Bajdi have build pretty interesting bot platform. To drive the bot he used four small stepper motors that are mounted on servo motors. Servo motors are used to change direction. Such construction looks pretty effective. Bot can change direction instantly by turning wheels while platform stays at same position.
It seems that small stepper motors are slow and have low torque. To compensate this he gave more power by attaching 3S LiPo battery. Stepper motors require 16 I/O pins. Plus 4 for servos. To reduce pin usage he used 74HC595 shift register. Instead of using Arduino library Bajdi wrote his own routine that gave him more confidence. And freedom while driving motors through shift registers.