CeAnn Chalker ceann@chalker.org Boomilever B & C – 2012-13 CeAnn Chalker ceann@chalker.org

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 No separate or detachable pieces

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 40.0 to 45.0 cm Test Wall Loading Block

Boomilever Dimension Limits Contact Depth The lowest distance the Boom may have in 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 Test Wall Center Line of Mounting Holes Contact Depth

Loading Block Accommodate a Loading Block – Loading Block must start – 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! 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

Right Triangles in Design 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