Adding a 4dof arm to my Autonomous Rover - Now I have to learn Inverse Kinematics

My wife has said for the past several months, that she would only be impressed with my "toy" when it was able to bring her a glass of wine... 

Sounds like a challenge to me...

So I set about acquiring, assembling, and getting  a  4dof (degree of freedom) arm  attached.  It is neither powered nor operational today, but I am in the process of understanding the art of Inverse Kinematics.

Note: I had initially called this a 5dof arm, thinking the open/close action of the grip was a degree of freedom. I stand corrected.

While at rest, the arm is tucked up and out of the way.  It rests mechanically upon itself so I can remove power.   It is not very clear in this image, but the arm at rest does not block either the front Sharp IR Sensor nor the OSLRF range finder.

 I am currently reaching out to my friends at LetsMakeRobots to understand what sensors I need to make this both a reliable and useful robotic arm.

Consensus is:

1. Electrical current sensor on the 5v rail feeding the servos to ensure that we do not damage them with weight.
2. Tactile Pressure Sensor or Flex Sensor  on the fingers to grip the glass.
3. Accelerometer so we don't spill the wine.
4. And of course rubber grips.

The Raspberry Pi Camera is able to see and webcast the entire range of motion of the arm. I *assume* that at some point in time OpenCV can help guide the manipulator.

Please let me know if you know of any good resources I should be looking at, or any "must have" sensory feedback I must include.

I will be updating this post over the next few weeks as this gets hooked up and active.

















Resources:

Wikipedia:  Inverse Kinematics
Wikipedia: Degrees of Freedom
LearnAboutRobots: Robot Inverse Kinematics 
Society of Robots: Robot Arm Tutorial
Robotic Arm Inverse Kinematics on Arduino (with sample code)
CMU.EDU: Mathematics of Inverse Kinematics
http://letsmakerobots.com/node/31729
https://code.google.com/p/robotic-arm-control/
http://www.huffingtonpost.com/2012/09/28/wine-robot-wall-ye_n_1923808.html
https://www.synthetos.com/the-robot-arm-is-working/

Controlling a Raspberry Pi / Arduino Bot from the Internet Part 2 of 3

This is part two of a three part Series to explain how I control my BotTwo semi-Autonomous Robot from a webpage on the Internet. 

In Part One, we talked about the Interaction and Communications between the end user device (laptop/tablet/phone), the Web Server presenting the control panel, and the socket service listening for commands on the Robot itself.

This series will allow you to operate your Robot like an RC Car via the Internet.

This is the mode described here, with code examples for each programming platform.  As part of my learning process, I chose a very simple DIY approach, as opposed to a framework like node.js 

For the sake of completion, here is how the Raspberry Pi and Arduino are connected via I2C

Raspberry Pi / Arduino I2C

In this posting, we will discuss how to use python on the Raspberry Pi to initialise a tcp socket listener for incoming commands from the Web Server.

We will take the incoming message, and repeat it via I2C to the Arduino that is managing the DC motors and wheel encoders.

        Note:  typically, there would be a validation step between receiving the command, and issuing it                      to the motor controllers.

You would want to ensure that the command made sense, but also ensure that it was not going to put the robot into danger.  This would include proximity / obstacle detection, as well as "cliff detection". In more advanced robots, you may also have environmental sensors that could ensure that the path chosen was safe to travel.

Ok... so... in my implementation, I rely heavily on the Adafruit Raspberry Pi python library for I2C communications both for existing I2C sensors, as well as for communicating with my Arduino's.  I fully admit to replicating an existing I2C sensor library, and then making it work with my motor controller Arduino.

Adafruit_I2C.py  provides a number of methods for sending and receiving data via I2C, in 8bit bytes, 16bit integers, or character array (python list) form.

I'm not going to explain how to prepare your Pi for I2C... 

please go here ->  Adafruit: Configuring the Pi for I2C

 I had looked at Quick2Wire, and WiringPi, but their implementations is based on python3, whereas it appears that more I2C connectivity libraries exist for python 2.x via Adafruit.

