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I'm considering building a machine that would have 4 axes, two of which would require two steppers each to allow for the desired mechanical layout. These pairs would have to run synchronously. That's six steppers in total. Given that the hardware I have at hand (a ramps 1.4 board) has only 5 A4988 drivers, I need to decide if I

  • connect two steppers in parallel to one driver
  • connect two steppers in series to one driver
  • should look for a board with 6 drivers, which would be considerably more expensive and less widely available.

Two steppers in parallel

The current is split between the two, and exactly how it is split depends on the individual characteristics of each stepper and its load. If one stepper fails, the other will continue to work. The driver's set current will now be supplied to just one stepper and possibly kill it.

Two steppers in series

Both steppers get the same current. The driver would have to supply at a higher voltage to do this, but that should be within bounds with a reasonably low current setting (for example with two 6V steppers and a 12V supply). If one fails open, the will be no current in the other steppers equivalent coil. Both steppers would appear fail in the same way (and stay in sync).

I guess that for this application it's more appropriate to connect the stepper pairs in series, but I might be wrong and there are surely more details to consider. I guess I mainly ask because I never connected two steppers to one driver, and doing so in series "just doesn't feel right". Please help me fill the gaps. The approach seems to be backed by this answer on 3d printing SE: https://3dprinting.stackexchange.com/a/6885/9559

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    \$\begingroup\$ Neither in series nor in parallel is appropriate. Ever (well, I really can't think of a use case). \$\endgroup\$
    – Eugene Sh.
    Sep 24, 2018 at 19:01
  • \$\begingroup\$ The winding resistance of the stepper motor will vary slightly, so connecting in parallel will give unbalanced currents. You should connect the stepper motor winding in series to minimize torque differences between the tow motors. You will have to increase the driving voltage to ensure you can build the current with more indictive load of course. If your driver is 12V now, then you should consider increasing this to say 20V to increase the aiming voltage for the driver. \$\endgroup\$ Sep 24, 2018 at 19:09
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    \$\begingroup\$ Wait, what, why? What are you going to do if any of them misses a step, in any configuration? \$\endgroup\$
    – PlasmaHH
    Sep 24, 2018 at 19:30
  • \$\begingroup\$ @PlasmaHH I think missing a step is not too much of an issue, because the torque, speed and acceleration requirements will be low in normal conditions. The point remains, though, because there may be some mishaps. But they wouldn't cause too much harm in this application. \$\endgroup\$
    – Christoph
    Sep 24, 2018 at 19:33
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    \$\begingroup\$ That was just one thing that can go wrong. Imagine one missing every 17th step, the other never. \$\endgroup\$
    – PlasmaHH
    Sep 24, 2018 at 19:35

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