I have 2 high-impedance stepper motors (this one: 42BYGH4418 with specs at http://hybridsteppermotor.sell.everychina.com/p-98150226-42bhh-nema-17-42bygh-square-hybrid-stepper-motor-2-4-pphase-42mm-stepper-motor.html) that I'm driving with DRV8825 stepper motor sticks. They're currently in 1/16 microstep mode. I know these stepper motor drivers are designed for low impedance steppers but do you think it will work at all with my setup? Should I lower the microstepping? I am missing steps at both 500 mm/minute (my goal speed) and at 100 mm/minute (way too slow). I have the stepper drivers adjusted to 380mA. The specs from the link above list a 32mH inductance, 30ohm resistance per coil. They are 6 wire steppers running in bipolar mode using 4 of the 6 wires.
I've got an example of concentric circles and a star (Captain America logo) that demonstrate the issue - the circles are not completely circular, they don't line up, and the start of the cut and the end of the cut for each circle don't line up (although given the circles, I'd expect the start/end to be misaligned by a larger amount).
This is a known problem with several of the hobby grade stepper drivers, but is especially bad with the DRV8825. The decay time is not chosen appropriately for some motors.
I dropped to 1/8th microstepping with no change. I'll have to investigate more tomorrow but since that didn't affect it, doesn't that mean the fast decay fix above wouldn't work? I'll see if I can attempt the diode fix detailed in one of the links.
MRedmon:
I am missing steps at both 500 mm/minute (my goal speed) and at 100 mm/minute (way too slow).
You don't say how many steps per second those numbers imply. I have some 0.33amp stepper motors working with A4988 drivers for a small CNC lathe. But maybe I am not expecting the same step rate as you are.
By the way what supply voltage are you using - with those motors you want as high as possible really, certainly
well above 12V so the chopper driver hsa voltage headroom. The lower speed issue will be resonance,
and mechanical damping can be used to reduce this (leadscrew drives are usually very torsionally resonant,
belt drives are much more damped by their nature).
I'm using 18v for the steppers. When I decreased the microstepping to 1/8th, I changed my resolution to 32 steps/mm. I was previously at 1/32 microstepping (I had meant to use 1/16 as I stated previously but must have forgotten to change the jumpers) and 128 steps/mm. The resulting motion is almost identical between the two settings as far as how much they deviate from the expected motion.
It looks like my issues were the result of a belt that had stretched with age and was too loose. A little more tension fixed it for now while I await a new belt. Thanks everyone!
