Welds are a
Articles/Constraints|constraint 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
BasePart/Anchored parts), such as for a vehicle.
- Being able to use a basic
Articles/Understanding CFrame(CFrame.new(#, #, #)).
- Knowing how to index and change the properties of an object, using a script.
Basic structure of a weld
The weld object is placed inside of a part, and a property is set to determine which other parts should be welded to the original part. Then two CFrames, the C0, and the C1, tell the weld how the parts should be placed.
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:
- Where blue is the C0 offset and red is C1 offset.
Setting the values
Figuring out what to set the C0 and C1 to is a bit finicky, but once you get good at it, it can go quite quickly.
For Welds, you don’t have to worry about the C1, it’s automatically 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 attach 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
To rotate the CFrame you must use the following command, which is case sensitive.
CFrame.fromEulerAnglesXYZ(#, #, #)
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
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
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)
- Open Roblox Studio
- Insert > Object > Part
- Rename Part to “Engine”
- Insert > Object > Part
- Rename Part to “Wing1”
- Group Engine and Wing1 together as “pln”
- Click “pln”
- Insert > Object > 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
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)