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ORTOP Workshop 3 - Robot Design

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Title: ORTOP Workshop 3 - Robot Design


1
ORTOP Workshop 3 - Robot Design
  • Robot Design, Navigation Missions

2
Workshop 3 Goals
  • Move your team up the ladder in navigational
    skills, and to increase their understanding and
    use of sensors
  • Provide tools to help give feedback to team
    members and guide their instruction
  • Questions from Workshops 1 or 2?

3
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
  • To help clarify concepts - Discussion
  • Convince yourself
  • Convince a friend
  • Convince a skeptic

4
Agenda
  • Going Straight
  • Making predictable moves
  • Moves - lab experiment
  • Background information on inaccuracies
  • Compensation for errors - attachments!
  • Turning
  • Making predictable turns
  • Turns - lab experiment
  • Gyro turns - lab experiment
  • Color and light sensor
  • Reading values from the color / light sensor
  • Detecting color areas inaccuracies
  • Buoy mission - putting it all together
  • Mission planning
  • Using dead reckoning
  • Using sensors

5
Going Straight
  • How do we make the robot go straight?
  • What if your were driving your car and it wobbled
    from side to side down the road?
  • What if your car always pulled to the right or to
    the left?

6
Going Straight
  • Experiment move 2ft, stop, run 4-5x
  • Program the robot to move 2 feet and stop
  • Tape 2 pieces of paper about 2 feet apart
  • Start the robot at exactly the same location for
    each run using front axles and rear ball as
    markers
  • Indicate where the robot stops by marking the two
    front forks and rear ball
  • Run 4-5 times at speeds of 20, 50, 100
    recording data for each run
  • Notice if the robot wobbles
  • Draw a box around the stopping points to show X
    and Y position error zones
  • Notice if speed affects where the robot stops
  • Go! 15 min.

7
Going Straight
  • S curve inaccuracy wobble
  • Motor rotation sensors
  • Inside each motor is a rotation sensor, similar
    to a speedometer / odometer in a car. The sensor
    provides wheel rotation and speed feedback to the
    Move Steering software in the EV3.
  • If one wheel slows, the Move Steering block
    senses the change and slows the other wheel,
    causing the robot to wobble and veer left or
    right.
  • The robot may stop or coast depending on
    selection of check or X

8
Going Straight
  • Team discussion
  • Does the robot stop at different X (side-side)
    and Y (front-back) points?
  • How does speed affect the X and Y position?
  • What might happen if the robot stops on a black
    line, at different speeds?
  • Be careful about speeding up runs and changing Y
    endpoints!

9
Going Straight
  • Compensation for navigational errors
  • Angled corners (back into a corner)
  • Wall follower wheels
  • Back against a wall
  • Width of attachment! (e.g. buoy fork)

10
Going Straight
  • Use a starting block from base

11
Navigation
  • Going straight variables
  • What are the variables that affect going
    straight?
  • software that senses wheel rotation

12
Going Straight
  • Variables that affect going straight
  • Starting box position, affect on X and Y stopping
    points
  • Speed, affect on stopping point
  • Battery charge, affect on speed
  • Tire size and axle flex and mounting
  • Motor friction, gear backlash (Google these
    terms)
  • EV3 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?

13
Turning
  • 2 wheel spin turn
  • on for degrees
  • steering slider all the way right or left
  • speed medium
  • wheel rotation 180 degrees to turn the robot 90
    degrees (depends on wheel size)
  • brake when finished
  • Accuracy of a 90 deg spin turn
  • tends toward a normal distribution,
  • SD 1.9 to 3.5 degrees
  • Lab discuss in your team
  • program spin turn

14
Turning
  • 1 wheel turn
  • on for rotations
  • medium speed
  • wheel rotation 360 degrees to turn the robot 90
    degrees (depends on wheel size)
  • brake when finished

15
Turning
  • Gyro sensor spin turn
  • reset Gyro sensor
  • Move Steering block - BC on for rotations
  • steering slider all the way right
  • medium speed
  • Wait - Gyro sensor compare angle gt 78 degrees
  • brake BC when finished

16
Turning
  • Gyro sensor spin turn
  • Run the following program in a loop
  • Change the gt to and observe results
  • Why turn 78 degrees?
  • Accuracy of a 90 deg Gyro turn
  • Gyro reading average 91 deg,
  • turn angle distributed greater than the
    programmed angle,
  • SD is 1.5 to 2 degrees
  • Lab Discuss in your team program a Gyro turn
  • Any final questions on turning?

