Getting your first custom rig moving usually involves a roblox motor6d script because, let's face it, WeldConstraints just don't cut it when you need things to actually move. If you've ever tried to attach a sword to a character's hand or build a custom mech and realized the parts just stay stuck in one place, you've hit the wall that only a Motor6D can climb. It's the backbone of basically every animated movement in the engine, from simple tool swinging to complex procedural walking systems.
The funny thing about Roblox is that it gives you plenty of ways to stick parts together, but most of them are "dumb" joints. Welds and ManualWelds are great for keeping a hat on a head, but they're static. If you want to use the Animation Editor or change the joint's rotation on the fly via code, you need that Motor6D. It's essentially a weld that has a "Transform" property, which is a fancy way of saying it can move without breaking the connection.
Why we bother with Motor6Ds anyway
You might wonder why we don't just use hinge constraints or ball-and-sockets. While those are awesome for physics-based stuff like cars or swinging ropes, they're a nightmare to control for character animations. Constraints react to forces; Motor6Ds react to data. When you play an animation, the engine is just feeding a series of CFrame offsets to the Motor6D.
If you're building a viewmodel for an FPS game, you're going to be living in a roblox motor6d script for a while. You need to connect the arms to the "invisible" camera part and the gun to the hands. Without a script to automate this, you'd be manually dragging joints into the Explorer every time a player spawns, which is obviously not going to work.
Setting up the basic connection script
Most people run into trouble when they try to script these joints manually because the offsets (C0 and C1) can be a bit brain-melting. Let's look at a simple scenario: you want to attach a tool to a player's hand using a script so that the Animation Editor recognizes it.
Usually, you'd put a script inside StarterCharacterScripts or a server script that listens for the CharacterAdded event. You'd create the instance, tell it what Part0 (the parent) and Part1 (the child) are, and then—this is the part everyone messes up—you set the C0 and C1.
lua local motor = Instance.new("Motor6D") motor.Name = "ToolGrip" motor.Part0 = character:WaitForChild("RightHand") motor.Part1 = toolHandle motor.Parent = character:WaitForChild("RightHand")
The reason we do this through a script instead of just using the default "RightGrip" weld that Roblox creates is control. The default grip is a basic Weld. You can't animate it. By deleting the default weld and replacing it with a roblox motor6d script setup, you suddenly have the power to make the character flip the sword or spin a pistol during a reload animation.
Understanding the C0 and C1 headache
If you've ever run a script and seen your character's arm fly off into the distance or the sword end up stuck inside the player's torso, your offsets are wrong. Think of C0 as the point on Part0 where the "hinge" is located, and C1 as the point on Part1 that attaches to that hinge.
Most of the time, if you're just trying to keep things in their current place, you can calculate the offset using the inverse of the parts' CFrames. It looks something like motor.C0 = part0.CFrame:Inverse() * part1.CFrame. It's a bit of math, but once you wrap your head around the idea that you're just defining where the "glue" sits relative to each part, it gets a lot easier.
Using Motor6Ds for FPS Viewmodels
This is probably the most popular use for a roblox motor6d script these days. When you're making a first-person shooter, you aren't usually moving the player's actual character model for the arms. You're moving a "viewmodel" that follows the camera.
You'll typically have a "Root" part that stays locked to the camera's position. Then, you use Motor6Ds to connect the left and right arms to that Root. Why? Because then you can play animations on those arms. When you reload a gun, the animation is just moving those Motor6D joints.
If you tried to do this by just setting the CFrame of the arms every frame, it would look jittery and you'd have to code every single finger movement by hand. No thanks. By using a Motor6D, you get to use the Animation Editor, which saves you roughly a thousand hours of frustration.
Procedural animation and the Transform property
Here is where things get really cool. Motor6Ds have a property called Transform. This is what the animation system uses to move parts around. But the cool part is that you can also mess with this property using a local script to add "procedural" movement.
Let's say you have a walking animation, but you also want the character's head to always look at where the mouse is pointing. You don't need a separate animation for every possible head angle. You just use a roblox motor6d script to calculate the angle between the neck and the mouse, then apply that to the Neck.Transform property every frame.
It blends perfectly with your existing animations. The character will still do the "walk" bobbing, but their head will stay locked onto the target. It makes the game feel way more modern and reactive.
Common pitfalls to avoid
I've seen a lot of people struggle with Motor6Ds because their parts are "Anchored." Here's a golden rule: if a part is connected via a Motor6D and you want it to move with an animation, it cannot be anchored. If Part1 is anchored, the whole system just locks up, or worse, the part just sits there while the rest of the character walks away.
Another issue is "Circular Dependencies." This is a fancy way of saying you've accidentally tried to make Part A the parent of Part B, while Part B is also trying to be the parent of Part A. Roblox will usually yell at you in the output log if you do this, but it's easy to do by accident when you're writing a complex roblox motor6d script that handles multiple limbs.
Also, watch out for the Active property. Sometimes joints can become "inactive" if they aren't properly parented within the character model. Always make sure your Motor6Ds are parented to a part that is actually inside the Workspace and part of a valid model hierarchy.
Wrapping it up
The roblox motor6d script is one of those things that feels like a hurdle when you're a beginner, but once you "get" it, it becomes your best friend. It's the difference between a game that feels stiff and robotic and one that feels fluid and professional.
Whether you're just trying to get a custom character to walk or you're building a high-end combat system with weapon sway and recoil, Motor6Ds are the tool for the job. Don't let the C0/C1 math scare you off. Just remember that it's all about creating a connection that's allowed to move. Once that connection exists, the possibilities for what you can animate are basically endless. Keep experimenting with the offsets, watch your output log for errors, and before you know it, you'll be rigging complex machines and characters without even thinking twice about it.