Joint
Attaches two objects to each other when an event fires — a hinge, or a rigid weld.
Inputs: trigger (event) · a (object, the anchor) · b (object, the attached)
Output: effect (wire into an Object Selector)
How it works
On the rising edge of trigger the two objects are joined, exactly as if you had used Physics ▸ Weld or Physics ▸ Hinge from the object menu: the joint becomes part of the scene, replicates to every peer, appears in saves, and can be undone with Ctrl+Z.
That is the difference between this and the rest of the physics nodes — Impulse and Set Velocity act on a running simulation and leave nothing behind, while Joint authors scene data.
Parameters
| Parameter | Default | Meaning |
|---|---|---|
| kind | revolute | revolute = a hinge that turns about one axis; weld = rigidly fixed together |
| axis | y | which axis the hinge turns about |
| vel | 0 | motor speed (rad/s) — leave at 0 for a free-swinging hinge |
| maxForce | 100 | how hard the motor may push to reach that speed |
Choosing the objects
a is the anchor and b is the thing attached to it. Wire an Object Selector into each. If you leave a unwired it falls back to the node's own target (the Object Selector it feeds, or its owner object), so the minimum wiring is one selector into b.
Start the objects world-aligned
A hinge axis is interpreted in both bodies' frames, so objects that begin with a rotation can make the solver fight itself and throw the assembly apart. Build the joint on unrotated objects and rotate the finished assembly, or use weld.
Practical example
A door that installs itself.
- A thin box for the door with a Dynamic body, a wall with a Static one.
- Put the door's origin on its hinge edge — a revolute joint anchors on the origin, which is what makes it swing on the hinge rather than the middle.
- On Click (the wall) → Joint
trigger,kind= revolute,axis=y. - Object Selector (wall) →
a; Object Selector (door) →b. - Press P and click the wall. The door is hinged for everyone, and it stays hinged in the saved scene.
A motorised wheel. kind = revolute, vel = 6, maxForce = 200, with the chassis in a and the wheel in b. See also the Motor node, which drives joints that already exist — and can drive one side of a vehicle at a time.