Prodriver stepper motor board and microstepping

Robotics
1

Hello folks,

I’m working with an arduino nano, a prodriver board and a Mercury Motor SM-42ByG011-25 stepper motor. I’ve tried most of the example code and it basically works fine. But I’m having some puzzling behavior with microstepping.

The code is simple - I set the step fraction, for example:

myProDriver.settings.stepResolutionMode = PRODRIVER_STEP_RESOLUTION_FIXED_1_4;

then call begin, and loop, calling step, then a delay in the loop:

for (j=0;j<800;j=j+1) {

myProDriver.step(1, 0);

Serial.println(j);

delay(100);

}

I’m trying to drive a telescope mount slow motion shaft, so I want small steps, and a very slow speed, hence the delay. What I’m getting is interesting. The motor is advancing the correct angular amount. For example, if I set 1/8 step and do 1600 steps, the motor does one full rotation (it’s a 200 step/revolution motor). However, the steps do not get smaller, and the stepping becomes irregular as I make the step fraction smaller. For example it might do two steps quickly, then pause, then do 2 more steps quickly and so on. It’s doing a lot less than 1600 steps in this example.

I’d be happy to provide any other details, but I’m not sure what’s relevant. I will of course continue experimenting but any suggestions or ideas would be appreciated. Thanks,

Doug

2

Ours worked fine after a few missteps; it could be a few different small things:

try powering them in this order: Board → Driver → MTR switch

Also try adjusting the small trim pot for current drive (pictured 3rd-from -the-bottom here) https://learn.sparkfun.com/tutorials/sp … e-overview

3

Adjusting the max current pot smoothed out the steps beautifully. It seemed that a smaller step required a lower current limit but I have to check that. I set it to 1/8 step and adjusted Vref to 0.13 for best step evenness, which corresponds to 143 mA. The setting the card came with was much too high, causing the steps to be jerky, erratic and too large.

A rough setting to drive my telescope would be about 375 mS/step, for one revolution of the Right Ascension control per 10 minutes with 1600 steps. If I did the math right that would be 160 steps across the field of view at 200x, which I think would be smooth enough for visual observation (maybe not astrophotography but I’m not doing that).

I am quite surprised by two things - 1. that this problem was so easy to fix, and 2.that I could get such knowledgable help so quickly with such a specific question. I’m really enjoying this project. Thanks so much!