Arduino 433Mhz Robot Car - Remote v2.1

/*
  Robot Car remote control v2.1

  This is one of my first Arduino projects.
  Code for the car is available at:
  https://pastebin.com/eDuD2shA
  Enjoy!

  The circuit:

   433Mhz RF trasmitter:
 ** DAT - pin 12

   Joystick module:
 ** VRx - pin A6
 ** VRy - pin A7

   Push button:
 ** button - pin A2

  created  1 Febr 2020
  modified 23 May 2020
  by Mate Z.

*/

#include <RH_ASK.h> //Radio Head RF library
#include <SPI.h> //previous one needs it
#include <string.h>

RH_ASK rf_driver;

int Xvalue;
int Yvalue;
int Bpress;
int Brel = 1;
char message[6];
char prevMessage[6];
int maxSpeed = 100;
int currentSpeed = 0;


#define Xpin A6
#define Ypin A7
#define Bpin A2

void setup() {
  // put your setup code here, to run once:
  rf_driver.init();
  pinMode(LED_BUILTIN, OUTPUT);
  pinMode(Xpin, INPUT);
  pinMode(Ypin, INPUT);
  pinMode(Bpin, INPUT);
  Serial.begin(9600);

}

void maxSpeedChg(){
  if(maxSpeed!=250) maxSpeed+=50;
  else maxSpeed=100;
}

void sendMsg(const String& output){
  char *message = output.c_str();

  if(strcmp(message, prevMessage)!=0 || (millis()%1000 < 3 && message[0] != 'D')){
    rf_driver.send((uint8_t *)message, strlen(message));
    rf_driver.waitPacketSent();
    Serial.print("Transmitting code:\t");
    Serial.println(message);
    strcpy(prevMessage, message);
  }
}


void loop() {
  // put your main code here, to run repeatedly:
  Xvalue=analogRead(Xpin)-525;
  Yvalue=analogRead(Ypin)-525;
  Bpress=digitalRead(Bpin);

  if(millis()%250==0){
    Serial.print("Joystick data: ");
    Serial.print("X: ");
    Serial.print(Xvalue);
    Serial.print(" Y: ");
    Serial.print(Yvalue);
    Serial.print("\tButton: ");
    Serial.println(Bpress);
  }
  String output;
  if(Bpress && Brel){
    maxSpeedChg();
    Serial.print("speed change: ");
    Serial.println(maxSpeed);
    Brel = 0;
  }
  else{
    if(!Bpress) Brel = 1;
    if(abs(Yvalue)<abs(Xvalue)){
      if (Xvalue > 120){ //FWD
        currentSpeed = map(sqrt(Xvalue), 10, sqrt(500), 60, maxSpeed);
        output = 'F';
      }
      else if (Xvalue < -120){ //BWD
        currentSpeed = map(sqrt(abs(Xvalue)), 10, sqrt(525), 60, maxSpeed);
        output = 'B';
      }
      else{ //DEF
        currentSpeed = 0;
        output = 'D';
      }
    }
    if(abs(Xvalue)<abs(Yvalue)){ //RGT
      if (Yvalue > 120){
        currentSpeed = map(sqrt(Yvalue), 10, sqrt(500), 80, maxSpeed);
        output = 'R';
      }
      else if (Yvalue < -120){ //LFT
        currentSpeed = map(sqrt(abs(Yvalue)), 10, sqrt(525), 80, maxSpeed);
        output = 'L';
      }
      else{  //DEF
        currentSpeed = 0;
        output = 'D';
      }
    }

  }
  //Serial.println(output);
  if(strlen(output.c_str())==0) output = 'D';
  if(currentSpeed<100){
    output += '0';
    if(currentSpeed<10) output += '0';
  }
  output += String(currentSpeed);
  sendMsg(output);
}