Building Events (Boom & Tower)

Towers and Boomilevers Instructor † Andrew A d Roberts R b t „ [email protected] „ Junior J i iin A Aerospace Engineering E i i „ 7 year participant in Science Olympiad † Multi event medal winner

„ Coached State Champions in Wright Stuff. „ Two year summer SO camp coach.

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Process † † † † † † † †

Read and understand the rules Research Brainstorm Supplies & Tools D i Design Build T t Test Analyze…Repeat last 4 steps

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Rules † Get the copy of the rules and make several copies † Identify all measurement points in the rules † Measure your drawing as you design to be sure you meet the rules you follow every y detail. † Make sure y † A bit big is better than a bit small „ You can always y sand it down 10/2007

Rules † Effi Efficiency i is i actually t ll all ll th thatt matters. tt † Efficiency equals mass held divided b mass off structure. by t t † A 30g structure holding 15kg has an efficiency ffi i off 500 † A 10g structure holding 10kg has an efficiency of 1000, twice as efficient and wins. 10/2007

Research / Bibliography † www.tx.ncsu.edu/science_olympiad/ www tx ncsu edu/science olympiad/ † www.turnertoys.com/G1/science_olympiad

† † † † † † †

www.garrettsbridges.com g g http://abcdpittsburgh.org www.geocities.com www.scioly.org www.soinc.org West point bridge Design Search on Towers or Boomilevers

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Brainstorm † Take a field trip trip. Look for towers towers, TV, TV Cell, Cell Bridges, Power line towers. Look at the angles and the joints. † Ask students to draw rough sketches of possible designs based on what they discovered in research † Talk about sketches discussing what they like and why. † Make sure they understand the device that holds the most weight does not necessarily win. 10/2007

Supplies/Tools † † † † † † † †

Copy of the Rules Drawing Board Paper/drafting Pencils Eraser Metal ruler T-square Testing equipment

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† † † † † † † † † †

Balsa Razors Saw Glue Accelerator W Wax paper/Clear /Cl T Tape Building Board o Acetone Sanding block Level

Balsa †H Has th the highest hi h t strength t th tto weight i ht ratio † Has H a greater t tensile t il strength t th th than compression strength † Is I easy to shape h and d work k with ih † It is cheap

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Balsa

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Adhesives † Wood Glue „ Mix with alcohol 1part to 1part

† † † †

Green Tube Glue Super Glue Accelerator Glue weight can be a major weight factor but it doesn factor, doesn’tt have to be be. You can easily use 1-2 grams of glue (or g boomilever. less)) on a 10-gram

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Design † Everything must be square and level † When they are not level, you have unequal forces and that puts excess strain on members. † Draw plan on paper and tape to rigid, flat surface. plans in a non stick surface † Cover the p like wax paper or clear packaging tape. 10/2007

Boomilever Design † Th There are two t basic b i types t off boomilevers. † First Fi t is i the th tension t i boomilever, b il where h the tension chord is longer than the compression chord. chord † Second is the compression boomilever which is the opposite of boomilever, the tension. 10/2007

Boomilever Design † Tension T i D Design i

† Compression Design

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Tensile Advantages † The tensile strength of balsa is much greater than it’s compression strength † Because of this, a compression style boomilever must have thicker main support beams and, therefore, a mass of approximately 1.25 grams more than a tensile boomilever to support the same load. 10/2007

Boomilever Tensile Advantages F1/L1=F2/L2

L1 L2

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F1

Boomilever Design † Th The mostt important i t t connection ti is i between the boomilever and the wall. † The important distance is from the wall ll to the h center off the h loading l di block.

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Tower Design † It Its important i t t tto remember b length l th must be compensated for in the drawing on the lower section because that part of the tower is at an angle † This can be accomplished with simple trigonometry. trigonometry

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Tower Design † The best base is the smallest base, base because it requires less material, and therefore less mass. † The hole cut in the test board is q , so the smallest base is not square, corner to corner, it is side midpoint to side midpoint † This distance is about 15 cm, as opposed to 20 cm 10/2007

Tower Base

~15cm

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Tower Design † Th There is i a greater t force f on the th main i beams on the lower half of the tower because they are angled. angled † Thi This means the h top supports should h ld be a little smaller than the bottom.

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Tower Design

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Tower Design † Only build two sides and then connect them to each other. You do not need to build 4 sides. Doing g so doubles the number of vertical supports † The top and bottom should be built separately and then attached to each other. † This allows the bottom to be angled like it should and the top to be vertical. vertical

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Joints † Lap Joint:

† The lap joint is one of the strongest, and you should use it whenever you can. It strengthens compression members because it adds stiffness. The lap joint has one d drawback, b k however. h The h joint is only l as strong as the face of the wood. 10/2007

Joints † End E dJ Joint: i t

† The end joint is not a very strong joint, especially for tension members. In tension, the two pieces of wood will just pull right away from each other. 10/2007

Joints † Notched N t h d Joint: J i t

† The notched joint gives more strength than the end joint, but less than the lap joint. It is more difficult to build, so it is not very common.

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Joints † Gussets: G t

† If you have to use an end joint, it is a good idea to add a gusset to make it stronger. The gusset creates a lap joint, which is strong in both tension and compression. 10/2007

Joints †O On your X b braces, they th mustt be b connected in the middle. Glue here!

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Trusses † Warren W T Truss

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Trusses † Pratt P tt

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Trusses † Howe H

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Trusses † K Truss T

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Boomilever Possible Designs Diagonals are in Tension Diagonals are in Compression

Howe Truss

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Pratt Truss

Boomilever Possible Designs

Warren Truss

Modified Warren Truss

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Boomilever Possible Designs Tension Design Beam connection should attach at the center of the loading block.

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Tower Possible Designs

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Boomilever Test Platform †B Build ild the th equipment i t for f testing. t ti You Y must have the chain, bucket, sand, block and a scale block, scale.

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