Nema 8 Stepper motor stalling issue

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1

Hi
We are using these nema 8 steppers in a project:

Wired up to the A4988 big easy driver.
The motors tend to stall even with no load - tried everything to prevent it but it still occurs. Has anyone used these motors and had a similar problem?
We are running them quite fast, but well within spec, and even slowing them down doesn’t seem to help

2

Hi, how are you powering the motor and the motor driver?

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3

We are using a buck converter board taking 12V down to 8V and are capable of 3A output current. For development we are using a bench power supply capable of 3A to provide the 12V. The driver and motor are powered by 8V. We have tried varying the voltage up to 24V and down to 8V but the stalling still occurs

4

Hi Timothy,

Have you got an idea of the current limit set on the A4988? While a NEMA-8 is pretty small and weak, it should be able to turn itself at the very least.

Are you able to share a photo of how you’ve got everything wired up?

Have you checked the status/error pins on the driver? Maybe it’s overheating?

Keen to get to the bottom of this one!
-James

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5

Hi James,

I have set the current based on Vref = Imot8Rsen which is 0.528V for 0.6A

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The driver doesn’t seem to get hot, if I turn up the current the motors get hot but still stall
Photo attached

Cheers,
Tim

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6

Hi Timothy,

Weird issue! Do you find that the motor “skips” backward when stalling? that would mean it’s missing steps and overwhelmed, but just not moving potentially points to issues in the driver or step/dir lines.

Keen to get to the bottom of this one!
-James

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7

Hi Tim
This is where an oscilloscope comes into its own. Use it to make sure the drive pulses are actually getting to the stepper or even getting to the driver board.
Cheers Bob

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8

They don’t go backwards, just stall and skip steps for a short while, then continue. I have looked at the drive signals and they all look fine
One strange thing I noticed is that if I place a finger on the coupler of each stepper lightly, they work perfectly. I have been researching stepper motor resonance and am wondering if there is something weird like that going on
I have literally tried everything but can’t prevent stalling. I am starting to wonder if these steppers have a flaw