BOOMILEVER 2019 BOOMILEVER 2019 BOOMILEVER 2019 UNDERSTANDING THE BOOMILEVER EVENT

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1 This is an Experimental Engineering event that places maximum emphasis on innovative design, efficient use of materials, and quality of construction Coaches primary job is to help students understand the expectations of the event; ALL competitors should arrive at competitions with TIER 1 boomilevers that can meet construction and competition requirements. Coaches primary job is to help students understand the experimental process; students should be encouraged to push the design envelope and learn what works through repeated structural failures, design revisions, and retests. Student experimentation with different designs, material selection, and construction techniques will result in gains in efficiency, and thus improved results. Think of a boomilever as a horizontal crane arm attached to a wall. The holdback for the load is a single mounting hook high on the wall, and the crane arm bears against the wall at one or more lower points. The load is suspended near the end of the boom. Experimental process. Student design, photographs, video and testing data records help document sequential boomilever designs, failure modes and improved results. SIGNIFICANT 2019 RULES Materials No manufactured composites, plies or laminates, bamboo or paper products No size limit on materials cross section Construction Must be a single structure with NO separate or detachable pieces Must be long enough to suspend load between 40cm and 45cm from wall Contact depth line is 20cm for Division B and 15cm for Division C ONE Mounting Hook will be used for both Division B and C Scoring A minimum load of 3,000 grams (3 KG) is required for TIER 1 A maximum load of 15,000 grams (15 KG) is used for score calculations TIER 3 is for competition or construction violations 1 st tiebreaker is the estimated load score <= the actual load score 2 nd tiebreaker is the lowest boomilever mass Scoring Tiers Tier 1 boomilevers have NO violations AND hold AT LEAST 3,000 g. SIMPLE Tier 2 boomilevers have NO violations AND hold LESS THAN 3,000 g. Tier 3 boomilevers have ANY violations AND hold any load. SCORE for Tiers 1,2&3 = Load held in grams / mass of boom in grams Tier 4 boomilevers are UNABLE TO BE LOADED CAN T BE TESTED. SCORE for Tier 4 = lowest mass of boom Tier 1 boomilevers are ranked by score, and beat ALL Tier 2, 3 & 4 booms. Tier 2 boomilevers are ranked by score, and beat ALL Tier 3 & 4 booms. Tier 3 boomilevers are ranked by score, and beat ALL Tier 4 booms. BOOMILEVERS in Tiers 2, 3 & 4 only result in TEARS

2 Photos of mounting hook installed on wall Photo of testing wall mounted on sand loading device (breaker) 2019 rules have only ONE mounting hook for both Div B & C Top of tape lines identify the Contact Depths for C (upper) and B (lower) Photo of testing wall mounted on sand loading device (breaker) 2019 rules have only ONE mounting hook for both Div B & C instead of the through-bolt shown in this image Top lines lines identify the Contact Depths for C (upper) and B (lower) Knowledge base General understanding of loads and forces on booms and structural girders; and the relative strength of materials (balsa wood) subjected to tension, compression, shear, bending & buckling loads Girder and truss designs for efficient, LIGHTWEIGHT load bearing structures; and how girders and trusses members are loaded (compression, tension); TRIANGLES for stiff and strong structures Construction & gluing techniques; the importance of precise dimensions and balanced designs to resist vertical (gravity) loads and compressive and tensile loads How to conduct Experimental Test Program, analyze failures, improve weak members, and achieve Predictable results UNDERSTANDING THE 2019 RULES The COACH shares the responsibility if a BOOMILEVER DOESN T MEET SPECS, but the students always pay the price Only those meeting the construction and competition specifications will compete for medals. Common mistakes include Boomilever LENGTH and structure won t support the load block assembly so the centerline of chain hangs between 40cm and 45cm from the testing wall (paragraphs 3.c and 3.d) Boomilever DEPTH exceeds the CONTACT DEPTH LINE where it touches the testing wall before and/or during testing (paragraph 3.e) or USING A PREVIOUS YEAR S SPECIFICATIONS EXPERIMENTING is the ONLY approach to high load scores The 2019 Tier 1 scoring rules require holding a minimum load of 3KG, and do not credit any load supported greater than 15 KG. A boomilever that will hold 20 KG has extra weight, and will lessen the load score (structural efficiency). Learn from it and build another, LIGHTER one.

3 Girder Designs SOUND DESIGN FUNDAMENTALS Gravity acts DOWN, VERTICALLY at the point of the load. The load will transfer through the boomilever structure to try to pull the Mounting Hook from the wall. Think of pulling a rope. TENSION. The load will transfer through the boomilever structure to push against the wall. Think a tower on its side. COMPRESSION & BENDING Triangles are more rigid than rectangles ALL Trusses should incorporate diagonal members. Yours should, too. Diagonal members should be incorporated in all three planes (L, W, H) Truss Beams or Laminated Beams are efficient for bending loads Place most of the material in these beams along edges where the TENSION loads and COMPRESSION loads occur MAXIMIZE glue joint surface area Arrange structural members face-to-face for strongest gluing Liberally use gussets for reinforcement of butt joints Never hang a load on a simple butt joint MENTORING THE Inclined BOOMILEVER EVENT STRENGTH OF MATERIALS AND JOINTS TYPE OF WOOD Balsa is the lightest wood available. Medal winning boomilevers are made from BALSA. Basswood has a high strength-to-weight ratio, but use it SPARINGLY, if at all. Spruce may also be available, but is MUCH TOO DENSE. GLUE JOINTS Strong sticks but weak joints equals a weak boomilever Strong glue joints maximize the surface area to be glued Gussets maximize the shear bonding area for glue joints Glue adds WEIGHT. Excess glue is excess weight Trim it off Use quick-set glue to build and test designs. Thin CCA glue runs like water. Use a special TIP to control it DROP by DROP. DON T USE GORILLA GLUE. SIZE OF STRUCTURAL MEMBERS Make Thicker structural members by gluing thinner sticks together (laminating). Custom laminating can place the weight (wood) where the greatest stress is. Cut sheet stock to size. A skin provides a lot of directional strength There are lots of good glues Its not so much which type of glue you use, its how you use it

