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Raspberry Pi Robotics Essentials
Raspberry Pi Robotics Essentials

Raspberry Pi Robotics Essentials: Harness the power of Raspberry Pi with Six Degrees of Freedom (6DoF) to create an amazing walking robot

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Raspberry Pi Robotics Essentials

Chapter 2. Building the Biped

Now that you've got your Raspberry Pi 2 Model B all configured and ready to go, you'll need to add some hardware to control and interface. In this chapter, you'll learn:

  • How to build a basic 10 Degrees of Freedom (DOF) biped
  • How to use a servo motor controller connected to the USB port of the Raspberry Pi to control the servos to make your robot move

Building robots that can walk

There are several choices when considering how to create a mobile robot. One of the more interesting choices is a robot that can walk. This normally comes in three versions: a biped robot with two legs, a biped robot with four legs, and a hexapod robot with six legs. While each offers an interesting and different set of possibilities, in this chapter, you'll build a basic, 10 DOF biped.

You'll be using a total of 10 servos for your project, as each leg has 5 points that can move, or 5 degrees of freedom (DOF). As servos are the most critical component of this project, it is perhaps useful to go through a tutorial on servos and learn how to control them.

How servo motors work

Servo motors are somewhat similar to DC motors. However, there is an important difference. While DC motors are generally designed to move in a continuous way—rotating 360 degrees at a given speed—servos are generally designed to move to a limited set of angles. In other words, in the DC motor world, you generally want your motors to spin with a continuous rotation speed that you control. In the servo world, you want your motor to move to a specific position that you control.

This is done by sending a Pulse-Width-Modulated (PWM) signal to the control connector of the servo. The length of this pulse will control the angle of the servo like this:

How servo motors work

These pulses are sent out with a repetition rate of 60 Hz. You can position the servo to any angle by setting the correct control pulse.

Building the biped platform

There are several approaches to building your biped platform. Perhaps the most simple is to purchase a set of basic parts; this is the example you'll see in this chapter. There are several kit possibilities out there, including one at http://www.robotshop.com/en/lynxmotion-biped-robot-scout-bps-ns-servos.html, a kit like the one offered at http://www.ebay.com/itm/10-DOF-Biped-Robot-Mechanical-Leg-Robot-Servo-Motor-Bracket-NO-Servo-Motor-good-/131162548695?pt=LH_DefaultDomain_0&hash=item1e89e5a9d7, or the one at http://www.amazon.com/gp/product/B00DR7GA4I/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1. This is the specific kit we'll use in this chapter.

In the end, your biped will work more like the legs of a Tyrannosaurus Rex of a human, but this will make it easier to program, and it will power down more gracefully. It will also be a bit more stable.

You'll also need 10 standard size servos. There are several possible choices, but Hitec servos...

Using a servo controller to control the servos

To make your biped walk, you first need to connect the servo motor controller to the servos. The servo controller you are going to use for this project is a simple servo motor controller utilizing the USB from Pololu—Pololu item number 1354 is available at pololu.com—that can control 18 servo motors. Here is a picture of the unit:

Using a servo controller to control the servos

Make sure that you order the assembled version. This piece of hardware will turn USB commands from Raspberry Pi into signals that control your servo motors. Pololu creates a number of different versions of this controller, and each one is able to control a certain number of servos. In this case, you may want to choose the 18 servo version, so that you can control all 12 servos with one controller, and you may also add an additional servo to control the direction of a camera or sensor. You could also choose the 12 servo version. One advantage of the 18 servo controller is the ease of connecting power to...

Communicating with the servo controller with a PC

Now that the hardware is connected, you can use some software provided by Polulu to control the servos. Let's do this using your personal computer. First, download the Polulu SW from www.pololu.com/docs/0J40/3.a, and install it based on the instructions on the website. Once it is installed, run the software, and you should see this screen:

Communicating with the servo controller with a PC

First, you will need to change the configuration in Serial Settings, so select the Serial Settings tabs, and you should see this:

Communicating with the servo controller with a PC

Make sure that USB Chained is selected; this will allow you to connect and control the motor controller over USB. Now, go back to the main screen by selecting the Status tab; now, you can actually turn on the 10 servos. The screen should look like this:

Communicating with the servo controller with a PC

Now you can use the sliders to actually control the servos. Turn on servo 0. Make sure that servo 0 moves the lower-right ankle servo. You can also use this to center the servos. Set servo 1 so that the slider is in the middle...

