Car rotation help for a mini game project - unity3d

Question

I have a mini project where i have a car that drives on a cylinder and is rotating around the cylinder. When i press left mouse click the car rotates to the left and goes to the left and when i press right mouse click it rotates right and it goes right. What i want is when i release the mouse click buttons i want the car to rotate back to face the forward direction of the cylinder and continue going forward along the cylinder i have a script that is working but it is not rotating the car back to forward direction.
//THIS SCRIPT IS ATTACHED TO THE CAR
void Update(){
//CHECKS IF MOUSE BUTTON ARE CLICKED
if (Input.GetMouseButton (0)) {
rotation = -1;
} else if (Input.GetMouseButton (1)) {
rotation = 1;
} else {
rotation = 0;
}
}
void FixedUpdate(){
//moves the car forward
//rgb is the rigidbody of the car
rgb.MovePosition(rgb.position - transform.right * moveSpeed * Time.fixedDeltaTime);
// THE LINES BELOW ROTATE THE CAR TO THE LEFT OR RIGHT
Vector3 yRot = Vector3.up * rotation * rotation_speed * Time.deltaTime;
Quaternion deltaRot = Quaternion.Euler(yRot);
Quaternion targetRot = rgb.rotation * deltaRot;
rgb.MoveRotation(Quaternion.Slerp(rgb.rotation, targetRot, 50f * Time.fixedDeltaTime));
}

Answer 1

This is because you are setting the variable "rotation" to 0.
Vector3 yRot = Vector3.up * rotation * rotation_speed * Time.deltaTime;
Which results to 0 and your object doesn't rotate.
I would recommend you to do something like this in your update method:
if (Input.GetMouseButton (0))
{
rotation = -1;
}
else if (Input.GetMouseButton (1))
{
rotation = 1;
}
else
{
//Now when the rotation is positive,
//the object starts to rotate towards negative, but stops at 0
//Same is true when the rotation is negative
if (rgb.rotation.y > 0)
{
rotation = -1;
}
else if (rgb.rotation.y < 0)
{
rotation = 1;
}
else
{
//This needs to be added here to stop the object from rotating
//when the y rotation is already 0
rotation = 0;
}
}
Now it rotates towards 0 when you don't press anything. Also don't use Time.deltaTime in FixedUpdate.
Edit:
So I noticed that with this method it doesn't quite never return to 0. It gets very close but not close enough. By adding this to FixedUpdate the y rotation gets rounded to 0.
if (Mathf.Abs(targetRot.y) < 0.00001f)
{
targetRot = Quaternion.Euler(new Vector3(targetRot.x, 0, targetRot.z));
}