If you've ever built a game where players keep bumping into each other at the spawn point or NPCs get stuck on invisible walls, you know you need a proper roblox collision groups script setup to keep things running smoothly. It's one of those things that seems a bit intimidating when you first look at the API, but once you get the hang of it, you'll wonder how you ever made a game without it. Essentially, collision groups let you decide exactly who (or what) can hit what.
In the old days of Roblox, we used to have to do all sorts of weird workarounds with CanCollide properties, but that's a total headache when you have hundreds of parts. Now, we have a dedicated service that handles the "who-touches-who" logic on a global scale. Whether you're trying to make players walk through each other or create a special "ghost" phase for a power-up, a script-based approach is almost always better than doing it manually in the editor.
Why Use a Script Instead of the Editor?
You've probably seen the Collision Group Editor in the Model tab of Roblox Studio. It's a nice little grid where you can check and uncheck boxes. It's fine for static objects, like making sure the "Leaves" group doesn't hit the "Branches" group. But as soon as your game gets a bit more complex—think dynamic team changes, spawning NPCs, or items that change properties mid-game—the editor just isn't enough.
A roblox collision groups script setup gives you the flexibility to handle things on the fly. If a player joins "Team Red," you can instantly swap their collision group so they can pass through Red doors but hit Blue walls. Doing that manually would be impossible. Plus, scripts are much easier to manage across different places or if you're working in a team; you can just copy-paste your "PhysicsManager" script rather than re-configuring a GUI window every time you start a new project.
The Core Logic: PhysicsService
Everything revolves around PhysicsService. This is the big boss of collisions. In your script, you're going to be talking to this service to register new groups and then tell those groups how to behave.
First off, you have to define the groups. You give them a name (a simple string like "Players" or "Projectiles"), and then you set the collision logic between two groups. It's basically a big "Yes" or "No" to the question: "Should these two things go 'bonk' when they hit?"
Setting Up the Basic Script
Let's look at how you'd actually write this out. You'll want to put this in a Script inside ServerScriptService. We do this on the server because physics and collisions are things the server needs to be the final judge on. If you do it on the client, you'll end up with "desync" issues where one player thinks they walked through a wall but the server thinks they're cheating.
Here's a simple way to start:
```lua local PhysicsService = game:GetService("PhysicsService")
-- Let's name our groups local playerGroupName = "Players" local npcGroupName = "NPCs"
-- Create the groups if they don't already exist -- We use a pcall or just check if they exist to avoid errors if not PhysicsService:IsCollisionGroupRegistered(playerGroupName) then PhysicsService:RegisterCollisionGroup(playerGroupName) end
if not PhysicsService:IsCollisionGroupRegistered(npcGroupName) then PhysicsService:RegisterCollisionGroup(npcGroupName) end
-- Now for the magic: tell them NOT to collide with each other PhysicsService:CollisionGroupSetCollidable(playerGroupName, playerGroupName, false) ```
In that last line, we're telling the game that anything in the "Players" group should ignore anything else in the "Players" group. This is the classic "anti-griefing" setup. Players can still hit the floor (which is in the "Default" group), but they'll slide right through their teammates.
Handling the Player Character
Creating the group is only half the battle. Now you actually have to put things into that group. This is where a lot of people get stuck, especially with player characters. Characters aren't just one part; they're a whole bunch of parts (Head, Torso, Arms, Legs, and those annoying little accessories).
You need to make sure every single part of the character is assigned to the group. If you miss one—like the "HumanoidRootPart"—the collision logic won't work perfectly.
You'll want a function that loops through a model and sets the group for every BasePart it finds. It looks something like this:
lua local function setCollisionGroup(model, groupName) for _, part in ipairs(model:GetDescendants()) do if part:IsA("BasePart") then part.CollisionGroup = groupName end end end
Then, you hook this up to the PlayerAdded event. But wait, there's a catch! You can't just do it when they join; you have to do it every time their character spawns.
lua game.Players.PlayerAdded:Connect(function(player) player.CharacterAdded:Connect(function(character) -- Sometimes we need a tiny delay to make sure everything has loaded task.wait(0.1) setCollisionGroup(character, "Players") end) end)
Advanced Logic: Team-Based Collisions
Let's say you're making a capture-the-flag game. You want Red Team to walk through Red Lasers, but Blue Team should hit them and well, explode. This is where the roblox collision groups script setup really shines.
You would create a "RedTeam" group and a "RedLasers" group. Then you'd set: PhysicsService:CollisionGroupSetCollidable("RedTeam", "RedLasers", false)
But for the Blue team, you'd leave it as true (which is the default). When a player changes teams, you just run your setCollisionGroup function again with the new group name. It's slick, it's fast, and it keeps your game feeling professional.
Common Pitfalls to Avoid
I've spent way too many hours debugging physics issues, so here are a few things that might trip you up.
First, don't forget the limit. Roblox only allows 32 collision groups. That sounds like a lot, but if you start making a unique group for every single item in your game, you'll hit that wall fast. Try to keep your groups broad. Instead of "Sword1," "Sword2," and "Sword3," just have one "Weapons" group.
Second, watch out for accessories. Hats and capes are parts too! If you don't use GetDescendants() to find all the parts in a character, the player's hat might still bump into other players even if their body doesn't. It looks super janky when a player's character passes through someone but their giant top hat knocks the other person off a ledge.
Third, default is your friend. Every part starts in the "Default" group. If you want something to collide with everything except one specific group, you don't need to change its group. Just change the interaction between "Default" and your new group.
Performance and Cleanup
You might wonder if having a bunch of scripts managing collisions will lag your game. The short answer is: No. In fact, it can actually help performance.
When the physics engine doesn't have to calculate collisions between fifty players in a small lobby, it saves a lot of CPU cycles. By telling the game "don't even bother checking if Player A hit Player B," you're making the engine's job a lot easier.
Just make sure you aren't running your setCollisionGroup function every single frame in a RenderStepped loop. You only need to set the group once when the object is created or when its status changes (like a team swap). Setting the property is a "set it and forget it" kind of deal.
Wrapping Things Up
Getting your roblox collision groups script setup right is one of those "level up" moments for a developer. It moves you away from "it just works" to "I am in control of how this world behaves."
It might take a few tries to get the recursive part-looping logic perfect, and you might accidentally make your players fall through the floor once or twice (we've all been there), but it's worth the effort. Once you have a solid script handling your physics layers, you can focus on the fun stuff—like making the game actually enjoyable to play—without worrying about players getting stuck in each other or NPCs breaking your maps.
Just remember: PhysicsService on the server, loop through all the parts, and keep your group count under 32. Do that, and you're golden. Happy scripting!