GenericMotor Class Usage

Here we explore different features of the GenericMotor class.

Class that represents a simple motor defined mainly by its thrust curve. There is no distinction between the propellant types (e.g. Solid, Liquid). This class is meant for rough estimations of the motor performance, therefore for more accurate results, use the SolidMotor, HybridMotor or LiquidMotor classes.

Creating a Generic Motor

To define a generic motor, we will need a few information about our motor:

• The thrust source file, which is a file containing the thrust curve of the motor. This file can be a .eng file, a .rse file, or a .csv file. See more details in Thrust Source Details

• A few physical parameters, which the most important are:

  • The burn time of the motor.

  • The combustion chamber radius;

  • The combustion chamber height;

  • The combustion chamber position;

  • The propellant initial mass;

  • The nozzle radius;

  • The motor dry mass.

The usage of the GenericMotor class is very similar to the other motor classes. See more details in the SolidMotor Class Usage, LiquidMotor Class Usage, and HybridMotor Class Usage pages.

from rocketpy.motors import GenericMotor

# Define the motor parameters
motor = GenericMotor(
  thrust_source = "../data/motors/cesaroni/Cesaroni_M1670.eng",
  burn_time = 3.9,
  chamber_radius = 33 / 100,
  chamber_height = 600 / 1000,
  chamber_position = 0,
  propellant_initial_mass = 2.5,
  nozzle_radius = 33 / 1000,
  dry_mass = 1.815,
  center_of_dry_mass_position = 0,
  dry_inertia = (0.125, 0.125, 0.002),
  nozzle_position = 0,
  reshape_thrust_curve = False,
  interpolation_method = "linear",
  coordinate_system_orientation = "nozzle_to_combustion_chamber",
)

# Print the motor information
motor.info()

Motor Details
Total Burning Time: 3.9 s
Total Propellant Mass: 2.500 kg
Structural Mass Ratio: 0.421
Average Propellant Exhaust Velocity: 2410.540 m/s
Average Thrust: 1545.218 N
Maximum Thrust: 2200.0 N at 0.15 s after ignition.
Total Impulse: 6026.350 Ns

Note

The GenericMotor is a simplified model of a rocket motor. If you need more accurate results, use the SolidMotor, HybridMotor or LiquidMotor classes.

The load_from_eng_file method

The GenericMotor class has a method called load_from_eng_file that allows the user to build a GenericMotor object by providing just the path to an .eng file.

The parameters available in the method are the same as the ones used in the constructor of the GenericMotor class. But the method will automatically read the .eng file and extract the required information if the user does not provide it. In this case, the following assumptions about the most relevant parameters are made:

• The chamber_radius is assumed to be the same as the motor diameter in the .eng file;

• The chamber_height is assumed to be the same as the motor length in the .eng file;

• The chamber_position is assumed to be 0;

• The propellant_initial_mass is assumed to be the same as the propellant mass in the .eng file;

• The nozzle_radius is assumed to be 85% of the chamber_radius;

• The dry_mass is assumed to be the total mass minus the propellant mass in the .eng file;

As an example, we can demonstrate:

from rocketpy.motors import GenericMotor


# Load the motor from an .eng file
motor = GenericMotor.load_from_eng_file("../data/motors/cesaroni/Cesaroni_M1670.eng")

# Print the motor information
motor.info()

Motor Details
Total Burning Time: 3.9 s
Total Propellant Mass: 3.101 kg
Structural Mass Ratio: 0.407
Average Propellant Exhaust Velocity: 1943.357 m/s
Average Thrust: 1545.218 N
Maximum Thrust: 2200.0 N at 0.15 s after ignition.
Total Impulse: 6026.350 Ns

Although the load_from_eng_file method is very useful, it is important to note that the user can still provide the parameters manually if needed.

Tip

The load_from_eng_file method is a very useful tool for simulating motors when the user does not have all the information required to build a SolidMotor yet.