Create SpringJoint with specfic distance or ConfigurableJoint

A quick SimpleJoint function I knocked up:

 Vector3 lTarg = rigidbody.transform.position
 Vector3 lVec = lTarg - mAttachedObject.rigidbody.position;
             
             
 mAttachedObject.rigidbody.AddForce(lVec * 15.0f);

15 is the force strength. It could do with dampening, etc, but it might well be useful for someone out there.

I've just had the same problem and noticed the anchor elements, which are configured automatically by default. It looks like they are both references to the owning element, and it seems to work a bit like a target length. Try turning off the default configuration, and then set the connectedAnchor to a vector length that you like, i.e. a short one.

 j.autoConfigureConnectedAnchor = false;
 j.connectedAnchor = new Vector3(0, 1, 0);

I've burned through many hours trying to accomplish something similar, with no luck. One solution I got working pretty well (I'm trying to create a magnet effect) it to use a trigger collider that triggers calls in FixedUpdate to continually add force to a rigidbody to move it to where I want it to go, and when it gets to where I want it to go (as indicated by a collision) I then add a FixedJoint to the object I moved, attaching it to an object with a rigidbody. Here's code snippet (I've only pasted the two relevant methods to simply the solution, hopefully the rest of the code is easy to deduce).

 private float inc = 0f;
         void FixedUpdate() {
             if (movingRB != null) {
                 if (boundM != null) {
                     movingRB = null;
                     return;
                 }
                 //Debug.LogError(gameObject.name + " magnet still binding " + movingRB.gameObject.name + " for " + secsBinding + " secs");
                 dist = Vector3.Distance(gameObject.transform.position, movingRB.gameObject.transform.position);
                 if(secsBinding > maxSecsToBind) {
                     secsBinding = 0f;
                     inc = 0f;
                     Debug.LogError(gameObject.name + " binding BROKEN to " + movingRB.gameObject.name + "::" + dist);
                     movingRB = null;
                     return;
                 }
                 moveInDirection = transform.position - movingRB.gameObject.transform.position;
                 inc += Time.deltaTime * attractSpeed;
                 movingRB.velocity = (moveInDirection * inc);
                 secsBinding += Time.fixedDeltaTime;
             }
         }
 
 
 
 void OnCollisionEnter(Collision hit) {
             Debug.LogError(gameObject.name + " hit by:" + hit.gameObject.name + ":" + enabled + ":" + hit.rigidbody);
             if (!enabled || hit.rigidbody == null || boundM != null) return;
             bool stickit = false;
             for (int i = 0; i < hit.contacts.Length; i++) {
                 Debug.LogError("magnet part hit--->" + hit.contacts[i].thisCollider.gameObject.name);
                 if (hit.contacts[i].thisCollider != null && hit.contacts[i].thisCollider.GetInstanceID() == stickPoint.GetInstanceID()) {
                     stickit = true;
                     break;
                 }
             }
 
             if (!stickit) return;
             
             I5Magnatizable m = hit.rigidbody.gameObject.GetComponent<I5Magnatizable>();
             if (m == null || !m.isMagnatizable || (letGoOfM != null && letGoOfM.GetInstanceID() == m.GetInstanceID())) return;
 
             if (movingRB == null) movingRB = hit.rigidbody;
             
             if (hit.rigidbody.GetInstanceID() == movingRB.GetInstanceID()) {
                 if (m == null) m = hit.rigidbody.gameObject.GetComponent<I5Magnatizable>();
                 if (m == null) {
                     movingRB = null;
                     return;
                 }
                 boundM = m;
                 movingRB = null;
                 hit.rigidbody.velocity = Vector3.zero;
                 boundRBOrigMass = hit.rigidbody.mass;
                 hit.rigidbody.mass = 0.01f;//to prevent banging into player
                 //Debug.LogError("binding:" + hit.gameObject.name);
                 if (hit.rigidbody.gameObject.transform.parent != null) hit.rigidbody.gameObject.transform.SetParent(null);
                 FixedJoint fj = hit.rigidbody.gameObject.GetComponent<FixedJoint>();
                 if (fj == null) fj = hit.rigidbody.gameObject.AddComponent<FixedJoint>();
                 fj.connectedBody = myRB;
                 m.bindingMagnet = this;
                 inc = 0f;
                 secsBinding = 0f;
             }
             if (magnatizableConnectedListeners != null) magnatizableConnectedListeners(m);
             Debug.LogError(gameObject.name + " magnet binding complete with " + hit.gameObject.name);
         }