Need help with limiting rotation.

I’m brand new to unity and scripting and I’m working on a vehicle in unity that will be able to avoid anything in it’s way.
It’s going to be pretty simple. I want it to drive forward, stop if it gets too close to a wall, then decide if it should turn right or left. It uses ray-casting to check for obstacles. The car body is a simple object I made in Blender and it is connected to cylinders with hinge joints for the wheels. Both the body and the wheels are rigidbodys. At the moment it drives forward just like I want it to, then it stops when it comes to a wall, then it sends rays out the sides to see if there is a wall on the right or left. If there is, it will start rotating away from the wall. My problem is I want to make it stop rotating when it was turn X amount of degrees. Anyone that knows how to do this please help. Below is a youtube link for a video showing what the vehicle does at the moment.

http://youtu.be/NWDuYYkna1k

Here is the script below for those that need to see it. By the way, it’s a JavaScript.

var mode : String = "nothing";
var force : float = 10;
var turnpower : float = 10;


function Start()
{
	yield(WaitForSeconds(3));
	mode = "gofwd";
}


function Update()
{
	var fwd = transform.TransformDirection(Vector3.forward);
	
	Debug.DrawRay(transform.position, fwd *15, Color.yellow);
	
	if(mode == "gofwd")
	{
		rigidbody.AddForce(0,0,force);
	}
	
	if(Physics.Raycast(transform.position, fwd, 15) && mode == "gofwd")
	{
		mode = "stop";
	}
	
	if(mode == "stop")
	{
		Turn();
	}
	
	if(mode == "rightorleft")
	{
		var left = transform.TransformDirection(Vector3.left);
		var right = transform.TransformDirection(Vector3.right);
		
		Debug.DrawRay(transform.position, left *40, Color.red);
		Debug.DrawRay(transform.position, right *40, Color.green);
		
		if(Physics.Raycast(transform.position, left, 40))
		{
			rigidbody.AddTorque (0, turnpower, 0);
		}
	}
}


function Turn()
{
	yield(WaitForSeconds(3));
	
	mode = "rightorleft";
}

There are a couple of ways to approach this problem. The simplest is probably to just use an absolute angle;

   var destAngle : float;  // At the top of the file;

This calcualtes a 45 degree right turn

   destAngle = Atan2(transform.forward.z, transform.forward.x) * Mathf.Rad2Deg;
   destAngle = destAngle - 45.0;

And this is how you might check it in Update()

var currAngle = Atan2(transform.forward.z, transform.forward.x) * Mathf.Rad2Deg); 
if (Mathf.Abs(Mathf.DeltaAngle(currAngle, destAngle) < threshold)) {
  ; // Code here to stop the turn;
}

Note, looking at your code, just because you are not still applying torque, doesn’t mean the car will straighten out. You will have to counteract the torque somehow…friction, drag, counter force…

Also you have to be careful about how you set threshold. It needs to be big enough so that a fps drop will not allow the car to skip on by and keep rotation another 360 degrees. As an alternative, you could save the previous angle from the previous frame and check to make sure it is decreasing. You would bail out of turning when the angle started climbing again. Note this might also cause the car to stop turning if it collided with something that effected his angular velocity.