Rigid Body Joint Constraint¶
The Rigid Body Joint constraint is very special, it is used to simulate a joint between its owner and its target. It offers four joint types: hinge type, ball-and-socket type, cone-twist type, and generic six-DoF type.
The joint point and axes are defined and fixed relative to the owner. The target moves as if it were stuck to the center point of a stick, the other end of the stick rotating around the joint/pivot point…
For a demo file that shows some of the different types, see: BGE-Physics-RigidBodyJoints.blend.
In order for this constraint to work properly, both objects (so the owner and the target object) need to have Collision Bounds enabled.
- Data ID used to select the constraints target, and is not functional (red state) when it has none.
- Joint Type
- Works like an ideal ball-and-socket joint, i.e. allows rotations around all axes like a shoulder joint.
Works in one plane, like an elbow: the owner and target can only rotate around the X axis of the pivot (joint point).
- Angular limits for the X axis.
- Cone Twist
Similar to Ball, this is a point-to-point joint with limits added for the cone and twist axis.
- Angular limits.
- Generic 6DOF
Works like the Ball option, but the target is no longer constrained at a fixed distance from the pivot point, by default (hence the six degrees of freedom: rotation and translation around/along the three axes). In fact, there is no longer a joint by default, with this option, but it enables additional settings which allow you to restrict some of these DoF:
- Linear and angular limits for a given axis (of the pivot) in Blender Units and degrees respectively.
- Child Object
- Normally, leave this blank. You can reset it to blank by right-clicking and selecting Reset to Default Value.
- Linked Collision
- When enabled, this will disable the collision detection between the owner and the target.
- Display Pivot
- When enabled, this will draw the pivot of the joint in the 3D Views. The most useful, especially with the Generic 6DOF joint type!
- These three numeric fields allow you to relocate the pivot point, in the owner’s space.
- These three numeric fields allow you to rotate the pivot point, in the owner’s space.