Mouse gimbal controller for Unity.

MouseGimbal.cs

using UnityEngine;

public class MouseGimbal : MonoBehaviour
{
   [SerializeField] [Range(0,89)] float maxRotationDegrees = 10.0f; // At 90+ gimbal oddities must be dealt with.
   [SerializeField] bool ClampToMaxRotationDegrees = true; // Disable for free rotation.
   [SerializeField] float rotationSpeed = 10.0f;

   const float fullArc = 360.0f;
   const float halfArc = 180.0f;
   const float nullArc = 0.0f;

   void Update () { Tilt(); }

   void Tilt()
   {
      // Apply the 'pre-clamp' rotation (rotation-Z and rotation-X from X & Y of mouse, respectively).
      if (maxRotationDegrees > 0) { SimpleRotation(GetMouseInput()); }

      // Clamp rotation to maxRotationDegrees.
      if (ClampToMaxRotationDegrees) { ClampRotation(transform.rotation.eulerAngles); }
   }

   void ClampRotation(Vector3 tempEulers)
   {
      tempEulers.x = ClampPlane(tempEulers.x);
      tempEulers.z = ClampPlane(tempEulers.z);
      tempEulers.y = nullArc; // ClampPlane(tempEulers.y); // *See GIST note below...
      transform.rotation = Quaternion.Euler(tempEulers);
      ///Debug.Log(tempEulers);
   }

   float ClampPlane(float plane)
   {
      if (OkayLow(plane) || OkayHigh(plane)) DoNothing(); // Plane 'in range'.
      else if (BadLow(plane)) plane = Mathf.Clamp(plane, nullArc, maxRotationDegrees);
      else if (BadHigh(plane)) plane = Mathf.Clamp(plane, fullArc - maxRotationDegrees, fullArc);
      else Debug.LogWarning("WARN: invalid plane condition");
      return plane;
   }

   Vector2 GetMouseInput()
   {
      Vector2 mouseXY;
      mouseXY.x = -Input.GetAxis("Mouse X"); // MouseX -> rotZ.
      mouseXY.y = Input.GetAxis("Mouse Y"); // MouseY -> rotX.
      return mouseXY;
   }

   void SimpleRotation(Vector2 mouseXY)
   {
      Vector3 rotation = Vector3.zero;
      rotation.x = mouseXY.y * Time.deltaTime * rotationSpeed;
      rotation.z = mouseXY.x * Time.deltaTime * rotationSpeed;
      transform.Rotate(rotation, Space.Self); 
   }

   void DoNothing()           {   }
   bool OkayHigh(float test)  { return (test >= fullArc - maxRotationDegrees && test <= fullArc); }
   bool OkayLow(float test)   { return (test >= nullArc && test <= maxRotationDegrees); }
   bool BadHigh(float test)   { return (test > halfArc && !OkayHigh(test)); }
   bool BadLow(float test)    { return (test < halfArc && !OkayLow(test)); }
}

link to video demo: https://www.youtube.com/watch?v=AIozwrQ6xzk