Designing for FLLDesigning for FLLwith Lego Mindstormswith Lego Mindstorms

Hints and TipsHints and Tips

Presented by:

Team Unlimited, FTC0001unlimited.syraweb.org

We acknowledge the efforts and copyrights of FIRST,We acknowledge the efforts and copyrights of FIRST,LEGO Education and LEGO with regards to the contentsLEGO Education and LEGO with regards to the contentsof this workshop. Without their generosity, the FIRSTof this workshop. Without their generosity, the FIRST

LEGO League would not exist!LEGO League would not exist!

2011/12 FTC TETRIX Hints and Tips Workshop

IntroductionIntroduction

� FLL season basics� NXT system basics� NXT robot chassis design� NXT robot navigation issues� NXT robot manipulator design� Questions & Wrap-up

� NXT/G coding is beyond the scope of this workshop

2011/12 FTC TETRIX Hints and Tips Workshop

� Each fall, a new themed challenge� The 2011 FLL challenge : Food Factor� Past challenges

� 2010 – Body Forward� 2009 – Smart Move� 2008 – Climate Connections� 2007 – Power Puzzle� 2006 – Nano Quest� 2005 – Ocean Odyssey� 2004 – No Limits� 2003 - Mission Mars� 2002 – City Sights� 2001 – Arctic Impact� 2000 – Volcanic Panic� 1999 – First Contact

FLL ChallengesFLL Challenges

2011/12 FTC TETRIX Hints and Tips Workshop

FLL ChallengesFLL Challenges

� Challenges include a series of robotic missions� Carried out on a custom mat on top of a 4 x 8’ playing

table, bordered by 2 x 4”s� Read all FLL Challenge documentation thoroughly!� Usually 8+ individual missions� Missions goals scored by object positions at end of 2.5

minute competition round� Technical presentation about the teams approach to the

challenge and their robot� Research Project presentation, as assigned� Core Values, as presented and/or demonstrated

2011/12 FTC TETRIX Hints and Tips Workshop

FLL AccountingFLL Accounting

� Team Registration - $225.00 for 2011 season� https://gofll.usfirst.org/

� Food Factor Field setup kit - $65.00� Basic LEGO Mindstorms NXT kit - $420

� Can use retail or educational kit, reuse each season� Useful, not required

� Extra NXT DC battery – $54.95� Extra NXT DC charger – $24.99� Extra NXT light sensor – $17.95� NXT color sensor - $34.95� Spare NXT motor - $18.95

� Each tournament will have a team registration fee

2011/12 FTC TETRIX Hints and Tips Workshop

LEGO Mindstorms NXT 2.0 kitLEGO Mindstorms NXT 2.0 kit

� This essential and reusable core set is the recommendedpackage for teams who are newcomers to FIRST® LEGO® League.� NXT NXT/G Educational Software with a FLL Team license.� 1 Intelligent NXT Brick� 1 Rechargeable DC Battery� 1 DC Battery Charger� 3 Interactive Servo Motors (rotation sensor built in)� 2 Touch, 1 sound, 1 light and 1 ultrasonic Sensors� 1 USB computer to Brick cable� 7 Connection cables of various lengths� 3 Lamp bricks� 3 Converter cables� 1,000+ LEGO elements� 2 Storage Boxes with Sorting Trays for organization

Can order at registrationCan order at registration –– p/np/n 979792979792

2011/12 FTC TETRIX Hints and Tips Workshop

Useful Building ResourcesUseful Building Resources

� Building Robots with LEGO Mindstorms NXT� David Astolfo, Mario Ferrari, Guilio Ferrari� Great overall reference for Mindstorms

robotics� Winning Design! LEGO Mindstorms NXT

� David J. Trobaugh� More specific to addressing challenges

� http://www.usfirst.org/roboticsprograms/fll/� http://www.techbrick.com/Lego/LEGO2011/

Resources/index.html� www.syraweb.org – links and resources� Many LEGO and FLL web resources available

� Use Google keyword searches

2011/12 FTC TETRIX Hints and Tips Workshop

LEGO NXT components allowedLEGO NXT components allowed

� LEGO electrical parts limited to :� One NXT microcontroller� Only 3 NXT Motors/with integrated rotation sensors

� Total quantity brought to the competition table!� Cannot add in extra motors in detachable modules!�� We really mean it!We really mean it!� Also, no pull-back mechanical motors

� Maximum of 6 LEGO-manufactured sensors� Touch, light, color and ultrasonic sensors

� Cables allowed as needed� All LEGO non-electric components are allowed

� In any quantity – BrickLink Marketplace� LEGO pneumatics are allowed

2011/12 FTC TETRIX Hints and Tips Workshop

NXT, motors & sensorsNXT, motors & sensors

� NXT (NeXT)� 4 Sensor inputs (plus rotation sensors on motors)� 3 Motor outputs� LCD and control buttons

� Sensors� Touch� Light� Sound� Ultrasonic

� Motors

2011/12 FTC TETRIX Hints and Tips Workshop

Robot systems block diagramRobot systems block diagram

� Chassis� Computer

(microcontroller)� Motors� Power� Sensors� Communications/co

ntrol

2011/12 FTC TETRIX Hints and Tips Workshop

Robot systemsRobot systems –– NXT ControllerNXT Controller

� Sensor ports - four input ports toattach sensors - 1, 2, 3 & 4.

