Hey there,

I'm building a large-ish CoreXY and wanted to control the Z axis with three NEMA 17's. Two on the front corners and one on the rear. I guess they could be operated separately for bed leveling but let's not worry about that just yet.

Anyway, I was hoping to run them in parallel from a standard Mega2560 and RAMPS 1.4 board.

Is this possible at all?

Motor specs would be this in a NEMA 17 package:

Step Angle: 1.8
Motor Length: 48mm
Rated Current: 1.8A
Phase Resistance: 1.8Ohm
Phase inductance: 3.2mH
Holding Torque: 78oz.in - 55.1N.cm - 5.62kg.cm
Detent Torque: 2.6N.cm
Rotor Inertia: 68g.cm2
Flying Lead Count: 4
Flying lead length: ~300mm
Step angle accuracy: ±5%(full step,not load)
Resistance accuracy: ±10%
Inductance accuracy: ±20%
Temperature rise: 80c Max(rated current,2 phase on)
Ambient temperature: 20c~+50c
Insulation resistance: 100M Min,500VDC
Insulation Strength: 500VAC for one minute

They're usually run off a single A4988 but the design I'm working from actually has 2x motors run in parallel. Guessing the ~5.4A required for three motors might be too much though haha.

I don't mind if it's a case that I need to put pins into the RAMPS headers and hook them up to something more beefy, sitting in a separate module. Just as long as there's a way to drive three steppers off the one "signal".

Help please!

Get yourself some modern electronics instead of RAMPS, run it from 24V, and connect the three Z motors in series. Then you won't need a high current driver.

The reason people connect two Z stepper motors in parallel is that RAMPS makes it easy and most people don't know any better. For the types of motors typically used, such as the ones you are using, it makes much more sense to connect them in series. You could easily drive two of those motors in series using 12V power. You might even get away with using 12V power and 3 motors in series, but as this is a new build it makes sense to design for 24V.

Edited 1 time(s). Last edit at 10/22/2015 03:12AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Consider using a single motor driving all three screws with a belt so that all screws always stay in sync. It makes it much faster and easier to work on the machine because when you want to raise or lower the bed you can just pull on the belt and turn all three screws at the same time. Every time I have to do anything like level or zero the bed or work on the extruder on the Taz at the makerspace I am reminded of one of the reasons why I have such disdain for dual motors and screws in the Z axis. I have to step through multiple menu selections to jog the axis up or down. It's an annoyingly slow process.

One of the few design decisions I made when I started designing my printer that has persisted in the latest incarnation of the machine is belt driven Z screws. If I want to raise or lower the bed, I pull the belt or turn one of the pulleys by hand and it's done. No menus, no waiting for computers to boot, etc. I can do it with the power on (if the motors are disabled) or off.

In a CoreXY design, if the screws get out of sync the bed tilts and can be brought back into alignment relatively easily. In the "standard" cartesian design with the X axis lifted by the Z screws, loss of sync in the screws destroys the X axis alignment. If you've ever tried to align the axes in a printer for orthogonality you know that it is not a quick process, and having alignment depending on two screws that a child can turn with their fingers is a very poor design decision.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]