23.5. Ball Joint

The Ball Joint (BALL_JOINT) removes all the translational DOF (degrees of freedom) and allows the Rigid Body to rotate around three axes. It can be used to simulate a ball and socket joint. It does not have range, lock or motors.

As with all the joints, there are two ways of attaching the Ball Joint:

  1. Attach it directly to an edge or an axis of a solid belonging to a Rigid Body, which attaches the joint between the Rigid Body and the world.

  2. Attach it between two separate solids (each belonging to a separate Rigid Body).

23.5.1. Usage

In the first case you simply select the ball joint tool from the ribbon menu and left-click on an edge or an axis of the Rigid Body you wish to add a joint to, a yellow Ball Joint icon will appear on the edge or axis. See Joint status.

In the second case where you wish to join two Rigid Bodies with a ball joint you simply select the Ball joint from the ribbon menu. Then, Ctrl-click somewhere on one of the Rigid Bodies, and then click the edge or axis on the other Rigid Body that the ball joint should rotate around. A purple Ball Joint icon will appear on the edge or axis. See Joint status.

BALL_JOINT_EXAMPLE

23.5.2. Properties

BALL_JOINT_PROPERTIES

23.5.2.1. Joint Properties

  • Enable: Specifies whether the joint is enabled or not.

  • Collision between Rigid Bodies: Specifies if there can be contacts generated between the two attached rigid bodies. Default is off. If collision is enabled, there might be jamming effects if the two bodies have overlapping geometry.

  • Type: Type of joint.

  • Solve type: Specifies which solver that will solve this joint.

    • Direct And Iterative: (Default), both the direct AND the iterative solver will see this joint. To get stable friction with the Split solver type for Material Pairs, both the iterative and the direct solver must see the joint.

    • Iterative - Only the iterative solver will see this joint. Will lead to instabilities for large mass ratios.

    • Direct - Only the direct solver will see this joint. This might lead to artifacts when involving a Material Pair with Split solve type.

  • Component1: Name of the first component associated to this joint.

  • Component2: Name of the second component associated to this joint.

  • Rigid Body1: Name of the first rigid body associated to this joint.

  • Rigid Body2: Name of the second rigid body associated to this joint.

  • Reverse direction: Visible only if joint is attached to two components. Will swap the two attached rigid bodies, effectively flip the direction of the joint.

  • Is Attached: A property that is set to true when the joint is directly attached to an edge/axis on a solid. When the joint is created, it is always directly attached to an edge/axis on a solid. If the solid is moved, the joint will follow the solid. However, if the joint is moved individually from the solid, this property is changed to false. This means that the joint will no longer follow the solid when the solid is moved, but will remain at its current world location. To reset the joint’s world position to the original solid position, set this flag to true.

23.5.2.2. Elasticity

Elasticity specifies the “stiffness” of the remaining degrees of freedom for the joint. The elasticity is specified in a local coordinate system relative to the constraint axis.

  • Translation X,Y,Z: Specifies elasticity in the three translational DOF.