I’ve used the DRV8834 for a number of projects, never had troubles. But now when I’m driving some steppers from NMB (PG15S and PG25), both gearbox motors have trouble going above a very embarrassing low pulse rate.
I always assume my work is the problem first, so I’ve checked a lot of things. First is a picture of my setup. I’m confident the wiring is right because low speed settings make the motor function.
Then here is a plot of the signal going to the DRV8834:
. The top line is the step signal and then the DIR signal is the third line, the other two are nSleep and nFault. This plot is showing output when the instructed speed is 1000 pps, or 1ms period between steps. Also I’ll note the motor is under no load
, so there shouldn’t be any problems. Notice it ramps up to speed, so I’m not trying to cold start the motor, it should ramp nicely. Here is a zoom view of the almost at full speed pulsing.
For low speeds, like if commanded 250pps, the motor performs nicely, it rotates the correct angle and everything is great. But then when I do the 1k pps setting, or even 500 pps, the motor hiccups as the pulse period is decreasing to its shortest (i.e. when getting to the high speeds). This happens with both of these motors.
I’m pretty sure it can’t be a current limit issue, the motors are unloaded, and I can monitor the current from the motor controller.
What should I test next to try and figure out how to handle the hiccups?
By the way, I’ve swapped in a Sanyo stepper motor and things work fine. It must be something about these motors!
Thanks for letting us know you found the issue. In case you haven’t already looked into it, you might check to be sure your coils are paired correctly on those old stepper motors.
Do you mean A-A instead of accidentally connected A-B? Just to check, there is no backwards version of A-A, correct? If yellow and orange are a pair, there is no directionality correct?
Either way I’ll go try swapping to what I presently consider A-B and see if things get better.
I switched from [Orange-Yellow, Brown-Black] to [Orange-Brown, Yellow-Black] and the motor didn’t move. I also switched them to check for directionality [Yellow-Orange, Brown-Black], and it performs the same, as I expected, still has the hiccups.
The coil pair connections on the DRV8834 are A1 and A2 for one pair and B1 and B2 for the other; it does not matter what order you connect the coil pairs to those connections.
One easy way to identify coil pairs is use a multimeter to test for continuity between the wires of each coil pair.
Can you tell me what you set the VREF voltage to when you set the current limit for the DRV8834? Also, what is the current per phase rating of the suspect motors?
I have a request out to the MNFR to get a torque curve at 5V. Right now I have the current limit set at about 400 mA (or 200 mV on VREF), when I think the motor should only draw maybe 200 mA. I’m certain I have the correct coil pairs - one way works fine at slow speed, the other way just vibrates. So its clear I think the pairing. Plus the cable sort of groups the four wires into pairs on the motor body.