Getting a proper roblox collision groups script setup running is usually the first thing I do when I realize my players are getting stuck inside each other or walking through walls they shouldn't. If you've ever played a game where players just phase through each other like ghosts, or maybe a team-based shooter where teammates don't block your movement, you're looking at collision groups in action. It's one of those backend things that players never notice until it's missing, and then suddenly the game feels like a chaotic mess.
Why you should stop using the Studio UI for this
Now, you can technically handle some of this through the Collision Group Editor in the Model tab in Roblox Studio. It's a nice little grid where you check boxes to decide who hits what. It works for simple stuff, but honestly, it's not the way to go if you want a professional roblox collision groups script setup.
When you script your collision groups, you have way more control. You can dynamically change how things interact based on what's happening in the game. Maybe a player picks up a "ghost" power-up and suddenly shouldn't collide with anything for ten seconds? You can't really toggle those checkboxes in the UI while the game is running. Scripting it also means that when you share your assets or move them to a new place, the logic goes with them. You don't have to remember which boxes you checked six months ago.
The core of the logic: PhysicsService
Everything revolves around PhysicsService. This is the built-in service that handles how parts acknowledge each other's existence. In the past, the methods were a bit different, but these days we use RegisterCollisionGroup.
The basic workflow is pretty straightforward: you create a group, you tell that group which other groups it can or cannot touch, and then you shove parts into those groups. It sounds simple, but the "shoving parts into groups" bit is where most people trip up because characters in Roblox are made of dozens of parts that don't always behave.
Setting up your basic script
Let's look at how a standard roblox collision groups script setup actually looks in your ServerScriptService. You want this to run as soon as the server starts.
First, you define your groups. Let's say we want a "Players" group and an "NPCs" group. You'd start by registering them. If the group already exists, Roblox might throw an error, so it's always smart to wrap it in a way that checks first or just handles the registration at the very top.
Once the groups are registered, the magic happens with CollisionGroupSetCollidable. This is where you say "Hey, Group A and Group B should just ignore each other." For example, if you want players to walk through each other, you set the "Players" group to not be collidable with the "Players" group. It feels a bit weird writing code that says something shouldn't hit itself, but that's how the engine understands that two different objects in that same category shouldn't bump heads.
Handling the character parts
This is the part that usually breaks for beginners. You can't just set a "Character" model to a collision group and expect it to work. In Roblox, a Model is just a container; it doesn't have physical properties. You have to iterate through every single part inside that model—the head, the torso, the legs, and even the tiny accessories—and assign each one to the group.
I usually write a helper function for this. Whenever a player joins and their character spawns, I run a loop that looks at every descendant. If that descendant is a BasePart (which covers almost everything physical), I use task.defer or a direct assignment to put it in the "Players" group.
You also have to keep an eye on accessories. Since characters load in pieces, sometimes a hat or a cape might spawn in a split second after your script runs. If you don't account for that, the player's body might pass through others, but their floating sword or top hat will still get stuck on people. It's a hilarious visual, but it definitely ruins the immersion.
Team-based collisions and doors
One of the coolest ways to use a roblox collision groups script setup is for team-specific areas. Imagine you have a Red Team and a Blue Team. You want the Red Team to walk through the Red Door, but the Blue Team should hit it like a brick wall.
To do this, you'd make three groups: RedTeam, BlueTeam, and RedDoors. You'd script it so the RedTeam group has Collidable = false with RedDoors, but BlueTeam stays true. This is way more efficient than using Touched events or invisible barriers that you manually turn on and off. The physics engine just handles it all natively, which is much better for performance.
Common headaches to avoid
I've spent way too many hours debugging why my roblox collision groups script setup wasn't working, only to realize I made a typo in the group name. String names are case-sensitive. "Players" and "players" are two different things to the engine, and it won't always tell you you've messed up; it'll just do nothing.
Another thing to watch out for is the default group. Every part starts in the "Default" group. If you don't explicitly tell your new group how to interact with the Default group, it will just follow the standard rules. Usually, you want your custom groups to still hit the floor and walls (which are Default), so you don't need to change those settings. Just focus on the specific interactions between your custom categories.
Also, don't forget about NPCs. If you have a lot of enemies in your game, they can get bunched up in a doorway, creating a mosh pit that players can't get through. Putting NPCs in their own group and disabling collisions between them makes their AI pathfinding look a lot smoother, as they won't be constantly shoved off-course by their buddies.
Performance considerations
You might wonder if having dozens of collision groups slows down your game. The short answer is: not really. In fact, it can actually help. When you tell the physics engine that two groups don't need to collide, you're actually saving the engine from doing the math to check for those collisions.
If you have 50 players in a small space and they all have collisions disabled with each other, the server doesn't have to calculate 50 individual hitboxes bumping into each other every frame. It just skips those checks. So, a solid roblox collision groups script setup is actually a bit of an optimization trick as much as it is a gameplay feature.
Wrapping it up
Setting this all up might feel like a chore when you just want to get to the "fun" parts of game dev, but it's the foundation of a polished experience. Nobody likes a game that feels "clunky," and unwanted collisions are the biggest culprit of clunkiness.
Once you have your script template ready, you can just drop it into any new project. It makes your game feel much more intentional. Whether you're making a social hangout, a complex RPG, or a high-speed racer, taking control of the physics through code is always the right move. Just remember to loop through those character parts carefully, check your spelling, and let PhysicsService do the heavy lifting for you. It's one of those small changes that makes a massive difference in how your game actually feels to play.