5v Stepper (28BYJ48) on a duet (12v)

  • I'm currently in the process of designing an ultra tiny (15x15cm cube, 6x6x4.5cm build area) FDM printer for ultra portability and maybe even using in a van/car. Really more as a design experiment but also to use a partly fried Duet wifi I have sat in a draw.

    Part of being so tiny it's gonna have to have tiny steppers, which I know will limit speed but this shouldn't be an issue with such a small build volume. I've sourced suitable steppers for the X,Y and Z but would need a worm gear arrangement for the extruder to get close to enough torque.

    I've found these (28BYJ48) tiny geared steppers that should provide just enough torque if run in bipolar mode skipping the +5v wire - I just wanted to sanity check that these will be fine to run on a 12v (or potentially 13.5v when in a car/van) system - pretty sure they will as the duet limits the current?

    Will doubtlessly be more questions as this is my first scratch built printer as lots of the parts will definitely not be standard!

  • administrators

    You can't drive that motor in bipolar mode unless you are able to disconnect the centre taps of the two windings from each other (they are both connected to the red wire).

    From the table at the bottom of https://www.emartee.com/product/41757/28BYJ 48 Stepper Motor 12V it looks like the 5V version has 60 ohms phase resistance. Which means it has a rated current of only 83mA. The Duet WiFi/Ethernet can do 100mA minimum, and Duet Maestro can offer 50mA or 100mA.

  • @dc42 said in 5v Stepper (28BYJ48) on a duet (12v):

    bipolar mode unless you are able to disconnect the centre taps of the two windings

    Here is a video explaining this process 🙂

  • Yeah, I've found some 12v native versions now too and they are likely to be to low torque, I have already modded a 5 wire one in the past to remove the link so that wasn't a concern.

    Good point on the minimum current, hadn't thought about that being a limitation, will have to rethink. On the WiFi is the current in 100ma steps or is it a continuously variable amount between 100 and 2400ma?

    Found some nice little steppers, should be about 300ma. My only concern is if current is only in 100na steps I'm gonna struggle to tune it accurately as I'm gonna have to push then pretty hard.

    Got the heated bed and all the X,Y and Z motion sorted, just need to think about a compact but usefully powerful extruder. The 300ma stepper is gonna need to gear them down by about 20:1 which takes up space. I'm determined to keep this under 15cm cubed and don't want to drop the build area any smaller than 6x6cm. My current CAD dimensions are coming out at 6.9cmx6.1cmx4.9cm, but I feel I may have been optimistic with the extruder size.

  • administrators

    On the WiFi the current is variable in 100mA steps.

    Another possible small geared stepper motor would be this one https://store.printm3d.com/collections/parts/products/quadfusion-extruder-motor. It's used to drive the extruders in the Duet Maestro-powered Crane Quad. They run it at 450mA.

  • Mmm, 100ma steps will definitely mean I have to be careful with temperatures when designing. No boxing the stepper in!

    Good shout on that stepper, I've got a spreadsheet going of the specs and sizes of All the options so far and that's looking pretty good although a tad larger than some of the other options I'd looked at.

    Probably need to start another topic but do you see stall detection homing working on a low current stepper for the X and Y axis? I know end stop switches are pretty small but thing I can omit is a bonus - this isn't gonna be a printer that's gonna need overly accurate homing or repeatability!

  • @dc42 do you have the model number for that motor? there is virtually no details on the M3D website

  • Yeah, if anyone has the model number or an alternative source that has a few more specs for that motor it'd be much appreciated! This has made it into the final 3 in my stepper comparison (and looking most likely for the extruder) but I can't find and real info.

  • administrators

    E3D uses the same or a very similar stepper motor in their tool change locking mechanism, so I expect they will offer it when they have caught up with tool changer pre-orders. You could ask on the E3D forum.

  • I ended up going for this one for my tool changer

  • @dc42 Thanks for the info, I'll give them a shout, they're super local to me (often drive past the door) so may even be able to grab a few to avoid postage 😂

    @jay_s_uk Yeah, I'd come across those, and will be using something very similar for the X/Y/Z motors, I found a Chinese source for something supposedly similar that should be adequate (although lower step/deg), if not these should almost be a direct swap. (and designing the frame to take these anyway)

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