Poor Man's Rigidbody Constraints (Unity 2.6)

Hello. I would like to know if there is a way to use constraints functionality for older (free license) versions of Unity which don't seem to support .constraints property of rigidbody. What I am trying to achieve is a rigidbody (which is subject to forces and attached by a spring joint to another body) to be rotateable on only one axis and rotation frozen on other two, like what freezeRotation does for all 3 axis but with one being free to rotate around.
Any outside libs or ideas how to solve this? It is a very active rigidbody and often updated in FixedUpdate so I don't think simple resetting two axis of rotation will do the trick, preferably it should work almost as smooth as freezeRotation without jerkiness.
Thanks.

 

Yup! You can use a ConfigurableJoint and its constraints. Depending on how active the joint is you might want to tweak the Projection Mode settings; this kind of joint-based constraint will be a little spongier/softer than the built-in constraints. You can either configure this purely in the Inspector (with no connected body the Rigidbody is pinned to the world), or via code with:

Code (csharp):

1.  
2. /**
3. * Create a configurablejoint with everything locked
4. */
5. static function Create2DJoint(from:Rigidbody, to:Rigidbody, at:Vector3):ConfigurableJoint
6. {
7.     var joint:ConfigurableJoint = from.gameObject.AddComponent(ConfigurableJoint);
8.      
9.     joint.connectedBody = to;
10.     joint.anchor = from.transform.InverseTransformPoint(at);
11.      
12.     joint.xMotion = ConfigurableJointMotion.Free;
13.     joint.yMotion = ConfigurableJointMotion.Free;
14.     joint.zMotion = ConfigurableJointMotion.Locked;
15.      
16.     joint.angularXMotion = ConfigurableJointMotion.Locked;
17.     joint.angularYMotion = ConfigurableJointMotion.Locked;
18.     joint.angularZMotion = ConfigurableJointMotion.Free;
19.      
20.     joint.projectionMode = JointProjectionMode.PositionOnly;
21.      
22.     joint.configuredInWorldSpace = true;
23.  
24.     return joint;
25. }
26.  

That's some JavaScript (from a Unity 2.x project!), but should be easy to change over to C#.