New Duex2,3,4,5?


  • administrators

    Continuing on from discussion about the Duex5 I though I would open a discussion to gauge interest for the DuexN? expansion board.

    The expansion header on the Duet Wifi has pins for up to 5 further stepper drivers. The aim with the Duex5 expansion board was to add a further 5 TMC 2660s to give 10 total stepper drivers. This is probably overkill for most applications. As David has already mentioned on another thread we will probably look to populate a varied number of drivers (2,3,4,5?)

    So how many steppers can you use?

    Cheers

    Tony



  • One for X, one for Y, initially one for Z. Diamond hot end so 3 extruders = minimum 6 so Duet plus 1. Z axis has three lead screws and longer term (when David gets around to writing the firmware for auto bed levelling) I'll need 3 for Z instead of 1 making a total of 8 (Duet plus 3). Longer term still - who knows? If someone comes out with a 5 input mixing hot end, I'd probably buy one. Could the expansion boards be stackable?



  • There was some talk about a true full color FDM printer in the SMC forums (and probably elsewhere), and that would require 5-6 colors (CMY, black, white, and support on a second smaller extruder potentially). 9-10 should be fine for anyone adventurous enough to try that. I only have plans for 1 hotend or maybe the cyclops, so the duet itself would be fine for me.



  • Left field but why can't a Duex design be both a breakout board and a driver expansion board, my brain is spinning around the idea of properly designed plugin driver modules using inverted component placement on 2oz copper with a cheap ram chip type heatsink on the top side for cooling…. This places the driver and other bits between the plugin board and the mainboard and provides the essential cooling on the top side that is not part of the design for other plugin modules.

    This gives a base board with multi use functionality that people could add the required number of stepper drivers they need.



  • It depends on what I look at.

    • high end monocular would need x,y,z and possible z2, with a motor for an extruder and three small motors for bed alignment (max). For a maximum of anything between 4 to 8

    • for a proper dual we would need an additional extruder and one additional motor to lift the head or pins to use magnets for it. So anything between 5 and 9

    • a the true color head we are building we will need x/y/z plus 5 extruders at least. So 8.


  • administrators

    Nice idea, but who would make the new-design plug-in modules? By itself, I don't think a Duet expansion board would be a big enough market to make it worth anyone's while to manufacture them. Also, advanced driver chips like the TMC2660s don't just need step/dir/en signals, they need SPI as well - so less suited for plug-in driver modules.

    I think we are looking at three boards:

    1. DueX5 as we originally planned, with 5 x TMC2660 drivers and some (probably 5) additional heater/thermistor channels. Perhaps also a facility for adding the same thermocouple and PT100 daughter boards that we use on the Duet WiFi, to allow a total of more than 4 thermocouples or PT100 sensors. Anything else?

    2. DueX2 (or X3), same board as the DueX5 but with only 2 or 3 channels populated, because although some people need more than 5 stepper drivers, very few need 10.

    3. Breakout board, providing 5V step/dir/enable outputs for external drivers, maybe Pololu-style sockets, maybe also a digipot chip to support software-controllable motor current on modified Pololu-style drivers. What else should this board support?



  • Honestly I would not make an expansion board specifically for something, but more like a breakout board with sockets.
    Either sockets for drivers or try to go the Mikroe route with a SPI like socket



  • Any idea about time scale for offering some sort of DueX? I'll be needing 6 stepper motors from day 1 and probably 8 (or more) later on so I'm holding off pre-ordering a Duet WiFi at this time.

    For what it's worth, I believe that what's holding back developments of multi material/multi colour printing is a lack of electronics that can support the additional extruders that are required, so having this capability could be a USP for you guys. (That's marketing speak for Unique Selling Point).


  • administrators

    hey deckingman

    We have had it with the Duet 0.8.5 and Duex4 for some time, including firmware support for setting up tools for mixing extruders.

