Unstable Fixed Joint

Hi,

We tried to use Fixed Joint between a cube and the VR controller, we found that if the cube is blocked by other obstacles and the controller is away from the cube, the cube starts to jump around (please see the images below). We except the cube to be stable on the obstacle, is there any settings of the Fixed Joint to achieve that?

BTW, we don't quite understand the usage of "Enable Preprocessing", we checked the docs
https://docs.unity3d.com/Manual/class-FixedJoint.html but still don't know what it means, can anyone explain it?

Thank you

 

You shouldn't use a fixed joint then. The fixed joint wants the green cube to be inside the blue cube. As this cannot happen, the physics solver goes nuts trying to resolve the conflict (basically, it puts the green cube outside the blue cube, but the joint keeps putting it inside).

To achieve the effect you're looking too, you should use a Spring Joint instead. The spring joint allows some distance between the anchor and the attached object, as if they were connected with a spring.

 

Hi Edy,

Thanks for your suggestion. We tried Spring Joint but it turns out that it doesn't meet our expectation when the green cube is not touching anything except the controller, the green cube will swing around but we want the green cube to be static relative to the controller in that case .

Now we use Configurable Joint with script to control joint's behavior and meet our requirement. We set the XYZ motion of the Configurable Joint to be Free when the green cube touches the static collider(the blue cube) and set the XYZ motion to Locked when the green cube doesn't not touch anything. We also use JointDrive which can attract the cube to the controller when the XYZ motion is free.

Here is the code snippet:

Code (CSharp):

1.     private ConfigurableJoint AddConfigurableJoint()
2.     {
3.         objectInHand.transform.position = this.transform.position;
4.         objectInHand.transform.rotation = this.transform.rotation;
5.  
6.         ConfigurableJoint cf = gameObject.AddComponent<ConfigurableJoint>();
7.         cf.anchor = new Vector3(0, 0, 0);
8.         cf.autoConfigureConnectedAnchor = false;
9.         cf.connectedAnchor = new Vector3(0, 0, 0);
10.  
11.         cf.xMotion = ConfigurableJointMotion.Locked;
12.         cf.yMotion = ConfigurableJointMotion.Locked;
13.         cf.zMotion = ConfigurableJointMotion.Locked;
14.         cf.angularXMotion = ConfigurableJointMotion.Locked;
15.         cf.angularYMotion = ConfigurableJointMotion.Locked;
16.         cf.angularZMotion = ConfigurableJointMotion.Locked;
17.  
18.         JointDrive xjd = new JointDrive();
19.         xjd.positionSpring = 1000.0f;
20.         xjd.maximumForce = 10000.0f;
21.         cf.xDrive = xjd;
22.  
23.         JointDrive yjd = new JointDrive();
24.         yjd.positionSpring = 1000.0f;
25.         yjd.maximumForce = 10000.0f;
26.         cf.yDrive = yjd;
27.  
28.         JointDrive zjd = new JointDrive();
29.         zjd.positionSpring = 10.0f;
30.         zjd.maximumForce = 10000.0f;
31.         cf.zDrive = zjd;
32.  
33.         JointDrive rxjd = new JointDrive();
34.         rxjd.positionSpring = 10.0f;
35.         rxjd.maximumForce = 10000.0f;
36.         cf.angularXDrive = rxjd;
37.  
38.         JointDrive ryzjd = new JointDrive();
39.         ryzjd.positionSpring = 10.0f;
40.         ryzjd.maximumForce = 10000.0f;
41.         cf.angularYZDrive = ryzjd;
42.  
43.         return cf;
44.     }

Code (CSharp):

1.     void checkEnterStaticCollider(Collider other)
2.     {
3.         if (!other.isTrigger && null == other.attachedRigidbody)
4.         {
5.            
6.             ConfigurableJoint cf = gameObject.GetComponent<ConfigurableJoint>();
7.             if (null != cf)
8.             {
9.                 cf.xMotion = ConfigurableJointMotion.Free;
10.                 cf.yMotion = ConfigurableJointMotion.Free;
11.                 cf.zMotion = ConfigurableJointMotion.Free;
12.                 cf.angularXMotion = ConfigurableJointMotion.Free;
13.                 cf.angularYMotion = ConfigurableJointMotion.Free;
14.                 cf.angularZMotion = ConfigurableJointMotion.Free;
15.             }
16.         }
17.     }
18.  
19.     void checkExitStaticCollider(Collider other)
20.     {
21.         if (!other.isTrigger && null == other.attachedRigidbody)
22.         {
23.            
24.             ConfigurableJoint cf = gameObject.GetComponent<ConfigurableJoint>();
25.             if (null != cf)
26.             {
27.                 cf.xMotion = ConfigurableJointMotion.Locked;
28.                 cf.yMotion = ConfigurableJointMotion.Locked;
29.                 cf.zMotion = ConfigurableJointMotion.Locked;
30.                 cf.angularXMotion = ConfigurableJointMotion.Locked;
31.                 cf.angularYMotion = ConfigurableJointMotion.Locked;
32.                 cf.angularZMotion = ConfigurableJointMotion.Locked;
33.             }
34.         }
35.     }