I have built a small test rig with a A4988, an STM32 evaluation board, a LM317 to generate a 3V from my 12V 4.2A supply, and a NEMA17 motor. I have wired it according to the minimal wiring requirements - I don’t see any issues there. However, whenever I send a step command via the microcontroller, the motor makes the hush sound and will not turn at all. Can you speculate what is happening? I’ve set the current limit to 1A per phase, but when I turn on the supply it sometimes draws over 2A (measurement accuracy…?). I have noticed that switching the phases at the pololu stops this behavior - is there a particular order to connect the motor wires (I suppose that the each pair that goes to one side of the motor should be connected to 1, the other to 2?). I have never worked with a stepper before (without support…) thus the newbie questions…
Thanks in advance!
I forgot to mention that it also seems that sometimes the motor with stop responding to step commands (no more hush sound). It the A4988 experiencing an over current event of some kind? I need to power cycle to make this go away. I have also experienced the motor “starting up” without any step commands…
Measuring the voltage of digital network, I found that it’s below 3V (about 2.75V), so I guess that’s an issue I need to address first. I am using a LM317 but still, when under load, the voltage falls below 3V. Any ideas why this might happen?
I did not place bypass capacitors around the LM317 - I thought they are redundant in my application (I have as 3V comsumers a STM32F0 discovery board that draw 50mA with some blinking LEDS, and the A4988). Surely, the LM317 should be able to maintain 3V…?
It sounds like you are using the LM317 to supply the VMOT pin on the A4988 with 3V. The A4988 is rated to operate with 8V to 35V on VMOT, so it is not surprising you are getting unexpected behavior from the driver. Also, I am not sure the regulator would be able to supply enough current to run a stepper motor without overheating.
You should be able to use the active current limiting feature on the A4988 to run a stepper motor with a 3V rating from 12V on the VMOT pin, as we mention in the FAQ for the driver. You can watch the video in this blog post to see more about how to set current limiting on our stepper driver carrier boards.