#include <Servo.h>    //to define and control servos
    #include "FlexiTimer2.h"//to set a timer to manage all servos
    /* Servos --------------------------------------------------------------------*/
    //define 12 servos for 4 legs
    char data = 0;
    Servo servo[4][3];
    //define servos' ports
    const int servo_pin[4][3] = { {2, 3, 4}, {5, 6, 7}, {8, 9, 10}, {11, 12, 13} };
    /* Size of the robot ---------------------------------------------------------*/
    const float length_a = 55;
    const float length_b = 77.5;
    const float length_c = 27.5;
    const float length_side = 71;
    const float z_absolute = -28;
    /* Constants for movement ----------------------------------------------------*/
    const float z_default = -50, z_up = -30, z_boot = z_absolute;
    const float x_default = 62, x_offset = 0;
    const float y_start = 0, y_step = 40;
    const float y_default = x_default;
    /* variables for movement ----------------------------------------------------*/
    volatile float site_now[4][3];    //real-time coordinates of the end of each leg
    volatile float site_expect[4][3]; //expected coordinates of the end of each leg
    float temp_speed[4][3];   //each axis' speed, needs to be recalculated before each movement
    float move_speed;     //movement speed
    float speed_multiple = 1; //movement speed multiple
    const float spot_turn_speed = 4;
    const float leg_move_speed = 8;
    const float body_move_speed = 3;
    const float stand_seat_speed = 1;
    volatile int rest_counter;      //+1/0.02s, for automatic rest
    //functions' parameter
    const float KEEP = 255;
    //define PI for calculation
    const float pi = 3.1415926;
    /* Constants for turn --------------------------------------------------------*/
    //temp length
    const float temp_a = sqrt(pow(2 * x_default + length_side, 2) + pow(y_step, 2));
    const float temp_b = 2 * (y_start + y_step) + length_side;
    const float temp_c = sqrt(pow(2 * x_default + length_side, 2) + pow(2 * y_start + y_step + length_side, 2));
    const float temp_alpha = acos((pow(temp_a, 2) + pow(temp_b, 2) - pow(temp_c, 2)) / 2 / temp_a / temp_b);
    //site for turn
    const float turn_x1 = (temp_a - length_side) / 2;
    const float turn_y1 = y_start + y_step / 2;
    const float turn_x0 = turn_x1 - temp_b * cos(temp_alpha);
    const float turn_y0 = temp_b * sin(temp_alpha) - turn_y1 - length_side;
    /* ---------------------------------------------------------------------------*/
    
      - setup function
       ---------------------------------------------------------------------------*/
    void setup()
    {
      //start serial for debug
      Serial.begin(9600);
      Serial.println("Robot starts initialization");
      
      //initialize default parameter
      pinMode(14, OUTPUT);
      set_site(0, x_default - x_offset, y_start + y_step, z_boot);
      set_site(1, x_default - x_offset, y_start + y_step, z_boot);
      set_site(2, x_default + x_offset, y_start, z_boot);
      set_site(3, x_default + x_offset, y_start, z_boot);
      for (int i = 0; i < 4; i++)
      {
        for (int j = 0; j < 3; j++)
        {
          site_now[i][j] = site_expect[i][j];
        }
      }
      //start servo service
      FlexiTimer2::set(20, servo_service);
      FlexiTimer2::start();
      Serial.println("Servo service started");
      //initialize servos
      servo_attach();
      Serial.println("Servos initialized");
      Serial.println("Robot initialization Complete");
    //   stand();
    //   delay(1000);
    //   hand_shake(2);
    //   Serial.println("hihihihihi");
    //   delay(1000);
    //   step_forward();
    //   step_forward();
    //   step_forward();
    //   step_forward();
    //   step_forward();
    //   step_forward();
    //   delay(1000);
    //   step_back();
    //   step_back();
    //   step_back();
    //   step_back();
    //   step_back();
    //   step_back();
    //   delay(1000);
         
    //   turn_left();
    //   turn_left();
    //   turn_left();
    //   turn_left();
    //   delay(1000);
    //   turn_right();
    //   turn_right();
    //   turn_right();
    //   turn_right();
    //   delay(1000);
    //   hand_wave(4);
    //   delay(1000);
    //   hand_shake(4);
    //   delay(1000);
    //   sit();
    //   delay(1000);
    }
    
    
    void servo_attach(void)
    {
      for (int i = 0; i < 4; i++)
      {
        for (int j = 0; j < 3; j++)
        {
          servo[i][j].attach(servo_pin[i][j]);
          delay(100);
        }
      }
    }
    
    void servo_detach(void)
    {
      for (int i = 0; i < 4; i++)
      {
        for (int j = 0; j < 3; j++)
        {
          servo[i][j].detach();
          delay(100);
        }
      }
    }
    
        
    
    
    /*
      - loop function
       ---------------------------------------------------------------------------*/
    void loop()
    {
     
      
      if(Serial.available() > 0)
       {
          data = Serial.read();        
          Serial.print(data);          
          Serial.print("\n");   
       
         
          
    
          if(data == 'F') 
            { 
             Serial.println("Step forward");
             step_forward();
            }
          else if(data == 'B')        
             { 
              Serial.println("Step back");
              step_back();
            }    
          else if(data == 'L')        
             { 
             Serial.println("Turn left");
             turn_left();
    
            }
          else if(data == 'R')        
            { 
              Serial.println("Turn right");
              turn_right();
    
            } 
            else if(data == 'X')
            {
             Serial.println("Stand");
             stand();
            }
             else if(data == 'x')
            {
              Serial.println("Sit");
              sit();   
            }
           else if(data == 'S' ||data == 'D' )       
              
            { 
    
            }
            
             else if(data == 'W')        
            { 
              digitalWrite(14, HIGH);
            } 
              else if(data == 'w')        
            { 
             digitalWrite(14, LOW);
            }
            else if(data == 'V')        
            { 
              Serial.println("Hand wave");
              hand_wave(3);
            } 
              else if(data == 'v')        
            { 
             Serial.println("Hand wave");
             hand_shake(3);
            }
             else if(data == 'U')        
            { 
              Serial.println("Body dance");
              body_dance(10);
            } 
              else if(data == 'u')        
            { 
              Serial.println("Body dance");
              body_dance(10);
            }
            while(Serial.available()) {Serial.read();}
       }
      
        
       
    }
    
    /*
      - sit
      - blocking function
       ---------------------------------------------------------------------------*/
    /*
      - spot turn to right
      - blocking function
      - parameter step steps wanted to turn
       ---------------------------------------------------------------------------*/
    void turn_right()
    {
        move_speed = spot_turn_speed;
    
        if (site_now[2][1] == y_start)
        {
          //leg 2&0 move
          set_site(2, x_default + x_offset, y_start, z_up);
          wait_all_reach();
    
          set_site(0, turn_x0 - x_offset, turn_y0, z_default);
          set_site(1, turn_x1 - x_offset, turn_y1, z_default);
          set_site(2, turn_x0 + x_offset, turn_y0, z_up);
          set_site(3, turn_x1 + x_offset, turn_y1, z_default);
          wait_all_reach();
    
          set_site(2, turn_x0 + x_offset, turn_y0, z_default);
          wait_all_reach();
    
          set_site(0, turn_x0 + x_offset, turn_y0, z_default);
          set_site(1, turn_x1 + x_offset, turn_y1, z_default);
          set_site(2, turn_x0 - x_offset, turn_y0, z_default);
          set_site(3, turn_x1 - x_offset, turn_y1, z_default);
          wait_all_reach();
    
          set_site(0, turn_x0 + x_offset, turn_y0, z_up);
          wait_all_reach();
    
          set_site(0, x_default + x_offset, y_start, z_up);
          set_site(1, x_default + x_offset, y_start, z_default);
          set_site(2, x_default - x_offset, y_start + y_step, z_default);
          set_site(3, x_default - x_offset, y_start + y_step, z_default);
          wait_all_reach();
    
          set_site(0, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
        else
        {
          //leg 1&3 move
          set_site(1, x_default + x_offset, y_start, z_up);
          wait_all_reach();
    
          set_site(0, turn_x1 + x_offset, turn_y1, z_default);
          set_site(1, turn_x0 + x_offset, turn_y0, z_up);
          set_site(2, turn_x1 - x_offset, turn_y1, z_default);
          set_site(3, turn_x0 - x_offset, turn_y0, z_default);
          wait_all_reach();
    
          set_site(1, turn_x0 + x_offset, turn_y0, z_default);
          wait_all_reach();
    
          set_site(0, turn_x1 - x_offset, turn_y1, z_default);
          set_site(1, turn_x0 - x_offset, turn_y0, z_default);
          set_site(2, turn_x1 + x_offset, turn_y1, z_default);
          set_site(3, turn_x0 + x_offset, turn_y0, z_default);
          wait_all_reach();
    
          set_site(3, turn_x0 + x_offset, turn_y0, z_up);
          wait_all_reach();
    
          set_site(0, x_default - x_offset, y_start + y_step, z_default);
          set_site(1, x_default - x_offset, y_start + y_step, z_default);
          set_site(2, x_default + x_offset, y_start, z_default);
          set_site(3, x_default + x_offset, y_start, z_up);
          wait_all_reach();
    
          set_site(3, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
    }
    
    /*
      - go forward
      - blocking function
      - parameter step steps wanted to go
       ---------------------------------------------------------------------------*/
    void step_forward()
    {
        move_speed = leg_move_speed;
    
        if (site_now[2][1] == y_start)
        {
          //leg 2&1 move
          set_site(2, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(2, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(2, x_default + x_offset, y_start + 2 * y_step, z_default);
          wait_all_reach();
    
          move_speed = body_move_speed;
    
          set_site(0, x_default + x_offset, y_start, z_default);
          set_site(1, x_default + x_offset, y_start + 2 * y_step, z_default);
          set_site(2, x_default - x_offset, y_start + y_step, z_default);
          set_site(3, x_default - x_offset, y_start + y_step, z_default);
          wait_all_reach();
    
          move_speed = leg_move_speed;
    
          set_site(1, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(1, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(1, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
        else
        {
          //leg 0&3 move
          set_site(0, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(0, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(0, x_default + x_offset, y_start + 2 * y_step, z_default);
          wait_all_reach();
    
          move_speed = body_move_speed;
    
          set_site(0, x_default - x_offset, y_start + y_step, z_default);
          set_site(1, x_default - x_offset, y_start + y_step, z_default);
          set_site(2, x_default + x_offset, y_start, z_default);
          set_site(3, x_default + x_offset, y_start + 2 * y_step, z_default);
          wait_all_reach();
    
          move_speed = leg_move_speed;
    
          set_site(3, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(3, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(3, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
    }
    
    /*
      - go back
      - blocking function
      - parameter step steps wanted to go
       ---------------------------------------------------------------------------*/
    void step_back()
    {
        move_speed = leg_move_speed;
        if (site_now[3][1] == y_start)
        {
          //leg 3&0 move
          set_site(3, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(3, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(3, x_default + x_offset, y_start + 2 * y_step, z_default);
          wait_all_reach();
    
          move_speed = body_move_speed;
    
          set_site(0, x_default + x_offset, y_start + 2 * y_step, z_default);
          set_site(1, x_default + x_offset, y_start, z_default);
          set_site(2, x_default - x_offset, y_start + y_step, z_default);
          set_site(3, x_default - x_offset, y_start + y_step, z_default);
          wait_all_reach();
    
          move_speed = leg_move_speed;
    
          set_site(0, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(0, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(0, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
        else
        {
          //leg 1&2 move
          set_site(1, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(1, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(1, x_default + x_offset, y_start + 2 * y_step, z_default);
          wait_all_reach();
    
          move_speed = body_move_speed;
    
          set_site(0, x_default - x_offset, y_start + y_step, z_default);
          set_site(1, x_default - x_offset, y_start + y_step, z_default);
          set_site(2, x_default + x_offset, y_start + 2 * y_step, z_default);
          set_site(3, x_default + x_offset, y_start, z_default);
          wait_all_reach();
    
          move_speed = leg_move_speed;
    
          set_site(2, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(2, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(2, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
    }
    