� Motor ports - 3 output ports toattach motors - A, B & C

� USB port – for code loading

� NXT ButtonsOrange button : On/Enter /RunLight grey arrows: Used to moveleft & right in the NXT menuDark grey button: Clear/Go back

� LEGO attachment points

� Loudspeaker

Specifications32-bit ARM7 microcontroller

256 Kbytes FLASH, 64 Kbytes RAM8-bit AVR microcontroller

4 Kbytes FLASH, 512 Byte RAMBluetooth wireless (Class II V2.0)

USB full speed port (12 Mbit/s)4 input ports, 6-wire cable digital

3 output ports, 6-wire cable digital100 x 64 pixel LCD graphical display

Loudspeaker - 8 kHz sound quality.Power source: 6 AA batteries

2011/12 FTC TETRIX Hints and Tips Workshop

Robot systemsRobot systems –– NXT motorsNXT motors

� Your robot is able to moveusing up to 3 servomotors.

� Turning speed is from 100-170 rpm

� NXT servo motors have anintegrated rotation sensor

� Two motors can besynchronized so that yourrobot will move in astraight line

2011/12 FTC TETRIX Hints and Tips Workshop

Robot systemsRobot systems –– NXT powerNXT power

� Batteries are placed inside of the NXT microcontroller� Flash memory – programs not lost when battery removed� 6 AA cells or 1 Lithium Ion rechargeable battery� Two different battery packs, AC or DC charger

2011/12 FTC TETRIX Hints and Tips Workshop

Robot systemsRobot systems –– NXT sensorsNXT sensors

� Sensors are used to provideinformation about the environmentto the microcontroller� Light sensor – used for line tracking, a

color with filter� Touch sensor – used to sense collisions� Ultrasonic sensor – sense proximity

(distance without touching)� Color sensor – sense colors, line

tracking

LightLight

TouchTouch

UltrasonicUltrasonic

ColorColor

2011/12 FTC TETRIX Hints and Tips Workshop

Bricks & BeamsBricks & Beams

� Standard LEGOs – bricks, hold together by friction only� LEGO Technics – standard beams, hold together by

friction and/or pins� LEGO Technics – studless beams, hold together by pins

2011/12 FTC TETRIX Hints and Tips Workshop

Liftarms & PinsLiftarms & Pins

� Studless beams alsocome in “bent” shapes

� Some connectors arecrossed for axles,others round

� Pins are differentlengths & tightness –the light grey ones willrotate in the holes

2011/12 FTC TETRIX Hints and Tips Workshop

Axles & Angle ConnectorsAxles & Angle Connectors

� Axles can be used for morethan just connectingwheels.

� With angle connectors, lightframeworks can be built

2011/12 FTC TETRIX Hints and Tips Workshop

40 24 16 840 24 16 8

Gears & Drive TrainsGears & Drive Trains

� Gears are designated by # of teeth� Motor speed starts at ~ 125 rpm� Smallest (8t) & largest (40t) give a 5 to 1 ratio

� Gearing down (small to large) increases torque (power) anddecreases speed

� Gearing up (large to small) decreases torque and increasesspeed

Spur GearsSpur Gears

2011/12 FTC TETRIX Hints and Tips Workshop

Technic GearsTechnic Gears

� Spur gears� 8t, 16t, 24t, 40t

� Crown gear� Double bevel gears� Single bevel gears� Worm gear� Clutch gear

2011/12 FTC TETRIX Hints and Tips Workshop

Technic Gear trainsTechnic Gear trains

� Gear up/gear down� Up for speed� Down for torque

� Idler gears� Only first and last gear

affect ratios

� Single stage gearing� Ratio between # of teeth

� Multi stage gearing� Multiplicative� 3:1 plus 3:1 becomes 9:1

2011/12 FTC TETRIX Hints and Tips Workshop

Worm Gears, Bevel Gears & PulleysWorm Gears, Bevel Gears & Pulleys

� Worm gear w/gear rack –equivalent of 1t gear� High torque� Difficult to back drive!

