Fixed Joint 2D
Switch to ScriptingUse the Fixed JointA physics component allowing a dynamic connection between Rigidbody components, usually allowing some degree of movement such as a hinge. More info
See in Glossary 2D to connect two GameObjectsThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
See in Glossary controlled by RigidbodyA component that allows a GameObject to be affected by simulated gravity and other forces. More info
See in Glossary 2D physics to keep them in a position relative to each other, so the GameObjects are always offset at a given position and angle. It is a spring-type 2D joint for which you don’t need to set maximum forces. You can set the spring to be rigid or soft.
Refer to Fixed Joint 2D and Relative Joint 2D for the differences between Fixed JointA joint type that is completely constrained, allowing two objects to be held together. Implemented as a spring so some motion may still occur. More info
See in Glossary 2D and Relative Joint 2DA 2D joint that allows two game objects controlled by Rigidbody physics to maintain in a position based on each other’s location. Use this joint to keep two objects offset from each other, at a position and angle you decide More info
See in Glossary.
| Property | Function |
|---|---|
| Enable CollisionA collision occurs when the physics engine detects that the colliders of two GameObjects make contact or overlap, when at least one has a Rigidbody component and is in motion. More info See in Glossary |
Enable this property to enable collisions between the two connected GameObjects. |
| Connected Rigid Body | Specify the other object this joint connects to. Leave this as None to have the other end of the joint fixed at a point in space defined by the Connected Anchor property. Select the circle icon to the right to view a list of GameObjects to connect to. |
| Auto Configure Connected Anchor | Enable this property to automatically set the anchor location for the other object this joint connects to. You do not need to enter coordinates for the Connected Anchor property if you enable this property. |
| Anchor | Define where (in terms of x, y-coordinates on the Rigidbody 2D) the end point of the joint connects to this GameObject. |
| Connected Anchor | Define where (in terms of x, y-coordinates on the Rigidbody 2D) the end point of the joint connects to the other GameObject. |
| Damping Ratio | Set the degree to suppress spring oscillation. In the range 0 to 1, the higher the value, the less movement. |
| Frequency | Set the frequency at which the spring oscillates while the GameObjects are approaching the separation distance you want (measured in cycles per second). In the range 0 to 1,000,000 - the higher the value, the stiffer the spring. Note: Setting Frequency to zero will create the stiffest spring type joint possible. |
| Break Action | Set the action taken when either the force or torque threshold is exceeded. |
| Break Force | Set the force threshold which if exceeded, will cause the joint to perform the selected Break Action. The default value is set to Infinity, which can never be exceeded and therefore the Break Action can never be taken while the threshold remains at this value. |
| Break Torque | Set the torque threshold which if exceeded, will cause the joint to perform the selected Break Action. The default value is set to Infinity, which can never be exceeded and therefore the Break Action can never be taken while the threshold remains at this value. |
Using this joint
The aim of this joint is to maintain a relative linear and angular offset between two points. Those two points can be two Rigidbody 2D components or a Rigidbody 2D component and a fixed position in the world. (Connect to a fixed position in the world by setting Connected Rigidbody to None).
The linear and angular offsets are based upon the relative positions and orientations of the two connected points, so you change the offsets by moving the connected GameObjects in your SceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
See in Glossary view.
The joint applies both linear and torque forces to connected Rigidbody 2D GameObjects. It uses a simulated spring that is pre-configured to be as stiff as the simulation can provide. You can change the spring’s value to make it weaker using the Frequency setting.
When the spring applies its force between the GameObjects, it tends to overshoot the desired distance between them and then rebound repeatedly, resulting in a continuous oscillation. The damping ratio determines how quickly the oscillation reduces and brings the GameObjects to rest. The frequency is the rate at which it oscillates either side of the target distance; the higher the frequency, the stiffer the spring.
Fixed Joint 2D has two simultaneous constraints:
- Maintain the linear offset between two anchor points on two Rigidbody 2D GameObjects.
- Maintain the angular offset between two anchor points on two Rigidbody 2D GameObjects.
You can use this joint to construct physical GameObjects that need to react as if they are rigidly connected. They can’t move away from each other, they can’t move closer together, and they can’t rotate with respect to each other, such as a bridge made of sections which hold rigidly together.
You can also use this joint to create a less rigid connection that flexes - for example, a bridge made of sections which are slightly flexible.
Comparing Fixed and Relative joints 2D
It is important to know the major differences between Fixed Joint 2D and Relative Joint 2D:
- Fixed Joint 2D is a spring-type joint. Relative Joint 2D is a motor-type joint with a maximum force and/or torque.
- Fixed Joint 2D uses a spring to maintain the relative linear and angular offsets. Relative Joint 2D uses a motor. You can configure a joint’s spring or motor.
- Fixed Joint 2D works with anchor points (it’s derived from script Anchored Joint 2D); it maintains the relative linear and angular offset between the anchors. Relative Joint 2D doesn’t have anchor points (it’s derived directly from script Joint 2D).
- Fixed Joint 2D cannot modify the relative linear and angular offsets in real time. Relative Joint 2D can.
Additional resources
- Refer to Joints 2D for more information about other 2D Joints.