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Tags: unity, joints, physics, hinge, spring, fixed, configurable, ragdoll, constraints, game-dev Last updated: 2026-06-27

Physics Joints & Constraints Cheatsheet

Quick Reference

Joint Type	Movement	Rotation	Best For
FixedJoint	None	None	Glue two objects together (breakable)
HingeJoint	None	1 axis	Doors, wheels, levers, pendulums
SpringJoint	Stretchy connection	Free	Bungee cords, elastic tethers
CharacterJoint	Limited all axes	Limited all axes	Ragdolls, articulated limbs
ConfigurableJoint	Fully customisable	Fully customisable	Anything (most powerful)

FixedJoint

Property	Description
Connected Body	Target Rigidbody to lock to
Break Force	Force threshold to break joint
Break Torque	Torque threshold to break joint
Enable Collision	Allow connected bodies to collide (usually false)

# Create breakable attachment
FixedJoint joint = gameObject.AddComponent<FixedJoint>();
joint.connectedBody = targetRigidbody;
joint.breakForce = 500f;
joint.breakTorque = 200f;

void OnJointBreak(float breakForce) {
    Debug.Log($"Joint broke at {breakForce}N");
}

HingeJoint

Property	Description
Axis	Rotation axis (local space)
Anchor	Pivot point (local space)
Use Motor	Apply rotational force
Motor Target Velocity	Target angular speed (deg/s)
Motor Force	Torque to reach target
Use Limits	Restrict rotation angle
Limits (min/max)	Min/max angle in degrees
Use Spring	Spring-back to target position

HingeJoint hinge = gameObject.AddComponent<HingeJoint>();
hinge.connectedBody = doorFrameRigidbody;

# Motor (spinning)
hinge.useMotor = true;
JointMotor motor = hinge.motor;
motor.targetVelocity = 360f;
motor.force = 100f;
hinge.motor = motor;

# Limits (door with 90° opening)
hinge.useLimits = true;
JointLimits limits = hinge.limits;
limits.min = 0f;
limits.max = 90f;
hinge.limits = limits;

# Spring (self-closing door)
hinge.useSpring = true;
JointSpring spring = hinge.spring;
spring.spring = 100f;
spring.damper = 10f;
spring.targetPosition = 0f;
hinge.spring = spring;

SpringJoint

Property	Description
Spring	Tension stiffness (higher = tighter)
Damper	Oscillation damping (higher = less bounce)
Min Distance	Minimum unstretched length
Max Distance	Maximum stretch length

SpringJoint spring = gameObject.AddComponent<SpringJoint>();
spring.connectedBody = targetRigidbody;
spring.spring = 50f;
spring.damper = 5f;
spring.minDistance = 0f;
spring.maxDistance = 3f;

CharacterJoint

Property	Description
Swing Axis	Primary rotation axis
Twist Limit Spring	Spring for twist constraint
Low Twist Limit	Min twist angle with bounciness
High Twist Limit	Max twist angle with bounciness
Swing 1 Limit	First swing axis (usually Y)
Swing 2 Limit	Second swing axis (usually Z)
Enable Projection	Snap back if bodies separate too far

Ragdoll Setup

Step-by-Step

Select the character’s bone hierarchy in the Hierarchy.
GameObject → 3D Object → Ragdoll… (Unity wizard).
Assign each bone: Pelvis, Spine, Head, Arms, Legs.
Unity auto-adds CharacterJoints, Colliders, and Rigidbodies.
Tune collider sizes to roughly match body parts.
Tweak joint limits: Twist -20 to 20 (knees/elbows more restrictive), Swing -45 to 45 for most limbs.

Ragdoll Activation Script

public void EnableRagdoll() {
    foreach (Rigidbody rb in GetComponentsInChildren<Rigidbody>()) {
        rb.isKinematic = false;
        rb.useGravity = true;
    }
    foreach (Collider col in GetComponentsInChildren<Collider>())
        col.enabled = true;
    GetComponent<Animator>().enabled = false;
    GetComponent<Collider>().enabled = false;
    GetComponent<Rigidbody>().isKinematic = true;
}

public void DisableRagdoll() {
    foreach (Rigidbody rb in GetComponentsInChildren<Rigidbody>())
        rb.isKinematic = true;
    foreach (Collider col in GetComponentsInChildren<Collider>())
        col.enabled = false;
    GetComponent<Animator>().enabled = true;
    GetComponent<Collider>().enabled = true;
}

ConfigurableJoint

Property	Description
Connected Body	Target Rigidbody
Anchor	Pivot in local space
Axis	Primary axis direction
X/Y/Z Motion	Locked / Limited / Free
Angular X/Y/Z Motion	Locked / Limited / Free
Target Position / Velocity	Drives linear motion
Target Rotation / Angular Velocity	Drives angular motion

Replicating Joint Types

Desired Joint	Config
FixedJoint	All Linear/Angular Motion = Locked
HingeJoint	Angular X Motion = Limited, rest = Locked
SpringJoint	Linear Y Motion = Limited (with spring)

ConfigurableJoint joint = gameObject.AddComponent<ConfigurableJoint>();
joint.connectedBody = targetRigidbody;

# Hinge-like
joint.angularXMotion = ConfigurableJointMotion.Limited;
joint.angularYMotion = ConfigurableJointMotion.Locked;
joint.angularZMotion = ConfigurableJointMotion.Locked;

SoftJointLimit limit = new SoftJointLimit();
limit.limit = 90f;
joint.angularXLimit = limit;

JointDrive drive = new JointDrive();
drive.positionSpring = 100f;
drive.positionDamper = 10f;
joint.angularXDrive = drive;

Joint Performance

Joints are more expensive than simple colliders.
Keep joint chains under ~20 bones for real-time ragdolls.
Disable unused joints (e.g. disable ragdoll when alive).
Use FixedJoint instead of parenting for breakable connections.
Lower solverIterations on low-priority joint chains.