FIRST LEGO League Chassis and Attachments Clinic

FIRST LEGO League
Chassis and Attachments Clinic
Patrick R. Michaud
Coach, FLL #27 “Republic of Pi”
pmichaud@pobox.com
Science and Engineering Education Center
University of Texas at Dallas
October 10, 2015
Presentation Outline
LEGO basics
Chassis design
Attachments
LEGO basics
Beams
Beams are the basic
building pieces for most
LEGO robots
Length of beam determined
by number of holes
2M
3M
5M
7M
9M
11M
13M
15M
Often called “M” or “L” units
Center-to-center distance is 8mm
Can be “thin” or “thick”
Quickly determining beam size
To quickly determine the size of a beam
Place a finger over the center hole
Count the holes on one side
Double that and add one
1
2
3
4
5
Pegs
Used to connect beams and other components
Fit inside beam holes
Friction pegs do not turn freely in holes
Connector peg with friction (“peg”)
 3M connector peg with friction (“long peg”)
 Connector peg with cross-axle (“axle peg”)
 Connector peg with cross-hole (“bushing peg”)
 Ball with friction snap

Pegs
Non-friction pegs will turn in beam holes
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Connector peg
3M connector peg
Connector peg cross axle
Connecting beams
Use pegs to connect beams
At least two pegs are needed to make a rigid
structure
Greater distance between pegs reduces flex
More pegs increases hold between beams
Axles
Used for wheels, gears,
and attachments
2
3
4
5
Length also measured
in “M” units
6
7
8
9
Grey axles are typically
odd lengths, black axles
are typically even lengths
Axles will rotate and slide in beam holes
unless constrained
10
12
Wheels
Many types of wheels and tires available
Wheel consists of “rim” and “tire”
Tire measurements printed on sidewall
Cross hole attaches to axles
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56908 Rim wide 43.2 x 26
41897 Tyre Low Wide 56 x 28
32020c01 Wheel 62.4 x 20, with Black Tire 62.4 x 20
Bushings
Used to hold axles on beams
Also used as spacers to prevent tires from hitting
beams or other elements
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32123 Half-bushing
6590 Bushing
Bushings
Other elements can also be used as bushings or
spacers
Axle connectors
Axles can be joined using a wide variety of
connectors
Angle beams
Allow beams to be
connected at rigid angles
Excellent for structure
Some beams have cross holes
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32526: 3x5 L beam
32140: 2x4 L beam
60484: 3x3 T beam
32009: 3x7 double-angle beam
32271: 3x7 angle beam
6629: 4x6 angle beam
32348: 4x4 angle beam
Structural strength
Weak
Strong
Strong
Strong
3:4:5 triangles
Angled bracing is very strong
10
Use 3:4:5 spacing to ensure right angles and
proper alignment
5
8
4
3
6
Useful LEGO pieces - frames and panels
These pieces are excellent for building large
structures and boxes
Holes in all three axes for multiple mounting
options
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64179: Beam frame 5x7 (“box frame”)
64170: Beam H frame 5x11 (“H frame”)
64782: Flat Panel
Useful LEGO pieces - cross blocks and beams
These allow connections in multiple directions
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42003: Cross block 3M
32184: Double cross block
48989: Beam 3M with 4 snaps
55615: Angular beam 90 degrees with 4 snaps
14720: Beam I-Frame 3x5 90 degrees
Useful LEGO pieces - cross blocks
These cross blocks have a wide
variety of uses
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32291: Cross block 2x1 (“Mickey”)
41678: Cross block fork 2x2 (“Minnie”)
Connect two parallel beams
Create holes at right angles
Mount axles in different
directions
Create “beams” with
even # of holes
Useful LEGO pieces - misc
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2654: Slide shoe round 2x2
(good for skids)
41531: Turbine 31.01 x 2
(wheels that also slide)
Robot design and strategy
Chassis and attachments
The chassis is the part of the robot that is
responsible for navigating the field and providing
a base for attachments
Attachments are the things added to the chassis
to solve missions and manipulate models
Design is about creating a chassis and
attachments that will perform well in the Robot
Game
Robot design and strategy
Great robot + poor strategy
→ inconsistent scores
Fair robot + good strategy
→ consistent scores
Robot Game Strategy - Base
The robot must always start from Base
Base is the only place where changes can be
made
Robot Game Strategy - Time
Matches are 2:30
When the Robot is in Base, it's not scoring
→ minimize time spent in Base
Travel on the field takes time
→ minimize time spent moving from place to place
→ solve multiple missions in the same region
Robot Game Strategy - reliability
Distance:
Error increases with distance
1 degree is 1.7cm error after 100cm
Missions that are close become easier
Missions that are far become harder
→ Use field elements (lines, walls, models) to
guide the robot to make things seem “close”
Size:
Large targets are easy to hit
Small targets are hard to hit
→ Use large attachments to make small targets
“bigger”
Robot game strategy - humans
The Robot does exactly what physics and
programming say to do
Humans (drivers) make mistakes and are
inconsistent
Design the robot and strategy to prevent human
mistakes
→ Always start robot from same location
→ Don't require humans to aim
→ Build safeties into robot
→ Robot must adapt to humans, not vice-versa
Republic of Pi's design mantra
Whenever the robot or humans
make a mistake in scoring,
redesign the robot so that mistake
cannot happen again.
