BOOMILEVER 2020 · BOOMILEVER 2020 Think of a boomilever as a horizontal crane arm attached to a...

BOOMILEVER 2020

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 far end of the boom. (note: the pictured boom will not meet the 2020 construction and competition rules

BOOMILEVER 2020This 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.

– Experimental process. Student design, photographs, video and testing data records help document sequential boomilever designs, failure modes and improved results.

UNDERSTANDING THE BOOMILEVER EVENT

SIGNIFICANT 2020 RULESMaterials … No manufactured composites, plies or laminates, bamboo or paper productsNo size limit on materials cross section

Construction … Must be a single structure with NO separate or detachable piecesMust be long enough to suspend load between 40cm and 45cm from wallContact DEPTH LINE is 20cm for Division B and 15cm for Division CContact WIDTH LINES are 4cm right & left of the centerline (@ hook)

Scoring …A maximum load of 15,000 grams (15 kg) is used for score calculationsA 5,000g (5kg) BONUS is awarded for holding the entire 15 kg loadTIER 2 is for competition or construction violations & it will hold a loadTIER 3 if the boomilever cannot be loaded (will not hold block & chain)1st tiebreaker is the estimated load score <= the actual load score2nd tiebreaker is the lowest boomilever mass


BOOMILEVER 2020

BOOMILEVER 2020


Scoring Tiers …

Tier 1 boomilevers have NO violations AND can be tested (hold at least the loading block & chainTier 2 boomilevers have CONSTRUCTION and/or COMPETITION violations AND can hold a (any) load.

A 5,000g (5kg) BONUS will be added to the load supported forboomilevers that support 15kg

SCORE for Tiers 1&2 = (Load held in grams + BONUS) / mass of boom in grams

Tier 3 boomilevers are UNABLE TO BE LOADED / CAN’T BE TESTED.

Tier 1 boomilevers are ranked by score, and beat ALL Tier 2 & 3 booms.Tier 2 boomilevers are ranked by score, and beat ALL Tier 3 booms. Tier 3 boomilevers are ranked by closest estimate, then by lowest mass.

BOOMILEVER 2020


Photo of testing wall mounted on sand loading device (breaker)

2020 rules have only ONE mounting hook

Top of horizontal tape lines identify the Contact Depths for C

(upper) and B (lower)

Vertical blue tape area lies within the CONTACT WIDTH

LINES (a new exclusion zone, where the boomilever can’t

touch the Testing Wall either before, nor throughout testing)

Photos of mounting hook

installed on wall

BOOMILEVER 2020


2020 rules have only ONE mounting hook for both Div B & C

Examples of successful designs for “holdbacks” that work with the single “Mounting Hook”.

Note that the hook is not disassembled during the boomilever setup for testing.

The boomilever “holdback” slips easily in the gap between the hook and the wall, and resists

the load by pulling on the curved part of the hook.

BOOMILEVER 2020


2020 rules have only

ONE mounting hook

Top of the horizontal lines

lines identify the Contact

Depths for C (15cm,

upper) and B (20cm,

lower)

Vertical blue tape area

lies within the

CONTACT WIDTH

LINES (a new exclusion

zone, where the

boomilever can’t touch

the Testing Wall either

before, nor throughout

testing)

BOOMILEVER 2020

• 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 2020 RULES”

Only those boomilevers 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)

Boomilever DEPTH exceeds the CONTACT DEPTH LINE where it touches the testing wall before and/or during testing (paragraph 3.d)

Boomilever touches the TESTING WALL between the (new) CONTACT WIDTHLINES (paragraphs 3.d and 5.a.v)

… or … USING A PREVIOUS YEAR’S SPECIFICATIONS …

MENTORING THE BOOMILEVER EVENT

BOOMILEVER 2020

“UNDERSTANDING THE 2020 RULES”

EXPERIMENTING (building and breaking boomilevers OR component parts of boomilevers) is the ONLY reliable approach to achieve high loading efficiency scores

The 2020 scoring rules give a 5,000g (5kg) BONUS to boomilevers that hold a minimum of 15kg

A boomilever that will hold substantially more than 15kg has extra weight,and will lessen the load score (structural efficiency)

BUT, under the 2020 rules, booms holding less than 15kg will be at an even greater competitive disadvantage (NO 5,000g BONUS).

Learn from your experiment(s) and build a boom STRONG ENOUGH to hold 15kg and earn the 5,000g BONUS.

ONLY THEN should you build LIGHTER boomilevers to improve your calculated efficiency score.


BOOMILEVER 2020

“UNDERSTANDING THE LOADS: BOOMILEVER”

Simple engineering statics and geometric relationships can be used to approximate the loads that will be experienced in the primary boomilevermembers_ (1) the “hook holdback”, (2) the “tension members” and (3) the “boom truss” (see next slide)

The magnitude of the loads can be understood by calculating the loads that will be experienced when 15kg is supported.

