Nosy Monster

I added an acceleration algorithm to the Nosy Monster. It helps a lot when stuck. One day I’ll document it and make the software available online.

PlottyBot is born

Years in the making, many prototypes, and I hope a software stack which brings novelty and ease of use to the world of pen plotting. It’s been a marathon building the final version and documenting the process carefully. I’m too pooped to say anything more about it for now.

Instructions here

Driving a 28BYJ-48 Stepper Motor & ULN2003 driver with a Raspberry Pi

Quick points about this motor & driver

They are wonderfully cheap and extremely accurate due to 1/64 gearing. They move by 0.087890625° per step! However, the gearing is made of plastic and will wear out overtime, especially if moving heavy objects. Lastly the motors can become a little toasty if you work them hard.

Circuit

Fritzing

Code

#!/usr/bin/python3
import RPi.GPIO as GPIO
import time

in1 = 17
in2 = 18
in3 = 27
in4 = 22

# careful lowering this, at some point you run into the mechanical limitation of how quick your motor can move
step_sleep = 0.002

step_count = 4096 # 5.625*(1/64) per step, 4096 steps is 360°

direction = False # True for clockwise, False for counter-clockwise

# defining stepper motor sequence (found in documentation http://www.4tronix.co.uk/arduino/Stepper-Motors.php)
step_sequence = [[1,0,0,1],
                 [1,0,0,0],
                 [1,1,0,0],
                 [0,1,0,0],
                 [0,1,1,0],
                 [0,0,1,0],
                 [0,0,1,1],
                 [0,0,0,1]]

# setting up
GPIO.setmode( GPIO.BCM )
GPIO.setup( in1, GPIO.OUT )
GPIO.setup( in2, GPIO.OUT )
GPIO.setup( in3, GPIO.OUT )
GPIO.setup( in4, GPIO.OUT )

# initializing
GPIO.output( in1, GPIO.LOW )
GPIO.output( in2, GPIO.LOW )
GPIO.output( in3, GPIO.LOW )
GPIO.output( in4, GPIO.LOW )


motor_pins = [in1,in2,in3,in4]
motor_step_counter = 0 ;


def cleanup():
    GPIO.output( in1, GPIO.LOW )
    GPIO.output( in2, GPIO.LOW )
    GPIO.output( in3, GPIO.LOW )
    GPIO.output( in4, GPIO.LOW )
    GPIO.cleanup()


# the meat
try:
    i = 0
    for i in range(step_count):
        for pin in range(0, len(motor_pins)):
            GPIO.output( motor_pins[pin], step_sequence[motor_step_counter][pin] )
        if direction==True:
            motor_step_counter = (motor_step_counter - 1) % 8
        elif direction==False:
            motor_step_counter = (motor_step_counter + 1) % 8
        else: # defensive programming
            print( "uh oh... direction should *always* be either True or False" )
            cleanup()
            exit( 1 )
        time.sleep( step_sleep )

except KeyboardInterrupt:
    cleanup()
    exit( 1 )

cleanup()
exit( 0 )

Stuff you might need for this to run:

sudo apt-get update --fix-missing && sudo apt-get install python3-rpi.gpio

Results

This motor takes 5.625*(1/64)° per step, this means 2048 steps for 180°:

and 4096 steps for 360°:

One thing that is super cool about the driver board are the LEDs. Projects are always cooler with blinky LEDs, but these guys also help show what is actually going on inside the stepper, and can help you find issues. They are supposed to light up in sequence.