Arduino-Arduino RF Communication, la tecla debe presionarse varias veces

Estoy comunicando dos Arduino, es decir, Arduio UNO como remitente & Arduino Mega como receptor a través del módulo transiver RF-433 MHz. La comunicación está funcionando, pero hay un problema. Si quiero enviar un mensaje, digamos, un número o un carácter, tengo que enviar ese número o carácter varias veces utilizando el monitor de serie Arduino. En otras palabras, tengo que presionar esa tecla y enviar varias veces antes de que el receptor pueda recibir el mensaje y actuar en consecuencia.

Pregunta: ¿Qué debo hacer para que mi receptor reciba el mensaje con solo presionar una tecla?

Mis códigos:

Código del transmisor:

/* Bomb Displacing and Disposing Robot
Transmitter Code (Arduino UNO)  */

#include <VirtualWire.h>
int wrongSignal = 8;
void setup()
{
  Serial.begin(9600);
  vw_setup(2400);
  vw_set_tx_pin(7);
  pinMode(wrongSignal,OUTPUT);
}
void loop()
{
 if(Serial.available())
{ 
  char c= Serial.read();

  if(c == '8')              //To move foreward
  {
    vw_send((uint8_t *)c, 1);    //send one bit i.e. 8
  }
  else if(c=='4')                //To move left
  {
    vw_send((uint8_t *)c, 1);    //send one bit i.e. 4
  }
  else if (c=='6')                //To move right
  {
  vw_send((uint8_t *)c, 1);        //send only one bit i.e. 6
  }
  else if(c=='2')                  // To move reverse
  {
  vw_send((uint8_t *)c, 1);        // send only one bit i.e. 2
  }
 else if(c=='5')                  // To stop
  {
  vw_send((uint8_t *)c, 1);        // send only one bit i.e. 5
  }

  else if(c=='0')                  // To stop
  {
  vw_send((uint8_t *)c, 1);        // send only one bit i.e. 5
  }
       Serial.println(c);
}
      else
            digitalWrite(wrongSignal, HIGH);

}

Código del receptor:

//Receiver Code (Arduino Mega ADK 2560)


#include <VirtualWire.h>
// extra pins --------------------------------      
const int wrongSignal = 8;      // for indication that user sending invalid command
const int enablePin = 12;       // enable of the ICs used in circuit
//---------------------------------------------

// base controling pins -------------------

    // Front Left motor M1
    const int frontLeft1 = 30;
    const int frontLeft2 = 31;

    // Front Right motor M2
    const int frontRight1 = 32;
    const int frontRight2 = 33;

    //Back Left motor M3
    const int backLeft1 = 34;
    const int backLeft2 = 35;

    //Back Right motor M4    
    const int backRight1 = 36;
    const int backRight2 = 37;
//------------------------------------------

void setup() {

  //Extra pins
  pinMode(enablePin, OUTPUT);   // initialize the enable pin as an output
  pinMode(wrongSignal, OUTPUT);   //initialize wrongSignal pin as output pin

  // for Motor drive IC pins
  pinMode(frontLeft1, OUTPUT);
  pinMode(frontLeft2, OUTPUT);

  pinMode(frontRight1, OUTPUT);
  pinMode(frontRight2, OUTPUT);

  pinMode(backLeft1, OUTPUT);
  pinMode(backLeft2, OUTPUT);

  pinMode(backRight1, OUTPUT);
  pinMode(backRight2, OUTPUT);

  digitalWrite(enablePin, HIGH);
  Serial.begin(9600);   // initialize serial communications:
   vw_setup(2400);      // baud rate is 2400
   vw_set_rx_pin(7);    // Receiver pin is pin 7
   vw_rx_start();        // start receiving
}
void loop()
{

  uint8_t buflen = VW_MAX_MESSAGE_LEN;
  uint8_t buf[buflen];

  if(vw_get_message(buf, &buflen))
  {

    for (int i = 0; i < buflen; i++)
    {
      if (buf[i] == '8')                  // move forward, all motors uni-direction
      { 
        digitalWrite(frontLeft1, HIGH);
        digitalWrite(frontLeft2, LOW);
        digitalWrite(frontRight1, HIGH);
        digitalWrite(frontRight2, LOW);
        digitalWrite(backLeft1, HIGH);
        digitalWrite(backLeft2, LOW);
        digitalWrite(backRight1, HIGH);
        digitalWrite(backRight2, LOW);
        }  

        else if (buf[i] == '4')              // move left, M1 >, M4 <
        {
        digitalWrite(frontLeft1, HIGH);    //M1
        digitalWrite(frontLeft2, LOW);
        digitalWrite(frontRight1, LOW);     //M2
        digitalWrite(frontRight2, LOW);
        digitalWrite(backLeft1, LOW);      //M3
        digitalWrite(backLeft2, LOW);
        digitalWrite(backRight1, LOW);      //M4
        digitalWrite(backRight2, HIGH);
      }

  // If the input is '0', turn off the ledPin i.e. send a low signal

  else if (buf[i] == '6')                // move right, M2>, M3<
  {
        digitalWrite(frontLeft1, LOW);      //M1
        digitalWrite(frontLeft2, LOW);
        digitalWrite(frontRight1, HIGH);      //M2
        digitalWrite(frontRight2, LOW);
        digitalWrite(backLeft1, LOW);      //M3
        digitalWrite(backLeft2, HIGH);
        digitalWrite(backRight1, LOW);      //M4
        digitalWrite(backRight2, LOW);
  }

    else if (buf[i] == '2')                // reverse
    {
        digitalWrite(frontLeft1, LOW);
        digitalWrite(frontLeft2, HIGH);
        digitalWrite(frontRight1, LOW);
        digitalWrite(frontRight2, HIGH);
        digitalWrite(backLeft1, LOW);
        digitalWrite(backLeft2, HIGH);
        digitalWrite(backRight1, LOW);
        digitalWrite(backRight2, HIGH);
  }    

    else if (buf[i] == '5')                  // all motors stop
    {
        digitalWrite(frontLeft1, LOW);
        digitalWrite(frontLeft2, LOW);
        digitalWrite(frontRight1, LOW);
        digitalWrite(frontRight2, LOW);
        digitalWrite(backLeft1, LOW);
        digitalWrite(backLeft2, LOW);
        digitalWrite(backRight1, LOW);
        digitalWrite(backRight2, LOW);
  }        

    else if (buf[i] == '0')                  // all motors stop
    {
        digitalWrite(frontLeft1, LOW);
        digitalWrite(frontLeft2, LOW);
        digitalWrite(frontRight1, LOW);
        digitalWrite(frontRight2, LOW);
        digitalWrite(backLeft1, LOW);
        digitalWrite(backLeft2, LOW);
        digitalWrite(backRight1, LOW);
        digitalWrite(backRight2, LOW);
  }        
       else
          digitalWrite(wrongSignal, HIGH);



  }
 }
}