Dual Z motor not staying together at rest
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Thanks for the info. If I do end up running them in parallel, do I need to change the motor assignments in the firmware as well as installing the jumpers?
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No firmware or configuration changes would be needed.
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Thanks for your help. This is one of the reasons I bought a DuetWifi. The RAMPS board on my Ultimaker II clone is on its way out and I'll probably replace it with another DuetWifi.
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Actually, you will need to make one configuration change if you wire the motors in parallel, which is to double the motor current. It's the Z parameter in the M906 command in config.g.
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Yup, you mentioned that above. Thanks for the reminder.
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Sorry, one more question. I'm thinking I need Z motors with more torque. Robotdigg sells the same setup with 60mm high torque motors. I believe they are 1.8a each. Would that still be OK for wiring them in parallel?
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how about these http://www.omc-stepperonline.com/3d-printer-nema-17-stepper-motor-59ncm84ozin-2a-17hs192004s-p-18.html
these are the same torque as the robotdigg ones and are a bit more compact but at a little more current
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I don't recommend parallel connection if the motors are rated over 1.4A, because you would have to run them well below their rated current, which reduces torque.
With the motors connected in series, how much do they move when yo power off?
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.5" on one side when wired individually. Only about .125" when wired together but that is both sides evenly.
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Update: I bought higher torque motors (Nema17 60mm 0.65N.m high torque) for the Z axis. They are now wired individually again (not connected together. They still stall individually going up if Max speed is set to over 1800 in config.g.
I have the motor current for Z set to 1000. Can it be set higher?
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Update: I bought higher torque motors (Nema17 60mm 0.65N.m high torque) for the Z axis. They are now wired individually again (not connected together. They still stall individually going up if Max speed is set to over 1800 in config.g.
I have the motor current for Z set to 1000. Can it be set higher?
Setting motor current to 85% of the motors maximum rating is usually thought to be a good rule of thumb.
30mm/sec is knocking on for the Z axis IMO. However, if you can't increase motor current, you might be able to get higher speed by reducing jerk and/or acceleration.
Reason for edit - typo
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Found out that the motors are 1.5a per phase
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DC, any thoughts on the Z motor stalling? My machine is big (almost 400mm tall build area) and I'd like the Z speed to be a little faster.
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Have you worked out whether your driver supply voltage is high enough to maintain torque up to your target speed? See https://duet3d.com/wiki/Choosing_stepper_motors#How_to_work_out_the_power_supply_voltage_you_need.
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I am not sure if i understand the problem, but for me it sounds more like a “mechanically” problem than an "electrical" one.
When 2 steppers move the same axis and you have also 2 e.g. linear rails, any even very small distance change between the rails or other geometry parameters can “block” a carriage or stepper very quickly.
Or if one steppers is quicker than the other it tries to twist the rails, which wont work. On big CNC mills with very stiff mechanics this is a common problem.What do you use as guides and are you able to increase the mechanical clearance or reduce stiffness ?
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@vp:
I am not sure if i understand the problem, but for me it sounds more like a “mechanically” problem than an "electrical" one.
When 2 steppers move the same axis and you have also 2 e.g. linear rails, any even very small distance change between the rails or other geometry parameters can “block” a carriage or stepper very quickly.
Or if one steppers is quicker than the other it tries to twist the rails, which wont work. On big CNC mills with very stiff mechanics this is a common problem.What do you use as guides and are you able to increase the mechanical clearance or reduce stiffness ?
This is my Z axis. it uses lead screws and vertical rods like an Ultimaker but I have them on both sides instead of just the rear. With no motors connected, they run free up and down with no binding. With the lead screws in place, the machine runs so free that one side can slide the build plate up and down easily. You can even get them (with no motors) 1/4" out of alignment and still move them up and down freely.
Also, at the slower speed I have set now, it transitions from top to bottom with the build plate staying flat with relation to the machine.
Edit: Just to be clear, the stall only happens on the up travel (going toward 0). Down is fine (gravity is wonderful).
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Have you worked out whether your driver supply voltage is high enough to maintain torque up to your target speed? See https://duet3d.com/wiki/Choosing_stepper_motors#How_to_work_out_the_power_supply_voltage_you_need.
I read through that but got lost with the fact that I'm running direct drive lead screws on the Z axis. Not using belts.
I'm currently at 85% of the spec 1.5a the motors are rated for. I've tried more and less with the same results.
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One more question. When you set a value for the Z motor current, does the board provide that figure to each of the Z motors or does it divide it between them?
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If the motors are connected in series (as the two Z motor connectors on the Duet are wired) or to separate drivers, they each get that current. If they are connected in parallel, the current is divided.
