SOLVED Duet2Wifi weird extruder jitter



  • I just got a Duet2WiFi to replace my kossel's MKSMini that got the extruder driver blown. Just finished the rewiring and initial setup and I'm experiencing a few issues for which I'll cut separate threads so if I get to resolve them, others can easily find the fixes for their issues in the future.

    2/22/2021, 11:17:12 PM	M115
    FIRMWARE_NAME: RepRapFirmware for Duet 2 WiFi/Ethernet 
    FIRMWARE_VERSION: 2.05.1 
    ELECTRONICS: Duet WiFi 1.02 or later FIRMWARE_DATE: 2020-02-09b1
    

    So Problem #2 is with the extruder: With the MKSMini I used to hook the printer via USB to my computer and used RepetierHost to drive the prints (with somewhat variable quality) but the whole point of getting a network enabled board like the duet was to make sure I can print stuff without locking the laptop to drive it. Long story short I hooked the printer to Cura via the Cura Duet plugin and started printing a calibration cube to verify my calibration and dimensions. Pretty soon the extruder (bowden) started experiencing some weird jitter, i.e. it acted as if it were pushing filament in the tube and by extension the hotend, but every mm or so it retracted. At first I decided I might've messed up the wiring (I didn't) or that the motor is bad - after all the issue with my previous controller was the extruder driver. May be one of the phases was bad? Even though I had it tested before with M302 P1 and through the DWC UI. It extrudes and retracts just fine, so it wasn't that. I cross-referenced with another motor (swapped it with X) and the motor seemed to be just fine.

    Now the question is could it be the slicer? With Repetier I used Slic3r so may be I messed up the cura config? It does act as if either the hotend was cold and the extruder wasn't able to push filament through, or as if there was jenky signal being sent to it. What should I check to troubleshoot this further?


  • Moderator

    @vlex sounds more like the extruder stalling and skipping back each full step, possibly due to over extrusion. Quick test is to disconnect filament feed, so there’s no pressure on extrusion, and see if it extrudes correctly. Alternatively, maybe the extruder motor current hasn’t been set high enough. How have you calibrated the extruder? Post config.g, extruder type and motor specs.

    Ian



  • Trying to extrude too fast, or too low a hotend temperature.

    I've experienced both several times.



  • It appears I had a blockage - I swapped the bowden a while ago and it came with new PTFE tubing fittings which apparently aren't as deep as the old ones, creating a void in the cool side of the hotend thus creating space to clog with molten filament that won't melt away the next time i turn on the heat element. It is weird that the fan won't turn on until the hotend reaches the specified temperature as this allows for heat creep up the hotend to the cool side. In any case this hotend was due a swap so I'll order one from e3d which probably would be better to begin with than this cheap chinesium I bought the printer with.

    Any idea how to keep PWM on the fan but have it on as soon as the heater goes on? I assume it'd be some g-code command I need to slip into the config.g?


  • Moderator

    @vlex said in Duet2Wifi weird extruder jitter:

    Any idea how to keep PWM on the fan but have it on as soon as the heater goes on? I assume it'd be some g-code command I need to slip into the config.g?

    Make it a thermostatically controlled fan: https://duet3d.dozuki.com/Wiki/Connecting_and_configuring_fans#Section_Thermostatically_controlled_fans

    Ian



  • The new volcano arrived a couple of days ago and I just finished assembling and reconfiguring the config.g to the new dimensions - the jitter turns out as suspected was due to a blockage in either the cold side or the heatbreak. Either way the new hotend now works just fine, except there's obviously some geometry quirks i need to take care (in a separate thread though).

    This matter could be considered resolved. Thanks for the help!


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