28BYJ-48 (bipolar modified) not moving

Hi,
I modified a 28BYJ-48 to bipolar.
I am using A4988 driver to drive it.

I had the motor working fine but now for some reason the motor is just making a sharp sound and it not moving.

I checked the voltage and current form the chip and I am getting 5V which is required to drive the motor.
I measured the current on one of the coil and i got 100milli amp.

I tried turning the potentiometer on the A4988 but still the motor didnt move.

Any idea what I can try to debug this?

You could try following the directions in the "How to use this forum" post.
That way you can hope for informed help.

Hi @jremington
Do you mean to say search the forum before posting?

I did that but could not find any post which was about modified 28BYJ stepper.

If you meant something else, please let me know if I violated any rules here...

Hi,
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Can you please post a picture of your project?

Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html then look down to item #7 about how to post your code.
It will be formatted in a scrolling window that makes it easier to read.

Thanks.. Tom... :slight_smile:

I modified a 28BYJ-48 to bipolar.
I am using A4988 driver to drive it.

When you first tested your configuration -> did you limit the current of the A4988 being driven through the coils by the voltage reference method?

Unfortunately I can't find a reference to what minimum current you can limit the A4988.
I suspect you might have fried at least one coil of your stepper motor with too much current flowing through it.

Can you measure the resistance of the two coils with a multimeter?
If my guess is right, you will only measure one coil's resistance in the magnitude of some Ohms and the other one either close to zero or "open".

Playing around with the potentiometer on the A4988 is never a good idea - this should only be used with no stepper connected and measuring/adjusting the reference voltage according to the current limiting formula (see Pololu's reference site on the A4988).

Hi,

I modified a 28BYJ-48 to bipolar.

How?
stepperwiring.jpg

Tom… :slight_smile:

Here is what I have done.

@TomGeorge There is a way to convert this stepper to bipolar.

You can see this video on how to do it:

After removing the red wire connection, the two coil connections for the motor are:
Blue-Yellow and Orange-Pink

After this hack, I am using A4988 driver. Here is how I connect the modified stepper:

I then downloaded the driver code form here:

More complete totorial on this is here:

My connections are exactly same.

This is what my code looks like:

#include <Arduino.h>
#include "A4988.h"

#define MOTOR_STEPS 200

#define DIR 8
#define STEP 9

A4988 stepper(MOTOR_STEPS, DIR, STEP);

void setup() {
    stepper.setRPM(120);
    stepper.setMicrostep(2);
}

void loop() {
    stepper.move(100);
    delay(5000);
}

Hi
Have you checked the resistance of each coil and that the coils are still isolated from each other?

Tom... :slight_smile:

TomGeorge:
Hi
Have you checked the resistance of each coil and that the coils are still isolated from each other?

Tom… :slight_smile:

Yes i checked that.
I connected a LED to the coil ends and when I turn the shaft, the LED lights up.
Than, after fiddling with the code a bit I a while ago i was able to make the stepper run in the anticlockwise direction. (chang ein the code is inside the loop()

#include <Arduino.h>
#include "A4988.h"

#define MOTOR_STEPS 200

#define DIR 8
#define STEP 9

A4988 stepper(MOTOR_STEPS, DIR, STEP);

void setup() {
    stepper.setRPM(120);
    stepper.setMicrostep(2);
}

void loop() {
    stepper.move(1);
    stepper.move(-1);
}

Now I am unable to figure out why this code works :frowning:
Logically this code should not work.

This leads me to think, could the A4988 be fried?

  1. what resistance do you measure for each coil and are they almost the same values?
  2. did you ever connect or disconnect the A4988 from the motor while it was still powered?
  3. still not yet answered: to what level have you limited (if at all) the current by using the voltage reference method?

Hi @rpt007

  1. I measured 44.7 Ohms on each coil. Exacts same values on each coil.
  2. No, I did not disconnect the drivers while the motors were powered.
  3. I have used the potentiometer to set the current using VREF*2.5 and I am getting about 100mA current.

OK, all values seem to be in the safe zone.
So yes, you might have fried your A4988 somehow.

As they are not that expensive, go ahead and get another one. By that occasion I would recommend to buy a DRV8825, which is a bit more robust and you could drive a bigger stepper in the future.