North Alabama Robotics Team Monkey Madness
FLL Intro Programming
Workshop
2012
Kim Daugherty
bongju328@gmail.com
256-955-9521
1
Goals
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Present NXT-G programming concepts
that you can teach your FLL team
Conduct a hands-on NXT workshop to
facilitate learning
Provide tips and strategies that have been
learned through trial and error over five
years
2
Agenda
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Introductions
Our motivation
NXT introduction
Basic movement
Sensors
Control flow (loops and switches)
Debugging
3
Our Motivation
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To help Alabama FLL teams be competitive at
the national (US Open) and international level
(World Festival)
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Robot design is typically not an obstacle for teams
– programming is…
Teams can design robust software if they are
given a few tips…
To help teams have a great FLL experience so
they consider continuing into FTC/FRC
4
NXT Introduction
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Programming window
Version checking
NXT brick basics
5
Start a New Program
1. Enter “MoveTest”
2. Click on Go to open program
TIP: Use descriptive program names written in mixed case
6
Programming Window 1 of 2
Move
Record/play
Sound
Display
Wait
Loop
Switch
Common palette
TIP: The common palette is usually sufficient for basic navigation
7
Programming Window 2 of 2
Common
Move
Action
Record/play
Sensor
Sound
Flow
Display
Data
Wait
Advanced
Loop
Switch
Complete palette
TIP: The complete palette contains advanced commands
8
Comment and Pan Tools
Comment tool allows you to add documentation
Pan tool allows you move the screen around
Pointer tool allows you to select and insert blocks
TIP: Document your program so you can remember what it does
9
NXT Version Number
Help->About
New Program
V2.1.f3
Patch f3 located at http://education.lego.com/en-gb/preschool-and-school/secondary11-18/11plus-lego-mindstorms-education/downloads/
TIP: Patch f3 reportedly fixes the Error 1003 Broken Wire problem in NXT 2.x10
Firmware Version Number
Tools>Update NXT Firmware…
Version 1.31 is the latest
TIP: Check the NXT firmware on the brick by going to Settings->NXT Version11
A
B
Before We Start
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Outputs for Motors/Lights (A,B,C)
Inputs for Sensors (1,2,3,4)
Buttons (Enter, Back, Left, Right)
USB port
Motors
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1 – Light
3 – Touch
The NXT
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C
Middle (A), Left (B), Right (C)
Sensors
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Light sensor (1), touch sensor (3), color
sensor, ultrasonic sensor, rotation sensor
12
Practice Robot
Horizontal mount points
Two light sensors
Caster wheel
Good balance and
weight distribution
over drive wheels
High torque for lifting
(small gear connected
to large gear)
Low center of
gravity for stability
Robot instructions obtained from Oregon Robotics Tournament and Outreach Program
13
(ORTOP) http://www.ortop.org/Workshops/index2011.html
Name Your Robot
This tab allows you to
delete files from the
brick
This is where you
name the brick
Connect robot to
laptop using USB cable
This button brings up
the NXT window
TIP: You can delete sound files and demo programs to free up space on the NXT 14
Basic Movement
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The easiest way to get around is the Move
block
This is the block you will use the most
15
A
B
Most Basic Command
1. Click here and drag a
Move block to the Start area
C
1 – Light
3 – Touch
2. Click here to download
the program to the brick
Speed control
Direction control
Motor selection
Steering
control
Degrees OR rotations
should be used; rarely
use seconds
It is usually better to
brake than coast
TIP: Get familiar with all aspects of the Move command
16
A
B
Run the Program
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C
1 – Light
3 – Touch
First menu is “My Files”
Select with orange button
Second menu is “Software Files”
Select with orange button
Use arrow keys to find “MoveTest”
Select with orange button
Press orange button to Run
17
A
B
Two Ways to Turn
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Use slider bar on steering control
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C
1 – Light
3 – Touch
Middle position means robot will go straight
The further the slider is from the middle (but not all
the way to one side), the sharper the curve will be
(swing turn)
If the slider is all the way to one side, the robot will
turn in place by turning one wheel forward and the
other backward
Make sure motors on steering control set to B and C
Move one wheel only
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Click on either port B or C, but not both
Only one wheel will turn; this is a pivot turn
TIP: Pivot turns are the most precise, but swing turns are faster
18
A
B
Experiment with Move
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1 – Light
3 – Touch
Write a program to:
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C
Move forward 100% speed for 2 rotations
Make a right pivot turn at 75% speed (hint 390 deg)
Move backward 50% speed for 360 degrees
Make a left swing turn at 75% speed for 1 second
Turn in place clockwise all the way around at 25%
speed (hint 800 deg)
Move forward 100% speed for 1 rotation
Observations?
