Double jump with Character motor

Somebody else already tried this with a sphere: AddForce to sphere
Maybe it can help you

Usa esto, te sirve y me sirve. Español...

 var rapides : float = 6.0;
 var gravedad : float = 20.0;
 var velocidadSalto : float = 8.0;  
 var velocidadSalto2 : float = 8.0;
     var esperarSalto : boolean;
     var esperarSalto2 : boolean;
     var dobleSalto : int = 0;
     var dobleSalto2 : int = 0;
     
     private var moveDirection : Vector3 = Vector3.zero;
     
     //undap
     function Update()
     {
     if( Input.GetKeyDown(KeyCode.Space) && esperarSalto == false)
     {
     Jump();
     }
     var controller : CharacterController = GetComponent(CharacterController);
     if (controller.isGrounded) {
         // We are grounded, so recalculate
         // move direction directly from axes
         moveDirection = Vector3(Input.GetAxis("Horizontal"), 0,
                                 Input.GetAxis("Vertical"));
         moveDirection = transform.TransformDirection(moveDirection);
         moveDirection *= rapides;
         
         if (Input.GetButton ("Jump")&& esperarSalto2 == false) {
         moveDirection.y = velocidadSalto;
         Jump2();
         }
          }
 
     // Apply gravity
     moveDirection.y -= gravedad * Time.deltaTime;
     
     // Move the controller
     controller.Move(moveDirection * Time.deltaTime);
     }
     //undap
     
     function Jump()
     {
      if (dobleSalto <= 1)
     {
     moveDirection.y = velocidadSalto;
     jumpTimer();
     }
     }
      
     function jumpTimer()
     {
     if (Input.GetButton ("Jump"))
     {
     dobleSalto ++;
     }
      
     if (dobleSalto > 1)
     {
     dobleSalto = 0;
     esperarSalto = true;
     yield WaitForSeconds (1.8);
     esperarSalto = false;
     }
     }
 //exra
 function Jump2()
     {
      if (dobleSalto2 <= 1)
     {
     jumpTimer2();
     }
     }
     
 function jumpTimer2()
     {
     if (Input.GetButton ("Jump"))
     {
     dobleSalto2 ++;
     }
      
     if (dobleSalto2 > 1)
     {
     dobleSalto2 = 0;
     esperarSalto2 = true;
     yield WaitForSeconds (1.5);
     esperarSalto2 = false;
     }
     }