LEGO Mindstorms

LEGO Mindstorms is a line of Lego sets combining programmable

bricks with electric motors, sensors, Lego bricks, and Lego Technic pieces

(such as gears, axles, and beams).

Mindstorms originated from the programmable sensor blocks used in

the line of educational toys. The first retail version of Lego Mindstorms was

released in 1998 and marketed commercially as the Robotics Invention

System (RIS). The current version was released in 2006 as Lego Mindstorms

NXT.

The hardware and software roots of the Mindstorms Robotics Invention

System kit go back to the programmable brick created at the MIT Media lab.

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This brick was programmed in Brick Logo. The first visual programming

environment, called LEGOsheets, for this brick was created by the University

of Colorado in 1994 and was based on AgentSheets.

The original Mindstorms Robotics Invention System kit contained two

motors, two touch sensors, and one light sensor. The NXT version has three

servo motors and four sensors for touch, light, sound, and distance. Lego

Mindstorms may be used to build a model of an embedded system with

computer-controlled electromechanical parts. Many kinds of real-life

embedded systems, from elevator controllers to industrial robots, may be

modelled using Mindstorms.

Mindstorms kits are also sold and used as an educational tool,

originally through a partnership between Lego and the MIT Media

Laboratory. The educational version of the products is called Lego

Mindstorms for Schools, and comes with the ROBOLAB GUI-based

programming software, developed at Tufts University using the National

Instruments Lab VIEW as an engine. The only difference between the

educational series, known as the "Challenge Set", and the consumer series,

known as the "Inventor Set", is another included light sensor and several

more gearing options.

Mindstorms is named after the book Mindstorms: Children, Computers,

and Powerful Ideas by Seymour Papert.

Robotics Invention System

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The first generation of Lego Mindstorms was built around a brick

known as the RCX. It contains a 8-Bit collision detector Renesas H8/300

microcontroller as its internal CPU. It also contains 32K of RAM that stores

the Firmware and User Programs. The brick is programmed by downloading

a program (written in one of several available programming languages) from

a PC or Mac to the brick's RAM via a special infrared (IR) interface. After the

user starts a program, an RCX-enabled Mindstorms creation may function

totally on its own, acting on internal and external stimuli according to the

programmed instructions. Also, two or several more RCX bricks can

communicate with each other through the IR interface, enabling inter-brick

cooperation or competition. In addition to the IR port, there are three sensor

input ports and three motor output ports (also usable for lamps, etc). There

is also an LCD that can display the battery level, the status of the

input/output ports, which program is selected or running, and other

information.

Version 1.0 RCX bricks feature a power adapter jack to allow

continuous operation instead of the limited operation time when using

batteries. In version 2.0 (as well as later 1.0s included in the RIS 1.5), the

power adapter jack was removed. Power adapter-equipped RCX bricks are

popular for stationary robotics projects (such as robot arms) or for

controlling Lego model trains. In the latter context, the RCX needs to be

programmed with Digital Command Control (DCC) software required for

automated model train operation..

The IR interface on the RCX is able to communicate with Spybots,

Scout Bricks, Lego Train, and the NXT (using a third-party infrared link

sensor.) The RCX 1.0 IR receiver carrier frequency is 38.5 KHz, while the

RCX 2.0 IR carrier frequency is 76 KHz. Both versions can transmit on either

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frequency. The carrier signal is generated by one of the RCX's internal

timers.

All versions of the RCX have a unique number printed on it. Little is known

about the reasoning behind this number, except for the use of technical

support and as a ID number of the RCX for your Lego Mindstorms account

on the now-defunct Lego Mindstorms RCX website. The first RCX produced is

marked "000001" and was on display at the Mindstorms 10th Anniversary

event.

Programming languages

Lego-supplied languages:

• RCX Code (included in the Mindstorms consumer version sold at

toystores)

• ROBOLAB (based on Lab VIEW and developed at Tufts University)

Popular third-party languages:

• http://roboteq.sourceforge.net/ open source programming with

graphical interface

• C and C++ under BrickOS (formerly LegOS)

• Java under leJOS or TinyVM

• NQC ("Not Quite C")

• pbFORTH (extensions to the Forth programming language)

• pbLua (An NXT API for the Lua programming language)

• Visual Basic (Through the COM+ interface supplied on the CD)

• RobotC (New Language and NXT Compatible)

• Interactive C (Language similar to C used in robotics competitions.)

• XSLisp an implementation of Lisp for the RCX (1 + 2) and NXT

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Parts Inventory

The parts included in retail version of the LEGO MINDSTORMS NXT set (8527) are pictured below.

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ROBOT ARM

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Using The Robot Arm

• Pressing the orange Enter button on the NXT brick will toggle the controls between "Rotate" and "Lift" modes.

• In "Rotate" mode, the gray left and right arrow buttons on the NXT brick will rotate the arm left and right as long as you hold the button down.

• In "Lift" mode, the left and right buttons will lift the arm up and down as long as you hold the button down.

• Pressing the touch sensor button will make the claw switch between grabbing and releasing.

The turntable and lifting arm motors both use gears to "gear down" the motion (decrease speed and increase force). You will notice that this keeps you from being able to turn the motors by hand.

To work around this problem, you can use the handle on the side of the arm

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lifting motor to adjust the arm's up/down position by hand when the program is not running. (When the program is running the NXT has the electric brakes on the motors and will not allow them to be turned by hand).

This design does not include a similar lever on the turntable motor. Can you figure out a way to add one?

Challenges

• Practice using the controls to pick up and move objects. Here is an example challenge. Place the red and blue balls on tire stands in different locations but both at the correct distance from the arm so that the claw will reach it, as shown below. Now try to use the robot arm to swap the positions of the two balls. What is smallest number of button presses that you think this can be done in?

• Think of some mechanical improvements you might make to this design. For example:

Come up with a way to keep the wires out of the way.

The claw is designed to be as simple as possible to keep it

light weight. However, it would be nice if both sides of it

opened and closed. Can you come up with a simple way to

do this?

The Arm Control program allows you to control the arm

using the buttons. Try making a program of your own that

controls the arm automatically by itself with a pre-

programmed sequence of moves. Here's a big challenge:

Can you write a program that will swap the balls as shown

in the challenge above?

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