Well, this is new. Running the new controller through some tests prior to hooking it up to the scope, and the stepper motor sometimes responds appropriately to commands from the controller and other times is stutters (essentially fails to rotate) and whistles.
I've adjusted the pot repeatedly to make sure that isn't it. The same behavior presents regardless of how far clockwise the pot is turned.
Does seem the be the drv8825's fault. I swapped it out with a different one and still had the same issue. I moved the controller over to another motor I have, and saw the same behavior there. So, that definitely narrows down where the issue lies. I've done basic continuity tests all around and those all pass (which I guess makes sense since it works some of the time).
I'm going to do some more debugging this weekend to see what I can learn.
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I would also check what voltage you have on VMOT pin of the drv8825. Perhaps the voltage is a bit low?
You do have a large capacitor fitted between vmot and gnd? - not sure if you are using a PCB
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First off, yes, for this iteration I have gone with one of your PCBs, specifically the DRV8825-HW203-M-MT-F-BT.
Now, regarding the voltage, when measuring the VMOT from underneath the board I'm getting about 11.4 volts. Interestingly, I first tried measuring it from the top of the DRV8825 where the VMO header pin sticks out and only got 5 volts there. Not sure if that's meaningful.
Either way, 11.4 is a bit low, correct?
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OK, I think we're onto something. I tested one of my solderless controllers, and it shows right at 12v (just shy 11.9). That is from both the top and bottom of the board/driver.
I'll gonna give a hard look at all the soldered spots in line from the power-in through to the drv board and see if that turns up anything interesting.
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On the PCB it should measure around 11v because of the DIODE in place (which has a voltage drop across it of about 1v)
Interestingly, I first tried measuring it from the top of the DRV8825 where the VMO header pin sticks out and only got 5 volts there.
It should be 11V at both top and underside of PCB for VMOT.
Different readings top/bottom indicates an issue.
It needs to be 11V to reliably move the motor.
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OK, re-tested from the top of the board, and it does look like it is 11+ volts there. Not sure how I messed that up yesterday. I just pulled of the stepper motor connection from another rig and used that to connect to J13 on the board in question. That didn't work either. So, I think, with all the various scenarios I've tested, narrows the issue down to the connection of the drv8825 to J13.
I'll closely examine (again) the soldering involved there. Seems like that's gotta be it.
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Well, this is new. Running the new controller through some tests prior to hooking it up to the scope, and the stepper motor sometimes responds appropriately to commands from the controller and other times is stutters (essentially fails to rotate) and whistles.
I've adjusted the pot repeatedly to make sure that isn't it. The same behavior presents regardless of how far clockwise the pot is turned.
Any ideas of where to look?
Video showing the issue: https://photos.app.goo.gl/AeHnRLwRe9jbsrjL9
https://www.dropbox.com/s/ks3cwabbg2cxcou/Stepper%20Motor%20Issues-01.mp4?dl=1
shows how to troubleshoot motor issues.
It might be a faulty drv8825. Please try the procedures in the attached video.
Thanks Robert, I'll give that a try tonight. I do have extra drv8825's. So,
I may just try swapping that first if that's a likely cause.
On Thu, Mar 25, 2021 at 7:29 AM brownrb brownrb@users.sourceforge.net
wrote:
I have noticed that even I get some dud drv8825's where the pot is basically broken and its full on and you cannot adjust the current
Does seem the be the drv8825's fault. I swapped it out with a different one and still had the same issue. I moved the controller over to another motor I have, and saw the same behavior there. So, that definitely narrows down where the issue lies. I've done basic continuity tests all around and those all pass (which I guess makes sense since it works some of the time).
I'm going to do some more debugging this weekend to see what I can learn.
I would also check what voltage you have on VMOT pin of the drv8825. Perhaps the voltage is a bit low?
You do have a large capacitor fitted between vmot and gnd? - not sure if you are using a PCB
Ah, good call, Robert.
First off, yes, for this iteration I have gone with one of your PCBs, specifically the DRV8825-HW203-M-MT-F-BT.
Now, regarding the voltage, when measuring the VMOT from underneath the board I'm getting about 11.4 volts. Interestingly, I first tried measuring it from the top of the DRV8825 where the VMO header pin sticks out and only got 5 volts there. Not sure if that's meaningful.
Either way, 11.4 is a bit low, correct?
OK, I think we're onto something. I tested one of my solderless controllers, and it shows right at 12v (just shy 11.9). That is from both the top and bottom of the board/driver.
I'll gonna give a hard look at all the soldered spots in line from the power-in through to the drv board and see if that turns up anything interesting.
On the solderless board it will measure 12v
On the PCB it should measure around 11v because of the DIODE in place (which has a voltage drop across it of about 1v)
It should be 11V at both top and underside of PCB for VMOT.
Different readings top/bottom indicates an issue.
It needs to be 11V to reliably move the motor.
OK, re-tested from the top of the board, and it does look like it is 11+ volts there. Not sure how I messed that up yesterday. I just pulled of the stepper motor connection from another rig and used that to connect to J13 on the board in question. That didn't work either. So, I think, with all the various scenarios I've tested, narrows the issue down to the connection of the drv8825 to J13.
I'll closely examine (again) the soldering involved there. Seems like that's gotta be it.