DRV8824-Q1: Motor not stepping reliably when using DRV8824

Hello,

Thanks for your post.

Andrew Kalman said:

We inherited a DRV8824-based design and are having problems driving the attached motor smoothly. VM is 28V, we only vary STEP and DIR, and the step rate is really very slow -- never higher than 500 steps/sec. Bulk capacitance is 20uF, and the motor is a LIN Engineering WO-416-07-05, with 0.6Amps/phase, 5.4Ohms/phase, and an unspecified inductance per phase. We're only full-stepping (MODE2-0 = 0).

Simply put, the motor does not step smoothly -- it hesitates / hiccups, sometimes reverses (even though DIR is being held constant at 1 or 0), and just runs very roughly.

I've observed a pervasive oscillation in the system -- for example, V_CAP has a couple of volts of oscillation, as do the AOUT and VOUT pins in voltage and in current. But if you step back far enough to view the A/B current waveforms, they do look like A/Bs should when stepping (except for the pervasive oscillation at the max pos and negative currents).

I could use some help in understanding -- in this configuration

1. whether these signals look correct,
2. whether the oscillation (in the current waveform, it's at 25kHz which is half of the PWM frequency, so perhaps that's normal) is to be expected, and
3. what I should be looking for to fix this very rough stepping of the motor.

I've attached the schematic and a capture with a zoomed-in view thereof.

Thank you for sharing the complete details for your use case. Electrically everything looks correct including the waveforms. What you are seeing is due to a phenomenon known as resonance with stepper motors while running in full-step mode. See this article from a stepper motor vendor. Using 1/2 Step or 1/4 Step mode could alleviate this resonance behavior for the same motor speed. If you must run with full-step mode change the steps/sec to a higher or lower value until you're out of the resonance region. The motor will return to normal operation away from the resonance step rate with full-step mode. 

Regards, Murugavel 

Wow, interesting. And thank you for the prompt reply.

I will see what we can do to i) drive it smoothly in a test configuration, and ii) implement changes required to do that.

Thanks again!

Sounds good, thank you. Please close this thread as RESOLVED. 

Regards, Murugavel 

I'd like to implement changes that remove the resonance, then I'll be comfortable marking it as resolved. I hope that's OK.

That's fine. Thanks.