Program your NXT robot with Imagine

Pavel PetrovičIDI NTNU, Trondheimppetrovic@acm.org

Outline

• Programmable LEGO • Logo and LEGO• NXT: features and the ways to program it• Why Logo for NXT?• NXT Logo!• Show…• Under the hood (NXT Logo internals)• The work remaining

Robotics in Education

Positive aspects:• demonstrate phenomena in novel and more ample ways,• provide creative platforms for hands-on exploration for

individual or group student work,• increase entertainment experience during the learning

process, • increase motivation for learning,• spawn interest in technology among students,

Drawbacks and challenges:• high cost of robots,• extra time, space, work and competence required from

teachers and schools,• shortage of curriculum materials and guidelines.

After-school Robotics Clubs

… perform important pioneering work

Programmable LEGO

• Early 90s: LEGO Dacta wired computer interface, well integrated into physics curriculum

• 1st autonomous: CodePilot (1997) programmed using barcodes

• Mindstorms (1998) based on 8-bit Microcontroller, 32KB RAM, IR serial communication, iconic programming language with parallel events: used in many competitions (First LEGO League, RoboCup, LineFollowing, Micromouse, etc.) Many alternative programming environments;

• NXT (2006) = RCX improved

Logo and LEGO

• Very close relation since the beginnings of robotics LEGO

• Successful product (LEGO Logo) for wired LEGO Dacta

• Powerful parallelism, direct and easy graphical visualization of data on screen

• Concept abandoned with the arrival of autonomous brick

NXT features and programming

• Compatible with RCX sensors and motors• Radio BT communication• Supports standard I2C bus/sensors• Programmed over USB cable• Graphical display• Powerful motors with built-in rotation sensors• Compact rechargeable Li-ion battery• Public full documentation of specifications• Programmed in new version of RoboLab

(LabView), RobotC, NXC, NBC, PbLua, Lejos, Microsoft R.S. etc.)

Why Logo for NXT?

• Shortcomings of RoboLab:– applications run only on robots despite BT

Radio, little support for making interactive projects

– difficult to learn– no textual form, slow, hard to maintain, debug

• Logo users love to use robots!• Large community of Logo users – large

potential for NXT robots

NXT Logo!

• Direct interactive control of NXT brick from Imagine controller project

• A loadable project with set of predefined procedures and operations that are supported by firmware

• Logo interpreter written in NBC – communicates interactively with Imagine

(remote remote-expression)

NXT Logo Internals

• Implemented in low-level language NBC for reasons of efficiency;

• NXT firmware: insufficient memory management, our own internal C-style memory management;

• Garbage collection on demand;• Careful handling of memory: use pointer

references where possible (each word stored only once, no destructive operations – i.e. shared structures);

NXT Logo Internals

• Parser – converts string expression to internal representation

• Printer – inverse to parser

• ‘Evaleval’ – performs one step of evaluation of list-expression (i.e. evaluates one number, word, or function call)

• Eval – evaluates complete list-expression, i.e. function body

NXT Logo Internals

• Word and variables stored in ordered symbol tables (for fast lookup), which also feature fast insert/delete

NXT Logo Internals

• NBC does not support recursion – we simulate it using stack structures and direct jumps

• More than 60 primitive procedures: conditions, iterations, variables, list operations, integer arithmetic, logic operations, NXT motor and sensor control, NXT file system, etc.

• Only prefix operations and fixed argument count – no parentheses!

• As compatible with Imagine Logo as possible• Expressions sent and returned directly between

Imagine running on PC and NXT Logo• Support for parallelism (not implemented yet)

Gears projectto measureRatio setsensor 1 “angle setsensor 2 “angle setsensor 1 “rst setsensor 2 “rst motor “A “power 50 ; rotate the first wheel 10-

times while [gt? 160 sensor 1] [ ] ; sensor2 measures the

opposite ; side, output the ratio op list sensor 1 sensor 2 end

Pulleys Projectto movePlatform setsensor 1 “lightA let “threshold 30 motor “C “power 15 motor “C “on while [lt? sensor

1 :threshold] [] motor “C “offend

Remaining Work

• Fill-in the missing blanks

• Update manual

• Make version independent from Imagine

• Brick to brick communication

• Advanced features, USB communication

• Provide more examples

• Find the user community

• Open-source project

Summary

• Functional language for NXT

• NXT control for Logo users

• Large NBC project

• Novel approach based completely

on interactive radio communication

• Bringing NXT closer to teachers, students, and classrooms

Thank you for attention…

… and see you at the workshop on Friday!