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Boomilever B & C – 2012-13. 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. - PowerPoint PPT Presentation
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CeAnn [email protected]
DisclaimerThis 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 DescriptionStudents will design and build the most
efficient cantilevered wooden structure (i.e. – lightest that holds the most weight up to 15 kg.)
Event ParametersOnly 1 structure entered per
teamNo ImpoundEvent Supervisor provides all
assessment devices
More Event ParametersTesting maximum load 15 kgStudents must wear proper eye
protection (ANSI Z87+)teams given a warning to obtain proper eye
protection
Construction ParametersMain Structure
Boomilever is a single structureMade of wood bonded by glue
Construction ParametersMain Structure
Unlimited laminations by students is allowedNo limit on the cross section size of individual
pieces of wood
Dimension Cue Sheet
Construction ParametersAttachment Base
Attach to one or more mounting holes on the Testing Wall
May not attach or hook on edge of Testing WallNo more than 1.3 cm thick
Attachment Base
1.3 cm maximum
Construction ParametersAttachment Base
one or more partsmade from any type or size of wood and
wood products w/in the rulesmust be a permanent part of the
Boomileverincluded in the mass of the structure
Boomilever Dimension LimitsHorizontal 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
40.0 to 45.0 cm
Loading Block
Boomilever Dimension LimitsContact Depth
The lowest distance the Boom may have in contact with the Testing Wall below the centerline of the mounting holesDiv. B – no more than 20.0 cmDiv. C – no more than 15.0 cm
Contact Depth
Center Line of Mounting Holes
Loading BlockAccommodate 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 WallProvided 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’dMiddle 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’dBoom attached using:one, two, or three ¼” diameter x 7.62
cm (3”) minimum length bolts19 cm (3/4”) O.D. flat washers wing nuts
Boomilever TestingOnly 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 TestingA ¼” threaded bolt, chain, S-hooks, and bucket
will be suspended through the Loading Block
Boomilever TestingStudents may adjust the structure until
they begin loading the sandStructures tested with sand or sand like
materialUp to maximum 15 kgTeams are given 10 minutes to load the
sand into the bucket
Boomilever Testing EndsWhen 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 LoadLoad Supported includes –
Loading blockEyeboltWasher(s)Wing nutBucketSand
Not pieces of the Boomilever!
Boomilever ScoringHighest Score winsStructural Efficiency = Load Supported (grams)/Mass of
the Structure (grams)Ties1 – Lowest Boomilever Mass2 – Least Contact Depth
Boomilever Scoring TiersTeams are ranked by the highest score
within each TierTier 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
Resourceswww.soinc.orgwww.scioly.orgSearch cantilever designs/structuresSearch bridge, truss designs – concepts
are adaptable to boomileverhttp://bridgecontest.usma.edu/
Where Do We Start?Brainstorm – after Rules Review!Research online – Cantilevers,
Bridges, & TrussesStudent drawn rough designsDiscuss 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 kg12000/15 = 800
Where Do We Start?Design & Draw
Draw designs on gridded paper Draw the thickness of the wood
piecesSquare and LevelMirror Sides/Matching Sides
Where Do We Start?Design & Draw
Measurements are within specs to the rules
Bigger is always better than too smallTape 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 withBalsa is less expensive than other woods
What Wood?Attachment Base (Not Balsa)
Poplar, Bass, SpruceHeavier and strongerWill hold up better when bolted to the
Testing WallNo need to use a large pieceConsider using 1, 2, or 3 separate pieces
just where the bolts attach
Bonding the WoodPick 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
brittleMore flexible, moves with the wood
Super Glue with Accelerator –quick but can dry out the woodRigid when dry
Boomilever - Tension DesignTension - 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 DesignCompression - a pushing force.Compression length is longer than the Tension
length
Load
Tensile AdvantagesBalsa’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 DesignThe Connection between the
Boomilever and the wallWall 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 JointOne of the strongestUse as often as possibleStrengthens compression pieces by adding
stiffnessFlaw – only as strong as the face of the wood!
Butt JointNot strong for tension membersUnder Tension will pull apartUnder Compression will stay together
Notched JointStronger than Butt JointLess strength than a Lap JointDifficult to build
Gusset JointCombine a Butt Joint with a Lap JointLap another piece of wood at the jointStrong in both tension and compression
Additional Joints
Diagonals and Cross BracingDiagonal Pieces & Cross Bracing are
important!Prevents structure from torquing/twistingAdds additional strength
If the Cross Braces cross (make an X), Glue them at the X
Glue here
Warren Truss
Pratt Truss
Right Triangles in DesignSlants Face Inward
Howe Truss
Right Triangles in DesignSlates 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
Warren Truss
Modified Warren Truss
Loading Block
Tension Design
Loading Block
Tension Designs
Great Variation in Designs
Notice the use of dowel rods