Redrex extruder upgrade kit

From the following page, an upgrade kit is offered, mainly containing a filament extruder motor with a gear reduction. The gear reduction would give the extruder more force to push the filament in.

The following information I was able to find:

• Increase the E-step value to 400¹⁾.

Extruder Frame Specifications:

• Material: Injection molding plastic
• Driving Gear Diameter: 12mm
• Driven Gear Diameter: 8mm
• Transmission Ratio: 3:1
• Stepper Motor Specifications:
• Motor Type: Bipolar Stepper
• Number of Phase: 2
• Step Angle: 1.8 deg.
• Rate Voltage: DC 3.0V
• Holding Torque:DC 1.2A
• Phase Resistance: 2.5ohms ±10%（20℃）
• Phase Inductance: 3.8mH ±20% (1KHz)
• Rotor Inertia: 30.8g.cm²
• Size: ±63*85*69mm
• Weight: ±290g

After following the extruder intake calibration procedure it was observed that instead of 100mm the intake was only 25mm²⁾, So this resulted into the following DEFAULT_AXIS_STEPS_PER_UNIT in Configuration.h:

//Old value: #define DEFAULT_AXIS_STEPS_PER_UNIT   { 160, 160, 800, 185.20 }
#define DEFAULT_AXIS_STEPS_PER_UNIT   { 160, 160, 800, E779.80 }

And after performing a second calibration, a distance from 19.9mm was measured, resulting in the following:

//Old value: #define DEFAULT_AXIS_STEPS_PER_UNIT   { 160, 160, 800, 185.20 }
#define DEFAULT_AXIS_STEPS_PER_UNIT   { 160, 160, 800, E780.58 }

For instructions, how to change the Configuration.h file, please see here.

With using the following test file:

• test_10x10_5mm_hole.stl.zip

We were able to compare the print result with the original extruder motor and the Redrex gear reduction extruder motor (Bowden-type):

Stringing comparison Redrex vs. original
First layer	Top layer

The main differences are that the stringing/oozing plastic is much less with the Redrex gear reduction extruder motor. The print result is substantially cleaner.

The layer height with the Redrex extruder motor was reduced to 0.1mm. This height was not satisfactory to realize with the original extruder motor (which was 0.2mm). The difference can be seen with the following comparison:

Layer comparison Redrex vs. original

• If other problems appear with filament not being able to pushed in, also the Zeelo dual drive extruder/motor could be a solution.
• Or similarly built out of metal: https://www.aliexpress.com/item/32973962746.html