*****************************************************************************************************************************************
#pragma config(Hubs, S1, HTMotor, HTServo, none, none)
#pragma config(Sensor, S1, , sensorI2CMuxController)
#pragma config(Motor, mtr_S1_C1_1, motorD, tmotorTetrix, openLoop)
#pragma config(Motor, mtr_S1_C1_2, motorE, tmotorTetrix, openLoop)
#pragma config(Servo, srvo_S1_C2_1, servo1, tServoNone)
#pragma config(Servo, srvo_S1_C2_2, servo2, tServoNone)
#pragma config(Servo, srvo_S1_C2_3, servo3, tServoNone)
#pragma config(Servo, srvo_S1_C2_4, servo4, tServoNone)
#pragma config(Servo, srvo_S1_C2_5, servo5, tServoNone)
#pragma config(Servo, srvo_S1_C2_6, servo6, tServoNone)
//*!!Code automatically generated by 'ROBOTC' configuration wizard !!*//

#include "JoystickDriver.c" // Tells ROBOTC to include the driver file for the joystick.
task main()
{
while(true)
{
getJoystickSettings(joystick); // Update Buttons and Joysticks

motor[motorD] = joystick.joy1_y1;
motor[motorE] = joystick.joy1_y1;

if (joystick.joy1_x1 > 0)
{
motor[motorD] = joystick.joy1_x1;
motor[motorE] = 0;
}
else
{
motor[motorE] = joystick.joy1_x1;
motor[motorD] = 0;
}
}
}
*****************************************************************************************************************************************
We're trying to control the base motors with only joystick.joy1_y1 and joystick.joy1_x1.
So what's wrong with this code? Any suggestions?

Please use the code tag like this:

It looks like you are trying to do arcade drive. If so, it should look something like this:

Will the robot be able to move backwards in this way?

Yes, it can move forward, backward, turn left and turn right. Whichever direction you want to command it.