int8_t checkDeadZone( int8_t joystickValue, uint8_t deadZone )
{
    if ( joystickValue < deadZone && joystickValue > -deadZone )
        return 0;
        
    if ( joystickValue < 0 )
        return map( joystickValue, -deadZone, -100, 0, -100 );
        
    return map( joystickValue, deadZone, 100, 0, 100 );
}

void Wheel (uint8_t * motor, int v) // v = motor speed, motor = pointer to an array of pins 
{
  if (v > 100) v=100;
  if (v < -100) v=-100;

  v = checkDeadZone( v, 20 );

  v = ease( v );

  ...

void Wheel (uint8_t * motor, int v) // v = motor speed, motor = pointer to an array of pins 
{
  if (v > 100) v=100;
  if (v < -100) v=-100;

  v = ease( v ); // just add this line

  ...

Wheel (RightMotor, RemoteXY.joystick_1_y - RemoteXY.joystick_1_x);
Wheel (LeftMotor, RemoteXY.joystick_1_y + RemoteXY.joystick_1_x);

int8_t ease( int8_t in )
{
    int8_t out = ( in * in ) / 100;
    return in >= 0 ? out : -out;
}

/* 
   -- 1st Robo Car Project (2) with horn(1) -- 
    
   This source code of graphical user interface 
   has been generated automatically by RemoteXY editor.
   To compile this code using RemoteXY library 2.3.3 or later version 
   download by link [url]http://remotexy.com/en/library/[/url]
   To connect using RemoteXY mobile app by link [url]http://remotexy.com/en/download/[/url]                   
     - for ANDROID 4.1.1 or later version; 
     - for iOS 1.2.1 or later version; 
     
   This source code is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.    
*/ 

//////////////////////////////////////////////
//        RemoteXY include library          //
//////////////////////////////////////////////

// RemoteXY select connection mode and include library 
#define REMOTEXY_MODE__SOFTSERIAL
#include <SoftwareSerial.h> 

#include <RemoteXY.h> 

// RemoteXY connection settings  
#define REMOTEXY_SERIAL_RX 2 
#define REMOTEXY_SERIAL_TX 3 
#define REMOTEXY_SERIAL_SPEED 9600 


// RemoteXY configurate   
#pragma pack(push, 1) 
uint8_t RemoteXY_CONF[] = 
  { 255,9,0,0,0,154,0,8,228,4,
  5,48,44,26,30,30,0,31,8,1,
  6,0,-84,-142,20,20,0,2,26,2,
  1,2,1,22,11,0,135,26,16,1,
  79,78,0,79,70,70,0,129,0,5,
  24,23,8,0,64,78,97,118,101,100,
  0,131,3,51,1,20,5,1,2,31,
  82,111,98,111,116,32,67,97,114,0,
  131,0,62,5,19,5,2,2,31,67,
  111,110,116,114,111,108,108,101,114,0,
  3,3,83,12,8,22,0,2,26,129,
  0,9,32,13,7,0,16,84,72,69,
  0,129,0,4,39,25,8,0,136,83,
  104,101,105,107,104,0,1,0,-34,-111,
  12,12,1,2,31,88,0,1,4,79,
  44,12,12,0,37,151,240,159,147,162,
  0 }; 
   
// this structure defines all the variables of your control interface 
struct { 

    // input variable
  int8_t joystick_1_x; // =-100..100 x-coordinate joystick position 
  int8_t joystick_1_y; // =-100..100 y-coordinate joystick position 
  uint8_t rgb_1_r; // =0..255 Red color value 
  uint8_t rgb_1_g; // =0..255 Green color value 
  uint8_t rgb_1_b; // =0..255 Blue color value 
  uint8_t switch_1; // =1 if switch ON and =0 if OFF 
  uint8_t select_1; // =0 if select position A, =1 if position B, =2 if position C, ... 
  uint8_t button_1; // =1 if button pressed, else =0 
  uint8_t button_2; // =1 if button pressed, else =0 

    // other variable
  uint8_t connect_flag;  // =1 if wire connected, else =0 

} RemoteXY; 
#pragma pack(pop) 

/////////////////////////////////////////////
//           END RemoteXY include          //
/////////////////////////////////////////////

#define PIN_BUTTON_2 12

#define PIN_SWITCH_1 13

//define right motor control pins
#define right_motor_A 8
#define right_motor_B 9
#define right_motor_speed 11 //enable pin

//define left motor control pins
#define left_motor_A 6
#define left_motor_B 7
#define left_motor_speed 10 //enable pin

//define two arrays with a list of pins for each motor
uint8_t RightMotor[3] = {right_motor_A, right_motor_B, right_motor_speed};
uint8_t LeftMotor[3] = {left_motor_A, left_motor_B, left_motor_speed};

//speed control of motors
void Wheel (uint8_t * motor, int v) // v = motor speed, motor = pointer to an array of pins 
{
  if (v > 100) v=100;
  if (v < -100) v=-100;
  if (v > 0){

    digitalWrite (motor [0], HIGH);
    digitalWrite (motor [1], LOW);
    analogWrite (motor [2], v * 2.55);
  }
  else if ( v<0 ){

    digitalWrite (motor [0], LOW);
    digitalWrite (motor [1], HIGH);
    analogWrite (motor [2], (-v) * 2.55);
  }
  else{
    digitalWrite (motor [0], LOW);
    digitalWrite (motor [1], LOW);
    analogWrite (motor [2], 0);
  }
}


void setup() 
{
  RemoteXY_Init (); 
  
  pinMode (PIN_SWITCH_1, OUTPUT);
    pinMode (PIN_BUTTON_2, OUTPUT);
   
  
  //initialization pins
  pinMode (right_motor_A, OUTPUT);
  pinMode (right_motor_B, OUTPUT);
  pinMode (left_motor_A, OUTPUT);
  pinMode (left_motor_B, OUTPUT);
  
}

void loop() 
{ 
  RemoteXY_Handler ();
  
  digitalWrite(PIN_SWITCH_1, (RemoteXY.switch_1==0)?LOW:HIGH);
    
  digitalWrite(PIN_BUTTON_2, (RemoteXY.button_2==0)?LOW:HIGH);
   
  //manage the right motor
  Wheel (RightMotor, RemoteXY.joystick_1_y - RemoteXY.joystick_1_x);
  Wheel (LeftMotor, RemoteXY.joystick_1_y + RemoteXY.joystick_1_x);


}