Here is my stripped down "library" for sending a command string to the Arduino Motor Controller via I2C.

Motion.py 

#!/usr/bin/python

# Python library for Arduino as I2C Motor Controller.

# Copyright 2014 Michael Ball  unix_guru at hotmail dot com

from Adafruit_I2C import Adafruit_I2C

class Motion(Adafruit_I2C):

    # Minimal constants carried over from Arduino library

    MOTION_ADDRESS          = 0x33 # I2C Device Address
    MOTION_DATA             = 0x00 # Sensor data 


    def __init__(self, busnum=-1, debug=False):
        self.move = Adafruit_I2C(self.MOTION_ADDRESS, busnum, debug)


    def getMotionData(self):
        return self.move.readU8(self.MOTION_DATA) # & 0x0F


    # Read the Motion sensors
    def read_sensors(self):
        raw = self.move.readList(self.MOTION_DATA, 8)
        res = []
        for i in range(0, 8, 2):
            g = (raw[i] << 8) | raw[i+1] 
            res.append(g)
        return res

    # Send Commands to Motion Controller
    def write_command(self, command):
err = self.move.writeList(self.MOTION_ADDRESS, map(ord,command))
return err

# Simple example prints wheel encoder data and then sends a 
# "Forward 200mm" command every 2 seconds:
# Please note that sending a string via I2C bus is not the most 
# efficient use of this bus.  
# Data register method will be shown in an upcoming article

if __name__ == '__main__':

    from time import sleep

    motion = Motion()

    print '[Motion lpulse/rpulse]'
    while True:
        print motion.getMotionData()

        print motion.read_sensors()
sleep(.5)
print motion.write_command("f, 200 \n\r");
        sleep(2)  

With no further ado... here is my python "command repeater"   aka tcp socket listener-I2C Master.

#! /usr/bin/python
#
#  Process_Socket_Commands.py   Michael Ball Feb 2014
#  Manage command/response between Arduino Motor/Sensor controller, 
#  and Raspberry Pi intelligent controller.
#  Using tcp socket listener to receive commands from end user, 
#  and I2C to communicate with Arduino

import socket               # Import socket module
import time
import thread

from Motion import Motion



####################################################################
# Global Variables
cmd_received = 0
rcvdCommand = ""


####################################################################
# Declare functions

# Retrieve commands from tcp socket if available, and send to I2C
def get_next_command():       

  while True:
    # Inside processing loop we wait for a connection
    client_socket, address = server_socket.accept()
    print 'Got connection from', address
    client_socket.send('Thank you for connecting')
    rcvdCommand = client_socket.recv(1024)

    # rcvdCommand is a comma separated string from the Webserver
    # that consists of a single character Command, plus a Parameter
    # Move forward 200mm  would be represented as "f,200\n\r"
    print rcvdCommand

    # Normally, you would insert validation checking here, 
    # like proximty / obstacle avoidance, or cliff checking


    #send command to arduino
    motion.write_command(rcvdCommand)
    rcvdCommand = "" # Clear the command 
    client_socket.close()               # Close the connection


def get_motor_status():

   while True:
    # Read Wheel Encoder info from arduino 
    print "Motion, LCount, RCount, Speed"
    print motion.read_sensors()
    time.sleep(1)


            
##########################################################################
#
#This is where all the good stuff starts...
#
print 'Arduino Bot Command Processor - Feb 2014'

#  Create and open the socket will be listening on
server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_socket.bind(("192.168.0.105", 5000))
server_socket.listen(5)

print "Running Socket Server"

# initialize I2C Arduino motor controller - 
# Note there are no condition checks here
# a robust implementation would ensure that 
# the motor controller was actually online
motion = Motion()        

print "Arduino I2C Motor Controller Initialized"


try:
    running = True
    # Start up a Command tcp socket listener thread
    thread.start_new_thread(get_next_command, ()) 

    # Start up a thread to receive feedback from the Arduino
    thread.start_new_thread(get_motor_status, ())
    while 1: # Continuous loop
       pass

  


except (KeyboardInterrupt, SystemExit): #when you press ctrl+c
    print "\nKilling Thread..."
    # db.close()
print "Done.\nExiting."