Common FLL robot characteristics
Two motors for drive wheels - one for each side
Multiple attachments for different missions
Attachments may be passive or powered
Third and fourth motors can be used for power
Maximum of four motors allowed during match
Robot design characteristics
From the Robot Design judging rubrics:
Evaluate the robot:
Does the robot break often?
Does it seem solid? Does it have a lot of “flex”?
Do the wheels make good contact with the surface?
Does it perform well in the game?
Chassis design
Chassis design considerations
The chassis gets the robot from place to place
Size
Smaller robots are easier to navigate
Robot must fit completely in Base when starting
Consistency and reliability
Robot needs to act consistently when moving
Speed
Faster robot → time to solve more missions
Slower robot → more consistent and accurate
Chassis basics
Good motor and wheel design are key to
consistency
Motor and wheel frame needs to be solid with
very little “flex”
“flex” produces inconsistent runs
Use cross bracing, frames, and angle beams to
increase structural stability
Wheels
Wheel selection is important
Larger wheels are faster, but may be less
accurate
Tire shape, pattern, and field mat surface affect
traction and consistency
Wheels that “slip” on the mat produce inconsistency
Wheels
Wheels should be mounted close to supporting
beam (but not rubbing against it):
Good
Poor
Axles do better when supported by at least two
beams. Beams on both sides of wheel are best.
Better
Best
Wheel styles
2 wheels and skid(s)
Works great, may have difficulty
with ramps/obstacles
2 wheels and caster
Caster wheel will make driving inconsistent
2 wheels and ball pivot (3-point design)
Works fine, may be a little unstable
2 wheels and 2 balls (4-point design)
Very nice
Wheel styles continued
4 wheels (4-point design)
Make sure non-driving wheels can slide while turning
#41531 Turbine has worked
well for my teams
6 wheels
Stable, but generally quite large and turning may be
imprecise
Treads
Good for obstacles, hard to predict turns
Exotics
Balance and center of gravity
Balance and center of gravity affects stability and
consistency of robot
Center of gravity is the average location of weight
of the robot
If the center of gravity is outside the wheelbase,
the robot will tip over
High center of gravity will make robot more likely
to tip
Weight
Heavier robots are more accurate, but slower and
use more battery
Try to keep weight over driving wheels (but watch
the center of gravity!)
Other chassis considerations
Put solid edges on robot
Align robot with solid edges,
not by sight
Robot can always start with
known location and heading
Provides attachment
mounting points
Place flat edge
against wall
Can be used for wall navigation
and aligning with mission models
Pick a marking
to align robot
To save match time,
always start from
same spot
Attachments
Attachments
Attachments are the things added to the chassis
to solve missions and manipulate models
Good attachment design makes solving missions
easy
Attachment design principles
Robot precision often limited to 1.5cm
If a target is small, try to make the attachment big
Use mission models and walls for precise
alignment
Things that seem easy for humans can be hard
for a robot
Manually test attachments with eyes closed
Mounting attachments
The best attachments are those that never need to be
added or removed from the robot
→ saves time during matches
If an attachment must be added or removed, make
sure it can be done quickly
Avoid using pegs for removable attachments
Use axles and axle pegs
Use gravity
Removing is usually faster than adding
Rubber bands can be used to snap attachments into
place
Attachment types
FLL missions usually involve
Pushing
Pulling
Lifting
Dropping / dumping
Placing / delivering
Releasing
Capturing / collecting
Shooting
Turning
Attachment building tips
Tend to use axles and plates when possible
Axles are easy to adjust, resize, and relocate
Plates and frames are better than walls of beams
Sources of energy for attachments
(in order of preference)
1. Gravity
2. Leverage
3. Elastics
4. Motors
Passive attachment: Pusher
One of the simplest (and useful) attachments is a
bumper.
A bumper can easily push/deliver objects
It can also provide places for other attachments
Passive attachment: Hook
A hook can be used to capture objects
Axles allow quick attach / removal
Passive attachment: Fork
A fork has multiple prongs for capturing objects
This helps make a wider target
Passive attachment: Dumper
Dumpers use gravity and simple pegs to release
contents
Passive attachment: Latch
photo coming soon
Elastic attachment: Catapult
photo coming soon
Powered attachment: Claw
photo coming soon
Powered attachment: Rotary Lift
photo coming soon
Powered attachment: Vertical lifts
Forklift will raise or lower as worm gear turns
The 8t gear
doesn't turn
Turn this gear
to raise/lower lift