What could improve repeatability and accuracy?
19
A
B
Wait Block
1. Click here, select 1st block
(time), and drag after Move
block
C
1 – Light
3 – Touch
3. Repeat until 5 Wait blocks
have been added
2. Enter 0.25 seconds
TIP: Waiting a short time after each move improves repeatability and accuracy
20
Help Screen
Move cursor over block
to get short description
in this window
Click here to
get detailed
help screen
TIP: Access help for selected block by clicking on “More help” on NXT right bottom21
For Improved Navigation
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Use Wait blocks after Move blocks to
allow robot motion to completely stop
Start in the same position in base each
time; it is common to have the robot
bumper pressed again the wall1
Use pivot turns instead of swing turns
Don’t exceed 50% power when turning
In previous years, FLL mat is centered East West and flush with South wall;
distance between East or West wall and mat can vary on different tables
1
22
A
B
Sensors
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C
1 – Light
3 – Touch
Allows the robot to feel (touch), see
(light), hear (sound), and measure
distance (ultrasonic)
Are often used to determine when to
stop moving
TIP: Light and touch sensors are more useful in FLL than ultrasonic and sound23
A
B
Developing an algorithm
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C
1 – Light
3 – Touch
An algorithm is a step-by-step logical
sequence
Example: Move forward until robot runs into
wall
 Step 1: Turn on motors 100% speed
 Step 2: Wait until touch sensor is pressed
 Step 3: Turn off motors
TIP: It is a good idea to write an algorithm before you start writing the program 24
A
B
Touch Sensor
C
1 – Light
3 – Touch
1. Click here to start a new
program
2. Click here and drag a
Move block to the Start area
6. Click here and drag a
Move block next to Wait
block
5. Change port to 3
4. Click here, select 2nd
block (touch), and drag next
to Move block
7. Select Stop for
direction
8. Save program and
name it TouchTest
9. Click here to download
the program to the brick
3. Select Unlimited
for Duration of
Move
TIP: Be sure to stop the motors after a Wait block
25
A
B
Experiment with Touch
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1 – Light
3 – Touch
Write a program to:
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C
Move forward 100% speed until robot touches wall
Move backwards 50% speed for 2 rotations
Make a right turn at 50% speed (Hint 390 deg)
Move forward 100% speed until robot touches wall
Move backwards 50% speed for 2 rotations
Make a right turn at 50% speed (Hint 390 deg)
Move forward 100% speed until robot touches wall
Move backwards 50% speed for 2 rotations
Make a right turn at 50% speed (Hint 390 deg)
Observations?
26
Questions?
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Did you use copy and paste?
Did you remember to add waits after
each move command?
27
A
B
One Way to Do It
C
1 – Light
3 – Touch
Repeat these blocks 3 times
Move
forward
100%
speed
unlimited
Move
backwards
50% speed
for 2
rotations
Right pivot
turn 50%
speed for
390
degrees
TIP: Copy and paste can save you a lot of time
28
A
B
The Loop Block (1 of 2)
C
1 – Light
3 – Touch
1. Click here and drag a
Move block next to Wait
block
2. Set Control to Count and
set Count to 3
3. Make sure Counter is not
checked
TIP: The Loop block allows you to repeat commands
29
A
B
The Loop Block (2 of 2)
1. Click and drag these
blocks inside the Loop block
C
1 – Light
3 – Touch
2. Delete the remaining 12
blocks
3. Save, download,
and run TouchTest
TIP: Wait for the Loop block to expand before you let go of the blocks
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Reusing Blocks
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You may have a specific block or a
sequence of blocks that you want to
repeat many times in the program
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Wait time block
a) Move unlimited block followed by b) Wait
sensor block followed by c) Move stop block
followed by d) Wait time block
One or more blocks can be captured in a
MyBlock which can be reused
31
A
B
Create MyBlock (1 of 4)
C
1 – Light
3 – Touch
1. Select Wait block and
then click on Create My
Block
2. Name block
WaitTimeBlock and
click Finish
TIP: Use mixed case and name MyBlock something descriptive
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A
B
Create MyBlock (2 of 4)
C
1 – Light
3 – Touch
3. Select WaitTimeBlock and drag to
previous locations of Wait blocks
4. You can edit the MyBlock
by double clicking on it
2. Delete these Wait blocks
1. Select Custom palette
TIP: When you edit a MyBlock, save it and download the main program
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Why is this Better?
