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Pololu A4988 StepStick is use to drive Stepper motors used in 3D Printer. This stepper drivers are used with Ramps1.4 electronics.
Depending upon your machine, whether it is single head or dual head; no of stepper drivers will be used.
for Single head 3D printer, 4 Stepper drivers are used (One each for X,Y,Z axis and Extruder).
For dual head 3D printer, 5 Stepper drivers are used (One each for X,Y,Z axis and two for extruder).