Getting your physics-based objects to bounce back correctly usually means you need a roblox torsion spring constraint script to handle the rotational force. If you've spent any time in Roblox Studio, you probably know that making things move is easy, but making them move well is a whole different story. Torsion springs are those unsung heroes that make doors swing shut, car suspensions feel bouncy, and mechanical traps snap into place.
If you're used to the standard SpringConstraint, you know it works on a linear axis—it pulls two points together like a rubber band. But a TorsionSpringConstraint is all about the twist. It's designed to push or pull an object back to a specific relative angle. Honestly, it's one of the most useful tools in the physics tab, but the scripting side of it can feel a bit finicky if you don't know which properties actually do the heavy lifting.
Why use a script for torsion springs?
You might wonder why you'd even bother with a roblox torsion spring constraint script instead of just setting it up in the Properties window and calling it a day. The reality is that static constraints are boring. If you want a door that gets harder to push the further it opens, or a catapult that increases its tension over time, you've got to handle that through code.
Dynamic adjustments are where the magic happens. Think about a vehicle. As the car goes faster, maybe you want the suspension's rotational stiffness to increase so it doesn't flip over in corners. Or maybe you're building a character's physical cape, and you want the "springiness" to change depending on how fast the player is falling. You can't do that with a static setup; you need a script to reach in and tweak those values on the fly.
Setting up the foundation
Before we even touch the code, we have to make sure the physical setup in Studio isn't a mess. A TorsionSpringConstraint needs two things: Attachment0 and Attachment1. These are the anchors that define the axis of rotation.
One mistake I see people make constantly is misaligning the attachments. If your orange and yellow arrows (the visual indicators for the attachments) aren't pointing in the same direction, the physics engine is going to have a literal meltdown. It'll try to rotate the part into a position that might be physically impossible, resulting in that classic "exploding parts" glitch we all know and love.
Once you've got your parts and attachments placed, you can either create the constraint manually or have your script do it. Personally, I prefer creating it via script if I'm building a modular system, as it makes the whole thing much easier to replicate across different models.
Writing the basic script
Let's look at a simple way to initialize this through a roblox torsion spring constraint script. Imagine we have two parts, a base and a swinging arm.
```lua local basePart = script.Parent.Base local armPart = script.Parent.Arm
-- Create the attachments if they don't exist local att0 = Instance.new("Attachment") att0.Name = "BaseAttachment" att0.Parent = basePart
local att1 = Instance.new("Attachment") att1.Name = "ArmAttachment" att1.Parent = armPart
-- Create the Torsion Spring local torsionSpring = Instance.new("TorsionSpringConstraint") torsionSpring.Name = "MyTorsionSpring" torsionSpring.Attachment0 = att0 torsionSpring.Attachment1 = att1
-- Tweak the physics properties torsionSpring.Stiffness = 500 torsionSpring.Damping = 10 torsionSpring.MaxTorque = 100000 torsionSpring.RestAngle = 0
torsionSpring.Parent = armPart ```
It's pretty straightforward, but the real control comes from those properties like Stiffness and Damping. If you set the stiffness too high, the part will snap back so fast it might clip through other objects. If it's too low, it'll just sag like a wet noodle.
Finding the sweet spot: Stiffness and Damping
This is where most developers lose their minds. Finding the right balance for your roblox torsion spring constraint script is mostly trial and error, but there's a bit of logic to it.
Stiffness is basically the "strength" of the spring. It's how hard the spring wants to get back to its RestAngle. If you're making a heavy metal vault door, you're going to need a massive stiffness value because the door has a lot of mass. For a light wooden door, you can keep it low.
Damping is the "friction" of the spring. Without damping, your object will oscillate forever. It'll swing past the rest angle, snap back, swing past it again, and just keep wobbling. Damping absorbs that energy. A good rule of thumb is to start with your damping at about 1/10th of your stiffness and adjust from there. If the movement feels "bouncy," increase the damping. If it feels like it's moving through molasses, turn it down.
Working with MaxTorque
Don't forget about MaxTorque. This is the ceiling on how much force the spring can exert. If you leave this at a low value, the spring might not have enough power to move the part at all, especially if the part is anchored to something else or is just really heavy. I usually set this to a very high number (like math.huge or 1000000) unless I specifically want the spring to "fail" or give up under heavy loads.
Practical application: The automatic swinging door
Let's say you want a door that players can walk through, but it always swings shut behind them. Using a roblox torsion spring constraint script is the perfect way to do this because it feels more "physical" than just tweening a CFrame.
You'd set the RestAngle to 0 (meaning the door is closed). When a player pushes the door, they are overcoming the Stiffness of the spring. As soon as they let go, the spring takes over and pulls it back to 0.
If you want to get fancy, you can script it so that when the door is opened past a certain point, the Stiffness increases. This gives the player the feeling that the door is heavy or has a hydraulic closer attached to it. It's these little details that make a game feel polished rather than amateur.
Common pitfalls to avoid
One thing that trips people up is the RestAngle. Remember, this is in degrees, not radians. Most of Roblox's math uses radians, but constraints often use degrees in the UI, so it's easy to get confused. Always double-check which one your script is feeding into the property.
Another issue is collision. If your parts are colliding with each other at the hinge point, the torsion spring will fight the collision box. This results in jittering. You should almost always use Collision Filtering or a NoCollisionConstraint between the two parts connected by a torsion spring to keep things smooth.
Also, watch out for the mass of your parts. Roblox physics are heavily dependent on mass. If your swinging part is extremely small and light, but your stiffness is 10,000, it's going to fly off into the sunset. If you can't get the spring to behave, try checking the density of your parts in the CustomPhysicalProperties section.
Debugging your script
If things aren't working, the first thing you should do is go to the "View" tab in Studio and turn on "Show Constraints". This will draw the spring and the attachments in real-time while the game is running. You'll be able to see if the attachments are misaligned or if the spring is stretching in a way you didn't expect.
If the part is spinning uncontrollably, it's usually because the RestAngle is unreachable or the attachments are facing the wrong way. If the part isn't moving at all, check if it's Anchored. An anchored part won't move, even if a torsion spring is yelling at it to rotate. You want the base to be anchored, but the swinging part must be unanchored.
Wrapping it up
Using a roblox torsion spring constraint script opens up a lot of doors—literally. It's the difference between a static, lifeless world and one that feels reactive and mechanical. It takes a bit of poking and prodding to get the values just right, but once you understand how Stiffness and Damping interact, you can create some really cool stuff.
Just keep your attachments aligned, watch your damping values, and don't be afraid to experiment with high torque settings. Physics scripting is as much an art as it is a science, so play around with it until it feels right. Happy building!