Tag Archives: python

Controlling two 28BYJ-48 Stepper Motors with Raspberry Pi

I’ve taken some code written by Stephen C Phillips and added/modified a few lines so its possible to run two motors at once, even with different directions.

#!/usr/bin/env python

# This code is written by Stephen C Phillips http://scphillips.com.
# and modified by Paul Petring http://defendtheplanet.net
# It is in the public domain, so you can do what you like with it
# but a link to our websites would be nice.

# It works on the [amazon &title=Raspberry Pi&text=Raspberry Pi] computer with the standard Debian Wheezy OS and
# the 28BJY-48 stepper motor with ULN2003 control board.

from time import sleep
import RPi.GPIO as GPIO
from thread import start_new_thread
import sys

class Motor(object):
    def __init__(self, pins):
        self.P1 = pins[0]
        self.P2 = pins[1]
        self.P3 = pins[2]
        self.P4 = pins[3]
        self.deg_per_step = 5.625 / 64
        self.steps_per_rev = int(360 / self.deg_per_step)  # 4096
        self.step_angle = 0  # Assume the way it is pointing is zero degrees
        for p in pins:
            GPIO.setup(p, GPIO.OUT)
            GPIO.output(p, 0)
    def __exit__(self, type, value, traceback):
       self.clean_pins_up()
    def _set_rpm(self, rpm):
        """Set the turn speed in RPM."""
        self._rpm = rpm
        # T is the amount of time to stop between signals
        self._T = (60.0 / rpm) / self.steps_per_rev

    # This means you can set "rpm" as if it is an attribute and
    # behind the scenes it sets the _T attribute
    rpm = property(lambda self: self._rpm, _set_rpm)
    def clean_pins_up(self):
        GPIO.output(self.P1, 0)
        GPIO.output(self.P2, 0)
        GPIO.output(self.P3, 0)
        GPIO.output(self.P4, 0)
def move_to(self, angle):
        """Take the shortest route to a particular angle (degrees)."""
        # Make sure there is a 1:1 mapping between angle and stepper angle
        target_step_angle = 8 * (int(angle / self.deg_per_step) / 8)
        steps = target_step_angle - self.step_angle
        steps = (steps % self.steps_per_rev)
        if steps > self.steps_per_rev / 2:
            steps -= self.steps_per_rev
            print "moving " + `steps` + " steps"
            self._move_acw(-steps / 8)
        else:
            print "moving " + `steps` + " steps"
            self._move_cw(steps / 8)
        #self.step_angle = target_step_angle #in case you want to keep track of the position
        self.step_angle = 0

    def _move_acw(self, big_steps):
        self.clean_pins_up()
        for i in range(big_steps):
            GPIO.output(self.P1, 0)
            sleep(self._T)
            GPIO.output(self.P3, 1)
            sleep(self._T)
            GPIO.output(self.P4, 0)
            sleep(self._T)
            GPIO.output(self.P2, 1)
            sleep(self._T)
            GPIO.output(self.P3, 0)
            sleep(self._T)
            GPIO.output(self.P1, 1)
            sleep(self._T)
            GPIO.output(self.P2, 0)
            sleep(self._T)
            GPIO.output(self.P4, 1)
            sleep(self._T)
        self.clean_pins_up()
def _move_cw(self, big_steps):
        GPIO.output(self.P1, 0)
        GPIO.output(self.P2, 0)
        GPIO.output(self.P3, 0)
        GPIO.output(self.P4, 0)
        for i in range(big_steps):
            GPIO.output(self.P3, 0)
            sleep(self._T)
            GPIO.output(self.P1, 1)
            sleep(self._T)
            GPIO.output(self.P4, 0)
            sleep(self._T)
            GPIO.output(self.P2, 1)
            sleep(self._T)
            GPIO.output(self.P1, 0)
            sleep(self._T)
            GPIO.output(self.P3, 1)
            sleep(self._T)
            GPIO.output(self.P2, 0)
            sleep(self._T)
            GPIO.output(self.P4, 1)
            sleep(self._T)
        self.clean_pins_up()
if __name__ == "__main__":  
    GPIO.cleanup()
    GPIO.setmode(GPIO.BCM)
    m_l = Motor([2,3,14,15])
    m_r = Motor([10,9,11,25])
    m_l.rpm = float(sys.argv[1])
    m_r.rpm = float(sys.argv[1])
    print "Pause in seconds: " + `m_l._T`
    i = 1
    while i < 5:
       start_new_thread(m_l.move_to,(int(sys.argv[2]),))
       start_new_thread(m_r.move_to,(int(sys.argv[3]),))
       sleep(2)
       i=i+1
    GPIO.cleanup()

