LEGO Mindstorms NXT

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LEGO Mindstorms NXT
SOURCES
Carnegie Mellon Dacta Lego Timothy Friez Miha
Štajdoharmiha.stajdohar_at_fri.uni-lj.si
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Principles of Robotics

• Integrity. Robots hold together throughout the
  competition (no small task when you are talking
  about robots built out of Legos).
• Accuracy. The robot's mechanical outputs and its
  location acquisition and feedback to the RCX and
  subsequent programming provide the intelligence
  for precise performance.
• Execution. The robot performs the tasks it was
  designed to accomplish.
• Repeatability. The robot can perform the exact
  routine time and time again.
• Ergonomics. The robot is easy to handle,
  reconfigure, and change batteries or reprogram if
  necessary.
• Efficiency. The robot's design makes optimal use
  of its parts to execute tasks, minimize
  friction, and use power.

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Why students learn more when they participate in
a real challenge?
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Sophisticated robots can be build

• Accuracy of mapping program and NXT
• Draw letter E
• Circle Program
• Light Following on simulation
• More videos at http//www.youtube.com/ece191nxt

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Examples of mobile and humanoid robots

• Motivation
• Project Overview
• Hardware Specification
• Lego Robot
• Programming Environments
• NXC
• RobotC
• Method and Approach
• Ideas
• Design

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Mindstorms NXT

• mindstorms.lego.com

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Mindstorms NXT

• mindstorms.lego.com

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Ideas

• youtube.com
• ...

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Brick

• 4 sensor inputs
• 3 sensor inputs / motor outputs
• Programmable

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Purchasing NXT Kits

• Two options (same price 250/kit)
• Standard commercial kit
• Lego Education kit
• http//www.lego.com/eng/education/mindstorms/
• Advantages of education kit
• Includes rechargeable battery (50 value)
• Plastic box superior to cardboard
• Extra touch sensor (2 total)
• Standard commercial kit
• Includes NXT-G visual language

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• From Idea to Pseudo-Code to software to robot
  behavior

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Thinking about Programming

• Creating a successful robot takes a team effort
  between humans and machines.

Role of the Robot The robot follows the
instructions it is given, thereby carrying out
the plan.
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Human/Machine Communication

1. Because humans and robots dont normally speak
   the same language, a special language must be
   used to translate the necessary instructions from
   human to robot.
2. These human-to-robot languages are called
   programming languages.
3. Instructions written in them are called programs.
4. ROBOTC is just one of many such programming
   languages that humans use to talk to machines.

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Think about Behaviors

• Behaviors are a convenient way to talk about what
  a robot is doing and what it must do.
• Moving forward, stopping, turning, looking for an
  obstacle these are all behaviors.

• Basic or Simple Behavior
• Some behaviors are small, like go forward for 3
  seconds.
• Big behaviors are actually made up of these
  smaller ones.

Complex Behavior Some behaviors are big, like
solve the maze.
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Planning the Behaviors
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The main principle is braking large behaviors
into hierarchies of smaller and smaller
behaviors. You have to understand every piece of
input-output behavior of a robot
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PSEUDOCODE

1. As the programmer becomes more experienced, the
   organization of the behaviors in English will
   start to include important techniques from the
   programming language itself, like if-else
   statements and loops.
2. This hybrid language, halfway between English and
   the programming language, is called pseudocode.
3. It is an important tool in helping to keep larger
   programs understandable.

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ROBOTC is text based!

1. Commands to the robot are first written as text
   on the screen.
2. They are then processed by the ROBOTC compiler
   into a machine language file that the robot can
   understand.
3. Finally, they are loaded onto the robot, where
   they can be run.

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Software development options

• Onboard programs
• RobotC
• leJOS
• NXC/NBC
• Remote control
• iCommand
• NXT_Python

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NXT Brick Features

• 64K RAM, 256K Flash
• 32-bit ARM7 microcontroller
• 100 x 64 pixel LCD graphical display
• Sound channel with 8-bit resolution
• Bluetooth radio
• Stores multiple programs
• Programs selectable using buttons

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Programming languages
IDE interactive development environment

• NBC, NXC
• NXT Python, .NET

http//www.teamhassenplug.org/NXT/NXTSoftware.html
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Programming Environments

• NXC
• A High-level language
• Similar to C
• Stand-alone language (No plug-ins or add-ons)
• The program runs in the robot itself.

