If you have troubles compiling your Arduino code for homework 3 under Linux, (and most likely also under Mac OS), it might be because you have to change the headers to

#include <MotorWheel.h>
#include <R2WD.h>
#include <PID_Beta6.h>
#include <PinChangeInt.h>
#include <PinChangeIntConfig.h>
#define _USE_MATH_DEFINES
#include <math.h>

Since the lab computers are Linux, you will also need to do this before compiling the code on the computers there.