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Designing for FLL
with Lego Mindstorms
Hints and Tips
Presented by:
Sharon Youth Robotics Association
sharonrobotics.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!
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
Introduction
FLL season basics
LEGO Mindstorms system basics
LEGO Mindstorms chassis design
LEGO Mindstorms navigation issues
LEGO Mindstorms manipulator design
Questions & Wrap-up
Coding is beyond the scope of this workshop
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
Each fall, a new themed challenge 2017 FLL challenge : Hydro Dynamics
Past challenges 2016 - Animal Allies
2014 – World Class
2013 – Nature’s Fury
2012 – Senior Solutions
2011 – Food Factor
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 Challenges
2017/18 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"x3" board borders
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
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
2016 FLL Accounting
Team Registration - $225.00 for 2017 season
http://www.firstinspires.org/robotics/fll/cost-and-registration
Hydro Dynamics Field setup kit - $75.00
Basic LEGO Mindstorms EV3 kit - $439
Can use retail or educational kit, reuse each season
Useful, not required
Extra EV3 DC battery – $84.95
EV3 Gyro sensor – $29.95
EV3 Large Servo Motor - $26.95
EV3 Medium Servo Motor - $19.95
EV3 various duplicate sensors – 23.95 and up
Each tournament will have a team registration fee
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
LEGO Mindstorms EV3 kit
The home and education versions are somewhat different
Both versions include:
1 Intelligent EV3 Brick
2 large and 1 medium servo motors
7 connection cables of various lengths
500+ LEGO elements
EV3 programming software
1 USB computer to EV3 Brick cable
Home version includes:
1 touch, 1 color and 1 infrared sensors, plus infrared remote
Education version includes: 2 touch, 1 color, 1 ultrasonic and 1 gyro sensors
1 rechargeable battery and charger
Can order education version at team registration
2017/18 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/G Software
1 Intelligent NXT Brick
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
500+ LEGO elements
Recommended additions 2 rechargeable DC batteries
1 DC battery charger
2017/18 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 LEGO robotics
Winning Design! LEGO Mindstorms NXT
Winning Design! Lego Mindstorms EV3
James J. Trobaugh
More specific to addressing challenges
https://www.firstinspires.org/robotics/fll
https://techbrick.com/fll-resources/fll2017
www.sharonrobotics.org – links and resources
Many LEGO and FLL web resources available
Use Google keyword searches
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
Recommended “Textbooks” for our teams
These books have guided this presentation
Winning Design! LEGO Mindstorms NXT
Winning Design! Lego Mindstorms EV3
Author - James J. Trobaugh
Experienced FLL coach from Georgia
Book oriented to FLL activities
These books are
recommended
solely on their
merits – SYRA has
no financial interest.
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
LEGO Mindstorms components allowed
LEGO electrical parts limited to :
One EV3, NXT or RCX microcontroller
Only 4 motors!
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
Any number of LEGO-manufactured sensors
Touch, light, color and ultrasonic sensors
LEGO cables allowed as needed
All LEGO non-electric components are allowed
In any quantity – BrickLink Marketplace is a source
LEGO pneumatics are allowed
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
NXT Brick, 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
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
EV3 Brick, motors & sensors
EV3 (3rd Evolution)
4 Sensor inputs (plus rotation sensors on motors)
4 Motor outputs
LCD and control buttons
Sensors
Touch
Color
Gyroscopic
Ultrasonic
Motors
Large & Medium
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
Robot systems block diagram
Chassis
Computer
(microcontroller)
Motors
Power
Sensors
Communications
and control
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
Robot systems – EV3 Controller
Sensor ports - four input ports to attach sensors - 1, 2, 3 & 4.
Motor ports - 4 output ports to attach motors - A, B, C & D
USB port – for code loading
EV3 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 ARM9 microcontroller
16 Mbytes FLASH, 64 Mbytes RAM
Bluetooth wireless (V2. DER)
USB 2.0 port, 489 Mbits/sec
Supports WiFi dongle
4 input ports, 6-wire cable digital
4 output ports, 6-wire cable digital
178 x 128 pixel LCD graphical display
Micro-SD card reader (32 GB max)
Power source: 6 AA batteries or LiIon
2017/18 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
2017/18 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.
Rotation ~ 170 rpm, 20 N/cm
NXT servo motors have an integrated rotation sensor
Two motors can be synchronized so that your robot will move in a straight line
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
Robot systems – EV3 motors
Your robot is able to move using up to 4 servo motors.
Rotation ~
Large 160 rpm, 20 N/cm; axle to either side
Medium 240 rpm, 8 N/cm; axle to front
EV3 servo motors have an integrated rotation sensor
Two motors can be synchronized so that your robot will move in a straight line
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
Robot systems – NXT & EV3 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
2017/18 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 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
Light
Touch
Ultrasonic
Color
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
Robot systems – EV3 sensors
EV3 sensors are similar to NXT
Touch sensor – used to sense contact
Color sensor – used to sense colors and
track lines
Gyroscopic sensor – used to estimate
robot motion
Ultrasonic sensor – used to sense
proximity (distance without touching)
Infrared sensor – used for homing on
beacons and remote control
Touch
Color
Ultrasonic Infrared
Gyro
2017/18 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
2017/18 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
2017/18 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
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
40 24 16 8
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
2017/18 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
2017/18 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
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
Worm Gears, Bevel Gears & Pulleys
Worm gear w/gear rack –
equivalent of 1st 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)
2017/18 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
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
Wheel Stability
1. Not Stable
2. Stable
3. More Stable
4. Most Stable
2017/18 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
2017/18 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, consider size of the base
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.
2017/18 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
2017/18 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].
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
Robot Chassis Design
Differential Drive - dual wheel pivot
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
Robot Chassis Design
Differential Drive - single wheel pivot
2017/18 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 important
Match motors for performance
Build jig to compare rotation speeds
Works best if you have many motors to choose from
2017/18 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
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
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
Navigation - Design Issues
2017/18 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
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
Demo robot from “Winning Design” book
used for examples
2017/18 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
0
2011/12 Building for FLL with LEGO - Hints and Tips Workshop
Demo robot enhancement
Adding a third motor on reverse end
Snap-on / snap-off
Cable to motor port A
2017/18 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
2017/18 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
2017/18 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
2017/18 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
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
Robot Manipulator Design - with motors
Only four motors
allowed in FLL
Two are used for
propulsion
Additional motors can be
attached to chassis or to
attachments themselves
If on the chassis,
attachments would be
designed to connect to
the fixed motor
NXT controller has only 3
motor ports, EV3 has 4
2017/18 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
2017/18 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
2017/18 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
2017/18 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!
2017/18 Building for FLL with LEGO - Hints and Tips Workshop
Questions & Wrap-up
Resources linked at our Sharon Youth
Robotics Association website
Including this presentation
sharonrobotics.org/resources.html
Recommended