BUG: motor coordinates

rocketpy/prints/rocket_prints.py

@@ -94,7 +94,8 @@ def rocket_geometrical_parameters(self):
             "Rocket Center of Dry Mass - Nozzle Exit Distance: "
             + "{:.3f} m".format(
                 abs(
-                    self.rocket.center_of_dry_mass_position - self.rocket.motor_position
+                    self.rocket.center_of_dry_mass_position
+                    - self.rocket.nozzle_position
                 )
             )
         )

rocketpy/rocket/rocket.py

@@ -100,11 +100,16 @@ class Rocket:
     Rocket.motor : Motor
         Rocket's motor. See Motor class for more details.
     Rocket.motor_position : float
-        Position, in m, of the motor's nozzle exit area relative to the user
-        defined rocket coordinate system. See
-        :doc:`Positions and Coordinate Systems </user/positions>`
-        for more information
+        Position, in meters, of the motor's coordinate system origin
+        relative to the user defined rocket coordinate system.
+        See :doc:`Positions and Coordinate Systems </user/positions>`
+        for more information.
         regarding the rocket's coordinate system.
+    Rocket.nozzle_position : float
+        Position, in meters, of the motor's nozzle exit relative to the user
+        defined rocket coordinate system.
+        See :doc:`Positions and Coordinate Systems </user/positions>`
+        for more information.
     Rocket.center_of_propellant_position : Function
         Position of the propellant's center of mass relative to the user defined
         rocket reference system. See
@@ -642,14 +647,15 @@ def add_motor(self, motor, position):
         self.motor_position = position
         _ = self._csys * self.motor._csys
         self.center_of_propellant_position = (
-            self.motor.center_of_propellant_mass - self.motor.nozzle_position
-        ) * _ + self.motor_position
+            self.motor.center_of_propellant_mass * _ + self.motor_position
+        )
         self.motor_center_of_mass_position = (
-            self.motor.center_of_mass - self.motor.nozzle_position
-        ) * _ + self.motor_position
+            self.motor.center_of_mass * _ + self.motor_position
+        )
         self.motor_center_of_dry_mass_position = (
-            self.motor.center_of_dry_mass_position - self.motor.nozzle_position
-        ) * _ + self.motor_position
+            self.motor.center_of_dry_mass_position * _ + self.motor_position
+        )
+        self.nozzle_position = self.motor.nozzle_position * _ + self.motor_position
         self.evaluate_dry_mass()
         self.evaluate_total_mass()
         self.evaluate_center_of_dry_mass()

rocketpy/simulation/flight.py

@@ -1173,7 +1173,10 @@ def __init_equations_of_motion(self):
 
     @cached_property
     def effective_1rl(self):
-        nozzle = self.rocket.motor_position
+        """Original rail length minus the distance measured from nozzle exit
+        to the upper rail button. It assumes the nozzle to be aligned with
+        the beginning of the rail."""
+        nozzle = self.rocket.nozzle_position
         try:
             rail_buttons = self.rocket.rail_buttons[0]
             upper_r_button = (
@@ -1187,7 +1190,10 @@ def effective_1rl(self):
 
