Build a Smart Arduino Quadruped Robot: Step‑by‑Step Guide

Components and supplies

Arduino Mega 2560

SG90 Micro-servo motor

SparkFun Ultrasonic Sensor - HC-SR04

5 mm LED: Red

5 mm LED: Green

LED, Blue

Male Header 40 Position 1 Row (0.1")

Custom PCB

Necessary tools and machines

Soldering iron (generic)

Apps and online services

Arduino IDE

About this project

Arduino-based quadruped! Quadruped stands for four-legged bot, which is basically look like a four-legged spider, so let's learn how the spider walks and try to replicate it with Arduino.

Supplies:

Step 1: Components Required

1 X Arduino Mega or Arduino Uno
1 X Drilled PCB
12 X Servo Motors(9g)
1 X HC-SR04 Ultrasonic Sensor
4 X RGB LED
Cardboard

Step 2: Maintaining CG

center of gravity (CG) is main factor while walking.Center of gravity remains in center of the body to stand balance if CG moves out of center on certain limits then balance will be affected and leads to falling down

So let us see about maintaining CG while walking.

If every leg is in 45 degree then the CG will be perfectly main in center, But if we moved any leg the cg will shift to that side so it lead to falling on that side.

So to avoid this the either end legs are maintained at an angle greater than 45 degree based on the bot size, so the three legs will form a triangle, were the CG will be inside it and the fourth leg will be free to move and CG will remain inside a triangle.

Step 3: Walking Procedure

This is the starting position, with two legs(C, D) extended out on one side, and the other two legs(A, B) pulled inward.
The top-right leg(B) lifts up and reaches out, far ahead of the robot.
All the legs shift backward, moving the body forward.
The back-left leg(D) lifts and steps forward alongside the body. This position is the mirror image of the starting position.
The top-left leg(B) lifts and reaches out, far ahead of the robot.
Again, all the legs shift backward, moving the body forward.
The back-right leg lifts(B) and steps back into the body, bringing us back to the starting position.

Step 4: Plans for Quadruped

LEGS.pdfBODY.pdf

Step 5: Construction of Body

Construct the body according to PDF.

Step 6: Circuit Connection

Make your own shield according to your requirement arduino mega has 15 pwm pin, use 12 of them for servo connections and 3 for RBG led and any two pins for ultrasonic sensor

Step 7: Intialization of Servo

Upload the program to arduino mega and start assembling the leg according to picture

#include <Servo.h>   
Servo servo[4][3];
//define servos' ports
const int servo_pin[4][3] = { {10,11,2}, {3,4,5}, {6,7,8}, {9, 12, 13} };
void setup()
{
 //initialize all servos
 for (int i = 0; i < 4; i++)
 {
   for (int j = 0; j < 3; j++)
   {
     servo[i][j].attach(servo_pin[i][j]);
     delay(20);
   }
 }
}
void loop(void)
{
 for (int i = 0; i < 4; i++)
 {
   for (int j = 0; j < 3; j++)
   {
     servo[i][j].write(90);
     delay(20);
   }
 }
}

