ORTOP Workshop 3 - robot Design
Robot Design, Navigation & Missions
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Goals
Move your team up the
ladder in navigational skills,
and the use of sensors
•
To help you as coach
assess where your team
is, and what is needed to
move them forward
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introduction
Workshop 3 Methodology
•
Explore a problem
Run a hands-on experiment
Get kids’ heads wrapped around a problem
Explain how it works
Show important aspects of the problem
Add background information and knowledge
Apply knowledge
Solve a more complex problem with what you now know
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Agenda
Navigation with basic robot moves and turns
Run an experiment to determine robot move error
The S curve inaccuracy and wobble
Compensation for errors - absolute positioning and other tricks
One and two wheel turns
Programming the Buoy Mission using dead reckoning
Navigation with light sensors
Run experiments with the light sensor
Light sensor hardware and software
Line following logic
Mission planning - memory, time, priority, points
Programming the Buoy Mission using the light sensor
Review / Reference
•
Any questions from workshops 1 & 2?
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Navigation
Buoy Mission - from base - note position error run 3x
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Navigation
Experiment: move 2ft, stop, run 4-5x
Program the robot to move 2 feet and stop - try
running different speeds
Mark: stop points and identify
position error
Add axles to the can-catcher to act as a pointers
(show class)
Mark points on the paper were the robot stops
Run 4-5 times - speeds 20, 50, 90
Notice the wobble as the robot moves
Draw a box around the stopping points to show X
and Y Position errors
Go! 15 min.
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Navigation
S curve inaccuracy & wobble
Motor sensors
Each motor has a rotation sensor that provides
position and velocity feedback to the NXT software in
the brick (video of S wobble)
•
•
If one wheel slows, the Move block software senses
the change and slows the other wheel causing the
robot to wobble and veer left or right (classroom demo
- show one wheel slows the other)
Is there wobble difference between rear skid design
and rear 3rd wheel design? why?
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Navigation
S wobble
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Navigation
Compensation for navigational
errors
Use mechanical means
Angled corners (back into a corner)
Wall follower wheels
Back against a wall
Width of attachment (e.g. buoy fork)
Use sensors
Light & touch sensors to re-establish exact
robot location
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NAVIGATION
Use a starting block from base
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Navigation
What are the variables that affect
going straight?
1
2
3
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Navigation
Variables that affect going straight
Starting box position
Speed
Battery charge
Tire size
Motor friction, gear backlash (Google these terms)
NXT software tries to keep both wheels moving at
same speed - S curve inaccuracy
What is distinct about the last two variables?
Any questions about going straight?
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Navigation
2 wheel turn
2 wheel “spin” turn - Move Block, with slider
at end (show Move block)
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Navigation
2 wheel “spin” turn
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Navigation
1 wheel turn
1 wheel turn - Move Block, turn off one motor
application? accuracy?
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NAVIGATION
1 wheel turn
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Mission
Buoy Mission - no sensors
Move from base to the green line and buoy
Grab the buoy and place it between the black lines
Go! 15 min
Review of problems & solutions
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Sensors
Now that we know how to move and turn with some precision,
lets take a look at sensors
Sensors we can use in FLL:
touch, light, rotation, distance
Teams sometimes give up on sensors because they seem
complex and don’t seem to work in a predictable manner
Most teams feel comfortable with the built-in rotation sensors in
the motors to determine the number of rotations/degrees
In this segment we’ll explore the light sensor in more detail to
help us navigate on the playing field
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Sensors
Light sensor variables
Sensor-to-mat distance - let’s record some data:
Mount the sensor on the robot about 1/8” from the mat
Record black, green, & white values using NXT VIEW function
Move the sensor to 3/8” from the mat, record values
How does the distance affect light sensor values?
As the robot moves it bounces, which distance do you think
would work best, and why?
Black
Green
White
1/8” from
mat
3/8” from
mat
3/4 “ from
mat
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Sensors
Light sensor variables
External light influence - let’s record some data:
Use your hands to cover the light sensor to simulate a
dark room
Record black, green, & white values using NXT view
function
What does this tell us about light sensor performance in
various room lighting conditions?
Black
Green
White
sensor
uncovered
sensor
covered
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Sensors
Trigger point calculation
LS returns value of reflected light
e.g. white = 62
Trigger point (programmed) =
(white - black) / 2 + black
Black = 31
Example: (62-31) / 2 + 31 = ?
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Uncalibrated
Uncalibrated light sensor values
Data from 7 light sensors - uncalibrated, room light on
What trigger point would we use to stop on black? On green
or black?