     @cached_property
     def effective_2rl(self):
-        nozzle = self.rocket.motor_position
+        """Original rail length minus the distance measured from nozzle exit
+        to the lower rail button. It assumes the nozzle to be aligned with
+        the beginning of the rail."""
+        nozzle = self.rocket.nozzle_position
         try:
             rail_buttons = self.rocket.rail_buttons[0]
             lower_r_button = rail_buttons.position
@@ -1377,7 +1383,7 @@ def u_dot(self, t, u, post_processing=False):
         )
         # c = -self.rocket.distance_rocket_nozzle
         c = (
-            -(self.rocket.motor_position - self.rocket.center_of_dry_mass_position)
+            -(self.rocket.nozzle_position - self.rocket.center_of_dry_mass_position)
             * self.rocket._csys
         )
         a = b * Mt / M
@@ -1632,7 +1638,7 @@ def u_dot_generalized(self, t, u, post_processing=False):
         r_CM_ddot = Vector([0, 0, r_CM_z.differentiate(t, order=2)])
         ## Nozzle gyration tensor
         r_NOZ = (
-            -(self.rocket.motor_position - self.rocket.center_of_dry_mass_position)
+            -(self.rocket.nozzle_position - self.rocket.center_of_dry_mass_position)
             * self.rocket._csys
         )
         S_noz_33 = 0.5 * self.rocket.motor.nozzle_radius**2
@@ -2411,23 +2417,10 @@ def aerodynamic_spin_moment(self):
     # Kinetic Energy
     @funcify_method("Time (s)", "Rotational Kinetic Energy (J)")
     def rotational_energy(self):
-        # b = -self.rocket.distanceRocketPropellant
-        b = (
-            -(self.rocket.motor_position - self.rocket.center_of_dry_mass_position)
-            * self.rocket._csys
-        )
-        mu = self.rocket.reduced_mass
-        Rz = self.rocket.dry_I_33
-        Ri = self.rocket.dry_I_11
-        Tz = self.rocket.motor.I_33
-        Ti = self.rocket.motor.I_11
-        I1, I2, I3 = (Ri + Ti + mu * b**2), (Ri + Ti + mu * b**2), (Rz + Tz)
-        # Redefine I1, I2 and I3 time grid to allow for efficient Function algebra
-        I1.set_discrete_based_on_model(self.w1)
-        I2.set_discrete_based_on_model(self.w1)
-        I3.set_discrete_based_on_model(self.w1)
         rotational_energy = 0.5 * (
-            I1 * self.w1**2 + I2 * self.w2**2 + I3 * self.w3**2
+            self.rocket.I_11 * self.w1**2
+            + self.rocket.I_22 * self.w2**2
+            + self.rocket.I_33 * self.w3**2
         )
         rotational_energy.set_discrete_based_on_model(self.w1)
         return rotational_energy
@@ -2564,41 +2557,6 @@ def static_margin(self):
         """Static margin of the rocket."""
         return self.rocket.static_margin
 
-    # Rail Button Forces
-    @cached_property
-    def effective_1rl(self):
-        """Original rail length minus the distance measured from nozzle exit
-        to the upper rail button. It assumes the nozzle to be aligned with
-        the beginning of the rail."""
-        nozzle = (
-            self.rocket.motor_position - self.rocket.center_of_dry_mass_position
-        ) * self.rocket._csys  # Kinda works for single nozzle
-        try:
-            rail_buttons = self.rocket.rail_buttons[0]
-            upper_r_button = (
-                rail_buttons.component.buttons_distance + rail_buttons.position
-            )
-        except IndexError:  # No rail buttons defined
-            upper_r_button = nozzle
-        effective_1rl = self.rail_length - abs(nozzle - upper_r_button)
-        return effective_1rl
-
-    @cached_property
-    def effective_2rl(self):
-        """Original rail length minus the distance measured from nozzle exit
-        to the lower rail button. It assumes the nozzle to be aligned with
-        the beginning of the rail."""
-        nozzle = (
-            self.rocket.motor_position - self.rocket.center_of_dry_mass_position
-        ) * self.rocket._csys
-        try:
-            rail_buttons = self.rocket.rail_buttons[0]
-            lower_r_button = rail_buttons.position
-        except IndexError:  # No rail buttons defined
-            lower_r_button = nozzle
-        effective_2rl = self.rail_length - abs(nozzle - lower_r_button)
-        return effective_2rl
-
     @cached_property
     def frontal_surface_wind(self):
         """Surface wind speed in m/s aligned with the launch rail."""

