ORTOP Workshop 3 - Robot Design Robot Design, Navigation & Missions

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?

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

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

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?

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.

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

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!

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)

Going Straight Use a starting block from base

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

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?

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

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

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

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?

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

Memory Memory Management Open Memory Browser Shows projects & memory allocation

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.

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

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: (62 - 31) / 2 + 31 = ? Take a minute to visualize the threshold value, and discuss in your teams. Does your answer make sense?

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

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

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

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?

Information Mission planning

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

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

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

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

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...

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

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 @ 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

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-FIRST-LEGO-League join the FIRST Forum, search forum for help, e.g. color sensor Winning Design!: LEGO Mindstorms NXT by James J. Trobaugh