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Calibration
Calibrated light sensor values
Calibration: a process to compensate for varying lighting conditions
Data from two sensors - uncalibrated (left), calibrated (right)
Calibration “spreads” values - lightest ~ 100, darkest ~ 0
Light Sensor 1
Light Sensor 2
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Calibration
Using the internal calibration program
Connect NXT brick to your computer
On the upper left corner, click “tools” and “calibrate sensors”
To calibrate, do the following:
Select
the light
sensor
and
the
port theasensor
is connected
to,
then
click
the
calibration
button.
This
will
download
small
program
to
the
NXT
and
run
it
automatically.
On the NXTs screen you will see text that reads “Min Value:” Point the light
sensor towards a material or spot that represents what the light sensor
should measure as dark. Press the orange Enter button on the NXT.
Next you will see text that reads “Max Value:” Point the light sensor towards
a material or spot that represents the brightest location the sensor will
encounter during the program. Press the orange Enter button again.
Calibration is complete.
Caution: After calibration, read light sensor values from the light sensor
program block to determine trigger points. Do not use NXT View
function, as View gives incorrect values for calibrated light sensors.
W1 shows how to turn off Calibration
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Sensors
Light sensor variables
Light sensor readings vary depending on:
Distance of sensor from the mat
Ambient light in the room
The particular light sensor you are using
Whether
the robot’s
light sensors have
been calibrated
or not
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Mission
Buoy Mission using sensors
Move along the black line using a line follower,
then up to the buoy
Grab the buoy and place it on the platform
Lets talk about line following...
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Line Follow
Line Following - is really edge following
Steer to black - turn _____
Steer to white - turn _____
Follows left edge of black line
Loop
Turn _____ , wait for dark
Turn _____ , wait for light
Loop
B
Go ahead and write a program to do this
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C
Line Follow
Line following - breaking out of the loop
Time
time is battery sensitive
(# of loops)
(Sensor input)
workshop 4 covers loops more thoroughly
Discuss line following in your team
Help all team members to understand line following
Judges will ask questions!
B
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C
information
simple line follower with left sensor stop on blue
robot steers to blue line, then away
note speed, zigzag & approach angle
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information
Mission planning
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mission
Buoy Mission
Begin by moving away from base
Use “simple line follower”
Plan precise moves & turns to capture the buoy
Pick up the buoy and place it on the platform
Go! 20 min.
Review of problems & solutions
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information
Simple line follower
Robot steers to line, then away, note speed & zigzag
Timed stop to break out of loop
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review
Help your teams focus on position error and
repeatability
1) By breaking missions down to basic moves and turns
2) By identifying error zones
3) By compensating for errors with attachments, positioning and sensors
4) By encouraging your team to make evidence based decisions
Help your team learn about robot behavior
1) Ask a simple question to focus their attention on a problem
2) Let them experiment with the problem - hands-on
3) Provide technical background information such as how to run an
experiment or program a loop
4) Get the team to use what they know to solve a complex problem
5) Review what they have learned, quiz them to make sure they
understand the problem and their solution - next slide has more on
questions...
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coaching
Homework: Write 2-3 Formative Assessment
questions that will help you determine where your
team is in the process
Subject-Centered Questions:
What causes the patterns you noticed?
What affects the number of xxx you can observe?
Person-Centered Questions:
How do you explain your observations?
What do you think is happening with the xxx?
Ask Formative Assessment questions during team meetings
Review the material as needed
Once you are satisfied they understand the material, move on to a Quiz
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quiz
How does the NXT software know when to stop
the robot?
1) With an internal GPS
2) By counting wheel rotations
3) By measuring light values
What causes the side-to-side wobble?
1) Move block software
2) Changes in light sensor values
3) The weight of the light sensor on one side
Ask quiz questions at the end of a segment or team meeting to help you
understand the team’s overall knowledge
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reference
Using Scientific Inquiry in Robot Design
Forming a Question or Hypothesis
What are the robot move and turn accuracies?
Learn to ask questions that can be investigated
Designing an Investigation
Run 2ft straight move, then turn 90 deg
Run test 5x @ 50% speed
Collecting and Presenting Data
Use pen & ruler to mark where robot lands
Analyzing and Interpreting Results
Be able to defend your conclusions
Ref: Oregon Department of Education - 2009 science standards
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Take Home Message
Help your team discover and use scientific
processes to understand robot moves and
behavior
Ask formative assessment questions to help you
as coach assess where your team is, and what is
needed to move them forward
Resources:
Scientific Inquiry: Oregon Department of Education ~ Inquiry
Exploratorium.edu ~ Institute for Inquiry
Winning Design!: LEGO Mindstorms NXT by James J. Trobaugh
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