Please read the comments.  This is a bare-bones implementation that takes a command string, and forwards it to The arduino via I2C for processing.   

You will need to add your proximity and safety testing to this.  As well, sending a string via I2C is not the most efficient use of the bus.   I simply did this so that I had both options available on the Arduino.

A proper Data Register method will be shown in an upcoming article.

As you will see in the next segment of this series,  I share the Command Interpreter / processor between the serial port and the I2C.  Commands can be received via either.

References:

http://dsscircuits.com/index.php/articles/78-arduino-i2c-slave-guide
http://gammon.com.au/i2c
Adafruit: Configuring the Pi for I2C
http://blog.oscarliang.net/raspberry-pi-arduino-connected-i2c/
https://wiki.python.org/moin/TcpCommunication
https://docs.python.org/3/howto/sockets.html
https://docs.python.org/2/library/socketserver.html
http://www.lucidtronix.com/tutorials/16
http://www.instructables.com/id/How-To-Make-an-Obstacle-Avoiding-Arduino-Robot/
https://github.com/adafruit/Adafruit-Raspberry-Pi-Python-Code
http://en.wikipedia.org/wiki/I%C2%B2C
http://www.robot-electronics.co.uk/acatalog/I2C_Tutorial.html
http://www.penguintutor.com/linux/raspberrypi-webserver
http://www.instructables.com/id/Raspberry-Pi-I2C-Python/?ALLSTEPS
http://raspberrypi4dummies.wordpress.com/2013/07/18/raspberry-pi-master-controls-arduino-uno-slaves-via-i2c/

Also read:

http://quick2wire.com/category/python/
https://github.com/quick2wire/trackbot
http://blog.chris.tylers.info/index.php?/archives/274-New-Pidora-Package-quick2wire-python-api.html
http://think-bowl.com/raspberry-pi/installing-the-think-bowl-i2c-libraries-for-python/
https://projects.drogon.net/raspberry-pi/wiringpi/i2c-library/

Controlling a Raspberry Pi / Arduino Bot from the Internet Part 1 of 3

This is a three part Series to explain how I control my BotTwo semi-Autonomous Robot from a webpage on the Internet. 

BotTwo has a few modes of operation.  

• In one of his Autonomous Modes, he can wander about aimlessly, simply avoiding objects, all the while building or refining a map of his surroundings for future use.  

• A second function in his Autonomous Modes allows you to select a location from his floorplan map, and he will find the shortest path to it, using A* algorithm. 

• In Manual Mode, you can drive him like an RC Car from a webpage. 

This is the mode that I will describe here, with code examples for each programming platform.  As part of my learning process, I chose a very simple DIY approach, as opposed to a framework like node.js 

---

This example starts with a HTML page that uses javascript to pass a Command variable and associated Parameter variable to a php script.

The php script opens a simple Web Socket to the Raspberry Pi on the Robot, and passes the command to it.  

This is just one of many ways to do this, but it works well for me, and may be a starting place for you.

I chose to run my webserver (Apache/Php/MySQL)  on a dedicated computer, as my Raspberry Pi is up and down as I'm working on it, or as the battery dies.   You may chose to run the webserver on your Pi.   

Here will present the HTML page, along with it's associated javascript, and php scripts that enable sending a command in real-time from a Button Control panel on your laptop/tablet/phone to your robot.

