Stepper Motor acts erratically

Hi I am new to this forum and looking for some help with my stepper motor. I have a UNO with a CNC controller board and Pololu A4988 drivers, using the CNC program. I have Nema 17 motors that are working correctly with the software and no problem but when I connect a 28BYJ-48 (12V and 5V, tried both) the steppers will run in any direction and not consistent. I have changed them to 4 wire bipolar from their normal unipolar configuration. The resistance on the Nema 17 is low, about 10ohms the resistance on the 28BYJ is about 180ohm or about 350ohm depending on which one. I would really like to get these small steppers working as the project is a small lathe and mill that cannot support the Nema 17. Any help would be appreciated. Have both modified steppers and unmodified ones to try.

Bignbad, I can tell it is your first time. Please provide code. do not give unnecessary info. it sounds like you are working with two projects. nema 17 motors and the smaller 28BYJ. so start over with posting code. give one example at a time. There are some great examples out there for the basic 28BYJ setup. use a sample and modify it from there. This will verify that wiring is ok. it also seems like your trying to use to small of a stepper for a lathe and mill project. Nema 17 motors will run a very small machine.

Thanks Weldsmith. I am using one project, I just used the Nema 17 motors to prove the CNC shield was working and that the stepper motors were moving correctly. The code I am using is grbl and GrblPanel to download the G-Code to the Uno. The steps are set on full step, I did have it on 1/8 step. The Nema17 will run the machine but are physically to big to mount on the cross slides.

Bignbad: I have Nema 17 motors that are working correctly with the software and no problem........ but when I connect a 28BYJ-48 (12V and 5V, tried both) the steppers will run in any direction and not consistent.

Ok.... Nema 17 motors.... working. But then you connect another stepper... 28BYJ-48 .... something unexpected will then happen.

Questions...... you then connect another stepper .... connect the stepper to what?

..... "the steppers will run in any direction and not consistent." ..... no-one can begin to answer this unless they understand what is connected to what (ie.... they need to understand the system you have, which isn't possible at the moment due to lack of details). So try to explain the situation clearly - more details please..... eg. power supply power rating.... type of power supply used, how your steppers are connected to your system.

28BYJ-48 are unipolar motors and they cannot be driven with an A4988 which is intended for bipolar motors.

…R
Stepper Motor Basics

Hi,

I don't think you will get your machine (properly) working with the cheap 28BYJ-48.

Some thoughts:

  1. The stepper normally comes with an ULN2003 board and this configuration can't be driven on a STEP/DIR basis (see these useful informations)

  2. If I understood your first post correctly, then you removed the ULN2003 and replaced the driver per axis by the A4988 (on your CNC shield)

  3. This will generally make the 28BYJ-48 run with GRBL -> as GRBL firmware only works with STEP/DIR

  4. As you already found out: the resistance of your small motor is pretty high (180 .. 350 Ohm) plus you have the 1:64 gear reduction - the resulting speed will be VERY VERY SLOW and there is no way to get it speedier than a little bit over 1-2 RPM (which might be ok for a laser CNC, but not for cutting wood or plastic - burn and melt will be the result, and with your lathe you won't have much fun)

  5. Nevertheless to get this stepper move with the A4988 you need to change the unipolar motor hardware to a bipolar motor (see this instruction); but as you said, you did that already - check it again if you did it the right way.

  6. Don't forget to set the current limit on the A4988 if don't want to fry your motor (see this link) - after that you could go with higher voltage as the current limit on the A4988 is the determining factor.

  7. If you can live with the speed limits, go ahead with your project, if not - there are NEMA14 and NEMA11 steppers which might have the right size for your machine -> this would be my favorite solution

@Robin2:

28BYJ-48 are unipolar motors and they cannot be driven with an A4988 which is intended for bipolar motors.

Correct, but apparently it can/will work after the stepper has been converted from unipolar to bipolar (Nr. 5 of my previous reply). Don't have personal experience with this special little motor, but I succeeded in converting a Howard stepper from unipolar to bipolar (was a bit challenging as you can see here, but it worked).

Thanks for the feed back rpt007. I did modify the motor as per the web site you refer to in No5. I ordered the little steppers to try them and see if I could get them to work properly, I am trying to build a test bed before I go full scale and did not want to blow the budget. I am using a Arduino Uno with a Protoneer CNC shield and two (to test first) A4988 drivers. I do have the original ULN2003 drivers (Bought separately) but as you pointed out they will not work with grbl. I have not been able to find a CNC 3 axis program to run a mill, that's why I am using grbl.