tests/conftest.py

@@ -111,16 +111,10 @@ def cesaroni_m1670():  # old name: solid_motor
 
 
 @pytest.fixture
-def calisto(cesaroni_m1670):  # old name: rocket
+def calisto_motorless():
     """Create a simple object of the Rocket class to be used in the tests. This
-    is the same rocket that has been used in the getting started guide for
-    years. The Calisto rocket is the Projeto Jupiter's project launched at the
-    2019 Spaceport America Cup.
-
-    Parameters
-    ----------
-    cesaroni_m1670 : rocketpy.SolidMotor
-        An object of the SolidMotor class. This is a pytest fixture too.
+    is the same rocket that has been used in the getting started guide for years
+    but without a motor.
 
     Returns
     -------
@@ -136,60 +130,71 @@ def calisto(cesaroni_m1670):  # old name: rocket
         center_of_mass_without_motor=0,
         coordinate_system_orientation="tail_to_nose",
     )
+    return calisto
+
+
+@pytest.fixture
+def calisto(calisto_motorless, cesaroni_m1670):  # old name: rocket
+    """Create a simple object of the Rocket class to be used in the tests. This
+    is the same rocket that has been used in the getting started guide for
+    years. The Calisto rocket is the Projeto Jupiter's project launched at the
+    2019 Spaceport America Cup.
+
+    Parameters
+    ----------
+    calisto_motorless : rocketpy.Rocket
+        An object of the Rocket class. This is a pytest fixture too.
+    cesaroni_m1670 : rocketpy.SolidMotor
+        An object of the SolidMotor class. This is a pytest fixture too.
+
+    Returns
+    -------
+    rocketpy.Rocket
+        A simple object of the Rocket class
+    """
+    calisto = calisto_motorless
     calisto.add_motor(cesaroni_m1670, position=-1.373)
     return calisto
 
 
 @pytest.fixture
-def calisto_liquid_modded(liquid_motor):
+def calisto_liquid_modded(calisto_motorless, liquid_motor):
     """Create a simple object of the Rocket class to be used in the tests. This
     is an example of the Calisto rocket with a liquid motor.
 
     Parameters
     ----------
+    calisto_motorless : rocketpy.Rocket
+        An object of the Rocket class. This is a pytest fixture too.
     liquid_motor : rocketpy.LiquidMotor
 
     Returns
     -------
     rocketpy.Rocket
         A simple object of the Rocket class
     """
-    calisto = Rocket(
-        radius=0.0635,
-        mass=14.426,
-        inertia=(6.321, 6.321, 0.034),
-        power_off_drag="data/calisto/powerOffDragCurve.csv",
-        power_on_drag="data/calisto/powerOnDragCurve.csv",
-        center_of_mass_without_motor=0,
-        coordinate_system_orientation="tail_to_nose",
-    )
+    calisto = calisto_motorless
     calisto.add_motor(liquid_motor, position=-1.373)
     return calisto
 
 
 @pytest.fixture
-def calisto_hybrid_modded(hybrid_motor):
+def calisto_hybrid_modded(calisto_motorless, hybrid_motor):
     """Create a simple object of the Rocket class to be used in the tests. This
     is an example of the Calisto rocket with a hybrid motor.
 
     Parameters
     ----------
+    calisto_motorless : rocketpy.Rocket
+        An object of the Rocket class. This is a pytest fixture too.
     hybrid_motor : rocketpy.HybridMotor
 
     Returns
     -------
     rocketpy.Rocket
         A simple object of the Rocket class
     """
-    calisto = Rocket(
-        radius=0.0635,
-        mass=14.426,
-        inertia=(6.321, 6.321, 0.034),
-        power_off_drag="data/calisto/powerOffDragCurve.csv",
-        power_on_drag="data/calisto/powerOnDragCurve.csv",
-        center_of_mass_without_motor=0,
-        coordinate_system_orientation="tail_to_nose",
-    )
+    calisto = calisto_motorless
     calisto.add_motor(hybrid_motor, position=-1.373)
     return calisto
 

tests/test_rocket.py

@@ -379,6 +379,87 @@ def test_add_fins_assert_cp_cm_plus_fins(calisto, dimensionless_calisto, m):
     )
 