This HTML document simply sets up an imagemap of a button console, and attaches javascript actions to the area shapes that comprise the buttons:   

<area shape="circle" 

    coords="43,43,32"      

    onClick="sendCommand(4,0);"

    onMouseOver="showButtons('Look Left');" 

    onMouseOut="showButtons('');"/>

A slider Control or  HTML5 <input type= "range"> is used to send speed control messages using the same methods described below.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml"

xml:lang="en">

<head>

    <title>Control Testing for Raspberry Pi/Arduino Autonomous Platform</title>

    <meta http-equiv="Content-Type"

    content="text/html; charset=iso-8859-1" />

    <script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js" type="text/javascript"></script>

    <script src='autonomous.js'></script>

</head>

<?PHP include("insert_commands.php"); ?>

<body  onload='init();' >    

<center> 

     <H1> Control Panel for Web Guided Robot </H1>

     <BR> <HR> <BR>

   <center><b>Navigation Controls</b></center>

   <div> 

  <center>

<style>

.help {

   background-color: #FFFF73;

   border-radius: 10px;

   display: none;

   opacity: 0.9;

   padding: 10px;

   z-index: 100;

}

.help_link:hover + span {

   display: inline;

}

</style>

<form name="myform">

  <center><b>Action:</b> <input type="text" name="stage" size="10" />

      <b>Param:</b>   <input type="text" name="param" alt="Param" id="param" size="3" value="100"/> 

      <br><a href="#" class="help_link">Help</a> 

<span class="help">Distance you want to travel in mm.</span><br />

      <b>Speed:</b>  

<input type="range" id="speed"  value="50" min="0" max="100"  onchange="changeSpeed();"/>

      <div id="uno">&nbsp;</div>

  </center>

</form>

<!-- Create  Mappings -->

<img src="button_box_new.png" alt="Navigational Buttons" 

border="0" usemap="#buttons"/>

<map name="buttons">

  <area shape="circle" 

   coords="43,43,32"

    

   onClick="sendCommand(4,0);"

   onMouseOver="showButtons('Look Left');" 

   onMouseOut="showButtons('');"/>

 

  <area shape="circle" 

   coords="130,43,32"

   onClick="sendCommand(6,0);"

   onMouseOver="showButtons('Look Ahead');" 

   onMouseOut="showButtons('');"/>

 

  <area shape="circle" 

   coords="217,43,32"

   onClick="sendCommand(5,0);"

   onMouseOver="showButtons('Look Right');" 

   onMouseOut="showButtons('');"/>

  <area shape="circle" 

   coords="43,130,32"

   onClick="sendCommand(8,135);"

   onMouseOver="showButtons('Look Up');" 

   onMouseOut="showButtons('');"/>

 

  <area shape="circle" 

   coords="130,130,32"

   onClick="sendCommand('f',100);" 

   onMouseOver="showButtons('Move Forward');" 

   onMouseOut="showButtons('');"/>

 

  <area shape="circle" 

   coords="217,130,32"

   onClick="sendCommand(6,45);"

   onMouseOver="showButtons('Look Toward');" 

   onMouseOut="showButtons('');"/>

  <area shape="circle" 

   coords="43,217,32"

   onClick="sendCommand('l',100)"

   onMouseOver="showButtons('Turn Left');" 

   onMouseOut="showButtons('')"/>

 

  <area shape="circle" 

   coords="130,217,32"

   onClick="sendCommand('x',0)"

   onMouseOver="showButtons('Full Stop');" 

   onMouseOut="showButtons('')"/>

 

  <area shape="circle" 

   coords="217,217,32"

   onClick="sendCommand('r',100)"

   onMouseOver="showButtons('Turn Right');" 

   onMouseOut="showButtons('')"/>

  <area shape="circle" 

   coords="43,304,32"

   onClick="sendCommand(2,5)"

   onMouseOver="showButtons('Sonar Scan');" 

   onMouseOut="showButtons('')"/>

 

  <area shape="circle" 

   coords="130,304,32"

   onClick="sendCommand('b',100)"

   onMouseOver="showButtons('Move Backward');" 

   onMouseOut="showButtons('')"/>

 

  <area shape="circle" 

   coords="217,304,32"

   onClick="sendCommand(3,5)"

   onMouseOver="showButtons('Sonar Sweep');" 

   onMouseOut="showButtons('')"/>

  

  <area shape="circle" 

   coords="43,391,32"

   onClick="sendCommand(10,0)"

   onMouseOver="showButtons('Sleep/Wake');" 

   onMouseOut="showButtons('')"/>

 

