pymotor 0.3.0

Generates motion and force profiles.

PyMotor

Overview

This is about the app.

Development Status

PyMotor is being developed with Python 3.7 using packages described in requirements.txt.

This is Alpha phase software. This means that features and usage are not fixed, the documentation is most likely incomplete, and there may be bugs.

Some versions of this package are uploaded to pypi.org and can be installed, at your own risk, like this:

$ pip install pymotor

Physics Equations

The math used to calculate force, inertia and torque is shown below. Note that angular velocity and angular acceleration in the equations below are in rad/s and rad/s², respectively. Internally, the software stores these values as Hz and Hz/s.

Physical Units

The native physical units used by the package are shown in the table below. Functions in the module conversions.py are provided so parameters can be entered in other units.

Parameter	Internal Symbol	Unit
Time	t	s
Length	x	m
Linear Velocity	v	m/s
Linear Acceleration	a	m/s2
Force	f	N
Rotations	revs	Revolutions
Angular Velocity	hz	Hz
Angular Acceleration	hzps	Hz/s
Torque	tau	N*m
Moment of Inertia	j	kg*m2
Angle	incline_angle	°

Usage

Creating a Linear Motion Profile

import pymotor as pm

lm_settings = {
    'fs': 10000.0,
    'max_velocity': pm.ipm(40),
    'acc_mode': 'time',
    'acc_value': 0.06, 
    'acc_smooth': True,
    'con_mode': 'distance',
    'con_value': pm.inch(.01),
    'dec_mode': 'acceleration',
    'dec_value': 0.25,
    'dec_smooth': False,
}

lm = pm.LinearMotion(lm_settings)
lm.plot()

Converting to a Linear Force Profile

lf_settings = {
    'safety_factor': 2,
    'moving_mass': 100,
    'preload_force': 0.1,
    'efficiency': 0.9,
    'incline_angle': 45,
    'friction_coef': 0.1,
    'gravity': 9.8,
}

lf = pm.LinearForce(lf_settings, lm)
lf.plot()

Defining a Motor Object

Motor objects contain torque curve and moment of inertia data. The method Motor.tau(hz) returns an interpolated torque value for a given angular velocity, which is used by AngularTorque objects to plot available motor torque vs required torque. Motor.plot() generates a plot of the torque curve which can be used for verification.

The curve_hz list defines the X axis values of the curve. The values must be positive, unique, and ascending.

The curve_tau list defines the Y axis values of the curve. The values must be positive.

curve_hz = [
    0, 
    pm.rpm(300), 
    pm.rpm(600),
    pm.rpm(900),
    pm.rpm(1200),
    pm.rpm(1500),
    pm.rpm(1800),
]

curve_tau = [
    2.5,
    2.2,
    1.3,
    0.9,
    0.7,
    0.6,
    0.5,
]

motor = pm.Motor(curve_hz=curve_hz, curve_tau=curve_tau, j=pm.gcm2(460))
motor.plot()

Defining Other Drivetrain Objects

Other necessary drivetrain objects are created in the following code. Gear ratios, drive screw lead, and moments of inertia are used in the torque generation process. The conversion functions gcm2() and inch() are used to convert from g*cm² and inches, respectively, to native units.

coupler = pm.Coupler(j=pm.gcm2(5))
gear = pm.Gear(ratio=0.5, j_in=pm.gcm2(10), j_out=pm.gcm2(15))
screw = pm.Screw(lead=pm.inch(.05), j=pm.gcm2(20))

Generating a Torque Profile

at = pm.AngularTorque(lf, motor=motor, coupler=coupler, gear=gear, drivetrain=screw)
at.plot()

Planned Changes

• More complete conversions.py module.
• Reduction of pandas DataFrame copy operations.
• Configurable plot units.
• Stepper motor table and three-phase motor signal generation.