ORTOP Workshop 3 - Robot Design

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ORTOP Workshop 3 - Robot Design

• Robot Design, Navigation Missions

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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

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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

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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?

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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.

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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

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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!

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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)

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Going Straight

• Use a starting block from base

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Navigation

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

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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?

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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

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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

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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

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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?

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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

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Memory

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

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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.

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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, 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

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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?

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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
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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
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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

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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?

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Information

• Mission planning

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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

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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
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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
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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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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...

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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

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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

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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
• 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