JointSpring is used add a spring force to HingeJoint and PhysicMaterial.
function Start() {
    var hinge = GetComponent.<HingeJoint>();
    // Make the spring reach shoot for a 70 degree angle.
    // This could be used to fire off a catapult.
    var spring = hinge.spring;
    spring.spring = 10;
    spring.damper = 3;
    spring.targetPosition = 70;
    hinge.spring = spring;
}
using UnityEngine; using System.Collections;
public class ExampleClass : MonoBehaviour { void Start() { HingeJoint hinge = GetComponent<HingeJoint>(); JointSpring spring = hinge.spring; spring.spring = 10; spring.damper = 3; spring.targetPosition = 70; hinge.spring = spring; } }
| damper | The damper force uses to dampen the spring. | 
| spring | The spring forces used to reach the target position. | 
| targetPosition | The target position the joint attempts to reach. |