Students can then design and test individual components to support these loads without building and testing the entire structure.

Once you are confident that you have adequately designed and built components that will support the design loads, then put them togetherinto a complete boomilever and continue testing to optimizing your structure.

You should not stop until you’re confident you can support 15kg, and earn the 5kg BONUS.


BOOMILEVER 2020

‘B’ Division Dimensions & Forces

Length b = 40 to 45 cm

Len

gth

a <

= 20

cm

Load

Block

Sand

Bucket

15 kg

Engineering statics shows that the forces in

members are proportional to the ratios of the

lengths of the members.

Use known forces and dimensions for your

BOOMILEVER to calculate approximate

forces in the main structural members.

Force b = ? kg

compression (push)

Force vector

diagram

Fc (horiz)

Fc

(ver

t)

RATIOS OF

LENGTHS

a/a =

b/a =

c/a =

FORCE

VECTORS (kg)

Fc vert =

Fc horiz =

Fb =

FORCES IN

MEMBERS (kg)

a = zero

b (compression) =

c (tension) =

Wall

hook

Contact

Depth

line


BO

OM

ILEVER

20

19G

irder

Design

s

MENTORING THE Inclined BOOMILEVER EVENT

SOUND DESIGN FUNDAMENTALSGravity 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 of a tower on its side. COMPRESSION & BENDING

“Triangles” are more rigid than rectanglesALL compression & bending resisting structures should incorporate diagonal

members. Yours should, too.Diagonal members should be incorporated in all three planes (x, y, z)

“Truss Beams” or “Laminated Beams” are efficient for bending loads Place most of the material in these beams along edges

where the maximum loads occur

MAXIMIZE glue joint surface area Arrange structural members face-to-face for strongest gluing

Liberally use gussets for reinforcement of “butt” jointsNever “hang” a load on a simple “butt” joint

BOOMILEVER 2020

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 boomileverStrong 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 offUse “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 gluesIts not so much which type of glue you use, its’ how you

use it



QUALITY CONSTRUCTION

NEATNESS REALLY DOES COUNTGLUE 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” ONETHE 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-DIMENSIONSUse triangles to resist loads in each direction

Always inspect glue joints !!!

Some students weigh and mark each “stick” to ensure “balanced” structure

Use a sanding block

Inspect each “stick” for flaws


BO

OM

ILEVER

20

20

The c

once

pt o

f gu

sset-

reinfo

rced joint

s

EXPERIMENTAL TESTING PROGRAMWHY ???

Students will load their own boomilevers during competitionsBottled Sand, Loose Sand, Combination of bottles and loose sand,

Hopper-loadingStudents 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-mo replay can show failure mode & locationTesting & analysis will identify the weak link in the designAlways improve the weak link in the next design

Always test to destruction !!!! Otherwise you don’t know how underbuilt (no BONUS) or overbuilt (AND OVERWEIGHT) a boomilever design is.


EXPERIENTIAL LEARNING WORKS.

BREAK STICKS/JOINTS BEFORE BREAKING BOOMILEVERSBREAK “MOUNTING HOOK” CONNECTIONS BEFORE BOOMS

BREAK WHOLE BOOMILEVERS BEFORE COMPETITIONS STRIVE TO BUILD FOR REPEATABLE RESULTS

EVOLVE DESIGN TO ACHIEVE MINIMUM STRENGTH of 15kg DOCUMENT YOUR TESTING AND DESIGN EVOLUTION [data

table, photos, videos]

BUILDING & BREAKING IS JUST TOO MUCH FUN

BOOMILEVER 2020



BOOMILEVER 2020Suggested Materials for your BOOMILEVER Team

TESTING SUPPORTSimulated Test Wall (see next slide)

paragraph 5.a.i2- 5cmx5cmx2cm loading blocksEye bolt, chain & S-hook(s)2- 5-gallon buckets50 # of dry, white sandDigital bathroom scale (reading to 0,1 kg)Digital balance, 0 to 100g, (reading 0.01g) Bubble level

CONSTRUCTION TOOLSMetric ruler, meter stick & caliper2ftx3ft sheets of masonite, plywood, etc. for cutting & gluing surfacesExacto knives (or balsa cutter) COACH CONTROLFine sandpaper, sanding block Engineering triangles (for right-angles)Thin tip extensions for CCA glue bottlesSaran wrap & wax paper for gluing surface

BOOMILEVER MATERIALSBalsa sticks_ various dimensions_ square & rectangular x-section_ from 3/16 to 1/32in dimensionsBalsa sheets_ from 3/16 to 1/32 thick, 2-ft longCCA glue (thin & gap-filling), Insta-cure, Un-cureWood glue (yellow type)

Photo of simulated testing wall (not using

mounting hook)


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.

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.


WHAT DO COMPETITIVE BOOMILEVERS look like ?

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 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)

BOOMILEVER 2020

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