Rails - Getting an error message from the model that is not a Validation error

So I have a method in a reservation model called add_equip. This method does some checking to make sure the added piece of equipment is valid (not conflicting with another reservation).

The checks work. If a added piece of equipment shouldn't be added it isn't, and if it should it is.

The problem is I can't figure out how to send the messages back up to the controller to be put in the flash message? I know I must be missing something here, but I've googled for a few hours now and can't really find any clear explanations how how to pass errors back up the the controller, unless they are validation errors.

add_equip in reservations_controller

    def add_equip
    @reservation = Reservation.find(params[:id])
    @addedEquip = Equip.find(params[:equip_id])

    respond_to do |format|
     if @reservation.add_equip(@addedEquip)
        flash[:notice] = "Equipment was added"
        format.html { redirect_to(edit_reservation_path(@reservation)) }
     else
        flash[:notice] = @reservation.errors
        format.html { redirect_to(edit_reservation_path(@reservation)) }
     end
    end
  end

add_equip in reservation model

def add_equip equip
   if self.reserved.find_by_equip_id(equip.id)
     self.errors.add_to_base("Equipment Already Added")
     return false
   elsif !equip.is_available?(self.start, self.end)
     self.errors.add_to_base("Equipment Already Reserved")
     return false
   else
     r = Reserved.new
     r.reservation = self
     r.equip = equip
     r.save
   end
  end

Any help would be greatly appreciated. I know I'm missing something basic here.