Boomilever B & C – 2012-13

1. BoomileverB & C – 2012-13 CeAnn Chalker ceann@chalker.org

2. 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.)

3. Event Parameters • Only 1 structure entered per team • No Impound • Event Supervisor provides all assessment devices

4. 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

5. Construction ParametersMain Structure • Boomilever is a single structure • Made of wood bonded by glue

6. Construction ParametersMain Structure • Unlimited laminations by students is allowed • No limit on the cross section size of individual pieces of wood

7. Dimension Cue Sheet

8. Construction ParametersAttachment 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

9. Construction ParametersAttachment 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

10. 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 Test Wall Loading Block

11. Boomilever Dimension LimitsContact 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

12. Loading Block • Accommodate 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

13. Vertical Testing Wall

14. 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

15. 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

16. 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

17. 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

18. 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

19. Boomilever Testing • A ¼” threaded bolt, chain, S-hooks, and bucket will be suspended through the Loading Block

20. 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

21. 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

22. Boomilever Testing Load • Load Supported includes – • Loading block • Eyebolt • Washer(s) • Wing nut • Bucket • Sand • Not pieces of the Boomilever!

23. Boomilever Scoring • Highest Score wins • Structural Efficiency = Load Supported (grams)/Mass of the Structure (grams) • Ties • 1 – Lowest Boomilever Mass • 2 – Least Contact Depth

24. 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

25. 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

26. Resources • www.soinc.org • www.scioly.org • Search cantilever designs/structures • Search bridge, truss designs – concepts are adaptable to boomilever • http://bridgecontest.usma.edu/

27. Where Do We Start?Brainstorm – after Rules Review! • Research online – Cantilevers, Bridges, & Trusses • Student drawn rough designs • Discuss what might work

28. 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 kg 12000/15 = 800

29. 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

30. 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

31. 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

32. 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

33. 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!

34. 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

35. 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

36. Boomilever - Compression Design • Compression - a pushing force. • Compression length is longer than the Tension length Load

37. 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)

38. 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)

39. 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!

40. Butt Joint • Not strong for tension members • Under Tension will pull apart • Under Compression will stay together

41. Notched Joint • Stronger than Butt Joint • Less strength than a Lap Joint • Difficult to build

42. Gusset Joint • Combine a Butt Joint with a Lap Joint • Lap another piece of wood at the joint • Strong in both tension and compression

43. Additional Joints

44. 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

45. Warren Truss

46. Pratt Truss Right Triangles in Design Slants Face Inward

47. Howe Truss Right Triangles in Design Slates Face Away from Center

48. K Truss Tough to Build!

49. Boomilever Trusses – Tension vs. Compression Diagonals in Tension Diagonals in Compression Howe Truss Pratt Truss

50. Tension & Compression Loading Block Warren Truss Modified Warren Truss