Designing for FLL with Lego Mindstorms Hints and Tips Presented by:

Team Unlimited, FTC0001 unlimited.syraweb.org We acknowledge the efforts and copyrights of FIRST, LEGO Education and LEGO with regards to the contents of this workshop. Without their generosity, the FIRST LEGO League would not exist!

Introduction

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 Building for FLL with LEGO - Hints and Tips Workshop

FLL Challenges Each fall, a new themed challenge The 2011 FLL challenge : Food Factor Past challenges 2010 2009 2008 2007 2006 2005 2004 2003 2002 2001 2000 1999

– Body Forward – Smart Move – Climate Connections – Power Puzzle – Nano Quest – Ocean Odyssey – No Limits - Mission Mars – City Sights – Arctic Impact – Volcanic Panic – First Contact

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

FLL 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 Building for FLL with LEGO - Hints and Tips Workshop

FLL 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 Building for FLL with LEGO - Hints and Tips Workshop

LEGO Mindstorms NXT 2.0 kit This essential and reusable core set is the recommended package 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 registration – p/n 979792 2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Useful 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 Building for FLL with LEGO - Hints and Tips Workshop

LEGO 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! 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 Building for FLL with LEGO - Hints and Tips Workshop

NXT, 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 Building for FLL with LEGO - Hints and Tips Workshop

Robot systems block diagram Chassis Computer (microcontroller) Motors Power Sensors Communications/co ntrol

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Robot systems – NXT Controller Sensor ports - four input ports to attach sensors - 1, 2, 3 & 4. Motor ports - 3 output ports to attach motors - A, B & C USB port – for code loading NXT Buttons Orange button : On/Enter /Run Light grey arrows: Used to move left & right in the NXT menu Dark grey button: Clear/Go back LEGO attachment points Loudspeaker

Specifications 32-bit ARM7 microcontroller 256 Kbytes FLASH, 64 Kbytes RAM 8-bit AVR microcontroller 4 Kbytes FLASH, 512 Byte RAM Bluetooth 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 digital 100 x 64 pixel LCD graphical display Loudspeaker - 8 kHz sound quality. Power source: 6 AA batteries

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Robot systems – NXT motors Your robot is able to move using up to 3 servo motors. Turning speed is from 100170 rpm NXT servo motors have an integrated rotation sensor Two motors can be synchronized so that your robot will move in a straight line

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Robot systems – NXT 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 Building for FLL with LEGO - Hints and Tips Workshop

Robot systems – NXT sensors Sensors are used to provide information about the environment to the microcontroller

Light

Light sensor – used for line tracking, a color with filter Touch Touch sensor – used to sense collisions Ultrasonic sensor – sense proximity (distance without touching) Color sensor – sense colors, line tracking

Color

Ultrasonic 2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Bricks & 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 Building for FLL with LEGO - Hints and Tips Workshop

Liftarms & Pins Studless beams also come in “bent” shapes Some connectors are crossed for axles, others round Pins are different lengths & tightness – the light grey ones will rotate in the holes

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Axles & Angle Connectors Axles can be used for more than just connecting wheels. With angle connectors, light frameworks can be built

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Gears & 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) and decreases speed Gearing up (large to small) decreases torque and increases speed

Spur Gears

40

24

16

8

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Technic Gears Spur gears 8t, 16t, 24t, 40t

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

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Technic 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 Building for FLL with LEGO - Hints and Tips Workshop

Worm 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 Building for FLL with LEGO - Hints and Tips Workshop

LEGO 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 Building for FLL with LEGO - Hints and Tips Workshop

Wheel Stability

1. Not Stable

2. Stable

3. More Stable

4. Most Stable

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Robot Design and Construction Planning – what does the team want to achieve and how 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 Building for FLL with LEGO - Hints and Tips Workshop

Robot 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 Building for FLL with LEGO - Hints and Tips Workshop

General Robot Chassis Design The chassis (body) of the robot is built using LEGO Technic components. It should be stable and rugged, so it does not fall apart under use. Remember – after it is built, you still need to get to the battery compartment on the bottom of the microcontroller.

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

General 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 Building for FLL with LEGO - Hints and Tips Workshop

Robot systems – NXT motors Each motor has a built-in Rotation Sensor to control the robot’s movements precisely. Rotations are measured in degrees or rotations [+/- 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-train makes precise movements difficult to reproduce exactly The built-in Rotation Sensor in each motor also lets you set different speeds for your motors [set different power parameters in software].

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Robot Chassis Design Differential Drive - dual wheel pivot

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Robot Chassis Design Differential Drive - single wheel pivot

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Navigation – Design 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 Building for FLL with LEGO - Hints and Tips Workshop

Navigation – Design 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 Building for FLL with LEGO - Hints and Tips Workshop

Navigation - Design Issues Uncalibrated light ranges from ~30 to ~70, 50 is a good center 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 2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Navigation - Design 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 the final 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 movement controlled by rotations and timers and sensor-based movement 2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Demo robot from “Winning Design” book used for examples

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Demo robot enhancement Adding an attachment connection Snap-on or slip-on Use long black friction pins They don’t pull out easily when the attachment is removed

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

0

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

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Robot Manipulator Design - no motors Simple pusher design – “bulldozer” Flat surface Snap-on or slide-on Move game elements independently or in a container

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Robot Manipulator Design - no motors Simple plow design – “cowcatcher” Angled surfaces Snap-on or slide-on Move game elements out of robot’s path

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Robot Manipulator Design – motors optional Fork and Hook attachments Can be combined with power assist to lift or sweep

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Robot Manipulator Design – motors optional Object trap Box opens only inward Capture objects to return to base

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Robot Manipulator Design - with motors Only three motors allowed in FLL Two are used for propulsion Third motor is best attached to chassis Attachments would be designed to connect to the fixed motor

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Robot Manipulator Design - with 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 motor with axle

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Robot Manipulator Design - with motors Lifting hook attachment Vertical pivot from attached motor Similar design could pivot horizontally as a grabber

2011/12 Building for FLL with LEGO - Hints and Tips Workshop

Robot Manipulator Design - with 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 Building for FLL with LEGO - Hints and Tips Workshop

Testing 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 Building for FLL with LEGO - Hints and Tips Workshop

Practicing 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 Building for FLL with LEGO - Hints and Tips Workshop

Questions & Wrap-up

Resources linked at our Sharon Youth Robotics Association website Including this presentation

www.syraweb.org/Resources.htm

2011/12 Building for FLL with LEGO - Hints and Tips Workshop