Building Mindstorms NXT
Robots
Dr. David Johnson
School of Computing
dejohnso@cs.utah.edu
What Is a Robot?
What Is a Robot?
• Sense
– Update information about the world
• Plan
– Modify original plan in response to this
sensed information
• Act
– Move in the world or make a change in the
world
Some Example Robots
• Big Dog
– http://www.youtube.com/watch?v=b2bExqhhWRI
• Planetary Exploration
– http://www.youtube.com/watch?v=nb2GsD7TAjU&feature=related
• Home assistance
– http://www.youtube.com/watch?v=GTxW3GWZ5hI
• Hobby
– http://www.youtube.com/watch?v=zX09WnGU6ZY
Resources for Learning About Robots
• Web
– Wikipedia
• http://en.wikipedia.org/wiki/Robot
– New Scientist
• http://www.newscientist.com/article/dn9973-instant-expertrobots.html
– Youtube
– MAKE magazine
– Boy Scout badge guide is quite nice and cheap
• Consider exercising your team’s FLL research
skills by having them look at some of these
resources
Mindstorms NXT
• Is it a robot? Can it
– Sense?
– Plan?
– Act?
Mindstorms NXT
• It can
– Sense
•
•
•
•
•
Light intensity and/or color
Sound intensity
Button presses
Distance to nearby objects
Wheel revolutions
– Plan
– Act
Mindstorms NXT
• It can
– Sense
– Plan
• Small computer brain
– “the brick”
• Graphical programming language
– Act
Mindstorms NXT
• It can
– Sense
– Plan
– Act
• Three motors that turn
• Make sounds
• Put words and pictures on its display
Robot Design Judging
• Teams demonstrate their robot on a field
• Discuss challenges and solutions
• Judges have a base rubric plus comments
–
–
–
–
How are sensors used?
Is the robot solidly built?
Modular design
Programming innovation
• Does something stand out?
– Reuse an attachment for different purposes
– Go over obstacles instead of around
– Programs that adapt to different risk levels
Goals For Today
• Raise your comfort level with Mindstorms
– Building
– Programming
– There is no substitute for doing it
• Try some common tasks
– Wheeled robot
– Respond to sensors
• Maybe a taste of competition…
Testing Equipment
• Plug in motors, sensors
• A critical thing to know is
the view program
– Let you read values from
sensors without writing a
custom program
Building
• Not “normal” LEGO pieces
– Based on the Lego Technic build system
– Pegs and holes
• Need to plan to make a solid robot
– Stable
• One peg makes a rotary joint
• Multiple pegs lock two pieces in place
– Strong
• Keep in close to the main body
• The wheel axles must not be wobbly and flex!
Building Resources
• There are lots of instructions for building things
online
– http://www.nxtprograms.com/
– Have the team try some out
• Learn things that work
• Then modify
– 5 minute bot
• A quick base
• Probably not good to adapt
for competition
Programming
• Programming teaches
– Breaking complex problems into solvable parts
– Precise thinking and specification
– Creative experimentation to discover and isolate
problems
• Programs are designed on a base computer
– Downloaded by USB cable to the brick
Programming the Brick
• LEGO Mindstorms NXT-G
– Default language for programming Mindstorms
• Designed to be friendly
– Nice tutorials
• Try them with your team
– Not based on traditional programming languages
– Easy to do very basic things
• More difficult to advance
• It does have some subtle actions that can cause confusion
Learning to Use the Tutorial
• Each tutorial is structured as
– Challenge
– Build
– Program
• The mobile base from the tutorials is not
my favorite
– Takes too long to build
– Difficult to modify
A Quick Programming Tour
• Control goes along the path
• Each block performs some action
– Most blocks are very flexible
– Learn the options at the bottom panel
– Many actions continue until
• A sensor is triggered
• Time has passed
• A commanded result is finished
A Quick Test
• Attach a motor to the brick (ports A)
• Attach a touch sensor to the brick (port1)
• Write a program
– Move block
• Set duration to unlimited
– Wait until touch
– Move block
• Set “Direction” to stop
• Download to brick
• Run it
• Let’s do this together
Additional Resources
• There is a lot to learn, but you can get started
pretty quickly
• I recommend
– Winning Design! LEGO Mindstorms NXT: Design
Patterns for Fun and Competition
• Most FLL-centric of the books
• Beginning to medium skill level
– If you don’t have prior experience, I think you would
be foolish not to look at this book.
Some Quick Hints
• Light sensors can
be tricky
• Light changes
– Time of day
– Clouds
– Flash photography
• Isolate the sensor
from the world
Using the Touch Sensor
• Add a bumper
Making Turns
• What would this do?
• Some help
– http://jamesreubenknowles.com/turn-robot-627
Driving Straight
• Some teams never get • Things to try
a robot to drive straight
– Check balance of
– Makes testing a
nightmare
– Use the field to squareoff
– Return to base so error
doesn’t accumulate
– See
http://www.youtube.com/watch?v=O
lAO9Ho-N58
robot
• Are the wheels equally
spaced?
• Axles straight?
• Weight balanced?
– Check motors
• Match up best two
• Move block tries to
compensate
– Check tires
Let’s have a competition!
1. Hit paper target
2. Go through maze
– Stop before unknown finish “wall”
• Development cycle
– Build, test, adjust, repeat
– Most kids do not understand how to test and
modify something until it works
• Quit or start new each time
– Really work with them on iterative
improvement
Teams!
• 2 or 3 per kit
• Start with the bot
– 5 minute bot
• Start building and testing the program
• Compete! Or, cooperete?
• Also, check out the School of Computing
technology camps
– www.cs.utah.edu/~dejohnso/GREAT