I just finalized the building of my K8400 printer (single extruder) and I am stuck with an extruder driver problem.
In the beginning I noticed that prints were lacking material (ABS). I checked the filament motion as it enters into the driving mechanism and noticed that on some occasion, the motor would stop, the filament would go backward a few mm reving the motor backward, generating a little “click”.
This video illustrates perfectly this observation: https://youtu.be/IMnBBsq-41k?list=PL8J9JvPQM5fUPl2GBDbsKw6qDk-3_Esn1. After a second or so, the stepper motor resumes operating. And so on.
I ran a print and checked the LED next to the extruder 1 driver (namely LD10), driven by the ~step line (trough T9 and its biasing resistors). Surprise, the LED blinks as expected while the stepper motor has a little nap. So it isn’t a software or a CPU problem.
Then I checked the threshold setting for over current: 0.9 V, just fine.
Swapping two drivers (Z <-> extr 1) did not help. So it isn’t a DRV8825 driver module problem.
Then I disassembled the driving mechanism in order to keep the stepper alone. And the problem persisted !
As a precaution, I swapped the X axis and the extruder steppers and the X axis stepper produced the same problem.
It comes obvious to me that it is not an assembly nor a component problem. Probably an over heat problem. As most drivers of this type, the chip is really hot although it features switching power supply. How much hot ? My fingers hate this question. I checked the DRV8825 datasheet and noticed that the diver is configured to work in micro-stepping mode. And this mode draws a lot of power as micro-stepping is achieved by biasing the stepper coils in a permanent manner… This thread confirms my assertions goo.gl/2G98TW
I placed a fan right in front of the chip and things went better which confirmed my hypothesis. Adding a small heat sink at the back of the module (where it should actually sit, on the copper pad and not on the plastic cap !!!) helped a bit more. But with still “clicks” once in a while.
Have I a defective lot of drivers, of motors ? Or is it a design problem really ? Any help appreciated
This could be a slightly clogged nozzle.
You may want to change the retraction settings in Cura.
Retraction 4mm
Retraction Speed 110mm
Hot End Temp 190C for PLA
It usually happens when the extruder is feeding more filament than the nozzle can extrude. You need to reduce the flow until it stops. Usually 70% is a suitable value. You can set it up in the Cura settings or adjust it during the print on the LCD to find the best value.
Of course a partially clogged nozzle can also reduce the amount of extruded filament and giving the same issue.
Also print PLA at 190°.
It’s a good idea to glue heat sinks on the stepper drivers as they indeed get really hot (and even better a fan blowing on them). Anyway the drivers can get over 100° before cutting the power.
[quote=“raby”]It usually happens when the extruder is feeding more filament than the nozzle can extrude. You need to reduce the flow until it stops. Usually 70% is a suitable value. You can set it up in the Cura settings or adjust it during the print on the LCD to find the best value.
Of course a partially clogged nozzle can also reduce the amount of extruded filament and giving the same issue.
Also print PLA at 190°.
It’s a good idea to glue heat sinks on the stepper drivers as they indeed get really hot (and even better a fan blowing on them). Anyway the drivers can get over 100° before cutting the power.[/quote]
Nope, You missed this explanation
“Then I disassembled the driving mechanism in order to keep the stepper alone. And the problem persisted !”
As I could not stand a non working new printer, I ordered some spare drivers and a fit for purpose fan (40x40x10), smaller than the temporary fan that I used to cool extruder 1 driver.
And without the help of forced cooling, this driver works letting me enjoy my first print: a basic 20x20x20 ABS cube ! I will confirm that with next prints.
I tried to investigate the driver chip and discovered no flaws in its thermal pad soldering…
Defective electronic components tens to be a very unlikely hypothesis, except when the fail
I hope that the support team will send me a spare driver under warranty.