Details of setup Power supply is 12V 3.5A Arduino Uno Protoneer CNC shield Pololo A4988 drivers 28BYJ-48stepper motors modified to bipolar (cut internal link and red wire) 12Vdc and 5Vdc tried. I also tested an unmodified motor and it did not even move just made a noise. Checked the wiring is correct I have not set the current yet but will try to night. grbl loaded on to Uno GrblPanel to down load control for X and Y movement to check if motors are moving. Connected the Nema 17 to check operation and steps, all worked. Disconnected and reconnected the 28BYJ and it goes CW when I press increase and CW when I press decrease, it then changes and goes CCW. If I select 10mm movement it can go CW ..CCW...CW continually.

Hope this clears some confusion.

Thanks again rpt007, I will try the current setup and I have a 24Vdc supply that I can connect.

rpt007: apparently it can/will work after the stepper has been converted from unipolar to bipolar

I was not aware that a 28BYJ could be converted from unipolar to bipolar. I thought the common connection between the coils is inside the motor and not accessible to the user.

...R

I have not set the current yet but will try to night.

This is very important and should always be STEP #0! if you don't want to buy a new motor.

Maybe this thread gives you some more useful information.

As said before, you won't be very happy with the 28BYJ steppers. But for testing the whole configuration they are ok.

Question: Do you have already an idea how strong (torque) your CNC should be? Depending on the material you want to cut, you will need torque and speed.

This one is only one of those cheap micro lathes you buy on ebay for$110+. The cnc gear costs more.

Robin2: I was not aware that a 28BYJ could be converted from unipolar to bipolar. I thought the common connection between the coils is inside the motor and not accessible to the user.

...R

It still can't be driven properly from an A4988 since the current setting on the A4988 is not fine enough for 30mA windings. However with a low voltage supply (perhaps about 7V), it will probably turn but the A4988 will simply be saturating all the time, no microstepping possible (or useful given the gear ratio!)

Bignbad,

Do not trust the original connector which is designed to be plugged in the 5 prone port in its controller.

You need to pair the pink wire with the blue wire and conversely the yellow with orange. Once you have the wire in the correct order the motor should start working as you expect.

I tested it with an 28BYJ-48 (5 volt) Arduino Uno with CNC Shield v3 (powered at 12 V) with Pololu DRV8825 driver running grbl and sending command with the universal gcode sender and it works like a charm.

Micro stepping was set to half step.

Merit goes to this post http://www.electronicsmayhem.com/?p=13

These are very affordable components you can prototype with.

I also purchased a set of MakerBeam which seems to be a good framework for prototyping skeletons

Hope this helps Ivan

Robin2: 28BYJ-48 are unipolar motors and they cannot be driven with an A4988 which is intended for bipolar motors.

...R Stepper Motor Basics

And even if you separate the two windings to make it bipolar, the current levels are probably too small for any standard chopper driver to function correctly.

And even if you separate the two windings to make it bipolar, the current levels are probably too small for
any standard chopper driver to function correctly.

Here is a link where somebody pretends to have achieved that:
A4988 drives 28BYJ-48

I think you should try "Override speed" from File Mode in GcodeSender. The driver can't work too fast and this is why it's not moving correctly. In my case this was the problem, I hope this will help you.

rpt007: Here is a link where somebody pretends to have achieved that: A4988 drives 28BYJ-48

Hi!

I know this is an old post, but I've been trying to make this work for a couple of days and haven't found more information on this subject.

I modified my 28byj-48 5V motors to make them bipolar and hooked them to A4988 drivers. They work beatifully, but they get extremely hoy in a couple of minutes (so hot they melted the 3d printed PLA gears attached to the shafts). I'm using Vmot=12V.

The motor datasheet doesn't state the coil current, so I'm not sure what Vref should be. I set it to 0.2V, but both motors still get hot.

Does anyone know if this configuration can work (I mean bipolar 28byj + A4988)? I know I can disable the drivers when the motors aren't moving, but from all the CNC/3d printer projects I can find on the web using these motors it looks like it wouldn't be necessary to disconnect them.

Thanks for any help on this.

Best regards, Santiago

sbayeta: The motor datasheet doesn't state the coil current, so I'm not sure what Vref should be. I set it to 0.2V, but both motors still get hot.

Connect one of the coils to a 5v supply and measure the current with your multimeter.

...R

They are normally about 50 ohm from 5V that means set the current to 0.1A (ie power dissipation is 0.5W total then)