� Crown & Bevel gears� Use to change angle of

rotation (90°) � Pulleys bridge distance� Low torque capacity (bands slip)

2011/12 FTC TETRIX Hints and Tips Workshop

LEGO WheelsLEGO Wheels

� Avoid tracks� Low friction/high slippage� Motion/turns not easily reproducible

� Large wheels go farther per revolution� Friction varies with different tires� Consider how well they pivot for turns, as well as straight

forward motion

� Wheel-axle support� More support – less wiggle/sag� Support from both sides is best

2011/12 FTC TETRIX Hints and Tips Workshop

Wheel StabilityWheel Stability

1. Not Stable

2. Stable

3. More Stable

4. Most Stable

2011/12 FTC TETRIX Hints and Tips Workshop

Robot Design and ConstructionRobot Design and Construction

� Planning – what does the team want to achieve andhow will they achieve it? Let the kids do it!

� Design iteration� Brainstorm (what to build)� Design (how to build it)� Build it!� Test it!� Repeat until it’s perfect (or good enough)

� Trade-offs: Good, Quick, Cheap – pick two (at most)!� Quality – Schedule – Budget

2011/12 FTC TETRIX Hints and Tips Workshop

Robot Design ConsiderationsRobot Design Considerations

� Size – navigate obstacles on board, motor power� Ruggedness – maintain structural integrity� Center of Gravity – avoid tipping with slopes, sharp

turns or stops, or in collisions� Chassis style

� 2 wheel� Balancing skid is usually fine if no ramps to climb

� 3 wheel� Caster wheel can change robot course (supermarket carts)

� 4 wheel� Usually one pair is without tires to slide while pivoting)

� 6 wheel� Larger than most FLL robots, smaller base this season

2011/12 FTC TETRIX Hints and Tips Workshop

General Robot Chassis DesignGeneral Robot Chassis Design

� The chassis (body) of therobot is built using LEGOTechnic components.

� It should be stable andrugged, so it does not fallapart under use.

� Remember – after it is built,you still need to get to thebattery compartment on thebottom of themicrocontroller.

2011/12 FTC TETRIX Hints and Tips Workshop

General Robot Chassis DesignGeneral Robot Chassis Design

� Two basic designs (many that are more complex)� Differential Drive

� “Tank-like” steering, one motor connected to each side� Powerful, easy to turn in place� Can be a challenge to go straight

� Steering Drive� “Car-like” steering, one motor to drive a pair of wheels,

another motor to steer� Less power (steering motor doesn’t add drive power), hard to

turn in place� Not often used in competition

2011/12 FTC TETRIX Hints and Tips Workshop

Robot systemsRobot systems –– NXT motorsNXT motors

� Each motor has a built-in RotationSensor to control the robot’smovements precisely. Rotationsare measured in degrees orrotations [+/- one degree].� 1 rotation = 360 degrees, if you

set a motor to turn 180 degrees,it will make half a turn.

� Slack in the internal gear-trainmakes precise movements difficultto reproduce exactly

� The built-in Rotation Sensor ineach motor also lets you setdifferent speeds for your motors[set different power parameters insoftware].

2011/12 FTC TETRIX Hints and Tips Workshop

Robot Chassis DesignRobot Chassis DesignDifferential DriveDifferential Drive -- dual wheel pivotdual wheel pivot

2011/12 FTC TETRIX Hints and Tips Workshop

Robot Chassis DesignRobot Chassis DesignDifferential DriveDifferential Drive -- single wheel pivotsingle wheel pivot

2011/12 FTC TETRIX Hints and Tips Workshop

NavigationNavigation –– Design IssuesDesign Issues

� Wheelbase – narrow turns easily, wide goes straighter� Like fighter jets, stability is less maneuverable

� Weight – heavy yields less tire slip� Weight placement affects balance, ability to turn

� Wheel support – flexing of axles makes erratic motion� Support from both sides, if possible

� Batteries – constant power levels are key� Replacement batteries are key

� Match motors for performance� Build jig to compare rotation speeds� Works best if you have many motors to choose from

2011/12 FTC TETRIX Hints and Tips Workshop

NavigationNavigation –– Design IssuesDesign Issues

� Wall following� Horizontal guide wheels, approach wall at shallow angle

� Line following� Use the light generated by the light sensor itself� For greatest accuracy, box light sensors to eliminate (as

much as possible) ambient light� Calibration can help to reduce the effect of changes in

external lighting, but is hard to eliminate� Light sensors tend to hunt – pivoting on one wheel (instead

of two) tends to be less jittery and make faster progress� Take advantage of knowing the proper course for the

mission – not a general-purpose line follower

2011/12 FTC TETRIX Hints and Tips Workshop

� Uncalibrated light ranges from ~30 to ~70, 50 is a goodcenter of the midrange� Look for a range, look for < & >, not equal to a single value

