[seanwitte]

Mount the four wheels so that the axles are all perpendicular. Label them North, South, East, and West clockwise. The following formulas will drive the wheels, where x, y, and r are in the range -127 to 127.

x = (signed int)p1_x - 127;
y = (signed int)p1_y - 127;
r = (signed int)p2_x - 127;

North = x - r;
South = -x - r;
East = -y - r;
West = y - r;

A joystick connected to port 1 will control forward/backward and strafe left/right. The joystick on port 2 will control the rotation clockwise/anti-clockwise.