    That said I am working on the test equipment for the Duet boards now and then will switch to the Duex5. I can't give a certain date yet as the priority is getting the DuetWifi production run off on time.

    Cheers

    Tony



  • @T3P3Tony:

    hey deckingman

    We have had it with the Duet 0.8.5 and Duex4 for some time, including firmware support for setting up tools for mixing extruders.

    That said I am working on the test equipment for the Duet boards now and then will switch to the Duex5. I can't give a certain date yet as the priority is getting the DuetWifi production run off on time.

    Cheers

    Tony

    Hi Tony. Sorry, I didn't make it clear that I'm currently using RRPs version of Duet (06?) and their expansion board to run a Diamond Hot end with 3 extruders using DC42s latest firmware (non WiFi version) and DWC on my ageing, creaking RRP Mendel. So, I'm well aware of the capabilities. Duex5 will be for the new printer I've started building - guess I'll just have to learn to be patient.

    Ian



  • I see four main reasons why someone would want significantly more than 5 stepper channels:

    1. Simple motor cloning. Serial and parallel motor wiring both have downsides. Separate drivers are ideal. This is particularly useful in large printers where large motors may need to run at high speeds, and where gantry spans may be long enough that belts or drive shafts are impractical for synchronizing opposite sides of a mechanism. The most extreme sensible usage case is 7 motion motors, for a 4-2-1 serial Cartesian 3D gantry arrangement. (These are fairly common in >1m working volume printers.) It's probably reasonable to imagine such a printer having two extruders, for 9 total.
    2. Triple-screw bed leveling, which is a serious killer app once it has mature firmware support and more people start to see the benefits. Minimum is 6 steppers for single extruder printers, 7 for dual.
    3. Mixing hot ends, which are currently limited to 3 channels due to: A) lack of commercial mixing extruders with more than 3 inlets, and B) lack of mature software support both in the slicing toolchain and firmware. (This bit is improving pretty fast but isn't 100% yet.) Solutions like the DueX and various MachineKit controllers already exist on the electronics support side. I would plan for 6 extruders, but anything more than CMYKW+support (such as multi-material) is so specialized it should get custom hardware. That's another 9-motor application.
    4. Machine kinematics with more than 3 motion axes, such as hexapods or serial arms. I don't personally see this as a large enough market segment to bother with, but 7 motion axes would cover almost all possible use cases. Plus one extruder makes 8.

    You can imagine combining these if you want to get silly. And you can add all sort of junk if you throw in CNC usage cases like tool changers and spindle indexers. (Thus why Smoothie v2 is planned to support infinite daisychained stepper modules.) But I really struggle to imagine a 3D printing scenario where you need more than 9 motion channels and would not build custom electronics.

    I see it as unlikely for anyone to need more than 4 temp control channels. Mixing hot ends only need one each. There are some three hot end options on the market (eg Polystroooder, whichever Cube). The Kraken plus a bed or chamber heater is the only usage case I know of for 5, and the Kraken is sufficiently awkward and niche that I wouldn't lose sleep over not supporting it. Dual-thermistor redundant sensing could justifiably use more than 4 channels, but I'd be surprised to see much community uptake of that.

    I would suggest servo channels as being more useful than a 10th stepper or additional temperature controllers. Lots of people use hobby servos for light-duty work.

    Another interesting option would be a spindle speed control channel that can accept a tach feedback. This has uses outside milling, for example to run mixer impellers (in the CMYKW hot end) or water-cooling pumps or pressure boost stages in paste type extruders.

    Cooling fan tach inputs is a useful safety feature, and I'm surprised no controllers offer it yet.

    Three quadrature encoder inputs could be a good feature for people who want to experiment with closed-loop control.

    RGB LED controllers are kind of nice – having the interior lighting change color with printer status is slick, although not super high value.