NXC On Bot
More Robust language Takes and uses values
Robust language can Graphically represent
Desired input and results
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NXT Python

• http//home.comcast.net/dplau/nxt_python/index.ht
  ml
• demo
• bluetooth
• remote control

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Python Programming Environments

• Python 2.4.4
• Scripted Programming Language
• Plug ins
• PyGame Simulated World
• PyODE Shapes, vectors
• PyBluez Bluetooth communication
• Python NXT Python Libraries for NXT
• Programs
• Light Sensor
• Ultrasound Sonar
• Sound Sensor

Python IDE
PyGame
PyODE
Python NXT
PyBluez
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Method and Approach

• Mapping Program
• Generate movement on NXT robot, record movement
  and plot robots path in real time in a simulated
  world.
• Python Simulator
• Thread function, lock on global objects
• NXC Simulator
• Separate program activates robot, simulator
  polls output values

Moves Robot
Starts Pygames
Draws readings on Pygames
Sends motor readings
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ROBOTC

• firmware
• tasks, program loop
• Sensors, motors
• data
• bluetooth, messages

www.robotc.net
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RobotC

• Commercially supported
• http//www.robotc.net/
• Not entirely free of bugs
• Poor static type checking
• Nice IDE
• Custom firmware
• Costly
• 50 single license
• 250/12 classroom computers

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Bluetooth

• PyBluez
• http//org.csail.mit.edu/pybluez/

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Motors

• Configured in terms of percentage of available
  power
• Built-in rotation sensors
• 360 counts/rotation
• No rotation sensors in old Lego

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Working with Motors

• Selecting Your Hardware Platform
• RobotC supports a variety of different hardware
  platforms.
• For these exercises we will configure RobotC to
  include support for the Tetrix/FTC robots as well
  as pure LEGO robots.
• The FIRST Tech Challenge (NXT) platform is a
  superset of the NXT platform.
• Whether your robot is using LEGO motors or the
  Tetrix 12V motors, you can control them with
  nearly identical code.

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• On the Robot / Platform Type menu make sure that
  you have FIRST Tech Challenge (NXT) selected.
• Click on the New icon on the RobotC toolbar to
  start a new program.

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Configuring your Motors

• You need to tell RobotC how your motors are
  attached to your NXT.
• On the Robot menu, open the Motors and Sensors
  Setup wizard and select the FTC Servo/Motor Ctrl
  tab.
• A. Using LEGO NXT Motors
• If your robot is using LEGO NXT motors for the
  drive wheels, select No controllers configured

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Using pragmas

• Two pragma statements and a comment line should
  have been inserted into your program looking
  something like this
• pragma config(Motor, motorA,
  motorLeft, tmotorNormal, PIDControl)pragma
  config(Motor, motorB, motorRight,
  tmotorNormal, PIDControl)
• //!!Code automatically generated by 'ROBOTC'
  configuration wizard !!//
• A pragma is an instruction to the RobotC
  compiler to change something about how your
  program gets compiled.
• The config() pragma tells RobotC to automatically
  include the necessary prefix code to configure
  your program to use the motor and sensor ports
  you specified in the wizard.

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Important recommendations to Robot C programmer

1. You should not modify these lines of code by
   hand.
2. If the configuration of your robot changes, go
   back into the Motor and Sensor Setup wizard and
   change the values there.
3. When you exit the wizard it will update the
   pragmas to reflect the changes you made.
4. Comment lines in RobotC begin with //.
5. Everything that follows a double-slash to the end
   of the line is ingored by the compiler.
6. The comment inserted by the wizard is a reminder
   that the pragmas preceeding it were
   automatically created for you.

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Using Tetrix 12 Volt Motors
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Using Tetrix 12 Volt Motors
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Using Tetrix 12 Volt Motors

• Three pragma statements and a comment line
  should have been inserted into your program
  looking something like this
• pragma config(Hubs, S1, HTMotor, HTServo,
  none, none)pragma config(Motor,
  mtr_S1_C1_1, motorRight, tmotorNormal,
  PIDControl, reversed)pragma config(Motor,
  mtr_S1_C1_2, motorLeft, tmotorNormal,
  PIDControl)//!!Code automatically generated by
  'ROBOTC' configuration wizard !!//
• A pragma is an instruction to the RobotC
  compiler to change something about how your
  program gets compiled.
• The config() pragma tells RobotC to automatically
  include the necessary prefix code to configure
  your program to use the motor and sensor ports
  you specified in the wizard.

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Using Tetrix 12 Volt Motors

1. You should not modify these lines of code by
   hand.
2. If the configuration of your robot changes, go
   back into the Motor and Sensor Setup wizard and
   change the values there.
3. When you exit the wizard it will update the
   pragmas to reflect the changes you made.

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Using Tetrix 12 Volt Motors

1. Comment lines in RobotC begin with //.
2. Everything that follows a double-slash to the end
   of the line is ingored by the compiler.
3. The comment inserted by the wizard is a reminder
   that the pragmas preceeding it were
   automatically created for you.

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First example of Programming Motors