CeAnn Chalker [email protected] Disclaimer This presentation was prepared using draft rules. There may be some changes in the final copy of the rules.
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Transcript CeAnn Chalker [email protected] Disclaimer This presentation was prepared using draft rules. There may be some changes in the final copy of the rules.
CeAnn Chalker
[email protected]
Disclaimer
This presentation was prepared
using draft rules. There may be
some changes in the final copy of
the rules. The rules which will be in
your published Rules Manual will be
the official rules.
Boomilever Description
Students will design and build the most
efficient cantilevered wooden structure
(i.e. – lightest that holds the most weight up to 15 kg.)
Event Parameters
Only 1 structure entered per
team
No Impound
Event Supervisor provides all
assessment devices
More Event Parameters
Testing maximum load 15 kg
Students must wear proper eye
protection (ANSI Z87+)
teams given a warning to obtain proper eye
protection
Construction Parameters
Main Structure
Boomilever is a single structure
Made of wood bonded by glue
Construction Parameters
Main Structure
Unlimited laminations by students is allowed
No limit on the cross section size of individual
pieces of wood
Dimension Cue Sheet
Construction Parameters
Attachment Base
Attach to one or more mounting holes on the
Testing Wall
May not attach or hook on edge of Testing Wall
No more than 1.3 cm thick
1.3 cm
maximum
Attachment Base
Construction Parameters
Attachment Base
one or more parts
made from any type or size of wood and
wood products w/in the rules
must be a permanent part of the
Boomilever
included in the mass of the structure
Boomilever Dimension Limits
Horizontal Length
Measured from the face of the Testing
Wall to the center of the Loading Block
same for both Div. B & Div. C
Between 40.0 cm – 45.0 cm
Test Wall
40.0 to 45.0 cm
Loading
Block
Boomilever Dimension Limits
Contact Depth
The lowest distance the Boom may have in
Contact
Depth
Test Wall
contact with the Testing Wall below the
centerline of the mounting holes
Div. B – no more than 20.0 cm
Div. C – no more than 15.0 cm
Center Line of
Mounting Holes
Loading Block
Accommodate a Loading Block –
5.0cm x 5.0cm x 2.0cm
¼ inch diameter center hole
Loading Block must start –
at any height above the bottom edge of
the Testing Wall
Vertical Testing Wall
Vertical Testing Wall
Provided by the Event Supervisor
Vertical, solid, rigid, smooth, low-friction
surface
At least 40.0 cm wide x 30.0 cm high, minimum
¾” plywood
Three Mounting Holes for ¼” bolts
Mounting Holes are centered approx. 5.0 cm
below the top of the wall
Vertical Testing Wall – cont’d
Middle hole centered on the face of the wall
Other 2 holes are 10.0 cm on either side of the
center hole on the same horizontal line
All measurements are taken from the center of each
hole
Vertical Testing Wall – cont’d
Lines marked on the Testing Wall
Centerlines of the holes
Horizontal lower limit line below the
centerline of the holes
Div. B – 20.0 cm
Div. C – 15.0 cm
Vertical Testing Wall – cont’d
Boom attached using:
one, two, or three ¼” diameter x 7.62 cm
(3”) minimum length bolts
19 cm (3/4”) O.D. flat washers
wing nuts
Boomilever Testing
Only Students are to handle their
Boomilevers throughout
measurement, setting up, and testing
No alterations, substitutions, or
repairs are allowed to the Tower after
check-in
Boomilever Testing
A ¼” threaded bolt, chain, S-hooks, and bucket
will be suspended through the Loading Block
Boomilever Testing
Students may adjust the structure until
they begin loading the sand
Structures tested with sand or sand like
material
Up to maximum 15 kg
Teams are given 10 minutes to load the
sand into the bucket
Boomilever Testing Ends
When maximum load is supported (15 kg)
When failure of the structure occurs
The inability of the Boomilever to carry any
additional load
Any part of the load is supported by anything
other than the Boomilever
When any part of the Attachment Base goes below
the Lower Limit Line on the Testing Wall
When 10 minute test time elapses
Boomilever Testing Load
Load Supported includes –
Loading block
Eyebolt
Washer(s)
Wing nut
Bucket
Sand
Not pieces of the Boomilever!