  • administrators

    Ryan, we already have tacho support on RepRapFirmware for the Duet 0.6, including display of the fan RPM in Duet Web Control. The snag is that you need to use 4-wire fans for the tacho output to work. and those fans typically can't run below 30% of full speed. So if you want to control the speed AND be able to turn them right off, you need to switch the supply voltage as well as giving them a PWM signal. Also, 4-wire fans are generally only available in 12V.

    It's possible that the tacho output of a 3-wire fan might work if we PWM'd the positive supply instead of the ground connection - I haven't tried that.

    The tacho support could easily be included in the Duet WiFi, we just need to assign an expansion connector pin to the tacho input.



  • I'm thinking of fan tachs as a "shut off heaters if they're not spinning" safety function. Consider your average PLA effector with an E3D or what have you… If the hot end fan stops, really bad things can happen. I wouldn't do any kind of speed control on it (the standard PWM fan function is fine for that).

    Honestly, could just be a pin that acts like a charge pump safety cutoff. Doesn't have to be fan-specific.

    Optional stuff either way.



  • This is a shameless bump but any update on timescale for Duex2,3,4,5? My printer build is coming along nicely, Duet WiFi is ordered as are the 3 off E3D Titan extruders but I won't be able to commission the beast properly until I can add at least one extra stepper. Then later on, when DC does the firmware to support auto bed levelling, I'll need another 2 steppers. Sorry to nag.



  • I'm planning a motor for z, a motor for y, two x motors for dual carriages, and two extruders. It might be nice to clone Y to run two motors instead of a shaft.

    7 total for me, Duex2 would work.



  • Another shameless bump but I haven't had a response to my last shameless bump of 24th July. So any news regarding Duex (n)? I'm going to need to be able to drive 3 extruders pretty soon now.


  • administrators

    I am actually working on the schematic right now. So far I have the following requirements:

    5 TMC2660 drivers (all my not be populated on Duex2/3)
    5 heater and thermistor channels (1 high power to use for a chamber heater/dual area heat bed)
    Headers to by pass the TMSc and connect external drivers
    5 Endstops (to use for filament out etc on each extruder or other purposes).

    The following are nice to have
    5 PWM fan channels
    "n" servo channels (1-5? how many?)

    What else?

    Cheers

    Tony



  • Is some of this easily obtained by hanging a custom board or two off an I2C/SPI pin? Presumably there would be problems using this for realtime applications, but most of these "extra" motors and sensors are much less critical. For that matter I have a Raspberry Pi "hat" that drives a zillion servos over I2C, and I could hook it up to the Duet if it had an accessible pin.


  • administrators

    Yes you can add as many expanders as there are i2c addresses if you want.

    What the expansion board will do for the stepper drivers is use existing E2-E6 channels which will be as quick as the on board TMCs.

    The fans and servos will be on I2C so not as "real time" although fine for fans, tool changers etc.



  • @T3P3Tony:

    I am actually working on the schematic right now. So far I have the following requirements:

    5 TMC2660 drivers (all my not be populated on Duex2/3)
    5 heater and thermistor channels (1 high power to use for a chamber heater/dual area heat bed)
    Headers to by pass the TMSc and connect external drivers
    5 Endstops (to use for filament out etc on each extruder or other purposes).

    The following are nice to have
    5 PWM fan channels
    "n" servo channels (1-5? how many?)

    What else?

    Cheers

    Tony

    Hi Tony,

    So it's looking like any sort of expansion board is still a long way off. As soon as my batch4 Duet WiFi arrives, I'll be at the final wiring and then commissioning stage for my new build. However, I can't run the Diamond hot end with only 2 extruders as filament will simply be forced up the unused input and then cause a blockage. So I fairly desperately need to be able to run three extruders (one more than the basic wifi will allow).

    What are my options? Do you or any one else fancy knocking me up something that I can plug in to get me up and running with 3 extruders until the proper expansion board is available? It doesn't have to be a proper pcb, just something to get me going. Happy to pay providing the cost is not extortionate. Feel free to pm or email me.

    Ian


 

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