Boomilever B

1
BoomileverB C 2012-13

• CeAnn Chalker
• ceann_at_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 contd

• 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 contd

• 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 contd

• 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 contd

• 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?Its 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
  (11)
• Longer to dry but doesnt 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

• Balsas Tensile strength is much greater than
  its 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
51
Tension Design
Loading Block
52
Tension Designs
53
Great Variation in Designs
54
(No Transcript)
55
(No Transcript)
56
(No Transcript)
57
(No Transcript)
58

• Notice the use of dowel rods

59
(No Transcript)
60
(No Transcript)