1. CeAnn Chalker ceann@chalker.org
Boomilever B & C –
CeAnn Chalker

2. 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.

3. 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.)

4. Event Parameters Only 1 structure entered per team No Impound
Event Supervisor provides all assessment devices
No separate or detachable pieces

5. 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

6. Construction Parameters Main Structure
Boomilever is a single structure
Made of wood bonded by glue

7. Construction Parameters Main Structure
Unlimited laminations by students is allowed
No limit on the cross section size of individual pieces of wood

8. Dimension Cue Sheet

9. 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

10. 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

11. 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

12. 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

13. 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

14. Vertical Testing Wall

15. 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

16. 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

17. 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

18. 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

19. 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

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

21. 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

22. 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

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

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

25. 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

26. 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

27. Resources www.soinc.org www.scioly.org
Search cantilever designs/structures
Search bridge, truss designs – concepts are adaptable to boomilever

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

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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!

35. 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

36. 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

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

38. 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)

39. 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)

40. 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!

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

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

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

44. Additional Joints

45. 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

46. Warren Truss

47. Right Triangles in Design
Pratt Truss
Right Triangles in Design
Slants Face Inward

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

49. K Truss
Tough to Build!

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

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

52. Tension Design
Loading Block

53. Tension Designs

54. Great Variation in Designs

59. Notice the use of dowel rods