  <area shape="circle" 

   coords="130,391,32"

   onClick="sendCommand(31,10)"

   onMouseOver="showButtons('Random Walk');" 

   onMouseOut="showButtons('')"/>

 

  <area shape="circle" 

   coords="217,391,32"

   onClick="sendCommand('t',5)"

   onMouseOver="showButtons('Turn Toward');" 

   onMouseOut="showButtons('')"/>

</map>

</center>

   </div>

      <center>

        <p>Copyright 2013 Michael Ball 

            <a href="http://arduino-pi.blogspot.com" target ="new">Arduino-Pi</a> 

            Email:  <a href="mailto:unix_guru@hotmail.com?Subject=Arduino-Pi" target="new">unix_guru@hotmail.com</a></p>

      </center>

</body>

</html>

On action, the Command and Parameter values are passed to php  via the sendCommand  function.

// #########################################################################

// autonomous.js

function showButtons(name){     / Show imagemap buttons values for controlling robot

  document.myform.stage.value = name;

}

function changeSpeed(){  // Slider control for managing robot speed 

    var speed=document.getElementById("speed");

    $.get("insert_commands.php", { command: 18, parameter: speed.value },                       // In my case '18' is the command

       function(command,parameter){  }, "json");      // to change motor speed

}

// This function passes both the Command and Parameter Variables from the Image map       // to a serverside PHP Script which will create a Websocket to the Robot. 

function sendCommand(command,parameter){                                          

    var parameter2=document.getElementById("param");

    if(parameter2 > 0) parameter = parameter2.value;    // Override default

    $.get("insert_commands.php", { command: command, parameter: parameter2.value },

       function(command,parameter){}, "json");

}

function init() {

    // Initalize the various page elements here...

    // in this case it is a dummy function...   

}

The php script accepts the Command and Parameter values, formats them into a string, and passes them to the Raspberry Pi, via a Web Socket. 

<?php

/*  

# BotTwo "insert_commands.php" Takes a Command/Paramater pair and sends 

# them to A listening robot via Web Socket

# 2014 Michael Ball  unix_guru at hotmail dot com

/*** robot address ***/

$robot_addr = '192.168.0.105';

/*** robot socket port ***/

$robot_sock = '5000';

if (isset($argv)) { // If running from the command line

   $command = $argv[1];

   $parameter = $argv[2];

}

else { // Else if called from a Web Page

   $command = $_GET['command'];

   $parameter = $_GET['parameter'];

}

// Initialize a Command string from the values passed in 'Command' and 'Parameter'

        $sock_cmd = $command . ", " . $parameter . "\n\r";  

if (isset($command)) { // If a command is available

// Create a TCP/IP socket to Robot

// http://www.php.net/manual/en/function.socket-create.php

$socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);

if ($socket === false) {

   return "Error: socket_create() failed: reason: " .

       socket_strerror(socket_last_error());

}

// Connect to the server running on the 'bot at  $robot_addr:$robot_sock

$result = socket_connect($socket, $robot_addr, $robot_sock);

if ($result === false) {

   return "Error: socket_connect() failed.\nReason: ($result) " .

       socket_strerror(socket_last_error($socket));

}

// Write the command string to the Robot

socket_write($socket, $sock_cmd, strlen($sock_cmd));

socket_close($socket);

}

?>

As I stated, this is an example... If you wish for me to go further into detailed explanation,   please comment below.

In the next article (2 of 3), I will describe how to receive and parse the command in python on the Raspberry Pi and forward it to an attached Arduino via the I2C bus.

And finally in article 3 of 3, I will describe the Arduino code that receives the I2C command, and turn it into motor actions to steer and run the robot. 

Edit (05/13/2014):  here is the button_box image... it's missing from my github... 

Resources:

https://code.google.com/p/phpwebsocket/

http://www.w3schools.com/tags/att_area_shape.asp

http://letsmakerobots.com/node/39791

http://www.php.net/manual/en/function.socket-create.php

http://www.php.net/manual/en/sockets.examples.php