SRFO5 HELP ROBOT

Hi everybody, I was wondering if anyone of you would know how to programm a SRF05 to stop two motors that i have in a robot chassis with the code that I have implemented already.
this is the code:

#include <Servo.h>
Servo servoloco;  // create servo object to control a servo 
char puertoserie; // variable to receive data from the serial port

int motor_izquierda[] = {3, 5};
int motor_derecha[] = {6, 9};
int val = 0;       // variable to store the value coming from the sensor
void setup() { 
  servoloco.attach(11);  // attaches the servo on pin 11 to the servo object v
  Serial.begin(9600);       // start serial communication at 9600bps

int i;
for(i = 0; i < 2; i++){
pinMode(motor_izquierda[i], OUTPUT);
pinMode(motor_derecha[i], OUTPUT);
}
}
void loop() {
  if( Serial.available() )       // if data is available to read
  {
    puertoserie = Serial.read();         // read it and store it in 'val'
  }
  if( puertoserie == 'w' )               
  {
    go_forward_both_motors_on();  
  } 
   if( puertoserie == 's' )               
  {
    go_backwards_both_motors_on(); 
  } 
   if( puertoserie == 'd' )               
  {
    go_right();  
  } 
   if( puertoserie == 'a' )              
  {
    go_left();  
  } 
  if( puertoserie == 'q' )              
  {
    stop_motors_both_motors_off(); 
  } 
  if ( puertoserie == 'o' ) 
  {
  } 
 if ( puertoserie == 'z' ) 
 {
  stop_motors_both_motors_off();
 } 
{ 
  servoloco.write(10);                  // sets the servo position according to the scaled value 
  delay(600);                           // waits for the servo to get there 
  servoloco.write(170);                  // sets the servo position according to the scaled value 
  delay(600);                           // waits for the servo to get there 
} 
}

void stop_motors_both_motors_off(){
digitalWrite(motor_izquierda[0], LOW);
digitalWrite(motor_izquierda[1], LOW);

digitalWrite(motor_derecha[0], LOW);
digitalWrite(motor_derecha[1], LOW);
}

void go_left(){
digitalWrite(motor_izquierda[0], HIGH);
digitalWrite(motor_izquierda[1], LOW);

digitalWrite(motor_derecha[0], HIGH);
digitalWrite(motor_derecha[1], LOW);
}

void go_right(){
digitalWrite(motor_izquierda[0], LOW);
digitalWrite(motor_izquierda[1], HIGH);

digitalWrite(motor_derecha[0], LOW);
digitalWrite(motor_derecha[1], HIGH);
}

void go_forward_both_motors_on(){
digitalWrite(motor_izquierda[0], LOW);
digitalWrite(motor_izquierda[1], HIGH);

digitalWrite(motor_derecha[0], HIGH);
digitalWrite(motor_derecha[1], LOW);
}

void go_backwards_both_motors_on(){
digitalWrite(motor_izquierda[0], HIGH);
digitalWrite(motor_izquierda[1], LOW);

digitalWrite(motor_derecha[0], LOW);
digitalWrite(motor_derecha[1], HIGH);
}


here a picture of how the robot looks like at the moment. also could anyone modify my code so it is better structured? im a newbie and my proframming skills are not that good.

thanks in advance