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  1. #11
    I can see the attraction of the AXBB-E for 4 axis systems with modest I/O, plus the inclusion of analogue outputs to control the VFD speed. It even has a jumper to allow either 5V or 10V range for the speed. I think for the majority of hobby users it would be a perfect little unit.

    But I need 5 stepper motor control, so the extra space for the additional board just to driver the 5th axis makes it similar to the UC300ETH+UCBB in terms of footprint. More thinking . . . .
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  2. #12
    Quote Originally Posted by routercnc View Post
    I can see the attraction of the AXBB-E for 4 axis systems with modest I/O, plus the inclusion of analogue outputs to control the VFD speed. It even has a jumper to allow either 5V or 10V range for the speed. I think for the majority of hobby users it would be a perfect little unit.

    But I need 5 stepper motor control, so the extra space for the additional board just to driver the 5th axis makes it similar to the UC300ETH+UCBB in terms of footprint. More thinking . . . .
    Well. I have mine stacked. I have uprights through the UCBB mount holes (3mm threaded rods + 4mm od brass tubes) going up to 2 ally straps. The UC300 is then fitted on top.
    I can still get to all the screw terminals of the UCBB. Looks a little bodged on mine but it saved a lot of space.

  3. #13
    OK yes I can see how that would work. For info, I have been emailing Balazs at CNCdrive today and he has been replying pretty quickly. Impressive given it is Sunday afternoon/evening, and a bank holiday (in the UK at least) ! Anyway I asked what would happen if 2 stepper drivers were connected to a single step/dir output E.g. if I went with the compact AXBB-E route which can drive 4 stepper drivers as standard, and connected both of my 2 Z step/dir to the same output to drive a total of 5 steppers. This saves the additional BoB, ribbon cable etc. In this scenario I would have:

    1: X axis
    2: Y axis
    3: Z axis & 2nd Z axis from same step/dir outputs
    4: A axis (slave for X axis)

    The answers from him were when using one output to drive 2 stepper drivers:

    Homing could not be controlled independently - well that is OK for me as they are either side of the Z axis which can't rack

    Issues for rack and pinion as often one side needs to rotate in the opposite direction - again that is OK as both turn the same way for me (plus I could swap 2 of the 4 motor cables)

    In theory one output on the AXBB-E could drive 2 step inputs on 2 stepper drives since the output can drive 20mA current max. and usually one stepper drive requires only 5-10mA of current for the step optocoupler, so 20mA should be OK. - this was my main concern but sounds like this will probably work


    So in summary I'm prepared to give the AXBB-E a go, double up on one step/dir output to drive 2 Z steppers, and if I do run into problems then I'll have to add the extra BoB for the 5th driver.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  4. #14
    Quote Originally Posted by routercnc View Post
    I have been emailing Balazs at CNCdrive today and he has been replying pretty quickly. Impressive given it is Sunday afternoon/evening, and a bank holiday (in the UK at least) !
    I regularly email and get replies from Balazs late on an evening, even at weekends, he's always very very helpful and certainly knows his stuff so if he's ok with it then I'd say certainly worth a try.
    -use common sense, if you lack it, there is no software to help that.

    Email: [email protected]

    Web site: www.jazzcnc.co.uk

  5. #15
    OK thanks. Although he has said this should work, I feel it is still on me as it is unusual.

    Thanks for your help too, and the others in this post. I've sent you an email for some prices, but no need to reply until back at work (Tues?).
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  6. #16
    Quote Originally Posted by routercnc View Post
    I've sent you an email for some prices, but no need to reply until back at work (Tues?).
    No problem and we don't do Bank holidays or 9 to 5 around here so will email you tomorrow...
    -use common sense, if you lack it, there is no software to help that.

    Email: [email protected]

    Web site: www.jazzcnc.co.uk

  7. #17
    OK great thank you
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  8. #18
    Quote Originally Posted by routercnc View Post
    OK yes I can see how that would work. For info, I have been emailing Balazs at CNCdrive today and he has been replying pretty quickly. Impressive given it is Sunday afternoon/evening, and a bank holiday (in the UK at least) ! Anyway I asked what would happen if 2 stepper drivers were connected to a single step/dir output E.g. if I went with the compact AXBB-E route which can drive 4 stepper drivers as standard, and connected both of my 2 Z step/dir to the same output to drive a total of 5 steppers. This saves the additional BoB, ribbon cable etc. In this scenario I would have:

    1: X axis
    2: Y axis
    3: Z axis & 2nd Z axis from same step/dir outputs
    4: A axis (slave for X axis)

    The answers from him were when using one output to drive 2 stepper drivers:
    Beings you're talking about a Z axis. My assumption is you won't need it ridiculously fast.
    It is my understanding that another option is you can run 2 steppers from a siingle driver as long as you follow ohms law.
    So example if you have 2 steppers rated at 4A, you can safely run both together using a 8A capable driver so you can up the running voltage Thus only needing to use one axis output from controller.

    A little research needed on this other option.

    These diagrams are in series. Apparently run better with higher voltages due to it being shared.
    They look slightly different so I assume one will spin both in same direction, one will spin them in opposite directions.
    Can also run parallel which shares current so then needs higher amp settings.


    Last edited by dazp1976; 30-08-2021 at 12:02 AM.

  9. #19
    Quote Originally Posted by dazp1976 View Post
    Beings you're talking about a Z axis. My assumption is you won't need it ridiculously fast.
    It is my understanding that another option is you can run 2 steppers from a siingle driver as long as you follow ohms law.
    So example if you have 2 steppers rated at 4A, you can safely run both together using a 8A capable driver so you can up the running voltage Thus only needing to use one axis output from controller.

    A little research needed on this other option.

    These diagrams are in series. Apparently run better with higher voltages due to it being shared.
    They look slightly different so I assume one will spin both in same direction, one will spin them in opposite directions.
    Can also run parallel which shares current so then needs higher amp settings.


    Looks good to me. The top diagram will run the motors in opposite directions, the bottom one will not.

    With the coils in series you only need a 4A rated driver for two 4A motors, it's the same four amps in both coils. Problem is they only get half the volts each so you won't get as much torque at speed (you can also interpret this as twice the inductance for the same voltage). An 8A driver would allow the motors to be connected in parallel but you cannot guarantee exact current sharing and so the risk of one motor stalling while the other still runs is possibly increased. My money would be on separate drivers being fed the same step and dir signals. If you're worried about having enough current then the signals could be buffered easily enough. A quid's worth of MOSFETs and a resistor or two should do the trick. This leaves you without auto-squaring, which you say you don't need anyway, but seems no different from using a slave axis but only one homing sensor.

    The other option is to use one big driver and one big motor driving both ballscrews with a belt.

    Kit
    An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.

  10. #20
    I don't know if this is just an academic quibble, but is there an issue with the concept of two steppers driving a single, very rigid, axis with no possibility of adjusting their relative position? I'm thinking that the typical micro-stepping driver (although possibly not the latest and greatest) will reset to the nearest full step at switch-on, and there is no reason to suppose that the "full-step" positions on both steppers will align. In the case of the typical both-ends-of-a-gantry setup, there is enough give to allow for this (and we are taking about quite small mis-alignments - a full step with a 5mm pitch screw is only 0.025mm) but auto-squaring takes this out anyway. But if this dual-drive Z axis is going to be much stiffer, is this an issue? Maybe this will be addressed at initial setup?

    I believe that some newer stepper drivers will maintain micro-step position across switch off/on, which might help.

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