run the code with the following command:

sudo python motor.py 10 +90 -90

10 stands for rpm (rounds per minute) and +90 -90 as the amount of degrees each motor should turn. I figured out that, with this code and motors the max RPM is around 16, which results in a speed of 16 * 2 * Pi * Radius of your Wheel in cm / m.

This code only demonstrates how to turn the motors with a certain speed and degree. Its not made for rotating wheels yet..

Have fun experimenting 🙂

Controlling a stepper motor 28BYJ-48 with a Raspberry Pi

Actually there is no need to explain more about stepper motors than that video does:

Currently I am using this python code to get the motors running:

#!/usr/bin/env python
 
# import required libs
import time
import RPi.GPIO as GPIO

GPIO.cleanup() #cleaning up in case GPIOS have been preactivated
 
# Use BCM GPIO references
# instead of physical pin numbers
GPIO.setmode(GPIO.BCM)
 
# be sure you are setting pins accordingly
# GPIO10,GPIO9,GPIO11,GPI25
StepPins = [10,9,11,25]
 
# Set all pins as output
for pin in StepPins:
  GPIO.setup(pin,GPIO.OUT)
  GPIO.output(pin, False)

#wait some time to start
time.sleep(0.5)
 
# Define some settings
StepCounter = 0
WaitTime = 0.0015
 
# Define simple sequence
StepCount1 = 4
Seq1 = []
Seq1 = range(0, StepCount1)
Seq1[0] = [1,0,0,0]
Seq1[1] = [0,1,0,0]
Seq1[2] = [0,0,1,0]
Seq1[3] = [0,0,0,1]
 
# Define advanced sequence
# as shown in manufacturers datasheet
StepCount2 = 8
Seq2 = []
Seq2 = range(0, StepCount2)
Seq2[0] = [1,0,0,0]
Seq2[1] = [1,1,0,0]
Seq2[2] = [0,1,0,0]
Seq2[3] = [0,1,1,0]
Seq2[4] = [0,0,1,0]
Seq2[5] = [0,0,1,1]
Seq2[6] = [0,0,0,1]
Seq2[7] = [1,0,0,1]

#Full torque
StepCount3 = 4
Seq3 = []
Seq3 = [3,2,1,0]
Seq3[0] = [0,0,1,1]
Seq3[1] = [1,0,0,1]
Seq3[2] = [1,1,0,0]
Seq3[3] = [0,1,1,0]
 
# set
Seq = Seq2
StepCount = StepCount2
 
# Start main loop
try:
  while 1==1:
    for pin in range(0, 4):
      xpin = StepPins[pin]
      if Seq[StepCounter][pin]!=0:
        #print " Step %i Enable %i" %(StepCounter,xpin)
        GPIO.output(xpin, True)
      else:
        GPIO.output(xpin, False)
    StepCounter += 1

  # If we reach the end of the sequence
  # start again
    if (StepCounter==StepCount):
      StepCounter = 0
    if (StepCounter<0):
      StepCounter = StepCount
 
  # Wait before moving on
    time.sleep(WaitTime)
except:
  GPIO.cleanup();
finally: #cleaning up and setting pins to low again (motors can get hot if you wont) 
  GPIO.cleanup();
  for pin in StepPins:
    GPIO.setup(pin,GPIO.OUT)
    GPIO.output(pin, False)

it is based on code by matt.hawkins but with some improvements I did.

Please be sure you set your GPIOs accordingly to your [amazon &title=Raspberry Pi&text=Raspberry Pi] Revision. So mine was REV 2.0.

Run the code with

sudo python nameOfTheFile.py

and hit [Ctrl]+[C] to stop it. All pins will be set to low afterwards.

In case you want control two motors of this type see another post I made here.

 

For a different version see:
http://www.intorobotics.com/control-stepper-motors-raspberry-pi-tutorials-resources/http://www.elektronx.de/tutorials/schrittmotorsteuerung-mit-dem-raspberry-pi/