In an aspect, a 3D printer is provided and includes a print head having an extruder motor (that is a stepper motor) positioned to feed a filament into a heater, a print head positioning system configured to move the print head relative to a print surface, a stepper driver that is connected to the extruder motor and is operable to control the operation of the extruder motor, a sensor module that includes a feed rate sensor positioned to detect a rate of feed of the filament, and a control system that is programmed to: receive signals from the sensor module that are indicative of the feed rate of the filament, and control the operation of the stepper driver based on the signals from the sensor module.