Designing for FLL with LEGO - Hints and Tips...Bricks & Beams Standard LEGOs – bricks, hold...

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


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

http://www.firstlegoleague.org/sitemod/design/layouts/default_no_banners/index.asp?pid=7520

http://www.firstlegoleague.org/default.aspx?pid=70


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


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







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


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


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

http://search.barnesandnoble.com/Building-Robots-with-Lego-Mindstorms-NXT/Mario-Ferrari/e/9781597491525?itm=6&usri=mindstorms+nxt

http://search.barnesandnoble.com/Winning-Design/James-J-Trobaugh/e/9781430229643?itm=2&usri=winning+design+mindstorms+nxt

https://www.barnesandnoble.com/w/winning-design-james-trobaugh/1125335451?ean=9781484221044

https://www.firstinspires.org/robotics/fll




http://www.sharonrobotics.org/


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.







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


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


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


Robot systems block diagram

Chassis

Computer

(microcontroller)

Motors

Power

Sensors

Communications

and control


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


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


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


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


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


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


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


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


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


Axles & Angle Connectors

Axles can be used for more

than just connecting

wheels.

With angle connectors, light

frameworks can be built


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


Technic Gears

Spur gears

8t, 16t, 24t, 40t

Crown gear

Double bevel gears

Single bevel gears

Worm gear

Clutch gear


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


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)


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


Wheel Stability

1. Not Stable

2. Stable

3. More Stable

4. Most Stable


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


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


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.


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


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].


Robot Chassis Design

Differential Drive - dual wheel pivot


Robot Chassis Design

Differential Drive - single wheel pivot


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


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


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


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


Demo robot from “Winning Design” book

used for examples


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


Demo robot enhancement

Adding a third motor on reverse end

Snap-on / snap-off

Cable to motor port A


Robot Manipulator Design - no motors

Simple pusher design – “bulldozer”

Flat surface

Snap-on or slide-on

Move game elements independently or in a container


Robot Manipulator Design - no motors

Simple plow design –

“cowcatcher”

Angled surfaces

Snap-on or slide-on

Move game elements out

of robot’s path


Robot Manipulator Design – motors optional

Fork and Hook

attachments

Can be combined with

power assist

to lift or sweep


Robot Manipulator Design – motors optional

Object trap

Box opens only inward

Capture objects to return

to base


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



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



Lifting hook attachment

Vertical pivot from

attached motor

Similar design could

pivot horizontally as a

grabber



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


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


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!


Questions & Wrap-up

Resources linked at our Sharon Youth

Robotics Association website

Including this presentation

sharonrobotics.org/resources.html

Designing for FLL with LEGO - Hints and Tips...Bricks & Beams Standard LEGOs – bricks, hold...

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