    // add by RegisHsu
    
    void body_left(int i)
    {
      set_site(0, site_now[0][0] + i, KEEP, KEEP);
      set_site(1, site_now[1][0] + i, KEEP, KEEP);
      set_site(2, site_now[2][0] - i, KEEP, KEEP);
      set_site(3, site_now[3][0] - i, KEEP, KEEP);
      wait_all_reach();
    }
    
    void body_right(int i)
    {
      set_site(0, site_now[0][0] - i, KEEP, KEEP);
      set_site(1, site_now[1][0] - i, KEEP, KEEP);
      set_site(2, site_now[2][0] + i, KEEP, KEEP);
      set_site(3, site_now[3][0] + i, KEEP, KEEP);
      wait_all_reach();
    }
    
    void hand_wave(int i)
    {
      float x_tmp;
      float y_tmp;
      float z_tmp;
      move_speed = 1;
      if (site_now[3][1] == y_start)
      {
        body_right(15);
        x_tmp = site_now[2][0];
        y_tmp = site_now[2][1];
        z_tmp = site_now[2][2];
        move_speed = body_move_speed;
        for (int j = 0; j < i; j++)
        {
          set_site(2, turn_x1, turn_y1, 50);
          wait_all_reach();
          set_site(2, turn_x0, turn_y0, 50);
          wait_all_reach();
        }
        set_site(2, x_tmp, y_tmp, z_tmp);
        wait_all_reach();
        move_speed = 1;
        body_left(15);
      }
      else
      {
        body_left(15);
        x_tmp = site_now[0][0];
        y_tmp = site_now[0][1];
        z_tmp = site_now[0][2];
        move_speed = body_move_speed;
        for (int j = 0; j < i; j++)
        {
          set_site(0, turn_x1, turn_y1, 50);
          wait_all_reach();
          set_site(0, turn_x0, turn_y0, 50);
          wait_all_reach();
        }
        set_site(0, x_tmp, y_tmp, z_tmp);
        wait_all_reach();
        move_speed = 1;
        body_right(15);
      }
    }
    
    void hand_shake(int i)
    {
      float x_tmp;
      float y_tmp;
      float z_tmp;
      move_speed = 1;
      if (site_now[3][1] == y_start)
      {
        body_right(15);
        x_tmp = site_now[2][0];
        y_tmp = site_now[2][1];
        z_tmp = site_now[2][2];
        move_speed = body_move_speed;
        for (int j = 0; j < i; j++)
        {
          set_site(2, x_default - 30, y_start + 2 * y_step, 55);
          wait_all_reach();
          set_site(2, x_default - 30, y_start + 2 * y_step, 10);
          wait_all_reach();
        }
        set_site(2, x_tmp, y_tmp, z_tmp);
        wait_all_reach();
        move_speed = 1;
        body_left(15);
      }
      else
      {
        body_left(15);
        x_tmp = site_now[0][0];
        y_tmp = site_now[0][1];
        z_tmp = site_now[0][2];
        move_speed = body_move_speed;
        for (int j = 0; j < i; j++)
        {
          set_site(0, x_default - 30, y_start + 2 * y_step, 55);
          wait_all_reach();
          set_site(0, x_default - 30, y_start + 2 * y_step, 10);
          wait_all_reach();
        }
        set_site(0, x_tmp, y_tmp, z_tmp);
        wait_all_reach();
        move_speed = 1;
        body_right(15);
      }
    }
    
    void head_up(int i)
    {
      set_site(0, KEEP, KEEP, site_now[0][2] - i);
      set_site(1, KEEP, KEEP, site_now[1][2] + i);
      set_site(2, KEEP, KEEP, site_now[2][2] - i);
      set_site(3, KEEP, KEEP, site_now[3][2] + i);
      wait_all_reach();
    }
    
    void head_down(int i)
    {
      set_site(0, KEEP, KEEP, site_now[0][2] + i);
      set_site(1, KEEP, KEEP, site_now[1][2] - i);
      set_site(2, KEEP, KEEP, site_now[2][2] + i);
      set_site(3, KEEP, KEEP, site_now[3][2] - i);
      wait_all_reach();
    }
    
    void body_dance(int i)
    {
      float x_tmp;
      float y_tmp;
      float z_tmp;
      float body_dance_speed = 2;
      sit();
      move_speed = 1;
      set_site(0, x_default, y_default, KEEP);
      set_site(1, x_default, y_default, KEEP);
      set_site(2, x_default, y_default, KEEP);
      set_site(3, x_default, y_default, KEEP);
      wait_all_reach();
      //stand();
      set_site(0, x_default, y_default, z_default - 20);
      set_site(1, x_default, y_default, z_default - 20);
      set_site(2, x_default, y_default, z_default - 20);
      set_site(3, x_default, y_default, z_default - 20);
      wait_all_reach();
      move_speed = body_dance_speed;
      head_up(30);
      for (int j = 0; j < i; j++)
      {
        if (j > i / 4)
          move_speed = body_dance_speed * 2;
        if (j > i / 2)
          move_speed = body_dance_speed * 3;
        set_site(0, KEEP, y_default - 20, KEEP);
        set_site(1, KEEP, y_default + 20, KEEP);
        set_site(2, KEEP, y_default - 20, KEEP);
        set_site(3, KEEP, y_default + 20, KEEP);
        wait_all_reach();
        set_site(0, KEEP, y_default + 20, KEEP);
        set_site(1, KEEP, y_default - 20, KEEP);
        set_site(2, KEEP, y_default + 20, KEEP);
        set_site(3, KEEP, y_default - 20, KEEP);
        wait_all_reach();
      }
      move_speed = body_dance_speed;
      head_down(30);
    }
    
    
    /*
      - microservos service /timer interrupt function/50Hz
      - when set site expected,this function move the end point to it in a straight line
      - temp_speed[4][3] should be set before set expect site,it make sure the end point
       move in a straight line,and decide move speed.
       ---------------------------------------------------------------------------*/
    void servo_service(void)
    {
      sei();
      static float alpha, beta, gamma;
    
      for (int i = 0; i < 4; i++)
      {
        for (int j = 0; j < 3; j++)
        {
          if (abs(site_now[i][j] - site_expect[i][j]) >= abs(temp_speed[i][j]))
            site_now[i][j] += temp_speed[i][j];
          else
            site_now[i][j] = site_expect[i][j];
        }
    
        cartesian_to_polar(alpha, beta, gamma, site_now[i][0], site_now[i][1], site_now[i][2]);
        polar_to_servo(i, alpha, beta, gamma);
      }
    
      rest_counter++;
    }
    
    /*
      - set one of end points' expect site
      - this founction will set temp_speed[4][3] at same time
      - non - blocking function
       ---------------------------------------------------------------------------*/
    void set_site(int leg, float x, float y, float z)
    {
      float length_x = 0, length_y = 0, length_z = 0;
    
      if (x != KEEP)
        length_x = x - site_now[leg][0];
      if (y != KEEP)
        length_y = y - site_now[leg][1];
      if (z != KEEP)
        length_z = z - site_now[leg][2];
    
      float length = sqrt(pow(length_x, 2) + pow(length_y, 2) + pow(length_z, 2));
    
      temp_speed[leg][0] = length_x / length * move_speed * speed_multiple;
      temp_speed[leg][1] = length_y / length * move_speed * speed_multiple;
      temp_speed[leg][2] = length_z / length * move_speed * speed_multiple;
    
      if (x != KEEP)
        site_expect[leg][0] = x;
      if (y != KEEP)
        site_expect[leg][1] = y;
      if (z != KEEP)
        site_expect[leg][2] = z;
    }
    
    /*
      - wait one of end points move to expect site
      - blocking function
       ---------------------------------------------------------------------------*/
    void wait_reach(int leg)
    {
      while (1)
        if (site_now[leg][0] == site_expect[leg][0])
          if (site_now[leg][1] == site_expect[leg][1])
            if (site_now[leg][2] == site_expect[leg][2])
              break;
    }
    
    /*
      - wait all of end points move to expect site
      - blocking function
       ---------------------------------------------------------------------------*/
    void wait_all_reach(void)
    {
      for (int i = 0; i < 4; i++)
        wait_reach(i);
    }
    
    /*
      - trans site from cartesian to polar
      - mathematical model 2/2
       ---------------------------------------------------------------------------*/
    void cartesian_to_polar(volatile float &alpha, volatile float &beta, volatile float &gamma, volatile float x, volatile float y, volatile float z)
    {
      //calculate w-z degree
      float v, w;
      w = (x >= 0 ? 1 : -1) * (sqrt(pow(x, 2) + pow(y, 2)));
      v = w - length_c;
      alpha = atan2(z, v) + acos((pow(length_a, 2) - pow(length_b, 2) + pow(v, 2) + pow(z, 2)) / 2 / length_a / sqrt(pow(v, 2) + pow(z, 2)));
      beta = acos((pow(length_a, 2) + pow(length_b, 2) - pow(v, 2) - pow(z, 2)) / 2 / length_a / length_b);
      //calculate x-y-z degree
      gamma = (w >= 0) ? atan2(y, x) : atan2(-y, -x);
      //trans degree pi->180
      alpha = alpha / pi * 180;
      beta = beta / pi * 180;
      gamma = gamma / pi * 180;
    }
    
    /*
      - trans site from polar to microservos
      - mathematical model map to fact
      - the errors saved in eeprom will be add
       ---------------------------------------------------------------------------*/
    void polar_to_servo(int leg, float alpha, float beta, float gamma)
    {
      if (leg == 0)
      {
        alpha = 90 - alpha;
        beta = beta;
        gamma += 90;
      }
      else if (leg == 1)
      {
        alpha += 90;
        beta = 180 - beta;
        gamma = 90 - gamma;
      }
      else if (leg == 2)
      {
        alpha += 90;
        beta = 180 - beta;
        gamma = 90 - gamma;
      }
      else if (leg == 3)
      {
        alpha = 90 - alpha;
        beta = beta;
        gamma += 90;
      }
    
      servo[leg][0].write(alpha);
      servo[leg][1].write(beta);
      servo[leg][2].write(gamma);
    }



NOTE--i am deleting some functions like void sit void stand as the maximum limit of characters was reached.


this is my esp32 code

    #include "Arduino.h"
    #include "WiFi.h"
    #include "Audio.h"
    
    #define I2S_DOUT      25
    #define I2S_BCLK      27
    #define I2S_LRC       26
    
    
    
    Audio audio;
    
    char data = 0;
    void setup()
    {
    
      Serial.begin(115200);
    
      WiFi.disconnect();
      WiFi.mode(WIFI_STA);
      WiFi.begin( "Physics", "299792458");
    
      while (WiFi.status() != WL_CONNECTED)
        delay(1500);
    
      audio.setPinout(I2S_BCLK, I2S_LRC, I2S_DOUT);
      audio.setVolume(100);
      audio.connecttospeech("Hello From akshit singh,,welcome to tapovan international school's project day ,,i am a smart walking robot ,you can also call me astra bot ", "en");
     
    }
    
    
    void loop(){
    if(Serial.available() > 0)      
       {
          data = Serial.read();        
          Serial.print(data);             
          if(data == 'A') 
            { 
             audio.connecttospeech("hello everyone ,welcome to tapovan international school's project day ", "en");
             Serial.println("done");
            }
            
          else if(data == 'B')        
            { 
             audio.connecttospeech("BYE Bye everyone", "hi");
             Serial.println("done 2"); 
            }  
          else if(data == 'C')        
            { 
             audio.connecttospeech("i am a smart walking robot ,you can also call me astra bot ", "hi");
             Serial.println("done 2"); 
            }  
    
          else if(data == 'F')        
            { 
             audio.connecttospeech("going forward ,sir", "hi");
             Serial.println("done 2"); 
            }  
    
          else if(data == 'b')        
            { 
             audio.connecttospeech("going backward ,sir", "hi");
             Serial.println("done 2"); 
    
            }  
          else if(data == 'L')        
            { 
             audio.connecttospeech("moving left, sir", "hi");
             Serial.println("done 2"); 
    
            }  
          else if(data == 'R')        
            { 
             audio.connecttospeech("moving right ,sir", "hi");
             Serial.println("done 2"); 
    
            }  
          
    
       }
    
    {
      audio.loop();
    }
    
      }
    
    void audio_info(const char *info) {
      Serial.print("audio_info: "); Serial.println(info);
    }

