USB as a format.



  • Duet 3 is a great idea, but food for thought.... Why not use USB instead of a proprietary format? I realize that hardware costs are a concern, and maybe that's the reason. But it sure would make everything very plug and play, easily providing power to all the 5v devices. I don't mind wiring connectors, but I think the manufacturers can do a much better job. The remaining power hungry electronics would obviously have to have a different source. Also, USB-C with USB PD can only go up to 5 amps so that is a limiting factor as well.



  • what do you want to power with 5v? the duet cpu runs on 3.3V and the steppers and heaters need at least 12V
    and i am not sure what you mean by proprietary format.



  • Well, for one a usb-c would easily be able to handle stepper, and thermister connections and fan connections. That would make the cable chain much lighter to be sure. I'm not really thinking about the power as you already have a board that can manage a separate connection to a power supply. That's what 3 wires maximum?



  • You mean the CAN RJ11 Port? Thats a normal Industrial port.... Nothing duet Developer. USB C has major drawbacks



  • Forgive me as I don't know either format very well, but what are the drawbacks? If it's good enough to supply video to a VR headset, I would imagine that it wouldn't be difficult for it to handle basically anything needed by a 3d printer.



  • i think that would cause a lot of problem.
    usb-c cables are not make equally. you would get people using usb-c 2.0 cables and wondering why its not working etc.
    the usb-c cables rated for 60W are really stiff.
    btw usb-c has 24n pin connections.
    the duet3 toolboard required 2 wires for canbus and 2 wires for power.

    so you would have a wire that might work for the duet 3 toolboard 1lc
    but it would not work for the Duet 3 Expansion board 3HC.
    that seems like a bad design decision.



    • usb c has no lock or better there is a lockable USB C in the specifications but pretty rare in the Markers.

    Look what Industrial devices use for communication.;) Even normal USB is rare



  • @Veti That's fair, and thanks for entertaing my random thought:) It might also be worth considering what could be done with that much data throughput though. I have to imagine that there are some real wins to be gained there sometime in the future.



  • @ericrane said in USB as a format.:

    , I would imagine that it wouldn't be difficult for it to handle basically anything needed by a 3d printer.

    the difference here is current.
    the video signal transfers data.
    i.e. voltage on or voltage off switching very fast.

    the duet 3 only needs 2 wires for its data connection.
    with this it can achieve a cable length of 40m.
    try finding a 40m usb-c cable, ignoring the cost for such a thing.


  • administrators

    There is another consideration. If you use the same socket type to connect things that take different voltages (e.g. stepper motors, and 5V or 3.3V devices), it's guaranteed that some users will swap them by mistake and blow up the device, the Duet, or both.

    Additionally, if you use USB cables to connect stepper motors, you would need to buy a USB cable (if you can find one with a high enough current rating), cut off one end, and splice it to the stepper motor cable - because nobody sells stepper motors with USB plugs attached.

    We chose the connectors we used for a reason:

    • The Molex KK series connectors that we mostly use are widely available and easy to crimp (preferably with a suitable crimp tool) and the pins can easily be removed from the shells if rewiring is needed
    • The JST VH connectors that we now use for higher current connections are likewise easy to crimp and easy to disassemble. A PA21 crimping tool does both VH and KK connectors.
    • The RJ11 connectors that we use for CAN except where space is constrained were chosen because twisted pair RJ11 cables are very readily available in some countries, and not difficult to make up using readily available and inexpensive tools.

    The other connectors that we use only where we have to are:

    • Molex Microfit 3.0 (which are favoured by E3D) are not difficult to crimp, but it's hard to remove the pins from the shells without an expensive tool. We use them only where we need a higher rated current than Molex KK but don't have the space (i.e. on the Smart Effector), or where we specifically intend to support E3D sensors.

    • JST PH (used on some other boards and on stepper motors) are harder to crimp than Molex KK. We use them on the Tool Board for the stepper motor, to save space.

    • We use JST ZH where space is tight. These are hard to crimp because they are so small, however connectors with pre-crimped wires are readily available.

    • We've moved away from terminal blocks because OEMs hate them, and they are only good at carrying high currents if the proper ferrules are crimped on to the wires. The barrier strips that we now use for power in and bed heater out on Duet Maestro and Duet 3 are more forgiving.



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