Weld

Welds are a joint that rigidly holds their parent part and another part in a fixed position relative to each other, such as holding one part 2 units to the right of another part. They can be used in places where parts need to be held together at odd angles, but still be able to move (meaning they will not work with Anchored parts), such as for a vehicle.

Prerequisites[edit]

  • Being able to use a basic CFrame (CFrame.new(#, #, #)).
  • Knowing how to index and change the properties of an object, using a script.

Basic structure of a weld[edit]

The weld object is placed inside of a part, and a property is set to determine which other part should be welded to the original part. Then two CFrames, the C0 and the C1, tell the weld how the parts should be placed.

Part0 This property of a weld is an Object, it must always be set to the part the weld is in for the weld to work
Part1 This property of a weld is an object and tells is which part it should be attaching its parent to
C0 determines how the [offset point] should be attached to the Part0
C1 determines how the Part1 should be attached to the [offset point]

Advanced[edit]

Part1.CFrame * C1 == Part0.CFrame * C0

Since C0 and C1 are both offsets this equation means that the weld must satisfy the condition that each part CFrame multiplied by its respective offset must end up being equal to each other. This looks like this:

Weld equality.gif

Where blue is the C0 offset and red is C1 offset.

Setting the values[edit]

Figuring out what to set the C0 and C1 to is a bit finicky, but one you get good at it, it can go quite quickly. For Welds, you dont have to worry about the C1, it's automaticaly set to a "unit" or unrotated CFrame, you only have to deal with C1 when working with motors, so ignore it for now. The C0 will tell the weld how it should attatch itself to the other part, eg.

[weld].C0 = CFrame.new(0, 2, 0)

This tells the weld that it should hold the part1 in a position 2 studs above the part0, simple eh?

Rotating the CFrame[edit]

To rotate the CFrame you must use the following command, which is case sensitive.

  CFrame.fromEulerAnglesXYZ(#, #, #) 

Or, alternatively:

CFrame.Angles(#, #, #)

This is used as follows:

weld.C0 = CFrame.new(0, 2, 0)*CFrame.fromEulerAnglesXYZ(0, math.pi, 0)

This tells the weld to attach the part1, two studs above the part0 AND rotate the part1 by 180 degrees relative to the part0

You use math.pi, as the number to rotate by, use it in the following fashion :

  • math.pi = 1/2 of a turn
  • math.pi/2 = 1/4 of a turn
  • math.pi/4 = 1/8 of a turn

Putting it all together[edit]

Now that you know how to use the basics of a weld, here's how you put it all together. Here's an example:

Let's say that this is in a script, in a vehicle:

local pln = script.Parent 
 
local w = Instance.new("ManualWeld") 
w.Parent = pln
w.Part0 = pln.Engine
w.Part1 = pln.Wing1 
w.C0 = CFrame.new(0, 0, 6)*CFrame.new(0, -math.pi/5, 0)

Walkthrough[edit]

  • Open Roblox Studio
  • Insert > Object > Part
  • Rename Part "Engine"
  • Insert > Object > Part
  • Rename Part "Wing1"
  • Group Engine and Wing1 together as "pln"
  • Click "pln"
  • Insert > Object > Script into "pln"
  • Copy and paste the script in "Putting it all together" above.
  • Test... Engine should have a "weld" logo in the Explorer menu.

Welding together two existing bricks[edit]

Sometimes, you want to just weld together two parts in their current positions, so that they remain in the same relative positions. This takes just a basic understanding of CFrame math and welds. As previously mentioned,

Part1.CFrame * C1 == Part0.CFrame * C0

And understanding that

CFrameA:inverse() * CFrameA

cancels out, we can apply some basic algebra

                         Part0.CFrame * C0 == Part1.CFrame * C1
Part0.CFrame:inverse() * Part0.CFrame * C0 == Part0.CFrame:inverse() * Part1.CFrame * C1
                                        C0 == Part0.CFrame:inverse() * Part1.CFrame * C1

So this means we can do :

local function weldBetween(a, b)
	--Make a new Weld and Parent it to a.
	local weld = Instance.new("ManualWeld", a)
	--Get the CFrame of b relative to a.
	weld.C0 = a.CFrame:inverse() * b.CFrame
	--Set the Part0 and Part1 properties respectively
	weld.Part0 = a
	weld.Part1 = b
	--Return the reference to the weld so that you can change it later.
	return weld
end

You can then do the following to weld two parts together:

local weld = weldBetween(game.Workspace.Part, game.Workspace.Brick)

See Also[edit]