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Change the wait from .25 seconds to 1.0
seconds; you only need to change it in
the MyBlock instead of changing every
Wait block
Don’t download the MyBlock; download
the program that uses the MyBlock
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A
B
Create MyBlock (3 of 4)
C
1 – Light
3 – Touch
1. Select first four blocks
and then click on Create My
Block
2. Name block
MoveTouchBlock and
click Finish
TIP: When selecting blocks in a Loop, click outside the loop then drag
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A
B
Create MyBlock (4 of 4)
C
1 – Light
3 – Touch
TIP: There is no way to remove the space without redoing the Loop block
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You Now Have Two MyBlocks
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WaitTimeBlock
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Wait a specified time
MoveTouchBlock
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a) Move unlimited block
b) Wait for touch sensor block
c) Move stop block
d) WaitTimeBlock
TIP: MyBlocks are useful for reusing specific blocks or sequences of blocks 37
Light Sensors
Left light sensor
connected to port 1
•
•
•
•
•
•
•
•
Turn on robot
Use arrow keys to move to “View”
Select with orange button
User arrow keys to find “Reflected Light”
Select with orange button
Use arrow keys to find “Port 1”
Select with orange button
Read different areas of the mat – values will be 0 to 100
Optimum height
above mat is
between ¼ and 1
inch; too low
saturates sensor
and too high gets
poor reading of
reflected light
TIP: Light sensors should be calibrated and shielded from ambient light
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Light Sensor Readings
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Percent Mode:
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5% = lowest dark, 100% = very bright
Reflected Light Mode: shines a red light
The light can be turned off – detecting
ambient light (surrounding light)
TIP: The light sensor reads reflected light over an area determined by its height 39
Simple Line Following
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Does not actually follow the line…
Then what does it follow?
HINT: Line following would NOT work
well on a very thin line
40
B
Another Algorithm
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C
1 – Light
3 – Touch
Follows Left Edge of Line
Two states: Left of desired position, Right of desired
position
Determine state to control robot movement
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If Sensor1 > Boundary (Left)
 Set Motor B to 60
 Stop Motor C
If Sensor1 < Boundary (Right)
 Set Motor C to 60
 Stop Motor B
TIP: It is a good idea to write an algorithm before you start writing the program 41
Line Following
5. Add Move blocks
1. Start new program
and name it LineFollow
2. Click and drag Loop
block
3. Click Switch block and
put into Loop
4. Select Control to be
Sensor and Sensor to be
Light Sensor
5. Make sure Port is 1
TIP: Make sure to set motor ports correctly when line following
42
Experiment with Line Following
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Write a program to:
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Test line following at 60 percent speed
Test line following at 40 percent speed
Test line following at 100 percent speed
Observations?
43
Line Following Observations
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Faster line following makes large
swerves back and forth and can lose
the line
Slower line following is smoother
It is good to have a strategy to end line
following
44
End Line Following
1. Click on Loop block
2. Select Control to be
Sensor and Sensor to be
Rotation Sensor
3. Make sure Port is B
4. Set Until to be >
500 degrees
TIP: Use the rotation sensor to stop line following after a specified distance
45
Put it All Together
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Use Line Following, WaitTimeBlock, and
MoveTouchBlock to navigate robot from
start of line to target area
46
A Possible Solution (1 of 2)
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Line follow for 1150 degrees at 60% speed
WaitTimeBlock
Right pivot turn at 50% speed for 390 degrees
WaitTimeBlock
MoveTouchBlock
Move backward 50% speed for 1 rotation
WaitTimeBlock
Left pivot turn at 50% speed for 390 degrees
WaitTimeBlock
MoveTouchBlock
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A Possible Solution (2 of 2)
48
Resources
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usfirst.org/roboticsprograms/fll – Official FLL site
www.alabamafll.com – Official Alabama FLL site
www.nxtprograms.com – NXT designs (not all robots) and sample programs
www.techbrick.com – Coaching tips and challenge worksheets
www.forums.usfirst.org/forumdisplay.php?f=24 – Get help from the FLL
community; must register to post
www.teammonkeymadness.com – Our team site
www.ortop.org/Workshops/index2011.html – Coaches workshop materials
www.ortop.org/NXT_Tutorial/index.html – Online NXT tutorial
www.education.rec.ri.cmu.edu/content/lego/curriculum/index.htm – Carnegie
Mellon Robotics Academy
www.hightechkids.org/for-teams/coaches-library – Coaches materials
http://www.legoeducation.us/eng/characteristics/ProductLine~LEGO%20Mind
storms%20Education – NXT Education Base set and Resource set
49
TIP: Be positive and always set a good example for your team