White
	ColorSequenceKeypoint.new(.5, Color3.new(1, .5, 0)), -- At t=.5, Orange
	ColorSequenceKeypoint.new( 1, Color3.new(1, 0, 0))   -- At t=1, Red
}
emitter.Color = ColorSequence.new(colorKeypoints)
local numberKeypoints = {
	-- API: NumberSequenceKeypoint.new(time, size, envelop)
	NumberSequenceKeypoint.new( 0, 1);    -- At t=0, fully transparent
	NumberSequenceKeypoint.new(.1, 0);    -- At t=.1, fully opaque
	NumberSequenceKeypoint.new(.5, .25);  -- At t=.5, mostly opaque
	NumberSequenceKeypoint.new( 1, 1);    -- At t=1, fully transparent
}
emitter.Transparency = NumberSequence.new(numberKeypoints)
emitter.LightEmission = 1 -- When particles overlap, multiply their color to be brighter
emitter.LightInfluence = 0 -- Don't be affected by world lighting

-- Speed properties
emitter.EmissionDirection = Enum.NormalId.Front -- Emit forwards
emitter.Speed = NumberRange.new(0, 0) -- Speed of zero
emitter.Drag = 0 -- Apply no drag to particle motion
emitter.VelocitySpread = NumberRange.new(0, 0)
emitter.VelocityInheritance = 0 -- Don't inherit parent velocity
emitter.Acceleration = Vector3.new(0, 0, 0)
emitter.LockedToPart = false -- Don't lock the particles to the parent 
emitter.SpreadAngle = Vector2.new(0,0) -- No spread angle on either axis

-- Simulation properties
local numberKeypoints2 = {
	NumberSequenceKeypoint.new(0, 0);  -- At t=0, size of 0
	NumberSequenceKeypoint.new(1, 10); -- At t=1, size of 10
}
emitter.Size = NumberSequence.new(numberKeypoints2)
emitter.ZOffset = -1 -- Render slightly behind the actual position
emitter.Rotation = NumberRange.new(0, 360) -- Start at random rotation
emitter.RotSpeed = NumberRange.new(0) -- Do not rotate during simulation

-- Create an attachment so particles emit from the exact same spot (concentric rings)
local attachment = Instance.new("Attachment", script.Parent)
attachment.Position = Vector3.new(0, 5, 0) -- Move the attachment upwards a little
emitter.Parent = attachment
		

			When you run the code sample, you should see particles that look like the provided animation.
		

			
				
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