The purple boards slotted into the pairs of SIL headers are Pololu Stepper motor drivers. Going this route makes replacing a burnt out chip as easy as plugging in a new module. The terminal block ...

grbl is stepper motor controller firmware for ... in this further EinW blog My small cnc mill project needs motors (so I am told) that are too powerful for the normal drivers included on grbl Arduino ...

Adjust the phase current, crank up the microstepping, and forget about it — that’s what most people want out of a stepper motor driver IC ... of the underlying Arduino through its AUX3 ...