1. MINDSTORMS NXT with JAVA
A guide to getting started
Berry Nall
Robotics Coach, Roma High School

2. I. Introduction

3. What is leJOS?
“leJOS NXJ is a Java programming environment for the LEGO MINDSTORMS NXT ®. It allows you to program LEGO ® robots in Java.”

4. Why would educators use leJOS?
Introduce students to text-based programming
Inspire student interest in JAVA, a widely-used programming language
Allow students to take advantage of leJOS’ superior performance
At the TCEA Region One Advanced Arena competition, the top 3 robots
and at least 4 of the top 6 finishers were programmed using text-based
programming (leJOS or RobotC).

5. Other Advantages of leJOS
(compared to NXT)
Faster loading and program execution
Programs use less memory
Greater accuracy
Scalable
Free!

6. Who can learn to use leJOS?
Anyone here (and your students) can learn enough to program for a TCEA competition.
We hope some of our students will go far beyond what we can do.

7. II. Eclipse IDE
An Integrated Development Environment is a program that allows you to write (and run) programs.

8. Uploading leJOS to the brick

9. If something goes wrong?
The brick will most likely make a ticking noise.
1. Reinstall the NXJ software using the LEGO-supplied program.
2. Upload the leJOS software again.

10. Exploring Eclipse Upload program Locate program files Edit program
Upload status

11. Eclipse helps This view is saved as the “leJOS” perspective.
In Eclipse, the view is called a “perspective.” Students may change it accidentally, causing confusion.
This view is saved as the “leJOS” perspective.
To restore, click “Window”, then choose “Reset perspective”
Current perspective

12. Eclipse helps
Eclipse tells you if there is a typing error or an illegal command:

13. Eclipse helps
Click here to load a program:

14. III. JAVA basics

15. JAVA Rules to remember
Capitalization matters! Ex: tcea is not TCEA is not tCeA
Every command ends with a semicolon
// means you are inserting a comment; everything after the slashes is ignored

16. IV. Writing programs

17. Program Sections Import statements File name Define pilot, sensors
import lejos.nxt.*;
import lejos.robotics.navigation.*;
import lejos.util.Stopwatch;
/**
*comment to name author (please change!) * */
public class TCEA {
//Variables and declarations go here
public static void main(String[] args)
// program goes here }
File name
Define pilot, sensors
Commands for robot to follow

18. To start: modify TCEA.java for your robot
Experimentally determine the wheel diameter.
Make the “travel” statement a comment and remove the comment slashes from the “rotate” statement.
Experimentally determine the wheel base. Note: the wheel base may need to be modified for different surfaces or designs even if the actual size doesn’t change.

19. Test your robot: TCEA1rectangle.java
If the wheel diameter and wheelbase are set correctly, the robot will travel in a rectangle and arrive where it started.

20. To program your robot: save the modified TCEA.java with a new name.
Change the class to the name of your file.
Add commands to make the robot move.