Using more than one stepper motor for X or Y axis? Parallel possible?

  • Hi fellow Duet Wifi owners!

    I'm constructing a new CNC machine which will be able to switch between basic routing, laser cutting (7W diode) and 3D printing. It's 1200x900mm and uses two motors for the Y axis, one motor for the X axis and two for the Z axis. Will there be an issue with the Y axis output going via a Y splitter to two NEMA 17 motors in parallel? Would I be better off using two external stepper drivers taking input from the step and dir pins for the Y axis? On an old RAMPS board this was not an issue however there is something different going on with my new Duet Wifi board looking at the need to have jumpers on the second Z motor header when not in use.

    With the 3D printer head attached there will be a 300x300mm heat bed platform that will lower itself down into the enclosure below the frame to give a 500mm build height.

    Also, the laser driver module I have uses a safety interlock which normally goes to a relay (NC). Is there already a macro in place to toggle an output pin on the expansion header to control that relay? M3/M6/M11? Or could I just use one of the spare PWM fan output's and just set it to S0 or S100 to create a low/high to toggle the relay? The relay I have uses TTL input and energises the relay coil when the input pin is at GND.

    Really looking forward to the release of an expansion board for the Duet Wifi so I can start tinkering with the Diamond hot end.

  • administrators

    It's normally better to connect multiple axis motors in series rather than in parallel, unless they are low current high inductance motors. That's how the two Z motor connectors are wired. The maximum speed you can use before the torque starts dropping off is reduced using a series connection, but I suspect you won't reach that speed on the Y axis of a Cartesian printer. You can maintain the torque to higher speeds by using 24V power instead of 12V.

    You can use M42 to toggle I/o pins. The voltage level is 3.3V which will probably be OK for your relay board - or use a spare fan output as you suggested.

  • Thanks for the info! Was hoping not to have a mixed bag of power supplies as I need 12V for most of the setup and adding a 24V supply just adds a reasonable bulk to the electronics I need. Curious to know how far off an updated expansion board for the Duet Wifi is? Also wondering if it is possible to remap the axis outputs in config.g to swap the Z outputs with Y rather than post-processing the gcode files to swap the axis values? Even the ability to use the second extruder output as a mirror of the Y axis output would be exactly what I need as far as amps and speed are concerned.

    The M42 command to toggle the I/O pins is perfect for what I need. Since the 8 relay board I have uses a low pin state to enable a relay it should not have any bearing on it that the high is only at 3.3V. I'll source the 5V from the PSU I'll be using to drive the relay coils. Sure to be a number of things that just need basic turning off and on on top of the laser driver interlock (water cooling, exhaust fans etc.)? Hopefully I will be able to work out how to use the same PWM to control the speed of a 700W spindle via a VFD? I think I need to create a board to convert the PWM to an analog 0-10V output? One of the relays can be used to flip between FWD and REV (although I have never run my existing 6040 CNC spindle on REV).

    I did play with the laser on my existing router with Mach3 / G540 controller however PWM just could not switch fast enough with the gcode S spindle speed changes (always a delay). And I did try an arduino to convert step/dir pulses to PWM however the time it took to output 256 pulses (with high velocity/acc set on the A axis) to set the PWM from zero to 100% also created delays so engraving images never worked out nicely unless the feed rate was set very low. Hoping that high feed rates and fast PWM changes will be possible with this new board?

  • ah, I think I found it in the reprapwiki. Hoping M569 P4 Y0 (extruder 2) and M569 P1 Y0 (regular Y output) drives both outputs at the same time with Y changes?

  • ah, M569 has moved to M584 and can now map more than one drive to an axis. Pays to read the wiki properly. My bad.

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