Constraints

The Constraints tab in Properties editor exposes constraints setups for current object.

Currently in UPBGE only the Rigid Body Joint constraint can be set through the user interface.

Rigid Body Joint Constraint

The Rigid Body Joint constraint is very special, it is used by the physics part of UPBGE 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.

Note

In order for this constraint to work properly, both objects (so the owner and the target object) need to have Collision Bounds enabled.

Options

Rigid Body Joint panel

Target

Object used to select the constraints target, and is not functional (red state) when it has none.

Pivot Type

Ball

Works like an ideal ball-and-socket joint, i.e. allows rotations around all axes like a shoulder joint.

Hinge

Works in one plane, like an elbow: the owner and target can only rotate around the X axis of the pivot (joint point).

Limits

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.

Limits

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:

Limits

Linear and angular limits for a given axis (of the pivot) in Blender Units and degrees respectively.

Note

The 6DOF constraint has a limitation due to it uses euler angles instead of quaternions. Basically, the rotation of Y-axis can be +/-90 degrees only, if you exceed that maximum the constrain will go haywire. A good solution to avoid issues is to modify your model in a way that the free rotation doesn’t match with the Y local axis of your object.

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 (in the physical engine of the BGE).

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!

Use Breaking

Allow breaking of constraint on high impulse.

Breaking Impulse Threshold

Break constraint on impulse greater than threshold.

Pivot

These three numeric fields allow you to relocate the pivot point, in the owner’s space.

Axis

These three numeric fields allow you to rotate the pivot point, in the owner’s space.