4 Always inspect glue joints!!! Some students weigh and mark each stick to ensure balanced Structure Use a sanding block Inspect each stick for flaws QUALITY CONSTRUCTION NEATNESS REALLY DOES COUNT GLUE WEIGHS MORE THAN BALSA CUT, DON T CRUSH BALSA ONLY NEW EXACTO OR RAZOR BLADES ARE SHARP A THIN GLUE JOINT IS STRONGER THAN A FAT ONE THE WOOD REALLY IS STRONGER THAN THE GLUE (IN TENSION) DON T LET WOOD SHRINKAGE or EXPANSION CREATE AN OUT OF SPECIFICATION BRIDGE (build it a tad longer, narrower, lower) THE BOOMILEVER WORKS IN 3-DIMENSIONS Use triangles to resist loads in each direction The concept of gusset-reinforced joints EXPERIMENTAL TESTING PROGRAM WHY??? Students will load their own boomilevers during competitions Bottled Sand, Loose Sand, Combination of bottles and loose sand, Hopper-loading Students need to be cautious, yet confident. Need to have done it before. Testing EARLY will identify your team s best builderencourage students to build boomilevers at home. Testing to failure will identify design deficiencies Video recording & slow-motion replay can show failure mode Testing & analysis will identify the weak link in the design Always improve the weak link in the next design Always test to destruction!!!! Otherwise you don t know how overbuilt (AND OVERWEIGHT) a boomilever design is.

5 EXPERIENTIAL LEARNING WORKS. BREAK STICKS/JOINTS BEFORE BREAKING BOOMILEVERS BREAK MOUNTING HOOK CONNECTIONS BEFORE BOOMS BREAK WHOLE BOOMILEVERS BEFORE COMPETITIONS STRIVE TO BUILD FOR REPEATABLE RESULTS EVOLVE DESIGN TO ACHIEVE MORE THAN 3-Kg held EVOLVE DESIGN TO ACHIEVE CLOSE TO 15-Kg held DOCUMENT YOUR TESTING AND DESIGN EVOLUTION [data table, photos, videos] BUILDING & BREAKING IS JUST TOO MUCH FUN Suggested Materials for your BOOMILEVER Team TESTING SUPPORT Simulated Test Wall (see next slide) paragraph 5.a.i 2-5cmx5cmx2cm loading blocks Eye bolt, chain & S-hook(s) 2-5-gallon buckets 50 # of dry, white sand Digital bathroom scale (reading to 0,1 kg) Digital balance, 0 to 100g, (reading 0.01g) Bubble level CONSTRUCTION TOOLS Metric ruler, meter stick & caliper 2ftx3ft sheets of masonite, plywood, etc. for cutting & gluing surfaces Exacto knives (or balsa cutter) COACH CONTROL Fine sandpaper, sanding block Engineering triangles (for right-angles) Thin tip extensions for CCA glue bottles Saran wrap & wax paper for gluing surface BOOMILEVER MATERIALS Balsa sticks_ various dimensions_ square & rectangular x-section_ from 3/16 to 1/32in dimensions Balsa sheets_ from 3/16 to 1/32 thick, 2-ft long CCA glue (thin & gap-filling), Insta-cure, Un-cure Wood glue (yellow type) PROTECT THE INVESTMENT Do not over-test the same boomilever. Boomilevers previously tested to loads nearing the breaking point may have been damaged. If you are getting consistent results, the smartest approach may be to build two identical boomilevers; one for testing to failure, and a second for the competition. Stress the fragility of the boomilever to the student(s), the lighter it is, the more easily it can be damaged through mishandling. The student should do all handling, assembling, and loading, as it is his/her responsibility. Even event staff have been known cause damage by mistake. Photo of simulated testing wall (not using mounting hook) Plastic & cardboard boxes are great for storage & transport of boomilevers. Foam inserts will restrict movements and limit damage from loose tools and objects inside the box.

6 Tips for a COMPETITIVE Boomilever (1)The Mounting Hook connection is critical, but don t overbuild it. Build and break this piece many times as a component, then attach it to your boom (2)Choose structural members of different x-sections for heavily-loaded and lightly-loaded uses and locations (3)Diagonal cross-bracing can be quite thin, but is important. It keeps long, compressed members from BUCKLING. Diagonals are needed in all 3 axes. (4)Square & rectangular x-sections of the same area have the same weight, but the rectangular x-section is much stronger if oriented properly (5)Your stronger structural members should be aligned with the wider edge resisting the direction it wants to bend (6) Larger strength members should always have rectangular, never square x- sections. You can laminate multiple square members to make a rectangular one (7)Precision, balanced assembly can allow a good design to EXCEL, whereas a more haphazard assembly of the same, good design may result in only half the failure load (and scoring efficiency) WHAT DO COMPETITIVE BOOMILEVERS look like?