    #include <Servo.h>    //to define and control servos
    #include "FlexiTimer2.h"//to set a timer to manage all servos
    /* Servos --------------------------------------------------------------------*/
    //define 12 servos for 4 legs
    char data = 0;
    Servo servo[4][3];
    //define servos' ports
    const int servo_pin[4][3] = { {2, 3, 4}, {5, 6, 7}, {8, 9, 10}, {11, 12, 13} };
    /* Size of the robot ---------------------------------------------------------*/
    const float length_a = 55;
    const float length_b = 77.5;
    const float length_c = 27.5;
    const float length_side = 71;
    const float z_absolute = -28;
    /* Constants for movement ----------------------------------------------------*/
    const float z_default = -50, z_up = -30, z_boot = z_absolute;
    const float x_default = 62, x_offset = 0;
    const float y_start = 0, y_step = 40;
    const float y_default = x_default;
    /* variables for movement ----------------------------------------------------*/
    volatile float site_now[4][3];    //real-time coordinates of the end of each leg
    volatile float site_expect[4][3]; //expected coordinates of the end of each leg
    float temp_speed[4][3];   //each axis' speed, needs to be recalculated before each movement
    float move_speed;     //movement speed
    float speed_multiple = 1; //movement speed multiple
    const float spot_turn_speed = 4;
    const float leg_move_speed = 8;
    const float body_move_speed = 3;
    const float stand_seat_speed = 1;
    volatile int rest_counter;      //+1/0.02s, for automatic rest
    //functions' parameter
    const float KEEP = 255;
    //define PI for calculation
    const float pi = 3.1415926;
    /* Constants for turn --------------------------------------------------------*/
    //temp length
    const float temp_a = sqrt(pow(2 * x_default + length_side, 2) + pow(y_step, 2));
    const float temp_b = 2 * (y_start + y_step) + length_side;
    const float temp_c = sqrt(pow(2 * x_default + length_side, 2) + pow(2 * y_start + y_step + length_side, 2));
    const float temp_alpha = acos((pow(temp_a, 2) + pow(temp_b, 2) - pow(temp_c, 2)) / 2 / temp_a / temp_b);
    //site for turn
    const float turn_x1 = (temp_a - length_side) / 2;
    const float turn_y1 = y_start + y_step / 2;
    const float turn_x0 = turn_x1 - temp_b * cos(temp_alpha);
    const float turn_y0 = temp_b * sin(temp_alpha) - turn_y1 - length_side;
    /* ---------------------------------------------------------------------------*/
    
      - setup function
       ---------------------------------------------------------------------------*/
    void setup()
    {
      //start serial for debug
      Serial.begin(9600);
      Serial.println("Robot starts initialization");
      
      //initialize default parameter
      pinMode(14, OUTPUT);
      set_site(0, x_default - x_offset, y_start + y_step, z_boot);
      set_site(1, x_default - x_offset, y_start + y_step, z_boot);
      set_site(2, x_default + x_offset, y_start, z_boot);
      set_site(3, x_default + x_offset, y_start, z_boot);
      for (int i = 0; i < 4; i++)
      {
        for (int j = 0; j < 3; j++)
        {
          site_now[i][j] = site_expect[i][j];
        }
      }
      //start servo service
      FlexiTimer2::set(20, servo_service);
      FlexiTimer2::start();
      Serial.println("Servo service started");
      //initialize servos
      servo_attach();
      Serial.println("Servos initialized");
      Serial.println("Robot initialization Complete");
    //   stand();
    //   delay(1000);
    //   hand_shake(2);
    //   Serial.println("hihihihihi");
    //   delay(1000);
    //   step_forward();
    //   step_forward();
    //   step_forward();
    //   step_forward();
    //   step_forward();
    //   step_forward();
    //   delay(1000);
    //   step_back();
    //   step_back();
    //   step_back();
    //   step_back();
    //   step_back();
    //   step_back();
    //   delay(1000);
         
    //   turn_left();
    //   turn_left();
    //   turn_left();
    //   turn_left();
    //   delay(1000);
    //   turn_right();
    //   turn_right();
    //   turn_right();
    //   turn_right();
    //   delay(1000);
    //   hand_wave(4);
    //   delay(1000);
    //   hand_shake(4);
    //   delay(1000);
    //   sit();
    //   delay(1000);
    }
    
    
    void servo_attach(void)
    {
      for (int i = 0; i < 4; i++)
      {
        for (int j = 0; j < 3; j++)
        {
          servo[i][j].attach(servo_pin[i][j]);
          delay(100);
        }
      }
    }
    
    void servo_detach(void)
    {
      for (int i = 0; i < 4; i++)
      {
        for (int j = 0; j < 3; j++)
        {
          servo[i][j].detach();
          delay(100);
        }
      }
    }
    
        
    
    
    /*
      - loop function
       ---------------------------------------------------------------------------*/
    void loop()
    {
     
      
      if(Serial.available() > 0)
       {
          data = Serial.read();        
          Serial.print(data);          
          Serial.print("\n");   
       
         
          
    
          if(data == 'F') 
            { 
             Serial.println("Step forward");
             step_forward();
            }
          else if(data == 'B')        
             { 
              Serial.println("Step back");
              step_back();
            }    
          else if(data == 'L')        
             { 
             Serial.println("Turn left");
             turn_left();
    
            }
          else if(data == 'R')        
            { 
              Serial.println("Turn right");
              turn_right();
    
            } 
            else if(data == 'X')
            {
             Serial.println("Stand");
             stand();
            }
             else if(data == 'x')
            {
              Serial.println("Sit");
              sit();   
            }
           else if(data == 'S' ||data == 'D' )       
              
            { 
    
            }
            
             else if(data == 'W')        
            { 
              digitalWrite(14, HIGH);
            } 
              else if(data == 'w')        
            { 
             digitalWrite(14, LOW);
            }
            else if(data == 'V')        
            { 
              Serial.println("Hand wave");
              hand_wave(3);
            } 
              else if(data == 'v')        
            { 
             Serial.println("Hand wave");
             hand_shake(3);
            }
             else if(data == 'U')        
            { 
              Serial.println("Body dance");
              body_dance(10);
            } 
              else if(data == 'u')        
            { 
              Serial.println("Body dance");
              body_dance(10);
            }
            while(Serial.available()) {Serial.read();}
       }
      
        
       
    }
    
    /*
      - sit
      - blocking function
       ---------------------------------------------------------------------------*/
    /*
      - spot turn to right
      - blocking function
      - parameter step steps wanted to turn
       ---------------------------------------------------------------------------*/
    void turn_right()
    {
        move_speed = spot_turn_speed;
    
        if (site_now[2][1] == y_start)
        {
          //leg 2&0 move
          set_site(2, x_default + x_offset, y_start, z_up);
          wait_all_reach();
    
          set_site(0, turn_x0 - x_offset, turn_y0, z_default);
          set_site(1, turn_x1 - x_offset, turn_y1, z_default);
          set_site(2, turn_x0 + x_offset, turn_y0, z_up);
          set_site(3, turn_x1 + x_offset, turn_y1, z_default);
          wait_all_reach();
    
          set_site(2, turn_x0 + x_offset, turn_y0, z_default);
          wait_all_reach();
    
          set_site(0, turn_x0 + x_offset, turn_y0, z_default);
          set_site(1, turn_x1 + x_offset, turn_y1, z_default);
          set_site(2, turn_x0 - x_offset, turn_y0, z_default);
          set_site(3, turn_x1 - x_offset, turn_y1, z_default);
          wait_all_reach();
    
          set_site(0, turn_x0 + x_offset, turn_y0, z_up);
          wait_all_reach();
    
          set_site(0, x_default + x_offset, y_start, z_up);
          set_site(1, x_default + x_offset, y_start, z_default);
          set_site(2, x_default - x_offset, y_start + y_step, z_default);
          set_site(3, x_default - x_offset, y_start + y_step, z_default);
          wait_all_reach();
    
          set_site(0, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
        else
        {
          //leg 1&3 move
          set_site(1, x_default + x_offset, y_start, z_up);
          wait_all_reach();
    
          set_site(0, turn_x1 + x_offset, turn_y1, z_default);
          set_site(1, turn_x0 + x_offset, turn_y0, z_up);
          set_site(2, turn_x1 - x_offset, turn_y1, z_default);
          set_site(3, turn_x0 - x_offset, turn_y0, z_default);
          wait_all_reach();
    
          set_site(1, turn_x0 + x_offset, turn_y0, z_default);
          wait_all_reach();
    
          set_site(0, turn_x1 - x_offset, turn_y1, z_default);
          set_site(1, turn_x0 - x_offset, turn_y0, z_default);
          set_site(2, turn_x1 + x_offset, turn_y1, z_default);
          set_site(3, turn_x0 + x_offset, turn_y0, z_default);
          wait_all_reach();
    
          set_site(3, turn_x0 + x_offset, turn_y0, z_up);
          wait_all_reach();
    
          set_site(0, x_default - x_offset, y_start + y_step, z_default);
          set_site(1, x_default - x_offset, y_start + y_step, z_default);
          set_site(2, x_default + x_offset, y_start, z_default);
          set_site(3, x_default + x_offset, y_start, z_up);
          wait_all_reach();
    
          set_site(3, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
    }
    
    /*
      - go forward
      - blocking function
      - parameter step steps wanted to go
       ---------------------------------------------------------------------------*/
    void step_forward()
    {
        move_speed = leg_move_speed;
    
        if (site_now[2][1] == y_start)
        {
          //leg 2&1 move
          set_site(2, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(2, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(2, x_default + x_offset, y_start + 2 * y_step, z_default);
          wait_all_reach();
    
          move_speed = body_move_speed;
    
          set_site(0, x_default + x_offset, y_start, z_default);
          set_site(1, x_default + x_offset, y_start + 2 * y_step, z_default);
          set_site(2, x_default - x_offset, y_start + y_step, z_default);
          set_site(3, x_default - x_offset, y_start + y_step, z_default);
          wait_all_reach();
    
          move_speed = leg_move_speed;
    
          set_site(1, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(1, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(1, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
        else
        {
          //leg 0&3 move
          set_site(0, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(0, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(0, x_default + x_offset, y_start + 2 * y_step, z_default);
          wait_all_reach();
    
          move_speed = body_move_speed;
    
          set_site(0, x_default - x_offset, y_start + y_step, z_default);
          set_site(1, x_default - x_offset, y_start + y_step, z_default);
          set_site(2, x_default + x_offset, y_start, z_default);
          set_site(3, x_default + x_offset, y_start + 2 * y_step, z_default);
          wait_all_reach();
    
          move_speed = leg_move_speed;
    
          set_site(3, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(3, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(3, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
    }
    
    /*
      - go back
      - blocking function
      - parameter step steps wanted to go
       ---------------------------------------------------------------------------*/
    void step_back()
    {
        move_speed = leg_move_speed;
        if (site_now[3][1] == y_start)
        {
          //leg 3&0 move
          set_site(3, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(3, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(3, x_default + x_offset, y_start + 2 * y_step, z_default);
          wait_all_reach();
    
          move_speed = body_move_speed;
    
          set_site(0, x_default + x_offset, y_start + 2 * y_step, z_default);
          set_site(1, x_default + x_offset, y_start, z_default);
          set_site(2, x_default - x_offset, y_start + y_step, z_default);
          set_site(3, x_default - x_offset, y_start + y_step, z_default);
          wait_all_reach();
    
          move_speed = leg_move_speed;
    
          set_site(0, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(0, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(0, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
        else
        {
          //leg 1&2 move
          set_site(1, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(1, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(1, x_default + x_offset, y_start + 2 * y_step, z_default);
          wait_all_reach();
    
          move_speed = body_move_speed;
    
          set_site(0, x_default - x_offset, y_start + y_step, z_default);
          set_site(1, x_default - x_offset, y_start + y_step, z_default);
          set_site(2, x_default + x_offset, y_start + 2 * y_step, z_default);
          set_site(3, x_default + x_offset, y_start, z_default);
          wait_all_reach();
    
          move_speed = leg_move_speed;
    
          set_site(2, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(2, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(2, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
    }
    
