Tuesday, 7 March 2017

Stage 3 - 101spiderman (Part 2)

The 101hero using A4988 stepper driver that is designed to work with bipolar motors. 28BYJ-48 is a unipolar motors but able to work in bipolar mode. You can get more information from here.

However I don’t see the motor using in 101hero had cut the common red wire inside the motor. Anyway I don’t care why they not do so but what I am sure is we can replace the 28BYJ-48 with NEMA motor directly without modify the circuit.

More information about stepper motor and stepper motor driver can be found from below.

The default setting of the steps/mm of the extruder motor is 975. Base on my calculation, the 28BYJ-48 should be running at 8 microstep mode.

To replace the 28BYJ-48 with NEMA motor, we only need to connect 4 wire to the connector using the 6 pin to 4 pin cable and leaving the pin for the red wire empty.

The step angle of the 28BYJ-48 is 5.625°, with 1/64 reduction gear, it take 4096 steps to rotate one circle. While the NEMA motor with 1.8° step angle only need 200 steps. However when I tuning the steps/mm with the NEMA motor, I expect it need 48 steps but finally found that it take 95.2 steps to move 1mm, This mean the stepper motor driver is using 16 microstep mode. I don’t understand why 28BYJ-48 and NEMA is running at difference step mode. May be it is because the red wire had not been cut. I hope some expert can figure it out. 

To change the extruder to bowden type is fairly easy, we only need to remove the motor and door from the extruder. Connect the bowden extruder to the hotend with a bowden tube and change the steps/mm setting for the extruder motor to 95.2 with the G-code ‘M92 E95.2’ (you may need to calibrate this figure).

Weight of the hot end reduced to 75g
To use the NEMA as the extuder motor, you need to add M92 E95.2 to your G-code file or the 101hero file if you are printing from SD card. Printing with Cura, you need to add this command in the printer start.gcode

Manually feed filament to the hot end through the Bowden tube is not difficult when the Bowden tube is short. However, I recommend to use some control program like Repetier to control the extruder, it is more convenience especially when you always need to change the filament.

Bowden extruder not only improve the print speed and quality, it is also the prerequisite setup if you want to upgrade the hotend. 

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