Step 8: Final Step

 /* Includes ------------------------------------------------------------------*/
#include <Servo.h>    //to define and control servos
#include <FlexiTimer2.h>//to set a timer to manage all servos
#define ledred 46
#define ledblue 44
#define ledgreen 45
/* Servos --------------------------------------------------------------------*/
//define 12 servos for 4 legs
Servo servo[4][3];
//define servos' ports
const int servo_pin[4][3] = { {2, 3, 4}, {20, 6, 7}, {8, 9, 17}, {16, 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()
{
  pinMode(ledred,OUTPUT);
pinMode(ledblue,OUTPUT);
pinMode(ledgreen,OUTPUT);
 //start serial for debug
 Serial.begin(115200);
 Serial.println("Robot starts initialization");
 //initialize default parameter
 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");
}
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()
{
 analogWrite(ledred,255);
 Serial.println("Stand");
 stand();
  delay(2000);
 analogWrite(ledred,0);
 analogWrite(ledblue,255);
 Serial.println("Step forward");
 step_forward(5);
 delay(2000);
 analogWrite(ledblue,0);
 analogWrite(ledgreen,255);
 Serial.println("Step back");
 step_back(5);
 delay(2000);
 analogWrite(ledgreen,0);
 analogWrite(ledred,255);
 analogWrite(ledblue,255);
  Serial.println("Turn left");
 turn_left(5);
 delay(2000);
 analogWrite(ledgreen,255);
 analogWrite(ledred,0);
 analogWrite(ledblue,255);
 Serial.println("Turn right");
 turn_right(5);
 delay(2000);
  analogWrite(ledgreen,255);
 analogWrite(ledred,255);
 analogWrite(ledblue,0);
 Serial.println("Hand wave");
 hand_wave(3);
 delay(2000);
 Serial.println("Hand wave");
 hand_shake(3);
 delay(2000);
 int x=100;
 for(int i=0;i<5;i++)
 {
  analogWrite(ledgreen,255);
 analogWrite(ledred,255);//white
 analogWrite(ledblue,255);
 delay(x);
  analogWrite(ledgreen,255);//yellow
 analogWrite(ledred,255);
 analogWrite(ledblue,0);
 delay(x);
  analogWrite(ledgreen,255);//cyan
 analogWrite(ledred,0);
 analogWrite(ledblue,255); 
 delay(x); 
 analogWrite(ledgreen,0);
 analogWrite(ledred,255);//purple
 analogWrite(ledblue,255); 
 delay(x) ;
 analogWrite(ledgreen,0);
 analogWrite(ledred,255);//red
 analogWrite(ledblue,0); 
 delay(x); 
 analogWrite(ledgreen,0);//blue
 analogWrite(ledred,0);
 analogWrite(ledblue,255); 
 delay(x); 
 analogWrite(ledgreen,255);
 analogWrite(ledred,0);
 analogWrite(ledblue,0); //green
 delay(x) ;
 }
 analogWrite(ledgreen,0);
 analogWrite(ledred,0);
 analogWrite(ledblue,0);
 //Serial.println("Body dance");
 //body_dance(10);
// delay(2000);    
 //Serial.println("Sit");
// sit();
 delay(1000);
}
/*
 - sit
 - blocking function
  ---------------------------------------------------------------------------*/
void sit(void)
{
 move_speed = stand_seat_speed;
 for (int leg = 0; leg < 4; leg++)
 {
   set_site(leg, KEEP, KEEP, z_boot);
 }
 wait_all_reach();
}
/*
 - stand
 - blocking function
  ---------------------------------------------------------------------------*/
void stand(void)
{
 move_speed = stand_seat_speed;
 for (int leg = 0; leg < 4; leg++)
 {
   set_site(leg, KEEP, KEEP, z_default);
 }
 wait_all_reach();
}
/*
 - spot turn to left
 - blocking function
 - parameter step steps wanted to turn
  ---------------------------------------------------------------------------*/
void turn_left(unsigned int step)
{
 move_speed = spot_turn_speed;
 while (step-- > 0)
 {
   if (site_now[3][1] == y_start)
   {
     //leg 3&1 move
     set_site(3, 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_default);
     set_site(2, turn_x1 + x_offset, turn_y1, z_default);
     set_site(3, turn_x0 + x_offset, turn_y0, z_up);
     wait_all_reach();
     set_site(3, 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(1, turn_x0 + x_offset, turn_y0, z_up);
     wait_all_reach();
     set_site(0, x_default + x_offset, y_start, z_default);
     set_site(1, x_default + x_offset, y_start, z_up);
     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(1, x_default + x_offset, y_start, z_default);
     wait_all_reach();
   }
   else
   {
     //leg 0&2 move
     set_site(0, x_default + x_offset, y_start, z_up);
     wait_all_reach();
     set_site(0, turn_x0 + x_offset, turn_y0, z_up);
     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_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(2, 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_up);
     set_site(3, x_default + x_offset, y_start, z_default);
     wait_all_reach();
     set_site(2, x_default + x_offset, y_start, z_default);
     wait_all_reach();
   }
 }
}
/*
 - spot turn to right
 - blocking function
 - parameter step steps wanted to turn
  ---------------------------------------------------------------------------*/
void turn_right(unsigned int step)
{
 move_speed = spot_turn_speed;
 while (step-- > 0)
 {
   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(unsigned int step)
{
 move_speed = leg_move_speed;
 while (step-- > 0)
 {
   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(unsigned int step)
{
 move_speed = leg_move_speed;
 while (step-- > 0)
 {
   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);
}

Connect the led pins

That's it, your quadruped is ready!
Upload the program.
Connect the servo according to the pins defined in the program.

Code

spider
spider_fix.ino

spiderArduino

 
/* Includes ------------------------------------------------------------------*/
#include <Servo.h>    //to define and control servos
#include <FlexiTimer2.h>//to set a timer to manage all servos
#define ledred 46
#define ledblue 44
#define ledgreen 45
/* Servos --------------------------------------------------------------------*/
//define 12 servos for 4 legs
Servo servo[4][3];
//define servos' ports
const int servo_pin[4][3] = { {2, 3, 4}, {20, 6, 7}, {8, 9, 17}, {16, 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()
{
   pinMode(ledred,OUTPUT);
pinMode(ledblue,OUTPUT);
pinMode(ledgreen,OUTPUT);
  //start serial for debug
  Serial.begin(115200);
  Serial.println("Robot starts initialization");
  //initialize default parameter
  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");
}


