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 To help clarify concepts - Discussion
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 Turning Color and light sensor
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 - B&C on for rotations
steering slider all the way right
medium speed
Wait - Gyro sensor compare angle >= 78 degrees
brake B&C when finished

16. Turning Gyro sensor spin turn Run the following program in a loop
Change the => 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 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/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) <
(white - black) / 2 + black
black = 31
Example: ( ) / = ?
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 - let’s 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 - let’s 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
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, and What 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 team’s 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 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 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
join the FIRST Forum, search forum for help, e.g. color sensor
Winning Design!: LEGO Mindstorms NXT by James J. Trobaugh