    // add by RegisHsu
    
    void body_left(int i)
    {
      set_site(0, site_now[0][0] + i, KEEP, KEEP);
      set_site(1, site_now[1][0] + i, KEEP, KEEP);
      set_site(2, site_now[2][0] - i, KEEP, KEEP);
      set_site(3, site_now[3][0] - i, KEEP, KEEP);
      wait_all_reach();
    }
    
    void body_right(int i)
    {
      set_site(0, site_now[0][0] - i, KEEP, KEEP);
      set_site(1, site_now[1][0] - i, KEEP, KEEP);
      set_site(2, site_now[2][0] + i, KEEP, KEEP);
      set_site(3, site_now[3][0] + i, KEEP, KEEP);
      wait_all_reach();
    }
    
    void hand_wave(int i)
    {
      float x_tmp;
      float y_tmp;
      float z_tmp;
      move_speed = 1;
      if (site_now[3][1] == y_start)
      {
        body_right(15);
        x_tmp = site_now[2][0];
        y_tmp = site_now[2][1];
        z_tmp = site_now[2][2];
        move_speed = body_move_speed;
        for (int j = 0; j < i; j++)
        {
          set_site(2, turn_x1, turn_y1, 50);
          wait_all_reach();
          set_site(2, turn_x0, turn_y0, 50);
          wait_all_reach();
        }
        set_site(2, x_tmp, y_tmp, z_tmp);
        wait_all_reach();
        move_speed = 1;
        body_left(15);
      }
      else
      {
        body_left(15);
        x_tmp = site_now[0][0];
        y_tmp = site_now[0][1];
        z_tmp = site_now[0][2];
        move_speed = body_move_speed;
        for (int j = 0; j < i; j++)
        {
          set_site(0, turn_x1, turn_y1, 50);
          wait_all_reach();
          set_site(0, turn_x0, turn_y0, 50);
          wait_all_reach();
        }
        set_site(0, x_tmp, y_tmp, z_tmp);
        wait_all_reach();
        move_speed = 1;
        body_right(15);
      }
    }
    
    void hand_shake(int i)
    {
      float x_tmp;
      float y_tmp;
      float z_tmp;
      move_speed = 1;
      if (site_now[3][1] == y_start)
      {
        body_right(15);
        x_tmp = site_now[2][0];
        y_tmp = site_now[2][1];
        z_tmp = site_now[2][2];
        move_speed = body_move_speed;
        for (int j = 0; j < i; j++)
        {
          set_site(2, x_default - 30, y_start + 2 * y_step, 55);
          wait_all_reach();
          set_site(2, x_default - 30, y_start + 2 * y_step, 10);
          wait_all_reach();
        }
        set_site(2, x_tmp, y_tmp, z_tmp);
        wait_all_reach();
        move_speed = 1;
        body_left(15);
      }
      else
      {
        body_left(15);
        x_tmp = site_now[0][0];
        y_tmp = site_now[0][1];
        z_tmp = site_now[0][2];
        move_speed = body_move_speed;
        for (int j = 0; j < i; j++)
        {
          set_site(0, x_default - 30, y_start + 2 * y_step, 55);
          wait_all_reach();
          set_site(0, x_default - 30, y_start + 2 * y_step, 10);
          wait_all_reach();
        }
        set_site(0, x_tmp, y_tmp, z_tmp);
        wait_all_reach();
        move_speed = 1;
        body_right(15);
      }
    }
    
    void head_up(int i)
    {
      set_site(0, KEEP, KEEP, site_now[0][2] - i);
      set_site(1, KEEP, KEEP, site_now[1][2] + i);
      set_site(2, KEEP, KEEP, site_now[2][2] - i);
      set_site(3, KEEP, KEEP, site_now[3][2] + i);
      wait_all_reach();
    }
    
    void head_down(int i)
    {
      set_site(0, KEEP, KEEP, site_now[0][2] + i);
      set_site(1, KEEP, KEEP, site_now[1][2] - i);
      set_site(2, KEEP, KEEP, site_now[2][2] + i);
      set_site(3, KEEP, KEEP, site_now[3][2] - i);
      wait_all_reach();
    }
    
    void body_dance(int i)
    {
      float x_tmp;
      float y_tmp;
      float z_tmp;
      float body_dance_speed = 2;
      sit();
      move_speed = 1;
      set_site(0, x_default, y_default, KEEP);
      set_site(1, x_default, y_default, KEEP);
      set_site(2, x_default, y_default, KEEP);
      set_site(3, x_default, y_default, KEEP);
      wait_all_reach();
      //stand();
      set_site(0, x_default, y_default, z_default - 20);
      set_site(1, x_default, y_default, z_default - 20);
      set_site(2, x_default, y_default, z_default - 20);
      set_site(3, x_default, y_default, z_default - 20);
      wait_all_reach();
      move_speed = body_dance_speed;
      head_up(30);
      for (int j = 0; j < i; j++)
      {
        if (j > i / 4)
          move_speed = body_dance_speed * 2;
        if (j > i / 2)
          move_speed = body_dance_speed * 3;
        set_site(0, KEEP, y_default - 20, KEEP);
        set_site(1, KEEP, y_default + 20, KEEP);
        set_site(2, KEEP, y_default - 20, KEEP);
        set_site(3, KEEP, y_default + 20, KEEP);
        wait_all_reach();
        set_site(0, KEEP, y_default + 20, KEEP);
        set_site(1, KEEP, y_default - 20, KEEP);
        set_site(2, KEEP, y_default + 20, KEEP);
        set_site(3, KEEP, y_default - 20, KEEP);
        wait_all_reach();
      }
      move_speed = body_dance_speed;
      head_down(30);
    }
    
    
    /*
      - microservos service /timer interrupt function/50Hz
      - when set site expected,this function move the end point to it in a straight line
      - temp_speed[4][3] should be set before set expect site,it make sure the end point
       move in a straight line,and decide move speed.
       ---------------------------------------------------------------------------*/
    void servo_service(void)
    {
      sei();
      static float alpha, beta, gamma;
    
      for (int i = 0; i < 4; i++)
      {
        for (int j = 0; j < 3; j++)
        {
          if (abs(site_now[i][j] - site_expect[i][j]) >= abs(temp_speed[i][j]))
            site_now[i][j] += temp_speed[i][j];
          else
            site_now[i][j] = site_expect[i][j];
        }
    
        cartesian_to_polar(alpha, beta, gamma, site_now[i][0], site_now[i][1], site_now[i][2]);
        polar_to_servo(i, alpha, beta, gamma);
      }
    
      rest_counter++;
    }
    
    /*
      - set one of end points' expect site
      - this founction will set temp_speed[4][3] at same time
      - non - blocking function
       ---------------------------------------------------------------------------*/
    void set_site(int leg, float x, float y, float z)
    {
      float length_x = 0, length_y = 0, length_z = 0;
    
      if (x != KEEP)
        length_x = x - site_now[leg][0];
      if (y != KEEP)
        length_y = y - site_now[leg][1];
      if (z != KEEP)
        length_z = z - site_now[leg][2];
    
      float length = sqrt(pow(length_x, 2) + pow(length_y, 2) + pow(length_z, 2));
    
      temp_speed[leg][0] = length_x / length * move_speed * speed_multiple;
      temp_speed[leg][1] = length_y / length * move_speed * speed_multiple;
      temp_speed[leg][2] = length_z / length * move_speed * speed_multiple;
    
      if (x != KEEP)
        site_expect[leg][0] = x;
      if (y != KEEP)
        site_expect[leg][1] = y;
      if (z != KEEP)
        site_expect[leg][2] = z;
    }
    
    /*
      - wait one of end points move to expect site
      - blocking function
       ---------------------------------------------------------------------------*/
    void wait_reach(int leg)
    {
      while (1)
        if (site_now[leg][0] == site_expect[leg][0])
          if (site_now[leg][1] == site_expect[leg][1])
            if (site_now[leg][2] == site_expect[leg][2])
              break;
    }
    
    /*
      - wait all of end points move to expect site
      - blocking function
       ---------------------------------------------------------------------------*/
    void wait_all_reach(void)
    {
      for (int i = 0; i < 4; i++)
        wait_reach(i);
    }
    
    /*
      - trans site from cartesian to polar
      - mathematical model 2/2
       ---------------------------------------------------------------------------*/
    void cartesian_to_polar(volatile float &alpha, volatile float &beta, volatile float &gamma, volatile float x, volatile float y, volatile float z)
    {
      //calculate w-z degree
      float v, w;
      w = (x >= 0 ? 1 : -1) * (sqrt(pow(x, 2) + pow(y, 2)));
      v = w - length_c;
      alpha = atan2(z, v) + acos((pow(length_a, 2) - pow(length_b, 2) + pow(v, 2) + pow(z, 2)) / 2 / length_a / sqrt(pow(v, 2) + pow(z, 2)));
      beta = acos((pow(length_a, 2) + pow(length_b, 2) - pow(v, 2) - pow(z, 2)) / 2 / length_a / length_b);
      //calculate x-y-z degree
      gamma = (w >= 0) ? atan2(y, x) : atan2(-y, -x);
      //trans degree pi->180
      alpha = alpha / pi * 180;
      beta = beta / pi * 180;
      gamma = gamma / pi * 180;
    }
    
    /*
      - trans site from polar to microservos
      - mathematical model map to fact
      - the errors saved in eeprom will be add
       ---------------------------------------------------------------------------*/
    void polar_to_servo(int leg, float alpha, float beta, float gamma)
    {
      if (leg == 0)
      {
        alpha = 90 - alpha;
        beta = beta;
        gamma += 90;
      }
      else if (leg == 1)
      {
        alpha += 90;
        beta = 180 - beta;
        gamma = 90 - gamma;
      }
      else if (leg == 2)
      {
        alpha += 90;
        beta = 180 - beta;
        gamma = 90 - gamma;
      }
      else if (leg == 3)
      {
        alpha = 90 - alpha;
        beta = beta;
        gamma += 90;
      }
    
      servo[leg][0].write(alpha);
      servo[leg][1].write(beta);
      servo[leg][2].write(gamma);
    }

NOTE: I am deleting some functions like void sit(void) stand as the maximum limit of characters was reached.

This is my esp32 code

    #include "Arduino.h"
    #include "WiFi.h"
    #include "Audio.h"
    
    #define I2S_DOUT      25
    #define I2S_BCLK      27
    #define I2S_LRC       26
    
    
    
    Audio audio;
    
    char data = 0;
    void setup()
    {
    
      Serial.begin(115200);
    
      WiFi.disconnect();
      WiFi.mode(WIFI_STA);
      WiFi.begin( "Physics", "299792458");
    
      while (WiFi.status() != WL_CONNECTED)
        delay(1500);
    
      audio.setPinout(I2S_BCLK, I2S_LRC, I2S_DOUT);
      audio.setVolume(100);
      audio.connecttospeech("Hello From akshit singh,,welcome to tapovan international school's project day ,,i am a smart walking robot ,you can also call me astra bot ", "en");
     
    }
    
    
    void loop(){
    if(Serial.available() > 0)      
       {
          data = Serial.read();        
          Serial.print(data);             
          if(data == 'A') 
            { 
             audio.connecttospeech("hello everyone ,welcome to tapovan international school's project day ", "en");
             Serial.println("done");
            }
            
          else if(data == 'B')        
            { 
             audio.connecttospeech("BYE Bye everyone", "hi");
             Serial.println("done 2"); 
            }  
          else if(data == 'C')        
            { 
             audio.connecttospeech("i am a smart walking robot ,you can also call me astra bot ", "hi");
             Serial.println("done 2"); 
            }  
    
          else if(data == 'F')        
            { 
             audio.connecttospeech("going forward ,sir", "hi");
             Serial.println("done 2"); 
            }  
    
          else if(data == 'b')        
            { 
             audio.connecttospeech("going backward ,sir", "hi");
             Serial.println("done 2"); 
    
            }  
          else if(data == 'L')        
            { 
             audio.connecttospeech("moving left, sir", "hi");
             Serial.println("done 2"); 
    
            }  
          else if(data == 'R')        
            { 
             audio.connecttospeech("moving right ,sir", "hi");
             Serial.println("done 2"); 
    
            }  
          
    
       }
    
    {
      audio.loop();
    }
    
      }
    
    void audio_info(const char *info) {
      Serial.print("audio_info: "); Serial.println(info);
    }

i made a spider robot using arduino and from esp i made an audio output device which is linked to python program which writes a particular data (when we speak a command) to esp board and accordingly the voice would be activated.now i want to link them together. if the esp32 sends a particular data the function in arduino is executed and hence i want to connect esp32 to arduino uno though Serial monitor and send data from esp 32 to arduino.I have only analog pins vacant as all digital pins are used for the servos. how can i achieve the required.

this i the main arduino file there are 2 more flexitimer and flexitimer2.cpp but there is no need of editing them and hence i am giving the code of main file.

