# Ball-Socket Joint

 Figure 1. Ball-n-Socket Joint Type.

This joint type can be used in the biomechanical editor to create a musculo-skeletal model. A ball and socket joint forces a point fixed in one biomechanical body part to be at the same location as that of a point fixed in another body, removing three degrees of freedom.  This ideal joint allows all rotations about the common point. This joint is also known as a spherical joint in the scientific literature. You can set a cone limit that will restrict the rotation of this joint around the point. The cone limit can be rotated and you specify the radius of the cone. When the body part reaches the cone the constraint prevents it from moving further.

## General Properties

 Figure 2. The properties of the ball-n-socket joint.

To see a description of the properties common to all bodies follow this link

## Ball-Socket Properties

These properties are specific to ball-socket only.

Constraints

Cone Half Angle
This determines how big the joint is in the editor window. A large radius produces a large editor graphic.
Default value: 5 cm
Acceptable range:Anything greater than 0.

Damping
Cone damping is a spring damping term applied to joints that have exceeded the cone limit. As with a spring, if both the stiffness and damping are set to zero, the limit is essentially deactivated.
Default value: 0 MN/m
Acceptable range:Anything greater than or equal to 0.

Enable Limits
If this is true then the constraint is turned on, if it is false then there are no constraints on the movement of the ball-n-socket joint.
Default value: True
Acceptable range: True/False

Restitution
The coefficient of restitution is the ratio of rebound velocity to impact velocity when the joint reaches the low or high stop. This is used if the limit stiffness is greater than zero. Restitution must be in the range zero to one inclusive.
Default value: 0 V/V
Acceptable range: 0-1.

Stiffness
When the angle between two bodies reaches the cone limit a stiffness value determines how the restoring force is applied. If this value is set high, there is perfect restitution when the limit is reached. Otherwise, there will be a degree of springiness between the two bodies at the limit.
Default value: 5 MN/m
Acceptable range: Anything greater than or equal to 0.