� Single light sensor line following� Following a grey value between the black line and the

white border

� Dual light sensor line following� One follows the black line, the other follows the white

border

� Triple light sensor line following� The middle one follows the black line, the outer ones

follow the white borders

NavigationNavigation -- Design IssuesDesign Issues

2011/12 FTC TETRIX Hints and Tips Workshop

NavigationNavigation -- Design IssuesDesign Issues

� Reorientation after turns� Squaring against walls can restore a known angle

� Push for a time, or use twin touch sensors� Contact surface of robot and wall must be smooth� Movement to a fixed point should be careful not to base only on

rotations – a timer can save the robot from never arriving at thefinal distance value

� Dual light sensors can be used to align along a line on the mat

� Arrival� Touch sensors can detect impact� Ultrasonic sensor can detect an approach without contact

� Successful designs tend to use a combination of movementcontrolled by rotations and timers and sensor-based movement

2011/12 FTC TETRIX Hints and Tips Workshop

Demo robot fromDemo robot from ““Winning DesignWinning Design”” bookbookused for examplesused for examples

2011/12 FTC TETRIX Hints and Tips Workshop

Demo robot enhancementDemo robot enhancement

� Adding an attachment connection� Snap-on or slip-on� Use long black friction pins

� They don’t pull out easily when theattachment is removed

0

2011/12 FTC TETRIX Hints and Tips Workshop

Demo robot enhancementDemo robot enhancement

� Adding a third motor on reverse end� Snap-on / snap-off� Cable to motor port A

2011/12 FTC TETRIX Hints and Tips Workshop

Robot Manipulator DesignRobot Manipulator Design -- no motorsno motors

� Simple pusher design – “bulldozer”� Flat surface� Snap-on or slide-on� Move game elements independently or in a container

2011/12 FTC TETRIX Hints and Tips Workshop

Robot Manipulator DesignRobot Manipulator Design -- no motorsno motors

� Simple plow design –“cowcatcher”� Angled surfaces� Snap-on or slide-on� Move game elements out

of robot’s path

2011/12 FTC TETRIX Hints and Tips Workshop

Robot Manipulator DesignRobot Manipulator Design –– motors optionalmotors optional

� Fork and Hookattachments

� Can be combined withpower assist� to lift or sweep

2011/12 FTC TETRIX Hints and Tips Workshop

Robot Manipulator DesignRobot Manipulator Design –– motors optionalmotors optional

� Object trap� Box opens only inward� Capture objects to return

to base

2011/12 FTC TETRIX Hints and Tips Workshop

Robot Manipulator DesignRobot Manipulator Design -- with motorswith motors

� Only three motorsallowed in FLL� Two are used for

propulsion� Third motor is best

attached to chassis� Attachments would be

designed to connect tothe fixed motor

2011/12 FTC TETRIX Hints and Tips Workshop

Robot Manipulator DesignRobot Manipulator Design -- with motorswith motors

� Carabineer arm� Passive clip open/close

� Spring or band tensioned� Principle can be used for grabbers. etc.

� Powered arm to raise/lower

attach to motorwith axle

2011/12 FTC TETRIX Hints and Tips Workshop

Robot Manipulator DesignRobot Manipulator Design -- with motorswith motors

� Lifting hook attachment� Vertical pivot from

attached motor� Similar design could

pivot horizontally as agrabber

2011/12 FTC TETRIX Hints and Tips Workshop

Robot Manipulator DesignRobot Manipulator Design -- with motorswith motors

� Forklift attachment� Uses worm gear, resists being back-driven

� Gearing is often used in powered attachments� Can provide extra torque or slower motion� Simultaneous motion (grabber arms coming together)� Can redirect angle of motion

2011/12 FTC TETRIX Hints and Tips Workshop

Testing FLL RobotsTesting FLL Robots

� Test robots in mission environment� Table/mat/mission objects

� Properly oriented and secured

� Time missions� Speed is important, but consistency is even more critical� Only 2.5 minutes total, include in-base time

� Modify design one change at a time� Too many variables can confuse issues� Don’t change code before you verify battery strength

� Weak batteries cause performance issues

2011/12 FTC TETRIX Hints and Tips Workshop

Practicing with FLL RobotsPracticing with FLL Robots

� Practice in mission environment� At first, just the individual mission� Then, in combination with others

� Time in base for change-over is critical� Best to practice in assigned pairs

� Plan for contingencies� When to grab robot and try again (or move on)� One of pair can follow robot down-field (quick grabs)� Alternate plan in case of difficulties

� Murphy’s Law (and its many corollaries)� Whatever can go wrong will go wrong, and at the

worst possible time, in the worst possible way� Murphy was an optimist!

2011/12 FTC TETRIX Hints and Tips Workshop

Questions & WrapQuestions & Wrap--upup

� Resources linked at our Sharon YouthRobotics Association website� Including this presentation

www.syraweb.org/Resources.htm