Nema 17 Motor Mount with 13mm Belt Clearance
Triple Z-Axis Independent Motors

The latest design update uses three Z-axis stepper motors. In this arrangement the belt routing to the stepper motor drive the lead screw. Each lead screw will be constrained by an MGN12 linear rail. This should also minimize vibrations that might be transferred from the motors to the z-axis. The belt to pulley ratio gives the steppers more torque and increases resolution. With the Duet Wifi we can drive 3 steppers and run an auto bed leveling routine using a proximity sensor or probe.

CoreXY Z-Axis

CoreXY Z-Axis Bed Lifters
CoreXY Z-Axis Bed Lifters

The typical corexy 3d printer parts arrangement has a single NEMA 17 stepper motor with the belt routing to all two or three lead screws which move together in sync. Originally we were working on a design that used this single z-axis motor configuration. But after having trouble sourcing the belt that was the perfect length I decided to just go with three stepper motors similar to the HeVort printer or Jubilee tool changing core xy platform.

Single Z-Axis vs Triple Z-Axis

Triple Independent Motors Z Axis 2
Single Z-Axis Motor With Shared Belt

Many 3d printer users frown upon the idea of multiple steppers for independent z motors due to syncing issues. But with a good electronics setup like the 32 bit Duet board and the RepRap Firmware keeping the three lead screws in sync should be fie. When powered up stepper motors tend to jump to the four steps that match the phase current. Some will jump forwards or backward after a number of power cycles.

Triple Independent Motors Z Axis 3
Single Z-Axis Motor With Shared Belt
Triple Independent Motors Z Axis 4

3-Point Bed Leveling Z-Axis Bracket

Download 3D Model

DuetWifi Duet Firmware

Three stepper motors can be more complicated for some control boards because the electronics will need to drive more independent stepper motors. With the Duet Wifi or Duet 3 Mainboard we can drive the 3 steppers and run an auto bed leveling routine using a proximity sensor or probe. The DuetWifi only has five independent motor ports and will need an expansion board.

While a single nema 17 motor could use a continuous closed loop belt routing to all three lead screws in sync. This can be avoided by adding code in RepRap Firmware to detect a power down moing the motors to the correct position ready for power up. The Duet WiFi has two power monitor circuits on board but it doesn’t matter because the machine will run an auto levelling at start up.

Bed Leveling

Bed leveling is necessary in order to print large objects.Mesh bed leveling creates a virtual grid of the print bed. As the layers are printed the motors will lower and raise the nozzle while printing to compensate for the uneven locations on the build plate. Auto Bed Leveling is a function of the Duet 2 board itself. 

  1. Specify at least 3 points using the G30 command and after.
  2. Last one you need to add the S Parameter. Then it will level automatically
  3. Heat up build plate 
  4. Click the “Bed Leveling” button or macro on the Duet Interface.

Once the build plate is level, it works quite well. One downside is the three stepper motors get out of sync. Resync the three motors you power up the machine with an auto level routine will be needed to keep the bed perpendicular to the print head.

Hevort – Non Planer Printing

In the future, we may see more non-planar printing implemented on the SolidCore. With non-planar printing becoming more and more popular, it’s not surprising that slicer toolpaths are available. This means you can optimize how your layers are printed and reduce support needed thanks to angled orientation. One problem with 3D printing is that it can be difficult to support overhangs. The Hevort 3-point bed tilt also changes the way parts need to be supported so for models with overhangs facing ‘uphill’ into the angle, supports aren’t needed. Although non-planar printing is not really widely implemented yet, there are new slicer post and processor components  for printing at fixed angles other than 90. 

Triple Z Motors

The advantage of triple z stepper motors allows an additional degree of freedom and bed leveling. Thermal expansion from the aluminum build plate can cause issues. The Hevort and Jubilee uses small springs on to fix the bed. The Maxwell coupling solution applied to the Z-axis by adding a third axis and mounting it with a Maxwell coupling. The Z-axis leveling algorithm is implemented by the RepRap firmware on a Duet Wifi or Duet 3 Mainboard.

Moving Z-Motors Individually- One at a Time

RepRap Firmware G-Code Command

M574 Z1 S1 P”!duex.e2stop + !duex.e3stop + !duex.e4stop 

This command is for the endstops and must be in order as M584.

M584 X0 Y1:2 Z5:6:7 E3 should be:

  • duex.e2stop is for Z5
  • duex.e3stop is for Z6
  • duex.e4stop is for Z7

 

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