17
Programming Help
  • Programming Help
  • Help tab at top
  • Show Context Help - highlight a program block,
    then click Context Help
  • Show EV3 Help - takes you to top level EV3 help -
    help files are on your computer

18
Memory
  • Memory Management
  • Open Memory Browser
  • Shows projects memory allocation

19
Buoy Mission
  • Buoy Mission - no sensors
  • Move N from base to black line, turn CW,
  • Move E to black line and pick up the buoy
  • Move S, place the buoy between the black lines
  • Go 15 min.

20
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, gyro
  • Teams sometimes give up on sensors because they
    seem complex and dont 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 well explore the light/color
    sensor in more detail to help us navigate on the
    playing field

21
Sensors
  • Threshold Value Calculation
  • From Workshop 1 Lab
  • Light Sensor returns value of RED reflected light
  • e.g. white 62
  • Threshold Value (less than) lt
  • (white - black) / 2 black
  • black 31
  • Example (62 - 31) / 2 31 ?
  • Take a minute to visualize the threshold value,
    and discuss in your teams. Does your answer make
    sense?

22
Sensors
  • Light sensor variables
  • Sensor-to-mat distance - lets record some data
  • Elevate the robot rear ball so the sensor is
    about 1/8 from the mat
  • Record black, green, white values - using EV3
    VIEW function - also verify values on computer
    screen
  • Level the robot so the sensor to 3/8 from the
    mat, record values
  • As the robot moves it bounces, which distance do
    you think would work best, and why? Discuss with
    your team

Black Green White
1/8 from mat
3/8 from mat
23
Sensors
  • Color sensor variables
  • Incorrect color sensing - lets record some data
  • Using the color cube, record values for blue,
    green, red, yellow - hold the sensor about 3/8
    inch from the cube
  • Record black, red, green, blue, white values from
    the white board
  • Team discussion what does this tell us about
    color sensor performance with various shades of
    color?

Black Red Green Blue Yellow White
color cube
mat values
24
Sensors
  • Setting up the color sensor
  • Wait for Color Sensor
  • Compare
  • Color
  • Then select color(s) you want to detect
  • The colored dot indicated selected colors

25
Sensors
  • Detecting a black line with the color sensor
  • Block by block, what does this program do?
    (Convince yourself, convince a teammate...)
  • Any final questions on the color sensor?

26
Information
  • Mission planning

27
Buoy Mission
  • Buoy Mission - color sensor
  • Move N from base, detect black line, turn CW
  • Move E, detect black line, pick up the buoy
  • Move S, place the buoy between the black lines

28
Line Follow
  • Extra credit Line Following - is really edge
    following
  • Steer to black, wait for _____
  • Steer to white, - wait for _____
  • Follows left edge of black line
  • Loop

B
C
Go ahead and write a program to do this
29
Line Follow
  • Line following - breaking out of the loop
  • Time
  • ( 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 Explain how this works, andWhat
    happens if...

B
C
30
Information
  • simple line follower with left sensor stop on
    blue
  • robot steers to blue line, then away
  • note speed, zigzag approach angle

31
Review
  • Help your teams focus on moves, turns and
    repeatability
  • By breaking missions down to basic moves and
    turns
  • By identifying error zones
  • By compensating for errors with attachments,
    positioning and sensors
  • By encouraging your team to make evidence based
    decisions
  • Help your team learn about robot behavior
  • Ask a simple question to focus their attention on
    a problem
  • Let them experiment with the problem - hands-on
  • Provide technical background information such as
    how to run an experiment or program a loop
  • Get the team to use what they know to solve a
    complex problem
  • Review what they have learned, quiz them to make
    sure they understand the problem and their
    solution - next slide has more on questions...

32
Quiz
  • How does the EV3 software know when to stop the
    robot?
  • With an internal GPS
  • By counting wheel rotations
  • By measuring light values
  • What causes the side-to-side wobble?
  • Move block software
  • Changes in light sensor values
  • 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 teams
    overall knowledge

33
Project
  • Using Scientific Inquiry in your team FLL
    Project
  • 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 _at_ 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

34
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
  • http//forums.usfirst.org/forumdisplay.php?24-FIRS
    T-LEGO-League
  • join the FIRST Forum, search forum for help, e.g.
    color sensor
  • Winning Design! LEGO Mindstorms NXT by James J.
    Trobaugh
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