#include <Servo.h>    //to define and control servos
#include "FlexiTimer2.h"//to set a timer to manage all servos
/* Servos --------------------------------------------------------------------*/
//define 12 servos for 4 legs
char data = 0;
Servo servo[4][3];
//define servos' ports
const int servo_pin[4][3] = { {2, 3, 4}, {5, 6, 7}, {8, 9, 10}, {11, 12, 13} };
/* Size of the robot ---------------------------------------------------------*/
const float length_a = 55;
const float length_b = 77.5;
const float length_c = 27.5;
const float length_side = 71;
const float z_absolute = -28;
/* Constants for movement ----------------------------------------------------*/
const float z_default = -50, z_up = -30, z_boot = z_absolute;
const float x_default = 62, x_offset = 0;
const float y_start = 0, y_step = 40;
const float y_default = x_default;
/* variables for movement ----------------------------------------------------*/
volatile float site_now[4][3];    //real-time coordinates of the end of each leg
volatile float site_expect[4][3]; //expected coordinates of the end of each leg
float temp_speed[4][3];   //each axis' speed, needs to be recalculated before each movement
float move_speed;     //movement speed
float speed_multiple = 1; //movement speed multiple
const float spot_turn_speed = 4;
const float leg_move_speed = 8;
const float body_move_speed = 3;
const float stand_seat_speed = 1;
volatile int rest_counter;      //+1/0.02s, for automatic rest
//functions' parameter
const float KEEP = 255;
//define PI for calculation
const float pi = 3.1415926;
/* Constants for turn --------------------------------------------------------*/
//temp length
const float temp_a = sqrt(pow(2 * x_default + length_side, 2) + pow(y_step, 2));
const float temp_b = 2 * (y_start + y_step) + length_side;
const float temp_c = sqrt(pow(2 * x_default + length_side, 2) + pow(2 * y_start + y_step + length_side, 2));
const float temp_alpha = acos((pow(temp_a, 2) + pow(temp_b, 2) - pow(temp_c, 2)) / 2 / temp_a / temp_b);
//site for turn
const float turn_x1 = (temp_a - length_side) / 2;
const float turn_y1 = y_start + y_step / 2;
const float turn_x0 = turn_x1 - temp_b * cos(temp_alpha);
const float turn_y0 = temp_b * sin(temp_alpha) - turn_y1 - length_side;
/* ---------------------------------------------------------------------------*/

  - setup function
   ---------------------------------------------------------------------------*/
void setup()
{
  //start serial for debug
  Serial.begin(9600);
  Serial.println("Robot starts initialization");
  
  //initialize default parameter
  pinMode(14, OUTPUT);
  set_site(0, x_default - x_offset, y_start + y_step, z_boot);
  set_site(1, x_default - x_offset, y_start + y_step, z_boot);
  set_site(2, x_default + x_offset, y_start, z_boot);
  set_site(3, x_default + x_offset, y_start, z_boot);
  for (int i = 0; i < 4; i++)
  {
    for (int j = 0; j < 3; j++)
    {
      site_now[i][j] = site_expect[i][j];
    }
  }
  //start servo service
  FlexiTimer2::set(20, servo_service);
  FlexiTimer2::start();
  Serial.println("Servo service started");
  //initialize servos
  servo_attach();
  Serial.println("Servos initialized");
  Serial.println("Robot initialization Complete");
//   stand();
//   delay(1000);
//   hand_shake(2);
//   Serial.println("hihihihihi");
//   delay(1000);
//   step_forward();
//   step_forward();
//   step_forward();
//   step_forward();
//   step_forward();
//   step_forward();
//   delay(1000);
//   step_back();
//   step_back();
//   step_back();
//   step_back();
//   step_back();
//   step_back();
//   delay(1000);
     
//   turn_left();
//   turn_left();
//   turn_left();
//   turn_left();
//   delay(1000);
//   turn_right();
//   turn_right();
//   turn_right();
//   turn_right();
//   delay(1000);
//   hand_wave(4);
//   delay(1000);
//   hand_shake(4);
//   delay(1000);
//   sit();
//   delay(1000);
}


void servo_attach(void)
{
  for (int i = 0; i < 4; i++)
  {
    for (int j = 0; j < 3; j++)
    {
      servo[i][j].attach(servo_pin[i][j]);
      delay(100);
    }
  }
}

void servo_detach(void)
{
  for (int i = 0; i < 4; i++)
  {
    for (int j = 0; j < 3; j++)
    {
      servo[i][j].detach();
      delay(100);
    }
  }
}

    


/*
  - loop function
   ---------------------------------------------------------------------------*/
void loop()
{
 
  
  if(Serial.available() > 0)
   {
      data = Serial.read();        
      Serial.print(data);          
      Serial.print("\n");   
   
     
      

      if(data == 'F') 
        { 
         Serial.println("Step forward");
         step_forward();
        }
      else if(data == 'B')        
         { 
          Serial.println("Step back");
          step_back();
        }    
      else if(data == 'L')        
         { 
         Serial.println("Turn left");
         turn_left();

        }
      else if(data == 'R')        
        { 
          Serial.println("Turn right");
          turn_right();

        } 
        else if(data == 'X')
        {
         Serial.println("Stand");
         stand();
        }
         else if(data == 'x')
        {
          Serial.println("Sit");
          sit();   
        }
       else if(data == 'S' ||data == 'D' )       
          
        { 

        }
        
         else if(data == 'W')        
        { 
          digitalWrite(14, HIGH);
        } 
          else if(data == 'w')        
        { 
         digitalWrite(14, LOW);
        }
        else if(data == 'V')        
        { 
          Serial.println("Hand wave");
          hand_wave(3);
        } 
          else if(data == 'v')        
        { 
         Serial.println("Hand wave");
         hand_shake(3);
        }
         else if(data == 'U')        
        { 
          Serial.println("Body dance");
          body_dance(10);
        } 
          else if(data == 'u')        
        { 
          Serial.println("Body dance");
          body_dance(10);
        }
        while(Serial.available()) {Serial.read();}
   }
  
    
   
}

/*
  - sit
  - blocking function
   ---------------------------------------------------------------------------*/
/*
  - spot turn to right
  - blocking function
  - parameter step steps wanted to turn
   ---------------------------------------------------------------------------*/
void turn_right()
{
    move_speed = spot_turn_speed;

    if (site_now[2][1] == y_start)
    {
      //leg 2&0 move
      set_site(2, x_default + x_offset, y_start, z_up);
      wait_all_reach();

      set_site(0, turn_x0 - x_offset, turn_y0, z_default);
      set_site(1, turn_x1 - x_offset, turn_y1, z_default);
      set_site(2, turn_x0 + x_offset, turn_y0, z_up);
      set_site(3, turn_x1 + x_offset, turn_y1, z_default);
      wait_all_reach();

      set_site(2, turn_x0 + x_offset, turn_y0, z_default);
      wait_all_reach();

      set_site(0, turn_x0 + x_offset, turn_y0, z_default);
      set_site(1, turn_x1 + x_offset, turn_y1, z_default);
      set_site(2, turn_x0 - x_offset, turn_y0, z_default);
      set_site(3, turn_x1 - x_offset, turn_y1, z_default);
      wait_all_reach();

      set_site(0, turn_x0 + x_offset, turn_y0, z_up);
      wait_all_reach();

      set_site(0, x_default + x_offset, y_start, z_up);
      set_site(1, x_default + x_offset, y_start, z_default);
      set_site(2, x_default - x_offset, y_start + y_step, z_default);
      set_site(3, x_default - x_offset, y_start + y_step, z_default);
      wait_all_reach();

      set_site(0, x_default + x_offset, y_start, z_default);
      wait_all_reach();
    }
    else
    {
      //leg 1&3 move
      set_site(1, x_default + x_offset, y_start, z_up);
      wait_all_reach();

      set_site(0, turn_x1 + x_offset, turn_y1, z_default);
      set_site(1, turn_x0 + x_offset, turn_y0, z_up);
      set_site(2, turn_x1 - x_offset, turn_y1, z_default);
      set_site(3, turn_x0 - x_offset, turn_y0, z_default);
      wait_all_reach();

      set_site(1, turn_x0 + x_offset, turn_y0, z_default);
      wait_all_reach();

      set_site(0, turn_x1 - x_offset, turn_y1, z_default);
      set_site(1, turn_x0 - x_offset, turn_y0, z_default);
      set_site(2, turn_x1 + x_offset, turn_y1, z_default);
      set_site(3, turn_x0 + x_offset, turn_y0, z_default);
      wait_all_reach();

      set_site(3, turn_x0 + x_offset, turn_y0, z_up);
      wait_all_reach();

      set_site(0, x_default - x_offset, y_start + y_step, z_default);
      set_site(1, x_default - x_offset, y_start + y_step, z_default);
      set_site(2, x_default + x_offset, y_start, z_default);
      set_site(3, x_default + x_offset, y_start, z_up);
      wait_all_reach();

      set_site(3, x_default + x_offset, y_start, z_default);
      wait_all_reach();
    }
}

/*
  - go forward
  - blocking function
  - parameter step steps wanted to go
   ---------------------------------------------------------------------------*/
void step_forward()
{
    move_speed = leg_move_speed;

    if (site_now[2][1] == y_start)
    {
      //leg 2&1 move
      set_site(2, x_default + x_offset, y_start, z_up);
      wait_all_reach();
      set_site(2, x_default + x_offset, y_start + 2 * y_step, z_up);
      wait_all_reach();
      set_site(2, x_default + x_offset, y_start + 2 * y_step, z_default);
      wait_all_reach();

      move_speed = body_move_speed;

      set_site(0, x_default + x_offset, y_start, z_default);
      set_site(1, x_default + x_offset, y_start + 2 * y_step, z_default);
      set_site(2, x_default - x_offset, y_start + y_step, z_default);
      set_site(3, x_default - x_offset, y_start + y_step, z_default);
      wait_all_reach();

      move_speed = leg_move_speed;

      set_site(1, x_default + x_offset, y_start + 2 * y_step, z_up);
      wait_all_reach();
      set_site(1, x_default + x_offset, y_start, z_up);
      wait_all_reach();
      set_site(1, x_default + x_offset, y_start, z_default);
      wait_all_reach();
    }
    else
    {
      //leg 0&3 move
      set_site(0, x_default + x_offset, y_start, z_up);
      wait_all_reach();
      set_site(0, x_default + x_offset, y_start + 2 * y_step, z_up);
      wait_all_reach();
      set_site(0, x_default + x_offset, y_start + 2 * y_step, z_default);
      wait_all_reach();

      move_speed = body_move_speed;

      set_site(0, x_default - x_offset, y_start + y_step, z_default);
      set_site(1, x_default - x_offset, y_start + y_step, z_default);
      set_site(2, x_default + x_offset, y_start, z_default);
      set_site(3, x_default + x_offset, y_start + 2 * y_step, z_default);
      wait_all_reach();

      move_speed = leg_move_speed;

      set_site(3, x_default + x_offset, y_start + 2 * y_step, z_up);
      wait_all_reach();
      set_site(3, x_default + x_offset, y_start, z_up);
      wait_all_reach();
      set_site(3, x_default + x_offset, y_start, z_default);
      wait_all_reach();
    }
}

/*
  - go back
  - blocking function
  - parameter step steps wanted to go
   ---------------------------------------------------------------------------*/
void step_back()
{
    move_speed = leg_move_speed;
    if (site_now[3][1] == y_start)
    {
      //leg 3&0 move
      set_site(3, x_default + x_offset, y_start, z_up);
      wait_all_reach();
      set_site(3, x_default + x_offset, y_start + 2 * y_step, z_up);
      wait_all_reach();
      set_site(3, x_default + x_offset, y_start + 2 * y_step, z_default);
      wait_all_reach();

      move_speed = body_move_speed;

      set_site(0, x_default + x_offset, y_start + 2 * y_step, z_default);
      set_site(1, x_default + x_offset, y_start, z_default);
      set_site(2, x_default - x_offset, y_start + y_step, z_default);
      set_site(3, x_default - x_offset, y_start + y_step, z_default);
      wait_all_reach();

      move_speed = leg_move_speed;

      set_site(0, x_default + x_offset, y_start + 2 * y_step, z_up);
      wait_all_reach();
      set_site(0, x_default + x_offset, y_start, z_up);
      wait_all_reach();
      set_site(0, x_default + x_offset, y_start, z_default);
      wait_all_reach();
    }
    else
    {
      //leg 1&2 move
      set_site(1, x_default + x_offset, y_start, z_up);
      wait_all_reach();
      set_site(1, x_default + x_offset, y_start + 2 * y_step, z_up);
      wait_all_reach();
      set_site(1, x_default + x_offset, y_start + 2 * y_step, z_default);
      wait_all_reach();

      move_speed = body_move_speed;

      set_site(0, x_default - x_offset, y_start + y_step, z_default);
      set_site(1, x_default - x_offset, y_start + y_step, z_default);
      set_site(2, x_default + x_offset, y_start + 2 * y_step, z_default);
      set_site(3, x_default + x_offset, y_start, z_default);
      wait_all_reach();

      move_speed = leg_move_speed;

      set_site(2, x_default + x_offset, y_start + 2 * y_step, z_up);
      wait_all_reach();
      set_site(2, x_default + x_offset, y_start, z_up);
      wait_all_reach();
      set_site(2, x_default + x_offset, y_start, z_default);
      wait_all_reach();
    }
}

