Duet3 + expansion = 9steppers. Can I get one more with these?



  • I'm making a coreXY printer with 5 print heads. That's 10 steppers total. I originally planned to buy the Duet2+Duex5 for 10 drivers, but now there's a bigger and better Duet3 board out there. 3 is greater than 2, so certainly it's superior in every way!

    It ain't necessarily so. While the Duet3-6HC and 3HC expansion are great, I find myself with one less driver than the previous generation. No worries, I thought, at least there's those extra expansion pins. Turns out they don't have those on the Duet3.

    So now I'm scrambling to figure out how I can drive this motor without buying another $150 expansion board. Can I somehow connect an external stepper driver to a GPIO pin? Could I maybe drive it through the SBC? Should I just return this and get a Duet2?





  • Eh, I should have said without buying any more expansion boards. I have spare IOs not spare dollars.



  • Don't think so. See this https://forum.duet3d.com/post/184536 maybe you could sell the 3HC and get the 5LC when its ready?



  • @Tiz-io
    the toolboard is £39.50



  • @bearer Tempting. Already waited months for tool changer parts though and now I just need to get this working. If I'm selling things, might as well sell the main board too and go to the Duet 2. I'd end up getting almost $80 back. That's a heck of a lot better than throwing another $60 at control boards and having to redesign the enclosure.

    The more I look at it, the more I realize the Duet2 is a much greater value.



  • @Tiz-io
    until you are able to afford it, you could wire 2 motors in parallel or in series



  • The current Duet 3 range is aimed at slightly more heavy duty machines than the Duet 2.

    The coming Duet 3 mini/5LC that is meant to replace the Duet 2 Maestro will be the value offering of the new range afaik.

    If series or paralleling a motor isn't an option, maybe you could replace part of the toolchange with a servo instead of a stepper?

    And drop the attitude, if the specs and value comes as a surprise after the fact then look to a mirror if you want to blame someone.



  • @bearer You're reading attitude where none is intended. I obviously (or so I thought) blame myself for missing the lack of ports. As I said, the 3 has some great stuff. But for me, the 2 would have been a better value.



  • After doing a deeper side-by-side exploration of the hardware, I'm finding even more to like about the Duet3. For anyone else comparing the two boards, the newer generation opens more doors by offering several more GPIOs and removing the link between the PWM and heaters. That's a big deal if you're trying to max out the functionality on this hardware.

    With all that IO, I was already building custom filament monitors and a safety interlock for the heated parts. I'll just add another pair of DPST relays to the extruder drive for heads 4/5.



  • @Tiz-io Just bear in mind that Duet3 has a number of firmware limitations with regard to expansion boards that do not exist with Duet 2. So before deciding on Duet3, check that list because, although the hardware exists, the firmware limitations might mean that you can't do what you had in mind. E.g., certain combinations of end stops and motors don't work, one cannot run PID tuning of heaters connected to expansion boards, the step pulse frequency is much lower (although that might be fixed in the latest beta firmware), etc.....



  • @deckingman Thanks for the insights! You're referring to some quirks I hadn't seen in the hardware overview and wiring diagram pages, but I was able to find more info here on the forums. I certainly appreciate that the docs mention several of the limitations in place today may well go away with future firmware revs.

    This exercise has been a good case study in reading the fine print and balancing conflicting features. I was able to create a spreadsheet "simulation" of a few different board combinations based on the port specs and known limitations. Fortunately I still have a path to success without giving up anything I really wanted. After putting it all together, one gets a really interesting view of the balancing act the hardware devs at Duet3D take on when creating new products.

    Reminds me of my college days when I had to choose between HW and SW eng. I ended up choosing software, in part because you can almost always just release a bug fix to handle your dumb mistakes (and also because the EE classes started at 6 in the bloody morning!)



  • @Tiz-io I'm away from home with no WiFi and limited phone access right now, otherwise I would post a link to the documented list of limitations. Searching the documention for gen 3 hardwate should bring up the relevant text. Be aware that the planned dates for fixing these issues keep getting pushed back and some have no planned date for being fixed. Personally, for those reasons and if I was building a printer which didn't need 13 motors, I would choose Duet2 over Duet3 every time.



  • Here is the link to the documented limitations https://duet3d.dozuki.com/Wiki/Duet_3_firmware_configuration_limitations


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