Also, another item I thought I'd mention. You might want to consider inverting your right side motors so that you don't have to multiply the output of the throttle by -1.
You can invert through the RobotDrive object.
Code:
robotDrive.setInvertedMotor(RobotDrive.MotorType.kFrontRight, true);
robotDrive.setInvertedMotor(RobotDrive.MotorType.kRearRight, true);
Just a recommendation, it isn't necessary but it is very convenient.