// add by RegisHsu

void body_left(int i)
{
  set_site(0, site_now[0][0] + i, KEEP, KEEP);
  set_site(1, site_now[1][0] + i, KEEP, KEEP);
  set_site(2, site_now[2][0] - i, KEEP, KEEP);
  set_site(3, site_now[3][0] - i, KEEP, KEEP);
  wait_all_reach();
}

void body_right(int i)
{
  set_site(0, site_now[0][0] - i, KEEP, KEEP);
  set_site(1, site_now[1][0] - i, KEEP, KEEP);
  set_site(2, site_now[2][0] + i, KEEP, KEEP);
  set_site(3, site_now[3][0] + i, KEEP, KEEP);
  wait_all_reach();
}

void hand_wave(int i)
{
  float x_tmp;
  float y_tmp;
  float z_tmp;
  move_speed = 1;
  if (site_now[3][1] == y_start)
  {
    body_right(15);
    x_tmp = site_now[2][0];
    y_tmp = site_now[2][1];
    z_tmp = site_now[2][2];
    move_speed = body_move_speed;
    for (int j = 0; j < i; j++)
    {
      set_site(2, turn_x1, turn_y1, 50);
      wait_all_reach();
      set_site(2, turn_x0, turn_y0, 50);
      wait_all_reach();
    }
    set_site(2, x_tmp, y_tmp, z_tmp);
    wait_all_reach();
    move_speed = 1;
    body_left(15);
  }
  else
  {
    body_left(15);
    x_tmp = site_now[0][0];
    y_tmp = site_now[0][1];
    z_tmp = site_now[0][2];
    move_speed = body_move_speed;
    for (int j = 0; j < i; j++)
    {
      set_site(0, turn_x1, turn_y1, 50);
      wait_all_reach();
      set_site(0, turn_x0, turn_y0, 50);
      wait_all_reach();
    }
    set_site(0, x_tmp, y_tmp, z_tmp);
    wait_all_reach();
    move_speed = 1;
    body_right(15);
  }
}

void hand_shake(int i)
{
  float x_tmp;
  float y_tmp;
  float z_tmp;
  move_speed = 1;
  if (site_now[3][1] == y_start)
  {
    body_right(15);
    x_tmp = site_now[2][0];
    y_tmp = site_now[2][1];
    z_tmp = site_now[2][2];
    move_speed = body_move_speed;
    for (int j = 0; j < i; j++)
    {
      set_site(2, x_default - 30, y_start + 2 * y_step, 55);
      wait_all_reach();
      set_site(2, x_default - 30, y_start + 2 * y_step, 10);
      wait_all_reach();
    }
    set_site(2, x_tmp, y_tmp, z_tmp);
    wait_all_reach();
    move_speed = 1;
    body_left(15);
  }
  else
  {
    body_left(15);
    x_tmp = site_now[0][0];
    y_tmp = site_now[0][1];
    z_tmp = site_now[0][2];
    move_speed = body_move_speed;
    for (int j = 0; j < i; j++)
    {
      set_site(0, x_default - 30, y_start + 2 * y_step, 55);
      wait_all_reach();
      set_site(0, x_default - 30, y_start + 2 * y_step, 10);
      wait_all_reach();
    }
    set_site(0, x_tmp, y_tmp, z_tmp);
    wait_all_reach();
    move_speed = 1;
    body_right(15);
  }
}

void head_up(int i)
{
  set_site(0, KEEP, KEEP, site_now[0][2] - i);
  set_site(1, KEEP, KEEP, site_now[1][2] + i);
  set_site(2, KEEP, KEEP, site_now[2][2] - i);
  set_site(3, KEEP, KEEP, site_now[3][2] + i);
  wait_all_reach();
}

void head_down(int i)
{
  set_site(0, KEEP, KEEP, site_now[0][2] + i);
  set_site(1, KEEP, KEEP, site_now[1][2] - i);
  set_site(2, KEEP, KEEP, site_now[2][2] + i);
  set_site(3, KEEP, KEEP, site_now[3][2] - i);
  wait_all_reach();
}

void body_dance(int i)
{
  float x_tmp;
  float y_tmp;
  float z_tmp;
  float body_dance_speed = 2;
  sit();
  move_speed = 1;
  set_site(0, x_default, y_default, KEEP);
  set_site(1, x_default, y_default, KEEP);
  set_site(2, x_default, y_default, KEEP);
  set_site(3, x_default, y_default, KEEP);
  wait_all_reach();
  //stand();
  set_site(0, x_default, y_default, z_default - 20);
  set_site(1, x_default, y_default, z_default - 20);
  set_site(2, x_default, y_default, z_default - 20);
  set_site(3, x_default, y_default, z_default - 20);
  wait_all_reach();
  move_speed = body_dance_speed;
  head_up(30);
  for (int j = 0; j < i; j++)
  {
    if (j > i / 4)
      move_speed = body_dance_speed * 2;
    if (j > i / 2)
      move_speed = body_dance_speed * 3;
    set_site(0, KEEP, y_default - 20, KEEP);
    set_site(1, KEEP, y_default + 20, KEEP);
    set_site(2, KEEP, y_default - 20, KEEP);
    set_site(3, KEEP, y_default + 20, KEEP);
    wait_all_reach();
    set_site(0, KEEP, y_default + 20, KEEP);
    set_site(1, KEEP, y_default - 20, KEEP);
    set_site(2, KEEP, y_default + 20, KEEP);
    set_site(3, KEEP, y_default - 20, KEEP);
    wait_all_reach();
  }
  move_speed = body_dance_speed;
  head_down(30);
}


/*
  - microservos service /timer interrupt function/50Hz
  - when set site expected,this function move the end point to it in a straight line
  - temp_speed[4][3] should be set before set expect site,it make sure the end point
   move in a straight line,and decide move speed.
   ---------------------------------------------------------------------------*/
void servo_service(void)
{
  sei();
  static float alpha, beta, gamma;

  for (int i = 0; i < 4; i++)
  {
    for (int j = 0; j < 3; j++)
    {
      if (abs(site_now[i][j] - site_expect[i][j]) >= abs(temp_speed[i][j]))
        site_now[i][j] += temp_speed[i][j];
      else
        site_now[i][j] = site_expect[i][j];
    }

    cartesian_to_polar(alpha, beta, gamma, site_now[i][0], site_now[i][1], site_now[i][2]);
    polar_to_servo(i, alpha, beta, gamma);
  }

  rest_counter++;
}

/*
  - set one of end points' expect site
  - this founction will set temp_speed[4][3] at same time
  - non - blocking function
   ---------------------------------------------------------------------------*/
void set_site(int leg, float x, float y, float z)
{
  float length_x = 0, length_y = 0, length_z = 0;

  if (x != KEEP)
    length_x = x - site_now[leg][0];
  if (y != KEEP)
    length_y = y - site_now[leg][1];
  if (z != KEEP)
    length_z = z - site_now[leg][2];

  float length = sqrt(pow(length_x, 2) + pow(length_y, 2) + pow(length_z, 2));

  temp_speed[leg][0] = length_x / length * move_speed * speed_multiple;
  temp_speed[leg][1] = length_y / length * move_speed * speed_multiple;
  temp_speed[leg][2] = length_z / length * move_speed * speed_multiple;

  if (x != KEEP)
    site_expect[leg][0] = x;
  if (y != KEEP)
    site_expect[leg][1] = y;
  if (z != KEEP)
    site_expect[leg][2] = z;
}

/*
  - wait one of end points move to expect site
  - blocking function
   ---------------------------------------------------------------------------*/
void wait_reach(int leg)
{
  while (1)
    if (site_now[leg][0] == site_expect[leg][0])
      if (site_now[leg][1] == site_expect[leg][1])
        if (site_now[leg][2] == site_expect[leg][2])
          break;
}

/*
  - wait all of end points move to expect site
  - blocking function
   ---------------------------------------------------------------------------*/
void wait_all_reach(void)
{
  for (int i = 0; i < 4; i++)
    wait_reach(i);
}

/*
  - trans site from cartesian to polar
  - mathematical model 2/2
   ---------------------------------------------------------------------------*/
void cartesian_to_polar(volatile float &alpha, volatile float &beta, volatile float &gamma, volatile float x, volatile float y, volatile float z)
{
  //calculate w-z degree
  float v, w;
  w = (x >= 0 ? 1 : -1) * (sqrt(pow(x, 2) + pow(y, 2)));
  v = w - length_c;
  alpha = atan2(z, v) + acos((pow(length_a, 2) - pow(length_b, 2) + pow(v, 2) + pow(z, 2)) / 2 / length_a / sqrt(pow(v, 2) + pow(z, 2)));
  beta = acos((pow(length_a, 2) + pow(length_b, 2) - pow(v, 2) - pow(z, 2)) / 2 / length_a / length_b);
  //calculate x-y-z degree
  gamma = (w >= 0) ? atan2(y, x) : atan2(-y, -x);
  //trans degree pi->180
  alpha = alpha / pi * 180;
  beta = beta / pi * 180;
  gamma = gamma / pi * 180;
}

/*
  - trans site from polar to microservos
  - mathematical model map to fact
  - the errors saved in eeprom will be add
   ---------------------------------------------------------------------------*/
void polar_to_servo(int leg, float alpha, float beta, float gamma)
{
  if (leg == 0)
  {
    alpha = 90 - alpha;
    beta = beta;
    gamma += 90;
  }
  else if (leg == 1)
  {
    alpha += 90;
    beta = 180 - beta;
    gamma = 90 - gamma;
  }
  else if (leg == 2)
  {
    alpha += 90;
    beta = 180 - beta;
    gamma = 90 - gamma;
  }
  else if (leg == 3)
  {
    alpha = 90 - alpha;
    beta = beta;
    gamma += 90;
  }

  servo[leg][0].write(alpha);
  servo[leg][1].write(beta);
  servo[leg][2].write(gamma);
}

NOTE--i am deleting some functions like void sit void stand as the maximum limit of characters was reached.

this is my esp32 code

#include "Arduino.h"
#include "WiFi.h"
#include "Audio.h"

#define I2S_DOUT      25
#define I2S_BCLK      27
#define I2S_LRC       26



Audio audio;

char data = 0;
void setup()
{

  Serial.begin(115200);

  WiFi.disconnect();
  WiFi.mode(WIFI_STA);
  WiFi.begin( "Physics", "299792458");

  while (WiFi.status() != WL_CONNECTED)
    delay(1500);

  audio.setPinout(I2S_BCLK, I2S_LRC, I2S_DOUT);
  audio.setVolume(100);
  audio.connecttospeech("Hello From akshit singh,,welcome to tapovan international school's project day ,,i am a smart walking robot ,you can also call me astra bot ", "en");
 
}


void loop(){
if(Serial.available() > 0)      
   {
      data = Serial.read();        
      Serial.print(data);             
      if(data == 'A') 
        { 
         audio.connecttospeech("hello everyone ,welcome to tapovan international school's project day ", "en");
         Serial.println("done");
        }
        
      else if(data == 'B')        
        { 
         audio.connecttospeech("BYE Bye everyone", "hi");
         Serial.println("done 2"); 
        }  
      else if(data == 'C')        
        { 
         audio.connecttospeech("i am a smart walking robot ,you can also call me astra bot ", "hi");
         Serial.println("done 2"); 
        }  

      else if(data == 'F')        
        { 
         audio.connecttospeech("going forward ,sir", "hi");
         Serial.println("done 2"); 
        }  

      else if(data == 'b')        
        { 
         audio.connecttospeech("going backward ,sir", "hi");
         Serial.println("done 2"); 

        }  
      else if(data == 'L')        
        { 
         audio.connecttospeech("moving left, sir", "hi");
         Serial.println("done 2"); 

        }  
      else if(data == 'R')        
        { 
         audio.connecttospeech("moving right ,sir", "hi");
         Serial.println("done 2"); 

        }  
      

   }

{
  audio.loop();
}

  }

void audio_info(const char *info) {
  Serial.print("audio_info: "); Serial.println(info);
}

I made a spider robot using arduino and from esp. I made an audio output device which is linked to python program which writes a particular data (when we speak a command) to esp board and accordingly the voice would be activated. Now I want to link them together.

