Stepper 288yj-48 - stop and restart from its latest position

Question

I have a stepper 288yj-48 and I want it to stop 36 times while completing a 360 degrees revolution. For each of the 36 stops, I need it to pause for 10 seconds before moving to the next position.

Here below the code I’m starting with. You'll see “for in range(14)” where 14 represents 1 of the 36 steps I need the stepper to stop at, but I'm not sure if this is the right way to go.

Any suggestion? Thanks

Here you can find the tutorial I took the code from: https://medium.com/@Keithweaver_/controlling-stepper-motors-using-python-with-a-raspberry-pi-b3fbd482f886

import time

GPIO.setmode(GPIO.BOARD)

control_pins = [7,11,13,15]

for pin in control_pins:
  GPIO.setup(pin, GPIO.OUT)
  GPIO.output(pin, 0)

halfstep_seq = [
  [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],
  [1,0,0,1]
]

for i in range(14):
  for halfstep in range(8):
    for pin in range(4):
      GPIO.output(control_pins[pin], halfstep_seq[halfstep][pin])

    time.sleep(0.001)

GPIO.cleanup()

Answer 1

The link to the tutorial you gave seems to be broken but I'm guessing it's this one while searching for that tutorial I also found this which has some additional information. First you need to determine how many half steps your motor takes to execute a full 360. From the second link you can see that the datasheet for the 288yj-48 stepper seems to indicate 4096 with a couple of caveats - it might actually be 4076 or if its the Adafruit small reduction gear stepper which uses the same form factor as the 288yj-48 it could be 513. Watching the video in your tutorial link I suspect that this is what they use because the tutorial code has i in range to 512 and the motor appears to make one full revolution.

So for 36 stops you want your stepper to step 10 degrees or 513/36 = 14.25 (4096/36 = 113.77) so the simplest way I can think to do that would be taking the code from the tutorial and modify it slightly - which you've started to do.

...  

for a in range(36):
  for i in range(14):
    for halfstep in range(8):
      for pin in range(4):
        GPIO.output(control_pins[pin], halfstep_seq[halfstep][pin])
      time.sleep(0.001)
  time.sleep(10)

Assuming that you have the 513 version of the stepper its going move 14 steps 36 times for a full revolution.

The problem I can see here is that you can't divide the stepper motor steps equally by 36 with integer values so after the pattern will drift by 9-10 half steps. You might be able to resolve that by changing the looping so that you do more of the halfstep loops for each i loop the trick would be to continue the halfstep sequence on the next i loop where the last i loop left off. If it could work then its something to experiment with.

I didn't see it in the tutorial you are following but please take note of the caution in the second tutorial link provided regarding powering the stepper motors - regardless of Pi or Arduino power the motors separately and not from the Pi/Arduino

Answer 2

that's great! Thanks so much for the time you put in being this detailed.

I actually moved forward in another forum where a guy helped me sorting out a solution. We pretty much did what you suggested - dividing 4096 by 36 and rounding up the results - but we re-wrote the code in a slightly different way.

You can see the thread in here: https://www.raspberrypi.org/forums/viewtopic.php?f=32&t=270132&p=1639068#p1639068

I'll have a look at the second link you suggested and thanks for spotting that mine was broken :)