 
+@pytest.mark.parametrize(
+    """cdm_position, grain_cm_position, nozzle_position, coord_direction, 
+    motor_position, expected_motor_cdm, expected_motor_cpp""",
+    [
+        (0.317, 0.397, 0, "nozzle_to_combustion_chamber", -1.373, -1.056, -0.976),
+        (0, 0.08, -0.317, "nozzle_to_combustion_chamber", -1, -1, -0.92),
+        (-0.317, -0.397, 0, "combustion_chamber_to_nozzle", -1.373, -1.056, -0.976),
+        (0, -0.08, 0.317, "combustion_chamber_to_nozzle", -1, -1, -0.92),
+        (1.317, 1.397, 1, "nozzle_to_combustion_chamber", -2.373, -1.056, -0.976),
+    ],
+)
+def test_add_motor_coordinates(
+    calisto_motorless,
+    cdm_position,
+    grain_cm_position,
+    nozzle_position,
+    coord_direction,
+    motor_position,
+    expected_motor_cdm,
+    expected_motor_cpp,
+):
+    """Test the method add_motor and related position properties in a Rocket
+    instance.
+
+    This test checks the correctness of the `add_motor` method and the computed
+    `motor_center_of_dry_mass_position` and `center_of_propellant_position`
+    properties in the `Rocket` class using various parameters related to the
+    motor's position, nozzle's position, and other related coordinates.
+    Different scenarios are tested using parameterization, checking scenarios
+    moving from the nozzle to the combustion chamber and vice versa, and with
+    various specific physical and geometrical characteristics of the motor.
+
+    Parameters
+    ----------
+    calisto_motorless : Rocket instance
+        A predefined instance of a Rocket without a motor, used as a base for testing.
+    cdm_position : float
+        Position of the center of dry mass of the motor.
+    grain_cm_position : float
+        Position of the grains' center of mass.
+    nozzle_position : float
+        Position of the nozzle.
+    coord_direction : str
+        Direction for coordinate system orientation;
+        it can be "nozzle_to_combustion_chamber" or "combustion_chamber_to_nozzle".
+    motor_position : float
+        Position where the motor should be added to the rocket.
+    expected_motor_cdm : float
+        Expected position of the motor's center of dry mass after addition.
+    expected_motor_cpp : float
+        Expected position of the center of propellant after addition.
+    """
+    example_motor = SolidMotor(
+        thrust_source="data/motors/Cesaroni_M1670.eng",
+        burn_time=3.9,
+        dry_mass=0,
+        dry_inertia=(0, 0, 0),
+        center_of_dry_mass_position=cdm_position,
+        nozzle_position=nozzle_position,
+        grain_number=5,
+        grain_density=1815,
+        nozzle_radius=33 / 1000,
+        throat_radius=11 / 1000,
+        grain_separation=5 / 1000,
+        grain_outer_radius=33 / 1000,
+        grain_initial_height=120 / 1000,
+        grains_center_of_mass_position=grain_cm_position,
+        grain_initial_inner_radius=15 / 1000,
+        interpolation_method="linear",
+        coordinate_system_orientation=coord_direction,
+    )
+    calisto = calisto_motorless
+    calisto.add_motor(example_motor, position=motor_position)
+
+    calculated_motor_cdm = calisto.motor_center_of_dry_mass_position
+    calculated_motor_cpp = calisto.center_of_propellant_position
+
+    assert pytest.approx(expected_motor_cdm) == calculated_motor_cdm
+    assert pytest.approx(expected_motor_cpp) == calculated_motor_cpp(0)
+
+
 def test_add_cm_eccentricity_assert_properties_set(calisto):
     calisto.add_cm_eccentricity(x=4, y=5)