If the esp32 sends a particular data the function in arduino is executed. Therefore I want to connect esp32 to arduino uno though Serial monitor and send data from esp 32 to arduino. I have only analog pins vacant as all digital pins are used for the servos. how can I achieve this?.

In the main arduino file there are 2 more flexitimer and flexitimer2.cpp files but there is no need of editing them and hence I am giving the code of main file.

    #include <Servo.h>    //to define and control servos
    #include "FlexiTimer2.h"//to set a timer to manage all servos
    /* Servos --------------------------------------------------------------------*/
    //define 12 servos for 4 legs
    char data = 0;
    Servo servo[4][3];
    //define servos' ports
    const int servo_pin[4][3] = { {2, 3, 4}, {5, 6, 7}, {8, 9, 10}, {11, 12, 13} };
    /* Size of the robot ---------------------------------------------------------*/
    const float length_a = 55;
    const float length_b = 77.5;
    const float length_c = 27.5;
    const float length_side = 71;
    const float z_absolute = -28;
    /* Constants for movement ----------------------------------------------------*/
    const float z_default = -50, z_up = -30, z_boot = z_absolute;
    const float x_default = 62, x_offset = 0;
    const float y_start = 0, y_step = 40;
    const float y_default = x_default;
    /* variables for movement ----------------------------------------------------*/
    volatile float site_now[4][3];    //real-time coordinates of the end of each leg
    volatile float site_expect[4][3]; //expected coordinates of the end of each leg
    float temp_speed[4][3];   //each axis' speed, needs to be recalculated before each movement
    float move_speed;     //movement speed
    float speed_multiple = 1; //movement speed multiple
    const float spot_turn_speed = 4;
    const float leg_move_speed = 8;
    const float body_move_speed = 3;
    const float stand_seat_speed = 1;
    volatile int rest_counter;      //+1/0.02s, for automatic rest
    //functions' parameter
    const float KEEP = 255;
    //define PI for calculation
    const float pi = 3.1415926;
    /* Constants for turn --------------------------------------------------------*/
    //temp length
    const float temp_a = sqrt(pow(2 * x_default + length_side, 2) + pow(y_step, 2));
    const float temp_b = 2 * (y_start + y_step) + length_side;
    const float temp_c = sqrt(pow(2 * x_default + length_side, 2) + pow(2 * y_start + y_step + length_side, 2));
    const float temp_alpha = acos((pow(temp_a, 2) + pow(temp_b, 2) - pow(temp_c, 2)) / 2 / temp_a / temp_b);
    //site for turn
    const float turn_x1 = (temp_a - length_side) / 2;
    const float turn_y1 = y_start + y_step / 2;
    const float turn_x0 = turn_x1 - temp_b * cos(temp_alpha);
    const float turn_y0 = temp_b * sin(temp_alpha) - turn_y1 - length_side;
    /* ---------------------------------------------------------------------------*/
    
      - setup function
       ---------------------------------------------------------------------------*/
    void setup()
    {
      //start serial for debug
      Serial.begin(9600);
      Serial.println("Robot starts initialization");
      
      //initialize default parameter
      pinMode(14, OUTPUT);
      set_site(0, x_default - x_offset, y_start + y_step, z_boot);
      set_site(1, x_default - x_offset, y_start + y_step, z_boot);
      set_site(2, x_default + x_offset, y_start, z_boot);
      set_site(3, x_default + x_offset, y_start, z_boot);
      for (int i = 0; i < 4; i++)
      {
        for (int j = 0; j < 3; j++)
        {
          site_now[i][j] = site_expect[i][j];
        }
      }
      //start servo service
      FlexiTimer2::set(20, servo_service);
      FlexiTimer2::start();
      Serial.println("Servo service started");
      //initialize servos
      servo_attach();
      Serial.println("Servos initialized");
      Serial.println("Robot initialization Complete");
    //   stand();
    //   delay(1000);
    //   hand_shake(2);
    //   Serial.println("hihihihihi");
    //   delay(1000);
    //   step_forward();
    //   step_forward();
    //   step_forward();
    //   step_forward();
    //   step_forward();
    //   step_forward();
    //   delay(1000);
    //   step_back();
    //   step_back();
    //   step_back();
    //   step_back();
    //   step_back();
    //   step_back();
    //   delay(1000);
         
    //   turn_left();
    //   turn_left();
    //   turn_left();
    //   turn_left();
    //   delay(1000);
    //   turn_right();
    //   turn_right();
    //   turn_right();
    //   turn_right();
    //   delay(1000);
    //   hand_wave(4);
    //   delay(1000);
    //   hand_shake(4);
    //   delay(1000);
    //   sit();
    //   delay(1000);
    }
    
    
    void servo_attach(void)
    {
      for (int i = 0; i < 4; i++)
      {
        for (int j = 0; j < 3; j++)
        {
          servo[i][j].attach(servo_pin[i][j]);
          delay(100);
        }
      }
    }
    
    void servo_detach(void)
    {
      for (int i = 0; i < 4; i++)
      {
        for (int j = 0; j < 3; j++)
        {
          servo[i][j].detach();
          delay(100);
        }
      }
    }
    
        
    
    
    /*
      - loop function
       ---------------------------------------------------------------------------*/
    void loop()
    {
     
      
      if(Serial.available() > 0)
       {
          data = Serial.read();        
          Serial.print(data);          
          Serial.print("\n");   
       
         
          
    
          if(data == 'F') 
            { 
             Serial.println("Step forward");
             step_forward();
            }
          else if(data == 'B')        
             { 
              Serial.println("Step back");
              step_back();
            }    
          else if(data == 'L')        
             { 
             Serial.println("Turn left");
             turn_left();
    
            }
          else if(data == 'R')        
            { 
              Serial.println("Turn right");
              turn_right();
    
            } 
            else if(data == 'X')
            {
             Serial.println("Stand");
             stand();
            }
             else if(data == 'x')
            {
              Serial.println("Sit");
              sit();   
            }
           else if(data == 'S' ||data == 'D' )       
              
            { 
    
            }
            
             else if(data == 'W')        
            { 
              digitalWrite(14, HIGH);
            } 
              else if(data == 'w')        
            { 
             digitalWrite(14, LOW);
            }
            else if(data == 'V')        
            { 
              Serial.println("Hand wave");
              hand_wave(3);
            } 
              else if(data == 'v')        
            { 
             Serial.println("Hand wave");
             hand_shake(3);
            }
             else if(data == 'U')        
            { 
              Serial.println("Body dance");
              body_dance(10);
            } 
              else if(data == 'u')        
            { 
              Serial.println("Body dance");
              body_dance(10);
            }
            while(Serial.available()) {Serial.read();}
       }
      
        
       
    }
    
    /*
      - sit
      - blocking function
       ---------------------------------------------------------------------------*/
    /*
      - spot turn to right
      - blocking function
      - parameter step steps wanted to turn
       ---------------------------------------------------------------------------*/
    void turn_right()
    {
        move_speed = spot_turn_speed;
    
        if (site_now[2][1] == y_start)
        {
          //leg 2&0 move
          set_site(2, x_default + x_offset, y_start, z_up);
          wait_all_reach();
    
          set_site(0, turn_x0 - x_offset, turn_y0, z_default);
          set_site(1, turn_x1 - x_offset, turn_y1, z_default);
          set_site(2, turn_x0 + x_offset, turn_y0, z_up);
          set_site(3, turn_x1 + x_offset, turn_y1, z_default);
          wait_all_reach();
    
          set_site(2, turn_x0 + x_offset, turn_y0, z_default);
          wait_all_reach();
    
          set_site(0, turn_x0 + x_offset, turn_y0, z_default);
          set_site(1, turn_x1 + x_offset, turn_y1, z_default);
          set_site(2, turn_x0 - x_offset, turn_y0, z_default);
          set_site(3, turn_x1 - x_offset, turn_y1, z_default);
          wait_all_reach();
    
          set_site(0, turn_x0 + x_offset, turn_y0, z_up);
          wait_all_reach();
    
          set_site(0, x_default + x_offset, y_start, z_up);
          set_site(1, x_default + x_offset, y_start, z_default);
          set_site(2, x_default - x_offset, y_start + y_step, z_default);
          set_site(3, x_default - x_offset, y_start + y_step, z_default);
          wait_all_reach();
    
          set_site(0, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
        else
        {
          //leg 1&3 move
          set_site(1, x_default + x_offset, y_start, z_up);
          wait_all_reach();
    
          set_site(0, turn_x1 + x_offset, turn_y1, z_default);
          set_site(1, turn_x0 + x_offset, turn_y0, z_up);
          set_site(2, turn_x1 - x_offset, turn_y1, z_default);
          set_site(3, turn_x0 - x_offset, turn_y0, z_default);
          wait_all_reach();
    
          set_site(1, turn_x0 + x_offset, turn_y0, z_default);
          wait_all_reach();
    
          set_site(0, turn_x1 - x_offset, turn_y1, z_default);
          set_site(1, turn_x0 - x_offset, turn_y0, z_default);
          set_site(2, turn_x1 + x_offset, turn_y1, z_default);
          set_site(3, turn_x0 + x_offset, turn_y0, z_default);
          wait_all_reach();
    
          set_site(3, turn_x0 + x_offset, turn_y0, z_up);
          wait_all_reach();
    
          set_site(0, x_default - x_offset, y_start + y_step, z_default);
          set_site(1, x_default - x_offset, y_start + y_step, z_default);
          set_site(2, x_default + x_offset, y_start, z_default);
          set_site(3, x_default + x_offset, y_start, z_up);
          wait_all_reach();
    
          set_site(3, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
    }
    
    /*
      - go forward
      - blocking function
      - parameter step steps wanted to go
       ---------------------------------------------------------------------------*/
    void step_forward()
    {
        move_speed = leg_move_speed;
    
        if (site_now[2][1] == y_start)
        {
          //leg 2&1 move
          set_site(2, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(2, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(2, x_default + x_offset, y_start + 2 * y_step, z_default);
          wait_all_reach();
    
          move_speed = body_move_speed;
    
          set_site(0, x_default + x_offset, y_start, z_default);
          set_site(1, x_default + x_offset, y_start + 2 * y_step, z_default);
          set_site(2, x_default - x_offset, y_start + y_step, z_default);
          set_site(3, x_default - x_offset, y_start + y_step, z_default);
          wait_all_reach();
    
          move_speed = leg_move_speed;
    
          set_site(1, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(1, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(1, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
        else
        {
          //leg 0&3 move
          set_site(0, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(0, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(0, x_default + x_offset, y_start + 2 * y_step, z_default);
          wait_all_reach();
    
          move_speed = body_move_speed;
    
          set_site(0, x_default - x_offset, y_start + y_step, z_default);
          set_site(1, x_default - x_offset, y_start + y_step, z_default);
          set_site(2, x_default + x_offset, y_start, z_default);
          set_site(3, x_default + x_offset, y_start + 2 * y_step, z_default);
          wait_all_reach();
    
          move_speed = leg_move_speed;
    
          set_site(3, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(3, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(3, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
    }
    
    /*
      - go back
      - blocking function
      - parameter step steps wanted to go
       ---------------------------------------------------------------------------*/
    void step_back()
    {
        move_speed = leg_move_speed;
        if (site_now[3][1] == y_start)
        {
          //leg 3&0 move
          set_site(3, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(3, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(3, x_default + x_offset, y_start + 2 * y_step, z_default);
          wait_all_reach();
    
          move_speed = body_move_speed;
    
          set_site(0, x_default + x_offset, y_start + 2 * y_step, z_default);
          set_site(1, x_default + x_offset, y_start, z_default);
          set_site(2, x_default - x_offset, y_start + y_step, z_default);
          set_site(3, x_default - x_offset, y_start + y_step, z_default);
          wait_all_reach();
    
          move_speed = leg_move_speed;
    
          set_site(0, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(0, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(0, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
        else
        {
          //leg 1&2 move
          set_site(1, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(1, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(1, x_default + x_offset, y_start + 2 * y_step, z_default);
          wait_all_reach();
    
          move_speed = body_move_speed;
    
          set_site(0, x_default - x_offset, y_start + y_step, z_default);
          set_site(1, x_default - x_offset, y_start + y_step, z_default);
          set_site(2, x_default + x_offset, y_start + 2 * y_step, z_default);
          set_site(3, x_default + x_offset, y_start, z_default);
          wait_all_reach();
    
          move_speed = leg_move_speed;
    
          set_site(2, x_default + x_offset, y_start + 2 * y_step, z_up);
          wait_all_reach();
          set_site(2, x_default + x_offset, y_start, z_up);
          wait_all_reach();
          set_site(2, x_default + x_offset, y_start, z_default);
          wait_all_reach();
        }
    }
    
