Repeatable crash



  • I have made a crazy 9x9x6 METER printer.

    My z-axis is run by four servos with step/direction interface and 8000 steps/360 degrees This is then geared 315 times and after some pulleys gives around 66000 steps/mm. I run it at 20mm/sec and if I do small moves - 10mm - everything works well, but if I move it 100mm in one command, the duet ethernet looses connection to the web interface. I think it reboots, but I am not sure. This is consistent - crashes every time.

    I will change the electronic gearing of the steppers to overcome it, but I thought I'd let you know.

    BTW, the four servos are all running on the same step/direction signals, so the DUET considers it one driver.

    Kulitorum



  • Probably has a rough time calculating that many steps. Does everything come to a complete stop when it looses connection with DWC?



  • Errr why? I mean why 66000 steps per mm? But also why 9 metres? At 20mm/ sec it'll take 7 and half minutes to travel that distance. Even at 100mm/sec it'll take 1 and half minutes to travel from one and to the other. What on earth are you going to print with it? A house?


  • administrators

    I am really looking forward to seeing a video of this!

    The max step rate of the Gen 2 duets (WiFi/Ethernet) is around 100Khz per axis see this thread:
    https://www.duet3d.com/forum/thread.php?pid=7655#p7655
    With all the gearing you are doing you can afford to make the microstepping courser to reduce the rate you need to produce steps.

    The fact the Duet crashes rather that fails gracefully is something David will be interested in when he gets back from holiday. What is the reason for reset given by M122 ?



  • Number40fan:
    No, the servo drivers has the steps buffered, and catches up, even if the step signals fade out.

    Deskingman:
    I did not go for 66000 steps, but my servo has a resolution of 8000steps/rev, This is a2.4Nm servo and I need to lift 1Tonnes on each motor (with a 4x safety factor) so I need a good gear. This one is 1:315 and this gives me 745Nm on the last axle. With a 60mm cog, this is sufficient.

    Yes, I am printing a house.

    T3P3Tony:
    I cannot change the microstepping, the external servo drivers don't care 🙂

    Videos will be released tomorrow night.


  • administrators

    Hi Kuli apologies I put it the wrong way - rather than change the microstepping on the Duet I meant change the steps/mm on the Duet and adjust the servo controller to a less steps/360 degrees if that's possible. If its not possible then your max speed is limited to ~1.5mm/s per axis which is obviously rather slow.



  • That's my kind of crazy. Also looking forward to seeing the video.


  • administrators

    The maximum rate at which the Generation 2 Duets can generate steps and still have some processing power left for other things is about 360kHz when driving one motor or 180kHz to three motors simultaneously. If you exceed that then the web server will be starved of CPU cycles because all of the CPU is being used by the step interrupt service routine. I've seen this happen when using high microstepping. The browser disconnected during the long homing move at the end of the print, but I was able to reconnect again.

    You can check how close to the limit you are by looking at the MaxReps figure in the M122 report. Keep it below 50 if possible, and certainly below 100.

    I'll add it to my change list to detect this situation, slow down movement and issue a warning message.





  • Can I ask a couple of questions about this technology? I understand if it's proprietary so no worries if it is.

    How long does the layer time need to be for the previous layer to support it?

    If you want to print a doorway or window I presume you have to add a preformed lintel?


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