Boomilever Scoring
Highest Score wins
Structural Efficiency
= Load Supported (grams)/Mass of the
Structure (grams)
Ties
1 – Lowest Boomilever Mass
2 – Least Contact Depth
Boomilever Scoring Tiers
Teams are ranked by the highest score
within each Tier
Tier 1 – Booms meeting all Construction
Parameters and no Competition
Violations
Tier 2 – Booms with one or more
Construction Parameters and no
Competition Violations
Boomilever Tiers cont’d
Tier 3 – Booms with one or more
Competition Violations
Tier 4 – Booms unable to be loaded for
any reason (including goggle violations)
are ranked by lowest mass
Resources
www.soinc.org
www.scioly.org
Search cantilever designs/structures
Search bridge, truss designs – concepts
are adaptable to boomilever
http://bridgecontest.usma.edu/
Where Do We Start?
Brainstorm – after Rules Review!
Research online – Cantilevers,
Bridges, & Trusses
Student drawn rough designs
Discuss what might work
Where Do We Start?
It’s All About Efficiency!
Efficiency =
Mass Held/Mass of Structure
Examples 20 g structure holds all 15 kg
15000/20 = 750
15 g structure holds 12 kg
12000/15 = 800
Where Do We Start?
Design & Draw
Draw designs on gridded paper
Draw
the thickness of the wood
pieces
Square and Level
Mirror Sides/Matching Sides
Where Do We Start?
Design & Draw
Measurements are within specs to the
rules
Bigger is always better than too small
Tape to building board (that can take pins)
Cover plans with –
Clear packing tape, plastic wrap, wax paper
What Wood?
Main Structure
Balsa has the highest strength to weight
ratio
Balsa has better tensile (pulling apart)
strength than compression strength
Balsa is very easy to work with
Balsa is less expensive than other woods
What Wood?
Attachment Base (Not Balsa)
Poplar, Bass, Spruce
Heavier and stronger
Will hold up better when bolted to the
Testing Wall
No need to use a large piece
Consider using 1, 2, or 3 separate pieces just
where the bolts attach
Bonding the Wood
Pick your Glue with care!
Use your Glue modestly!
Glue weight is a place to cut down on
overall structure weight!
Too much glue!
What Glue?
Wood vs. Super
Wood Glue - Dilute with water or rubbing
alcohol (1:1)
Longer to dry but doesn’t make the wood
brittle
More flexible, moves with the wood
Super Glue with Accelerator –
quick but can dry out the wood
Rigid when dry
Boomilever - Tension Design
Tension - the pulling force exerted by a string,
cable, chain, or similar solid object on another
object
Tension length is longer than the Compression
length
Load
Boomilever - Compression Design
Compression - a pushing force.
Compression length is longer than the Tension
length
Load
Tensile Advantages
Balsa’s Tensile strength is much greater
than it’s Compression strength
A Compression Boomilever must have
longer and thicker main support beam(s)
to support the same load (adds more
weight)
Key to Boomilever Design
The Connection between the
Boomilever and the wall
Wall to center of the Loading Block
Distance (40 – 45 cm).
Contact Depth may not exceed 20.0 cm
(Div B) or 15.0 cm (Division C)
Lap Joint
One of the strongest
Use as often as possible
Strengthens compression pieces by adding
stiffness
Flaw – only as strong as the face of the wood!
Butt Joint
Not strong for tension members
Under Tension will pull apart
Under Compression will stay together
Notched Joint
Stronger than Butt Joint
Less strength than a Lap Joint
Difficult to build
Gusset Joint
Combine a Butt Joint with a Lap Joint
Lap another piece of wood at the joint
Strong in both tension and compression
Additional Joints
Diagonals and Cross Bracing
Diagonal Pieces & Cross Bracing are important!
Prevents structure from torquing/twisting
Adds additional strength
If the Cross Braces cross (make an X), Glue
them at the X
Glue here
Warren Truss
Pratt Truss
Right Triangles in Design
Slants Face Inward
Howe Truss
Right Triangles in Design
Slates Face Away from Center
K Truss
Tough to Build!
Boomilever Trusses –
Tension vs. Compression
Diagonals in Tension
Diagonals in Compression
Howe Truss
Pratt Truss
Tension & Compression
Loading Block
Warren Truss
Modified Warren Truss
Tension Design
Loading Block
Tension Designs
Great Variation in Designs
Notice the use of dowel rods