Introduction to Lego Mindstorms

1
Introduction to Lego Mindstorms

• Myles McNally
• LMICSE Workshop
• November 19 - 21, 2004
• University of Mississippi

2
The Lego Mindstorms Kit

• The RCX (the brains)
• Two Geared Motors
• Two Touch Sensors
• One Light Sensor
• Lots of Lego Pieces
• A USB IR Tower
• A CD-ROM
• The Constructopedia

RCX Brick and Standard Sensors and Motors
3
A Basic Robot Design

• The Constructopedia is a building guide.
• Shown at left is the basic Roverbot from the
  Constructopedia
• A robust design
• Allows attachment of any of
• double bumper (shown)
• wheel sets (shown)
• single bumper
• light sensor
• tank like treads
• A recommended design starting point

Basic Roverbot Configuration
4
The RCX Itself (1)

• Hitachi H8 series microcontroller
• 8 bit CPU at 16 MHz
• 32 KByte RAM
• 16 KByte ROM for the BIOS
• Serial I/O (input/output)
• ADC (analog digital converter)
• Built-in timers

RCX Brick
5
The RCX Itself (2)

• Liquid crystal display (LCD)
• Four push buttons
• One small internal speaker
• Three sensor inputs
• Three motor outputs
• One infrared (IR) interface with a proprietary
  protocol
• Requires 6 AA batteries

RCX Brick
6
Actuators

• With Kit
• Geared Motors
• Available From Lego
• High-speed Motors
• Mini-motor
• Light Brick
• Available third party
• Servo Motor/Servo Controller

Servo Controller w/ 2 Servo Motors
Ungeared and Geared Motors
7
Sensors Basics

• Mindstorms sensors come in two types
• Active RCX supplies power
• Example Light sensor (supplied with kit)
• Passive RCX just detects changes in resistance
• Example Touch sensor (supplied with kit)

8
Sensors Available from Lego

• Touch
• Passive
• Supplied with Kit
• Light
• Active
• Supplied with Kit
• Rotation (Angle)
• Active
• Add-on

Touch, Light and Rotation Sensors
9
Third Party Sensors (1)

• The sensor interface is well documented
• Many building instructions for sensors exist, for
  example see Michael Gasperis website
• http//www.plazaearth.com/usr/gasperi/lego.htm
• Two commercial suppliers we know of
• http//www.mindsensors.com
• http//www.hitechnic.com

10
Third Party Sensors (2)

• Sonar (Ultrasonic range)
• Available both from Mindsensors and Hitechnic
• Magnetic Compass Sensor
• Available from Hitechnic
• Active and Passive Multiplexor
• Available from Mindsensors
• And many others

Hitechnic Sonar
Mindsensors Active Multiplexor
Hitechnic Compass
11
Software Architecture
Typical Software Architecture Levels
12
Software Architecture

• System ROM Layer
• Low Level Control Software
• Allows a second piece of software - the firmware
• Can be bypassed for direct control of the hardware

13
Lego Firmware

• The Lego firmware provides an environment for the
  execution of programs on the RCX.
• Must be downloaded (just once) before programming
  the RCX.
• Other firmware solutions are available.
• Lego Firmware v. 2.0 permits
• 5 separate programs
• 10 threads
• 32 global variables
• 16 local variables per thread
• Broadcast IR protocol

14
Alternative Firmware

• Firmware replacements further push the limits of
  the RCX
• Popular replacements are tied to alternative
  programming environments
• Examples
• LejOS (Java)
• see http//lejos.sourceforge.net/
• BrickOS (C/C)
• see http//brickos.sourceforge.net
• RCXLisp (Lisp)
• Part of the LMICSE project
• See http//robotics.csc.villanova.edu/

15
Programming the RCX

• Mindstorms ships with its own iconic programming
  language, but this is a very limited language.
• So others have developed for the RCX almost all
  the usual programming languages, including
• C
• C
• Java
• Ada
• Lisp
• Forth
• Smalltalk