Introduction

I bought a Raspberry Pi thinking that I might find a new hobby that I can do indoors during lockdown. I thought that if I could control the motor, it would be useful in experiments later, so I bought a stepper motor together, so I will try to control it. It is interesting just to rotate at a constant speed, but the goal was to be able to do any exercise. Knowledge of electrical and electronic circuits I started from almost zero, but I could easily do it because there was a lot of information on the net. I really appreciate it. It seems that it can be controlled in various ways, but I would like to introduce the method that I found the easiest.

hardware

Below is a list of the hardware used.

Raspberry Pi 4B 2GB
NEMA17 Stepper Motor ([Amazon](https://www.amazon.co.jp/s?k=nema17&___mk_ja_JP=%E3%82%AB%E3%82%BF%E3%82%AB%E3%83% 8A & ref = nb_sb_noss_2) 2000)
L298N Dual H Bridge DC Stepper Motor Driver --Cheap motor driver. It seems that it is often used to control Arduino + stepper motors / DC motors. Amazon See It seems that it is not very popular in Japan because there is no review at all (?)
12V power supply

Constant speed rotation

First is the basic constant speed rotation. Use RpiMotorLib, A Raspberry pi python motor library on GitHub. It seems that not only stepper motors but also DC motors and servo motors can be controlled. You can install it from the terminal with sudo pip install rpimotorlib. After installing the library, wire it according to the Very polite tutorial and just copy and paste the code to turn the motor. I will. I wired it as follows (sorry for the hand-drawn rough drawing). The resolution of the image is poor and it is difficult to see, but the wiring is as shown in the table below.

Raspberry GPIO	driver	motor
17	IN1	-
18	IN2	-
27	IN3	-
22	IN4	-
-	OUT1	A-
-	OUT2	B-
-	OUT3	A+
-	OUT4	B+

The main function is motor_run (GpioPins, wait, steps, ccwise, verbose, steptype, initdelay). The explanation of each argument is as follows.

GpioPins: Raspberry GPIO pins to use. From the left, pins that connect to IN1, IN2, IN3, and IN4 of the driver.
wait: Time between pulses. If you want to rotate at a rotation speed f [Hz] in half step mode, NEMA17 has a step angle of 1.8 °, so $ wait = (1/2) \ times (1 / f) \ times (1.8 / 360) $.
steps: Number of step control signals. In any step mode, 50 steps make one rotation, that is, one step moves 7.2 ° (see the tutorial for the reason).
ccwise: Counterclockwise. 'True' is counterclockwise, 'False' is clockwise. The default is 'False'.
verbose: When set to 'True', the status etc. will be displayed. The default is 'False'.
steptype: Step mode, 'full','half', 'wave'. See the tutorial for the strengths and weaknesses of each.
initdelay: Time from initialization of GPIO pin to motor operation.

For example, if you want to rotate 5Hz counterclockwise at a rotation speed of 0.5Hz in half-step mode, the code is as follows. It's very simple.

`python`


import time 
import RPi.GPIO as GPIO
from RpiMotorLib import RpiMotorLib  
    
GpioPins = [17, 18, 27, 22]  #GPIO pin. IN1 from the left, IN2, IN3,Pin to connect to IN4.

f = 0.5  #Rotational speed[Hz]
Rev = 5  #Rotate 5 times
s_angle = 1.8  #Step angle[deg]
wait = (1/f)*(s_angle/360)/2  #Time between pulses. Half-Divide by 2 for step mode

#Give the motor a name and specify the motor type (Nema or 28BYJ).
mymotortest = RpiMotorLib.BYJMotor('MyMotorOne', 'Nema') 

#Main. Arguments are GPIO pin, wait, number of steps, reverse rotation, verbose, step mode, first delay from the left[ms]
mymotortest.motor_run(GpioPins, wait, Rev*50, True, False, 'half', 0.05)

#Finally clean up the pins
GPIO.cleanup()

pleasant!

I want to do any exercise

Since I was able to turn it, I think I can do any exercise depending on the chord. I would like to make the motor move arbitrarily. As an example, let's make a sine wave pitch motion. 7 in 1 step.Since it rotates 2 °, the amplitude\theta_0Should be a multiple of that. This time it will be 72 °. periodTWas set to 2 seconds. Angular velocity\omega = \dot{\theta}(In this example\cos)but,waitCan only take a positive value, so take an absolute valuewait = (1/2)\times(1/|\omega|)\times(1.8/360)Is passed. And\omega < 0WhenccwiseTo'True'All you have to do is pass.\theta，\omega，|\omega|，waitは下図のようToなります．

The code is as follows.

`python`


GpioPins = [17, 18, 27, 22]

T = 2  # Period [s]
N_period = 2  # No. of periods
amp = 72
unit_angle = 7.2
s_angle = 1.8  # [deg]
N = int(4*amp/unit_angle)

theta = amp*sin(np.linspace(0, 2*pi, N))  # Angle time history [deg]
dt = T/len(theta)  # time-step [s]
omega = np.gradient(theta, dt)/360  # [Hz]
omega_pos = abs(omega)
pm = omega < 0  # boolean for CW/CCW 
wait = (1/omega_pos)*(s_angle/360)/2

mymotortest = RpiMotorLib.BYJMotor, 'MyMotorOne', 'Nema')
time.sleep(0.002)

for _ in np.arange(N_period):
    for k in np.arange(N):
        mymotortest.motor_run(GpioPins, wait[k], 1, pm[k], False, "half", 0)

GPIO.cleanup()

did it!

[PYTHON] [Raspberry Pi] Stepping motor control with Raspberry Pi

Introduction

hardware

Constant speed rotation

`python`

I want to do any exercise

`python`

Other referenced sites