I've been troubleshooting a weird issue with some DRV8825 stepper drivers. I am using them to drive all my motors on a RAMPS setup.
My setup is this:
Marlin firmware on RAMPS, with bed autoleveling enabled
DRV8825 set to 1/32 microstepping, driving dual Z motors in parallel.
So during printing, as autoleveling is being used, the Z motors will move smoothly for partial step and then pop into a position, it is quite audible and annoying of a sound, and obviously not microstepping properly. During infills etc, this pop can be heard repeatably as the nozzle passes over specific areas of the bed, adjusting the the same Z step levels as it travels.
To troubleshoot this, I have a little test jig set up where i can measure the current inline going to one of the motor coils with a multimeter, and manually send a step signal one at a time by pressing a button. I set this up the same with my motors in parallel as they are on my printer, and recorded the current measurements. The stepper driver was set beforehand to roughly 1.2A max current.
Here is a link to a spreadsheet with measured values charted as current vs steps.
[docs.google.com]
I only measured part of the waveform before my multimeter decided to auto shutoff and I didn't feel like continuing, but you can see that it does a weird jump from around 0 to .66A, instead of properly microstepping the entire waveform, thus causing the hard pops I was hearing at certain points during autoleveling. Does anyone know the reason it does this?
I suspected it might have something to do with the decay mode, which I had read about, though I admit I don't fully understand the exact effect of changing these modes. I tried tying the DECAY pin to 5V and it didn't seem to have any effect on this behavior of "skipping" microsteps. Just to be clear it never actually loses track of steps, which is why i put "skipping" in quotes, but it is ignoring the microstepping for a portion of the waveform.
After more searching online for similar issues, I read that its best to wire motors in series rather than parallel. So I made a wiring harness to accomplish this, and tested again, measuring the current. This made a significant improvement, but I still saw a jump from 0 to 0.22A or so which was not as smooth as it should . I wish I knew how to eliminate it entirely.
My setup is this:
Marlin firmware on RAMPS, with bed autoleveling enabled
DRV8825 set to 1/32 microstepping, driving dual Z motors in parallel.
So during printing, as autoleveling is being used, the Z motors will move smoothly for partial step and then pop into a position, it is quite audible and annoying of a sound, and obviously not microstepping properly. During infills etc, this pop can be heard repeatably as the nozzle passes over specific areas of the bed, adjusting the the same Z step levels as it travels.
To troubleshoot this, I have a little test jig set up where i can measure the current inline going to one of the motor coils with a multimeter, and manually send a step signal one at a time by pressing a button. I set this up the same with my motors in parallel as they are on my printer, and recorded the current measurements. The stepper driver was set beforehand to roughly 1.2A max current.
Here is a link to a spreadsheet with measured values charted as current vs steps.
[docs.google.com]
I only measured part of the waveform before my multimeter decided to auto shutoff and I didn't feel like continuing, but you can see that it does a weird jump from around 0 to .66A, instead of properly microstepping the entire waveform, thus causing the hard pops I was hearing at certain points during autoleveling. Does anyone know the reason it does this?
I suspected it might have something to do with the decay mode, which I had read about, though I admit I don't fully understand the exact effect of changing these modes. I tried tying the DECAY pin to 5V and it didn't seem to have any effect on this behavior of "skipping" microsteps. Just to be clear it never actually loses track of steps, which is why i put "skipping" in quotes, but it is ignoring the microstepping for a portion of the waveform.
After more searching online for similar issues, I read that its best to wire motors in series rather than parallel. So I made a wiring harness to accomplish this, and tested again, measuring the current. This made a significant improvement, but I still saw a jump from 0 to 0.22A or so which was not as smooth as it should . I wish I knew how to eliminate it entirely.