Building robots that can walk


There are several choices when considering how to create a mobile robot. One of the more interesting choices is a robot that can walk. This normally comes in three versions: a biped robot with two legs, a biped robot with four legs, and a hexapod robot with six legs. While each offers an interesting and different set of possibilities, in this chapter, you'll build a basic, 10 DOF biped.

You'll be using a total of 10 servos for your project, as each leg has 5 points that can move, or 5 degrees of freedom (DOF). As servos are the most critical component of this project, it is perhaps useful to go through a tutorial on servos and learn how to control them.

How servo motors work


Servo motors are somewhat similar to DC motors. However, there is an important difference. While DC motors are generally designed to move in a continuous way—rotating 360 degrees at a given speed—servos are generally designed to move to a limited set of angles. In other words, in the DC motor world, you generally want your motors to spin with a continuous rotation speed that you control. In the servo world, you want your motor to move to a specific position that you control.

This is done by sending a Pulse-Width-Modulated (PWM) signal to the control connector of the servo. The length of this pulse will control the angle of the servo like this:

These pulses are sent out with a repetition rate of 60 Hz. You can position the servo to any angle by setting the correct control pulse.

Building the biped platform


There are several approaches to building your biped platform. Perhaps the most simple is to purchase a set of basic parts; this is the example you'll see in this chapter. There are several kit possibilities out there, including one at http://www.robotshop.com/en/lynxmotion-biped-robot-scout-bps-ns-servos.html, a kit like the one offered at http://www.ebay.com/itm/10-DOF-Biped-Robot-Mechanical-Leg-Robot-Servo-Motor-Bracket-NO-Servo-Motor-good-/131162548695?pt=LH_DefaultDomain_0&hash=item1e89e5a9d7, or the one at http://www.amazon.com/gp/product/B00DR7GA4I/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1. This is the specific kit we'll use in this chapter.

In the end, your biped will work more like the legs of a Tyrannosaurus Rex of a human, but this will make it easier to program, and it will power down more gracefully. It will also be a bit more stable.

You'll also need 10 standard size servos. There are several possible choices, but Hitec servos are relatively...

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Description

If you are a programmer with an interest in building advanced robotics projects using inexpensive hardware and open source software, then this book is for you. Some experience with computer programming and implementing simple mechanical systems is required.

Who is this book for?

If you are a programmer with an interest in building advanced robotics projects using inexpensive hardware and open source software, then this book is for you. Some experience with computer programming and implementing simple mechanical systems is required.

What you will learn

  • Build a basic biped platform, a servobased robot that can walk
  • Add Six Degrees of Freedom (6DoF) to your robot and make it free to move forward/backward, up/down, and left/right
  • Add vision through a webcam so that the biped can "see" the world around it
  • Implement path planning so that the biped can move around autonomously
  • Add wireless communication so that you can see what the robot is seeing and control the robot from a distance

Product Details

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Publication date : Jun 19, 2015
Length: 158 pages
Edition : 1st
Language : English
ISBN-13 : 9781785285646
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Product Details

Publication date : Jun 19, 2015
Length: 158 pages
Edition : 1st
Language : English
ISBN-13 : 9781785285646
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Concepts :

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Table of Contents

8 Chapters
1. Configuring and Programming Raspberry Pi Chevron down icon Chevron up icon
2. Building the Biped Chevron down icon Chevron up icon
3. Motion for the Biped Chevron down icon Chevron up icon
4. Avoiding Obstacles Using Sensors Chevron down icon Chevron up icon
5. Path Planning and Your Biped Chevron down icon Chevron up icon
6. Adding Vision to Your Biped Chevron down icon Chevron up icon
7. Accessing Your Biped Remotely Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

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Cute Jul 13, 2015
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Author already help us did a lot of homework about hardware, software and settings. This is really practical and save us a lot of time to do the same thing. It's not academic but straight forward.If you are an experienced engineer or expert but not familiar with the raspberry pi. It's a good book for beginning.
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404 Jul 22, 2015
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This is a great essentials guide for those who are interested in robotics and electronics perspective of Raspberry Pi. The topics and contents are beautifully curated and presented. Step by step examples are enriched with a plethora of screenshots. You can never go wrong. Recommended.
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Anil Vijay Sep 03, 2015
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I found this book to be very helpful in understanding key concept in using Raspberry Pi for robotics. It presents all relevant software setup steps and information to buy hardware at one place. No need to search any other place. A great reference guide.
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cericus Jul 06, 2019
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A great introductory book for those interested in robotics. The writing is clear and coherent and there is a range of content covered.
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Lluiset Jan 09, 2019
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Bien explicado para principiantes
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