CeAnn Chalkerceann@chalker.org

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