A roblox collisiongroup script is usually the first thing developers look for when they realize that default physics are just too chaotic for a professional game. You've probably seen it a million times: players pushing each other off platforms in a lobby or vehicles getting stuck inside the environment because every single part is trying to occupy the same space. It's annoying for the player and looks messy for the dev. Fortunately, the way Roblox handles these interactions has evolved quite a bit over the years, and writing a script to manage them is actually pretty straightforward once you get the hang of it.
If you're coming from the old-school way of doing things, you might remember toggling CanCollide on and off manually. While that works for a single door or a simple wall, it's a nightmare for complex systems. That's where collision groups come in. They allow you to categorize parts and then tell the physics engine exactly which categories are allowed to hit each other and which should just pass through like ghosts.
Why You Actually Need This
Let's be real—without a proper roblox collisiongroup script, your game's physics are basically a free-for-all. Imagine you're building a racing game. You want the cars to hit the walls, but maybe you don't want the players' avatars to get knocked around by the cars while they're standing in the pit lane. Or, more commonly, you want to stop players from "colliding" with each other to prevent trolling.
By default, every part in Roblox belongs to the "Default" collision group. This means everything hits everything. By using a script to move specific parts into custom groups, you gain total control. You can have a "Players" group that ignores other "Players," but still hits the "Ground" and "Walls." It's all about creating a collision matrix that makes sense for your specific gameplay loop.
Setting the Foundation with PhysicsService
To get started, you're going to be spending a lot of time with PhysicsService. This is the built-in service that manages all the collision logic. In the past, we used to use IDs for groups, but Roblox updated things a while back to use strings (names), which is way easier to read. No one wants to remember if "Group 3" was for the NPCs or the projectiles.
Here's the basic flow of a roblox collisiongroup script: 1. Register a new group name. 2. Set the collision logic (tell Group A if it can hit Group B). 3. Assign parts or models to that group.
It sounds simple because it is, but there are a few "gotchas" when it comes to timing—especially when dealing with player characters that haven't fully loaded in yet.
The Basic Script Structure
Let's look at how you'd actually write this. You'd typically put this in a Script inside ServerScriptService. You don't want the client handling this because physics filtering is a server-side authority thing. If you let the client decide what they collide with, you're basically inviting hackers to walk through your walls.
```lua local PhysicsService = game:GetService("PhysicsService")
-- Create the groups if they don't exist local playerGroupName = "Players" local ghostGroupName = "Ghosts"
-- It's good practice to check if the group exists first to avoid errors if not pcall(function() PhysicsService:RegisterCollisionGroup(playerGroupName) end) then print("Group already exists or something went wrong") end
PhysicsService:RegisterCollisionGroup(ghostGroupName)
-- Now the magic: tell the groups to ignore each other -- This makes it so Ghosts cannot hit other Ghosts PhysicsService:CollisionGroupSetCollidable(ghostGroupName, ghostGroupName, false)
-- But Ghosts CAN still hit the Players (if you want) PhysicsService:CollisionGroupSetCollidable(ghostGroupName, playerGroupName, true) ```
In the example above, the CollisionGroupSetCollidable function is the heavy lifter. The first two arguments are the group names, and the third is a boolean. false means they pass through each other; true means they go bonk.
Handling Players (The Most Common Use Case)
The number one reason people look for a roblox collisiongroup script is to stop players from bumping into each other. It's a classic problem in "Obby" games where one player stands on a thin platform and blocks everyone else.
To fix this, you can't just set the group once; you have to wait for every player to join and then assign every single part of their character to the group. Characters are made of many parts (Head, Torso, Arms, Legs), and every single one needs to be in the "Players" group for the logic to work.
```lua local PhysicsService = game:GetService("PhysicsService") local Players = game:GetService("Players")
local playerGroup = "Players" PhysicsService:RegisterCollisionGroup(playerGroup) PhysicsService:CollisionGroupSetCollidable(playerGroup, playerGroup, false)
local function setCollisionGroup(character) for _, part in ipairs(character:GetChildren()) do if part:IsA("BasePart") then part.CollisionGroup = playerGroup end end end
Players.PlayerAdded:Connect(function(player) player.CharacterAdded:Connect(function(character) setCollisionGroup(character)
-- Sometimes parts are added a split second later (like hats/accessories) character.DescendantAdded:Connect(function(descendant) if descendant:IsA("BasePart") then descendant.CollisionGroup = playerGroup end end) end) end) ```
Notice how I added a DescendantAdded connection? That's a pro tip. Roblox characters load in pieces. If you only run the loop once when CharacterAdded fires, you might miss the hats, hair, or tools the player is holding. If those items aren't in the group, the players might still get snagged on each other's accessories.
Dealing with Tools and Accessories
Speaking of accessories, they can be a real pain. Tools are even worse because players can drop them or pick them up. If a player is holding a sword and that sword isn't part of the "No Collision" group, players will still be able to push each other around using the sword's hitboxes.
When writing your roblox collisiongroup script, you need to decide if tools should be "ghostly" too. Most of the time, the answer is yes. You can handle this by looking for any BasePart within a tool and setting its CollisionGroup property whenever it's equipped.
The Collision Matrix: Keeping it Organized
As your game grows, you might end up with five or six different groups. You might have: * Players: Don't hit other players. * NPCs: Hit players, but not each other. * Debris: Small parts that shouldn't trip up players but should hit the floor. * Projectiles: Should hit NPCs and Walls, but maybe not the person who fired them.
Trying to keep track of this in your head is a recipe for a headache. I usually recommend writing out a quick grid on a piece of paper (or a comment block in your code) to visualize who hits who. In your script, you'll just have a bunch of CollisionGroupSetCollidable lines that act as your master settings.
Performance Considerations
One thing people worry about is if a roblox collisiongroup script will lag their game. The short answer is: No. In fact, it usually improves performance.
When you tell the physics engine that Group A and Group B don't collide, the engine stops doing the math for those interactions entirely. It doesn't have to check if they are touching, which saves CPU cycles. If you have 50 players in a server and they are all constantly colliding, that's a lot of physics math. If you turn those collisions off via groups, the server breathes a sigh of relief.
Just make sure you aren't running your "assign to group" logic in a fast loop like RunService.Heartbeat. You only need to set a part's CollisionGroup once. After that, Roblox remembers it.
Troubleshooting Common Issues
If you've set up your script and things still aren't working, check a few things. First, make sure you aren't accidentally setting CanCollide to false on everything. Collision groups don't override CanCollide = false. If a part is set to not collide at all, it won't hit anything regardless of its group.
Second, check the Collision Group Editor in the Model tab of Roblox Studio. It's a visual tool that shows you all your groups. Even if you're using a script, the editor will update in real-time while you're play-testing. It's a lifesaver for seeing if your script actually successfully registered the groups and if the checkboxes for "Collidable" are marked correctly.
Lastly, remember that CollisionGroup is a property of BasePart. If you're trying to set it on a Model, it won't work. You have to iterate through the model's children and apply it to the parts inside.
Final Thoughts
Mastering the roblox collisiongroup script is really a turning point for any Roblox dev. It's one of those things that feels a bit technical at first, but once you have a solid template script, you just drop it into every project you start. It makes the world feel more professional, prevents players from griefing each other, and can even give your server a little performance boost.
So, next time you see players stacking on top of each other or glitching through your carefully designed vehicles, just remember that a few lines of PhysicsService code can fix the whole mess. Happy scripting!