GBX Update April 19 2021

GBX Klipper Configuration

Klipper configuration has continued for the first GBX XLT beta unit with Klipper and a 32 bit board. The beta unit has finished its pre-testing and has completed its first 5 hour print. During the testing so far, the following issues were troubleshooted and resolved:



X homing error

X endstop state logic was flipped

X, Y, and Z position movements were not accurate

X, Y, and Z microsteps and rotation_distance were updated to correspond with GBX’s motors

All thermocouples and the bed read 0C

Added missing configuration for the third “extruder”

Heater 2 did not heat

The heater wire was connected to the fan wire at the head cable

A fuse on the board blew whenever all 3 heaters were heating

Confirmed that all the components associated with that fuse were rated from 20 amps. The installed fuse was 5amps, so it was swapped out for a 15 amp fuse.

Overtemp warning error would shut down the printer a few seconds after homing both X and Y.

The mosfets on the board were heating to over 130C when the motors were engaged. Optimized a bbcmlks value in the Klipper firmware to 10 to correspond with a changed resistor on the board. The final steady state temperature was 58C.

Extruder motor movement rate was at least 20x slower than expected.

Adjusted the extruder motor rotation_distance assuming that the 32 bit board was using 32 microstep for the extruder motor, whereas the Azteeg board was using 1 microstep.

Shifting in X direction

Retensioned the X and Y belts and increased the X motor current from 0.8 to 1.2 amps

Extruder motor skipping during print

Increased the extruder motor current to 1.5 amps

A few of the encountered issues involved controlling the temperature of the components on the 32 bit board. According to the manufacturers, the maximum operating temperature for the board is 65C. Operating the board at higher temperatures decreases the lifespan of the components and makes them more prone to failure.

FLIR image of the 32 bit board during a print with bbmclks set to 10, no fan duct, and all motor currents set to 0.8 amps.


The hottest parts of the board during printing were the mosfets and the motor drivers. Optimizing the bbmclks value in the firmware brought the temperature of those components down from over 130C to 58C. However, further testing determined that the 0.8 amp current supplied to the X motor and extruder motor was not sufficient, and both motor currents were increased to prevent X shifting and extruder motor skipping. Although increasing the current solved those problems, it increased the mosfet steady state temperatures to 82C during printing.

An electrical box fan duct was in development during this testing, and all the previous testing was done without a fan duct installed, with the components exposed to ambient 74F air. Once the fan duct was installed, the maximum steady state temperature of the board was around 57C. This was confirmed after 1 hour and 5 hours of printing.

FLIR image of the 32 bit board during a print with bbmclks set to 10, a fan duct installed, and all motor currents optimized.


rPET Material Testing

Material testing continued with EMC2 PHX rPET flake. After validating that a moai could be printed from the material, printing tensile bars was attempted to collect tensile data to compare to other rPET samples. The tensile bars print settings included a 0.25mm layer height, 1mm layer width, and 45 degree infill. Due to the layer height and layer width values, a 0.8mm nozzle was chosen.

Unfortunately, attempts to optimize print settings for the tensile bars were unsuccessful due to inconsistent extrusion. Signs of inconsistent extrusion were present in previous testing: when extruding 200 mm for five trials, the average mass of extrudate was 5.12g, with a 0.59g standard deviation. Furthermore, previous testing was performed with a 1.75mm nozzle, and printing with a 0.8mm nozzle may amplify the effect of contaminants or crystallization on extrusion consistency.

Due to the inconsistent results, tensile bars were attempted again with a 1.75mm nozzle with a 0.6033mm layer height and a 2.1mm layer width. However, switching to the larger nozzle did not resolve the inconsistent extrusion issue. The settings for trial 29 were used to print seven tensile bars one after another sequentially, and all the tensile bars exhibited variations in extrusion rate, despite having the same print settings.

EMC2 PHX rPET tensile bars Trial 29


In conclusion, although this material could print geometries like a moai, it did not have consistent enough extrusion to reliably print tensile bars without macro voids that would affect their tensile strength.


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