    // add by RegisHsu
    
    void body_left(int i)
    {
      set_site(0, site_now[0][0] + i, KEEP, KEEP);
      set_site(1, site_now[1][0] + i, KEEP, KEEP);
      set_site(2, site_now[2][0] - i, KEEP, KEEP);
      set_site(3, site_now[3][0] - i, KEEP, KEEP);
      wait_all_reach();
    }
    
    void body_right(int i)
    {
      set_site(0, site_now[0][0] - i, KEEP, KEEP);
      set_site(1, site_now[1][0] - i, KEEP, KEEP);
      set_site(2, site_now[2][0] + i, KEEP, KEEP);
      set_site(3, site_now[3][0] + i, KEEP, KEEP);
      wait_all_reach();
    }
    
    void hand_wave(int i)
    {
      float x_tmp;
      float y_tmp;
      float z_tmp;
      move_speed = 1;
      if (site_now[3][1] == y_start)
      {
        body_right(15);
        x_tmp = site_now[2][0];
        y_tmp = site_now[2][1];
        z_tmp = site_now[2][2];
        move_speed = body_move_speed;
        for (int j = 0; j < i; j++)
        {
          set_site(2, turn_x1, turn_y1, 50);
          wait_all_reach();
          set_site(2, turn_x0, turn_y0, 50);
          wait_all_reach();
        }
        set_site(2, x_tmp, y_tmp, z_tmp);
        wait_all_reach();
        move_speed = 1;
        body_left(15);
      }
      else
      {
        body_left(15);
        x_tmp = site_now[0][0];
        y_tmp = site_now[0][1];
        z_tmp = site_now[0][2];
        move_speed = body_move_speed;
        for (int j = 0; j < i; j++)
        {
          set_site(0, turn_x1, turn_y1, 50);
          wait_all_reach();
          set_site(0, turn_x0, turn_y0, 50);
          wait_all_reach();
        }
        set_site(0, x_tmp, y_tmp, z_tmp);
        wait_all_reach();
        move_speed = 1;
        body_right(15);
      }
    }
    
    void hand_shake(int i)
    {
      float x_tmp;
      float y_tmp;
      float z_tmp;
      move_speed = 1;
      if (site_now[3][1] == y_start)
      {
        body_right(15);
        x_tmp = site_now[2][0];
        y_tmp = site_now[2][1];
        z_tmp = site_now[2][2];
        move_speed = body_move_speed;
        for (int j = 0; j < i; j++)
        {
          set_site(2, x_default - 30, y_start + 2 * y_step, 55);
          wait_all_reach();
          set_site(2, x_default - 30, y_start + 2 * y_step, 10);
          wait_all_reach();
        }
        set_site(2, x_tmp, y_tmp, z_tmp);
        wait_all_reach();
        move_speed = 1;
        body_left(15);
      }
      else
      {
        body_left(15);
        x_tmp = site_now[0][0];
        y_tmp = site_now[0][1];
        z_tmp = site_now[0][2];
        move_speed = body_move_speed;
        for (int j = 0; j < i; j++)
        {
          set_site(0, x_default - 30, y_start + 2 * y_step, 55);
          wait_all_reach();
          set_site(0, x_default - 30, y_start + 2 * y_step, 10);
          wait_all_reach();
        }
        set_site(0, x_tmp, y_tmp, z_tmp);
        wait_all_reach();
        move_speed = 1;
        body_right(15);
      }
    }
    
    void head_up(int i)
    {
      set_site(0, KEEP, KEEP, site_now[0][2] - i);
      set_site(1, KEEP, KEEP, site_now[1][2] + i);
      set_site(2, KEEP, KEEP, site_now[2][2] - i);
      set_site(3, KEEP, KEEP, site_now[3][2] + i);
      wait_all_reach();
    }
    
    void head_down(int i)
    {
      set_site(0, KEEP, KEEP, site_now[0][2] + i);
      set_site(1, KEEP, KEEP, site_now[1][2] - i);
      set_site(2, KEEP, KEEP, site_now[2][2] + i);
      set_site(3, KEEP, KEEP, site_now[3][2] - i);
      wait_all_reach();
    }
    
    void body_dance(int i)
    {
      float x_tmp;
      float y_tmp;
      float z_tmp;
      float body_dance_speed = 2;
      sit();
      move_speed = 1;
      set_site(0, x_default, y_default, KEEP);
      set_site(1, x_default, y_default, KEEP);
      set_site(2, x_default, y_default, KEEP);
      set_site(3, x_default, y_default, KEEP);
      wait_all_reach();
      //stand();
      set_site(0, x_default, y_default, z_default - 20);
      set_site(1, x_default, y_default, z_default - 20);
      set_site(2, x_default, y_default, z_default - 20);
      set_site(3, x_default, y_default, z_default - 20);
      wait_all_reach();
      move_speed = body_dance_speed;
      head_up(30);
      for (int j = 0; j < i; j++)
      {
        if (j > i / 4)
          move_speed = body_dance_speed * 2;
        if (j > i / 2)
          move_speed = body_dance_speed * 3;
        set_site(0, KEEP, y_default - 20, KEEP);
        set_site(1, KEEP, y_default + 20, KEEP);
        set_site(2, KEEP, y_default - 20, KEEP);
        set_site(3, KEEP, y_default + 20, KEEP);
        wait_all_reach();
        set_site(0, KEEP, y_default + 20, KEEP);
        set_site(1, KEEP, y_default - 20, KEEP);
        set_site(2, KEEP, y_default + 20, KEEP);
        set_site(3, KEEP, y_default - 20, KEEP);
        wait_all_reach();
      }
      move_speed = body_dance_speed;
      head_down(30);
    }
    
    
    /*
      - microservos service /timer interrupt function/50Hz
      - when set site expected,this function move the end point to it in a straight line
      - temp_speed[4][3] should be set before set expect site,it make sure the end point
       move in a straight line,and decide move speed.
       ---------------------------------------------------------------------------*/
    void servo_service(void)
    {
      sei();
      static float alpha, beta, gamma;
    
      for (int i = 0; i < 4; i++)
      {
        for (int j = 0; j < 3; j++)
        {
          if (abs(site_now[i][j] - site_expect[i][j]) >= abs(temp_speed[i][j]))
            site_now[i][j] += temp_speed[i][j];
          else
            site_now[i][j] = site_expect[i][j];
        }
    
        cartesian_to_polar(alpha, beta, gamma, site_now[i][0], site_now[i][1], site_now[i][2]);
        polar_to_servo(i, alpha, beta, gamma);
      }
    
      rest_counter++;
    }
    
    /*
      - set one of end points' expect site
      - this founction will set temp_speed[4][3] at same time
      - non - blocking function
       ---------------------------------------------------------------------------*/
    void set_site(int leg, float x, float y, float z)
    {
      float length_x = 0, length_y = 0, length_z = 0;
    
      if (x != KEEP)
        length_x = x - site_now[leg][0];
      if (y != KEEP)
        length_y = y - site_now[leg][1];
      if (z != KEEP)
        length_z = z - site_now[leg][2];
    
      float length = sqrt(pow(length_x, 2) + pow(length_y, 2) + pow(length_z, 2));
    
      temp_speed[leg][0] = length_x / length * move_speed * speed_multiple;
      temp_speed[leg][1] = length_y / length * move_speed * speed_multiple;
      temp_speed[leg][2] = length_z / length * move_speed * speed_multiple;
    
      if (x != KEEP)
        site_expect[leg][0] = x;
      if (y != KEEP)
        site_expect[leg][1] = y;
      if (z != KEEP)
        site_expect[leg][2] = z;
    }
    
    /*
      - wait one of end points move to expect site
      - blocking function
       ---------------------------------------------------------------------------*/
    void wait_reach(int leg)
    {
      while (1)
        if (site_now[leg][0] == site_expect[leg][0])
          if (site_now[leg][1] == site_expect[leg][1])
            if (site_now[leg][2] == site_expect[leg][2])
              break;
    }
    
    /*
      - wait all of end points move to expect site
      - blocking function
       ---------------------------------------------------------------------------*/
    void wait_all_reach(void)
    {
      for (int i = 0; i < 4; i++)
        wait_reach(i);
    }
    
    /*
      - trans site from cartesian to polar
      - mathematical model 2/2
       ---------------------------------------------------------------------------*/
    void cartesian_to_polar(volatile float &alpha, volatile float &beta, volatile float &gamma, volatile float x, volatile float y, volatile float z)
    {
      //calculate w-z degree
      float v, w;
      w = (x >= 0 ? 1 : -1) * (sqrt(pow(x, 2) + pow(y, 2)));
      v = w - length_c;
      alpha = atan2(z, v) + acos((pow(length_a, 2) - pow(length_b, 2) + pow(v, 2) + pow(z, 2)) / 2 / length_a / sqrt(pow(v, 2) + pow(z, 2)));
      beta = acos((pow(length_a, 2) + pow(length_b, 2) - pow(v, 2) - pow(z, 2)) / 2 / length_a / length_b);
      //calculate x-y-z degree
      gamma = (w >= 0) ? atan2(y, x) : atan2(-y, -x);
      //trans degree pi->180
      alpha = alpha / pi * 180;
      beta = beta / pi * 180;
      gamma = gamma / pi * 180;
    }
    
    /*
      - trans site from polar to microservos
      - mathematical model map to fact
      - the errors saved in eeprom will be add
       ---------------------------------------------------------------------------*/
    void polar_to_servo(int leg, float alpha, float beta, float gamma)
    {
      if (leg == 0)
      {
        alpha = 90 - alpha;
        beta = beta;
        gamma += 90;
      }
      else if (leg == 1)
      {
        alpha += 90;
        beta = 180 - beta;
        gamma = 90 - gamma;
      }
      else if (leg == 2)
      {
        alpha += 90;
        beta = 180 - beta;
        gamma = 90 - gamma;
      }
      else if (leg == 3)
      {
        alpha = 90 - alpha;
        beta = beta;
        gamma += 90;
      }
    
      servo[leg][0].write(alpha);
      servo[leg][1].write(beta);
      servo[leg][2].write(gamma);
    }



NOTE--i am deleting some functions like void sit void stand as the maximum limit of characters was reached.


this is my esp32 code

    #include "Arduino.h"
    #include "WiFi.h"
    #include "Audio.h"
    
    #define I2S_DOUT      25
    #define I2S_BCLK      27
    #define I2S_LRC       26
    
    
    
    Audio audio;
    
    char data = 0;
    void setup()
    {
    
      Serial.begin(115200);
    
      WiFi.disconnect();
      WiFi.mode(WIFI_STA);
      WiFi.begin( "Physics", "299792458");
    
      while (WiFi.status() != WL_CONNECTED)
        delay(1500);
    
      audio.setPinout(I2S_BCLK, I2S_LRC, I2S_DOUT);
      audio.setVolume(100);
      audio.connecttospeech("Hello From akshit singh,,welcome to tapovan international school's project day ,,i am a smart walking robot ,you can also call me astra bot ", "en");
     
    }
    
    
    void loop(){
    if(Serial.available() > 0)      
       {
          data = Serial.read();        
          Serial.print(data);             
          if(data == 'A') 
            { 
             audio.connecttospeech("hello everyone ,welcome to tapovan international school's project day ", "en");
             Serial.println("done");
            }
            
          else if(data == 'B')        
            { 
             audio.connecttospeech("BYE Bye everyone", "hi");
             Serial.println("done 2"); 
            }  
          else if(data == 'C')        
            { 
             audio.connecttospeech("i am a smart walking robot ,you can also call me astra bot ", "hi");
             Serial.println("done 2"); 
            }  
    
          else if(data == 'F')        
            { 
             audio.connecttospeech("going forward ,sir", "hi");
             Serial.println("done 2"); 
            }  
    
          else if(data == 'b')        
            { 
             audio.connecttospeech("going backward ,sir", "hi");
             Serial.println("done 2"); 
    
            }  
          else if(data == 'L')        
            { 
             audio.connecttospeech("moving left, sir", "hi");
             Serial.println("done 2"); 
    
            }  
          else if(data == 'R')        
            { 
             audio.connecttospeech("moving right ,sir", "hi");
             Serial.println("done 2"); 
    
            }  
          
    
       }
    
    {
      audio.loop();
    }
    
      }
    
    void audio_info(const char *info) {
      Serial.print("audio_info: "); Serial.println(info);
    }