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()
{
  analogWrite(ledred,255);
  Serial.println("Stand");
  stand();
   delay(2000);
   
  analogWrite(ledred,0);
  analogWrite(ledblue,255);
  Serial.println("Step forward");
  step_forward(5);
  delay(2000);
  
  analogWrite(ledblue,0);
  analogWrite(ledgreen,255);
  Serial.println("Step back");
  step_back(5);
  delay(2000);
  
  analogWrite(ledgreen,0);
  analogWrite(ledred,255);
  analogWrite(ledblue,255);
   Serial.println("Turn left");
  turn_left(5);
  delay(2000);
  
  analogWrite(ledgreen,255);
  analogWrite(ledred,0);
  analogWrite(ledblue,255);
  Serial.println("Turn right");
  turn_right(5);
  delay(2000);
   analogWrite(ledgreen,255);
  analogWrite(ledred,255);
  analogWrite(ledblue,0);
  Serial.println("Hand wave");
  hand_wave(3);
  delay(2000);
  Serial.println("Hand wave");
  hand_shake(3);
  delay(2000);
  int x=100;
  for(int i=0;i<5;i++)
  {
   analogWrite(ledgreen,255);
  analogWrite(ledred,255);//white
  analogWrite(ledblue,255);
  delay(x);
   analogWrite(ledgreen,255);//yellow
  analogWrite(ledred,255);
  analogWrite(ledblue,0);
  delay(x);
   analogWrite(ledgreen,255);//cyan
  analogWrite(ledred,0);
  analogWrite(ledblue,255); 
  delay(x); 
  analogWrite(ledgreen,0);
  analogWrite(ledred,255);//purple
  analogWrite(ledblue,255); 
  delay(x) ;
  analogWrite(ledgreen,0);
  analogWrite(ledred,255);//red
  analogWrite(ledblue,0); 
  delay(x); 
  analogWrite(ledgreen,0);//blue
  analogWrite(ledred,0);
  analogWrite(ledblue,255); 
  delay(x); 
  analogWrite(ledgreen,255);
  analogWrite(ledred,0);
  analogWrite(ledblue,0); //green
  delay(x) ;
  }
  analogWrite(ledgreen,0);
  analogWrite(ledred,0);
  analogWrite(ledblue,0);
  //Serial.println("Body dance");
  //body_dance(10);
 // delay(2000);    
  //Serial.println("Sit");
 // sit();
  delay(1000);
}

/*
  - sit
  - blocking function
   ---------------------------------------------------------------------------*/
void sit(void)
{
  move_speed = stand_seat_speed;
  for (int leg = 0; leg < 4; leg++)
  {
    set_site(leg, KEEP, KEEP, z_boot);
  }
  wait_all_reach();
}

/*
  - stand
  - blocking function
   ---------------------------------------------------------------------------*/
void stand(void)
{
  move_speed = stand_seat_speed;
  for (int leg = 0; leg < 4; leg++)
  {
    set_site(leg, KEEP, KEEP, z_default);
  }
  wait_all_reach();
}


/*
  - spot turn to left
  - blocking function
  - parameter step steps wanted to turn
   ---------------------------------------------------------------------------*/
void turn_left(unsigned int step)
{
  move_speed = spot_turn_speed;
  while (step-- > 0)
  {
    if (site_now[3][1] == y_start)
    {
      //leg 3&1 move
      set_site(3, 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_default);
      set_site(2, turn_x1 + x_offset, turn_y1, z_default);
      set_site(3, turn_x0 + x_offset, turn_y0, z_up);
      wait_all_reach();

      set_site(3, 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(1, turn_x0 + x_offset, turn_y0, z_up);
      wait_all_reach();

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

      set_site(0, turn_x0 + x_offset, turn_y0, z_up);
      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_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(2, 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_up);
      set_site(3, x_default + x_offset, y_start, z_default);
      wait_all_reach();

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

/*
  - spot turn to right
  - blocking function
  - parameter step steps wanted to turn
   ---------------------------------------------------------------------------*/
void turn_right(unsigned int step)
{
  move_speed = spot_turn_speed;
  while (step-- > 0)
  {
    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(unsigned int step)
{
  move_speed = leg_move_speed;
  while (step-- > 0)
  {
    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(unsigned int step)
{
  move_speed = leg_move_speed;
  while (step-- > 0)
  {
    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);
}

spider_fix.inoArduino

// Locate the initial position of legs 
// RegisHsu 2015-09-09

#include <Servo.h>   

Servo servo[4][3];

//define servos' ports
const int servo_pin[4][3] = { {10,11,2}, {3,4,5}, {6,7,8}, {9, 12, 13} };

void setup()
{
  //initialize all servos
  for (int i = 0; i < 4; i++)
  {
    for (int j = 0; j < 3; j++)
    {
      servo[i][j].attach(servo_pin[i][j]);
      delay(20);
    }
  }
}

void loop(void)
{
  for (int i = 0; i < 4; i++)
  {
    for (int j = 0; j < 3; j++)
    {
      servo[i][j].write(90);
      delay(20);
    }
  }
}

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