// Set the joint to bounce off when hitting the lower limit
var limits = hingeJoint.limits;
limits.minBounce = 1;
hingeJoint.limits = limits;

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public JointLimits limits = hingeJoint.limits;
    void Example() {
        limits.minBounce = 1;
        hingeJoint.limits = limits;
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public limits as JointLimits = hingeJoint.limits

    def Example():
        limits.minBounce = 1
        hingeJoint.limits = limits