We are still committing to changing the stepper driver boards. Now we adjust the potentiometer to set the maximum current that each stepper motor will receive. This protects the steppers from burnout. The motor drivers will have had their stepper mode set up. Also remember, the X/Y/Z motors use 1.75A, and the extruder motor uses 1A.
Use following references for setting stepper mode & current limit/voltage levels of the boards a) For A4988 see Pololu datasheet https://www.pololu.com/product/1182 b) For DRV8255 use the pololu datasheet https://www.pololu.com/product/2133 c)tutorial on A4988 go here https://www.makerguides.com/a4988-steppe...
Current limits are set by adjusting the potentiometer on the A4988, or the DRV8255. The Boxzy has a tutorial on replacing A4988 drive boards located here Replacing a Stepper Motor Driver Different boards (including different versions of A4988, as well as DRV8255 use different formula to set limit current)
Know where to measure the voltages. Use a digital multimeter, set it to measure voltage, and use it to measure the voltage setting. Use the multimeter to measure the voltage between the metal potentiometer on the board and the ground pin on the board. Note: In this tutorial, all pictures show DRV8255 control boards.
Step #1: Make sure the BOXZY is UNPLUGGED from 24 VDC. Now PLUG IN USB CABLE ONLY TO THE PC. This will provide the reference 5VDC voltage needed by the control board required for our adjustments. NOTE*** SKIP THESE STEPS IF YOU ARE USING THE ORIGINAL A4988 DRIVERS PROVIDED BY BOXZY WITHOUT MAKING ADJUSTMENTS, AND JUST RE-ATTACH THE COVER).
Step #2 (BOXZY ORIGINAL A4988 ONLY): If using original A4988 motor drivers that came with BOXZY, or A4988 motor drivers from before 2017, use formula VREF=8⋅IMAX⋅RCS, where RCS = 0.05Ohm. So for limit current =1.75A for X/Y& Z motors), set VRef =0.05*8*1.75 = 0.7V = Vref. For the extruder, with limit current 1A, Vref = 1*0.8*0.05=0.4V.
Step #3 (A4988 FROM 2017 OR LATER): If replacing the motor driver with A4988 from 2017 or later, use formula VREF=8⋅IMAX⋅RCS, where RCS = 0.068Ohm. So for a limit current of 1.75A for the X/Y/Z motors), set VRef =0.068*8*1.75 = 0.952V. For the extruder that operates at 1A, set VRef = 0.068*8*1 = 0.544V
Step #4 (DRV8255 ONLY): If replacing the motor driver with a DRV8255, use formula VREF=0.5*IMax. So for a limit current of 1.75A for the X/Y/Z motors, set the VRef =0.5*1.75 = 0.875V. For the extruder that operates at 1A, set VRef = 0.5*1 = 0.5 = Vref.
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