3 independent Z axis motors



  • I am interested in using 3 independent Z axis motors. When I look at the diagram ( https://duet3d.com/wiki/Duet_WiFi_wiring_diagrams ) it appears they make 1 or 2 stepper ZA/ZA+ZB configurations possible in series. Ideally I'd like to have each stepper on its own driver so it can be adjusted.

    Is there an expansion board for the Duet Wifi that could give me access to this? I saw one for the previous Duet but the text on the same page said it would not be compatible with the Duet Wifi. What I'm shooting for of course is a way to level a large bed using the steppers.


  • administrators

    The schematic of the DueX5 expansion board is about to be finalized. Bed levelling using 3 independent Z motors is already on the wish list.



  • @dc42 if there's anything I can do for you to get in on this DueX5 fun just let me know. I saw your thread seeking input on desired features and it's a dreamy idea. For now I was just hoping to at least get them wired up (which the DueX5 would likely take care of nicely).

    So again if there's anything at all I could do to expedite this or help out otherwise, I'm all ears!


  • administrators

    There are several people interested in DueX5 boards, so it may be worth us offering pre production boards at a reduced price to would-be testers, as we did with the Duet WiFi itself.



  • Sign me up. I'll pre-order one right this second.



  • @dc42:

    There are several people interested in DueX5 boards, so it may be worth us offering pre production boards at a reduced price to would-be testers, as we did with the Duet WiFi itself.

    Me me me…........ I have 3 extruders and it won't take much to add 2 more Z axis steppers too.



  • And Me it would spur me on to get My long stalled CoreXY Going (was always going to use 3 leadscrews for the Z axis anyway) and would also allow me to press my Kraken Hot End into Service.

    Doug



  • @dc42 in the interim till you guys nail down the specifics for DueX5, any suggestions on how best to handle more than 1 stepper on the same axis? Even if it's just 1:1 steps for now.

    As for DueX5 if there's anything I can do. Pizza. Beer. Red Bull. Just say the word.



  • Matt,

    For info and I don't know if it helps in your situation, but I built my triple screw corexy with a single motor and continuous belt with a view to upgrading it to 3 motors as and when David gets around to implementing auto bed levelling (he has a very long job list). The bed is 400x 400 and weighs around 7kg (big thick lump of aluminium) and I was concerned that a single motor might struggle but now that I've started commissioning, my fears have been allayed as it will move the bed at 240mm/min with no probs at all. It'll probably go faster but that's good enough for me.

    So I guess what I'm saying is that 3 motors aren't necessary, even for a big heavy bed, unless you want auto levelling. A caveat to that - I'm using 1mm pitch screws - coarser pitch might require gearing. Also, I have quite a high torque Nema 17 stepper.

    Ian



  • Hi Ian,

    The triple Z axis was in preparation for the bed leveling down the road. The wise guy inside me was thinking "build it once". Until the feature was fully implemented each motor could be jogged manually. But I think I see a flaw in this game plan as power loss could possibly lead to a very uneven plane… not exactly what I want.

    I suspect I will have the lead screws tied together with timing belts for the time being. If nothing else once it's leveled manually hopefully it will retain its accuracy for awhile. I have some belts on the way for this scenario but that overseas shipping is killer.

    Did you gear up anything fancy to make timing adjustments on each lead screw or are you just loosening the set screws?

    Cheers


  • administrators

    Matt, if you just want to have more than one stepper motor on one axis you can connect two motors in serial or parallel from one driver. This is how the dual header for the Z axis works (serial).

    If you need more than one driver on the same axis stepping 1:1 then you can use one of the 5 additional channels on the expansion header to control external drivers in tandem.

    What are you looking to achieve?



  • Hi Matt,

    Off topic I know but no I didn't do anything fancy it the way of adjusting each screw - just slacken the pulley retaining screws. I'm hoping that either, I won't have to adjust it often or if I get 3 motors fitted, it becomes a moot point. Having said that, I did design it such that the lead screws can be individually adjusted without imparting any flexing or twisting forces to the bed (not that it should if it's built right). The lead screws are fully floating, just sitting on thrust bearings and retained by conventional ball bearings at the bottom. Guidance is provided by separate linear rails. There is an "O" ring between the nut and the bed attachment which is just slightly under compression but can be compressed more and the attachment to the linear guides is via a ball joint. So, it allows the bed to be "tilted" slightly in any direction but without any twisting, flexing or binding. There are details and links to pics on the build I've posted elsewhere on these forums.

    From what I've read, there can be issues with 2 or more motors driving an axis. It's to do with them jumping to the nearest whole step when initially powered up. DC42 will explain that better than I can, so I think for now a single motor/continuous belt might be the better option. Just my twopence worth….

    Ian


  • administrators

    As well as plans to allow 3 separate Z motors driven independently for bed levelling, I intend to solve the problem of multiple Z motors getting out of sync. The idea is that when the fimware detects that the power is going down, it will move the motors to a position that matches the way the motor phases are energized at power up.



  • @dc42:

    As well as plans to allow 3 separate Z motors driven independently for bed leveling, I intend to solve the problem of multiple Z motors getting out of sync. The idea is that when the fimware detects that the power is going down, it will move the motors to a position that matches the way the motor phases are energized at power up.

    That sounds great! Thank you. I have plans to link two sides of my Y axis with a belt, using one stepper, but if the need arises, being able to run 2 motors in sync would be great.


 

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