motorcalc - A package to calculate and plot DC - motors

Gerrit Kocherscheidt KOCO MOTION / KOCO automotive, March 2023

Intention

With this package a simple calculation of DC motor parameters based on the input voltage, no-load current, terminal resistance and torque constant is performed. Motor performance curves can be plotted.

Installation

Installation using pip

pip install motorcalc

Installation of sources from Github

git clone https://github.com/KOCOMOTION/motorcalc.git

Basic usage

To create a DC-motor object use the following code

import motorcalc.dcmotor as dcm

m = dcm.CDCmotor(U_N=12.0, I_0=0.02, k_M=0.014, R=25.0)

Here the parameter are

• U_N: Driving voltage [V]
• I_0: No-load current [A]
• k_M: Torque constant [Nm/A]
• R: Terminal resistance [Ohm]

Note that if not stated explicitely, parameter in this package are considered to be in SI-units without magnitude scaling, i.e., I use ampere instead of milli-ampere etc.

Get information about the object

To get information about the object the print function can be used

print(m)

INPUT PARAMETER:
------------------------------------------------------------------------------------------------------
parameter	voltage		term. resist.	no-load cur.	no-load speed	torque const.
------------------------------------------------------------------------------------------------------
unit		Volt		Ohm		    Ampere		RPM		    Nm/A
value		12.0		25.00		0.020		7844		0.014

PERFORMANCE DATA:
------------------------------------------------------------------------------------------------------
parameter	unit	no-load		@max eff.	@max power	stall		@working point
------------------------------------------------------------------------------------------------------
speed		RPM	7844		6514		3922		0		    7844
current		A	0.020		0.098		0.250		0.480		0.020
torque		Nm	0.000		0.001		0.003		0.006		0.000
power		W	0.00		0.74		1.32		0.00		0.00
eff.		%	0.0		    63.3		44.1		0.0		    0.0

In addition parameter can be plotted with the list_spec_table()-function of the CDCMotorExport-Module.

import motorcalc.dcmotorexport as dcmexp

dcmexp.CDCMotorExport(m).list_spec_table()

+----+-----------------------+---------+----------+
| No | Parameter             | Unit    | Value    |
+----+-----------------------+---------+----------+
| 1  | Voltage               | V       | 12       |
+----+-----------------------+---------+----------+
| 2  | Terminal resistance   | Ω       | 25       |
+----+-----------------------+---------+----------+
| 3  | Terminal inductance   | mH      | 0        |
+----+-----------------------+---------+----------+
| 4  | No-load speed         | rpm     | 7844     |
+----+-----------------------+---------+----------+
| 5  | No-load current       | A       | 0.020    |
+----+-----------------------+---------+----------+
| 6  | Nominal torque        | mNm     | 0        |
+----+-----------------------+---------+----------+
| 7  | Nominal speed         | rpm     | 7844     |
+----+-----------------------+---------+----------+
| 8  | Nominal current       | A       | 0.020    |
+----+-----------------------+---------+----------+
| 9  | Max. output power     | W       | 1.323    |
+----+-----------------------+---------+----------+
| 10 | Max. efficiency       | %       | 63.342   |
+----+-----------------------+---------+----------+
| 11 | Back-EMF constant     | mV/rpm  | 133.690  |
+----+-----------------------+---------+----------+
| 12 | Torque constant       | mNm/A   | 14       |
+----+-----------------------+---------+----------+
| 13 | Speed/torque gradient | rpm/mNm | 1218.023 |
+----+-----------------------+---------+----------+
| 14 | Rotor inertia         | gcm^2   | 0        |
+----+-----------------------+---------+----------+

Additional parameter

Missing or additional parameter can be added either on construction or by directly accessing the member variables of the CDCMotor-class.

m = dcm.CDCMotor(U_N=12.0, I_0=0.002, k_M=0.014, R=25.0, H=1.0E-3 Theta=1.0E-8, nPoints=100, n_WP=6000.0, M_WP=0.0015, motor_name:str='test-motor' application:str='test-application')

Parameters
----------
U_N : float
    nominal Voltage in V
I_0 : float
    noload current in A
k_M : float
    torque constant in Nm/A
R : float
    terminal resistance in Ohm
H : float
    terminal inductance in mH (for information only)
Theta : float
    rotor moment of inertia in gcm^2 (for information only)
nPoints : int
    number of points to be plotted in graph
n_WP : float
    required speed at working point
M_WP : float
    required torque at working point
motor_name : str
    name of the motor used for graph plotting
application : str
    short description of application for graph plotting

Plotting

To plot performance curves the CDCMotorPlot-class from the dcmotorplot-module is needed.

import motorcalc.dcmotorplot as dcmplt
dcmplt.CDCMotorPlot(m).plot_curves()

With this command the following Matplotlib-graph is generated:

To-Do: Description of the motorcalc.physics module

This module shall be used to store material parameter und formulas for mechanical and electrical calculations needed for a motor project calculation