Introduction to Lego Mindstorms

LMICSE Workshop

June 14 - 17, 2005

Alma College

The Lego Mindstorms Kit

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

RCX Brick and StandardSensors and Motors

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

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

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

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 andGeared Motors

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)

Sensors Available from Lego

• Touch• Passive• Supplied with Kit

• Light• Active• Supplied with Kit

• Rotation (Angle)• Active• Add-on

Touch, Light and Rotation Sensors

Third Party Sensors (1)

• The sensor interface is well documented• Many sets of building instructions for sensors exist, for example

see Michael Gasperi’s website • http://www.plazaearth.com/usr/gasperi/lego.htm

• Two commercial suppliers we know of:• http://www.mindsensors.com• http://www.hitechnic.com

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

Software Architecture

Typical Software Architecture Levels

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

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

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/

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

So What Now?

Let’s play

with

some Legos!