Rubber Band Car*Rubber Band Car*by Shawn Beightol,

Michael Krop Sr. High School, Miami, FL

September 08, 2006

*Adapted from Brad Nunn’s (Purdue University) Feb 25, 2006 Presentation*Adapted from Brad Nunn’s (Purdue University) Feb 25, 2006 Presentation

The Mantra:The Mantra: Smaller!Smaller! Lighter! Lighter! Farther!Farther!

Say it again!Say it again!

Do the Math…Do the Math…

Today’s ActivitiesToday’s Activities

Typical rubber band cars Typical rubber band cars Propeller based designsPropeller based designs Review competition rulesReview competition rules Component designComponent design Build!Build!

Typical Rubber Band Typical Rubber Band CarsCars

Typical Rubber Band Typical Rubber Band CarsCars

Typical Rubber Band Typical Rubber Band CarsCars

Typical Rubber Band Typical Rubber Band CarsCars

Dixie RollerDixie Roller

Propeller Rubber Band Propeller Rubber Band KitKit

Propeller Rubber Band Propeller Rubber Band CarsCars

Propeller Rubber Band Propeller Rubber Band KitKit

Review RulesReview Rules

Refer to Go Cart Refer to Go Cart Competition Competition Construction and Construction and Operating RulesOperating Rules

Go-Car t Compet it ion Construction and Operation Rules 1. Each team will consist of one or two students. 2. Each school will enter one Go-Cart of their own design using common construction materials such as, but not limited to: cardboard, dowels, paper clips, rubber bands, etc. All cars must be packed in a container to facilitate handling. 3. On the day of the competition, but prior to the running of the car, an actual operating Go-Cart must be submitted in order to compete.

Note: At this time, each entry must pass a visual inspection (see # 4 & 5 below). Entries that fail inspection will be given ONE opportunity to make whatever modifications are needed to pass inspection prior to the beginning of the competition. Then it will be weighed and measured. 4. The Go-Cart must be self-propelled and powered only by rubber bands. 5. The cart must run on a minimum of three wheels. 6. The frame and size of the body, the size of the wheels will depend on the team’s chosen design. It can be as long or as short as desire. 7. The cart will run on a smooth surface. The distance will be measured from the starting line to the stopping point utilizing a straight line between the two points. 8. There will be two runs for each car. The best single performance will be used for final scoring. 9. The formula used to judge the performance of the car will give the best score for the shortest, lightest, and farthest traveling car.

The formula used to determine the winner is:

F = 1 D 2 W L

F = Final Score D = Longest single distance traveled in a straight line. D = 2500 if Go-Cart traveled 2500 centimeters or more.

L = Longest dimension in any direction (length, width, height) in centimeters. W = Weight of the Go-Cart in grams.

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Review ScoringReview Scoring

F = F = 11 DD 22

* *

W LW L

•Consider tradeoffs - (D+L squared)Consider tradeoffs - (D+L squared)•Smaller!•Lighter!•Farther!

TerminologyTerminology

Potential to kinetic Potential to kinetic energy transferenergy transfer

TorqueTorque AccelerationAcceleration SpeedSpeed MomentumMomentum FrictionFriction

DesiredDesired OutcomesOutcomes A small car that travels 2500 cm and A small car that travels 2500 cm and

doesn’t weigh muchdoesn’t weigh much• Smaller!Smaller!• Lighter!Lighter!• Farther!Farther!

A gradual transfer of energy that has A gradual transfer of energy that has just enough torque to establish just enough torque to establish motionmotion

A sustained transfer of energy that A sustained transfer of energy that delivers sufficient momentum to delivers sufficient momentum to cover the distancecover the distance

Competitive BenchmarksCompetitive Benchmarks

TEAM INFO SCORING SUMMARYOPERATION1 g cm ft ft cm cm calc calc calc

School Name Rank Perf w W L D1 D2 D1 D2 Best (D) Max (D) FBen Sheppard 1 607 1 40.1 13.5 69.1 65.45 2106.168 1994.916 2106.168 2106 607Rainbow Park 2 317 1 47.9 20.3 72.5 84.85 2209.8 2586.228 2586.228 2500 317Ernest R. Graham 3 67 1 60.5 39.4 82.4 83.82 2511.552 2554.834 2554.8336 2500 67Joella C. Good 4 38 1 144.1 22.5 52.6 54.35 1603.248 1656.588 1656.588 1657 38R. R. Moton 5 30 1 71.7 22.5 22.77 34.1 694.0296 1039.368 1039.368 1039 30Lakeview 6 29 1 97.6 30.6 46.23 53.5 1409.09 1630.68 1630.68 1631 29Hialeah Gardens 7 23 1 219.3 35 83.85 77.5 2555.748 2362.2 2555.748 2500 23Phyllis Ruth Miller 8 22 1 50 18.7 20.55 15.63 626.364 476.4024 626.364 626 22W. A. Chapman 9 11 1 50.5 18.5 14.08 10.47 429.1584 319.1256 429.1584 429 11Eugenia B. Thomas 10 6 1 161.2 22.2 22.4 12.47 682.752 380.0856 682.752 683 6

TEAM INFO 2005 SCORING SUMMARY 2005 OPERATION1 g cm ft ft cm cm calc calc calc

School Name Rank Local PontsPerf w W L D1 D2 D1 D2 Best (D) Max (D) FBen Sheppard 1 100 406 1 20.6 13 25.2 39 768 1189 1189 1189 406Joella C. Good 2 95 175 1 52.7 26 57.8 90 1762 2743 2743 2500 175R. R. Moton 3 90 70 1 69.2 28 64.1 59.2 1954 1804 1954 1954 70North Dade Center Modern Languages4 85 29 1 123 41.6 0 93 0 2835 2835 2500 29Earlington Heights 5 80 22 1 84.5 29 40.8 29 1244 884 1244 1244 22Barbara Hawkins 6 75 15 1 108.6 42.2 0 55.4 0 1689 1689 1689 15Lake Stevens 7 70 15 1 100.8 42.6 27.2 54.6 829 1664 1664 1664 15Bunche Park 8 65 6 1 111.3 43 36.6 9.6 1116 293 1116 1116 6W. A. Chapman 9 60 1 1 98.9 41.4 5.5 12 168 366 366 366 1Hubert O. Sibley 10 55 1 1 185.5 28.6 9.4 287 0 287 287 1Irving and Beatrice Peskoe 11 50 0 1 241.5 1600.2 93.4 2847 0 2847 2500 0

0 1 0 0 0 0 00 1 0 0 0 0 0

Peskoe used a "slingshot" rubber band that made the effective length of their car 1600.2 cm rather than the car only length of 23.6 cm

•2004-5:2004-5:

•2003-4:2003-4:

Score = f(L)

Score L-2.5

R2 = 0.3

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10 15 20 25 30 35 40 45

Length (cm)

Score

Score as a function of LengthScore as a function of Length

Score as a function of MassScore as a function of MassF=f(W)

Score W-2.0

R2 = 0.5

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W (g)

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Thoughts from analysis of Thoughts from analysis of competition data:competition data:

Competition formula suggests Competition formula suggests F F 1/L 1/L2 2 – this should be most significant– this should be most significant

Data supports this with a power function of 2.5Data supports this with a power function of 2.5 Correlation is low! (0.3)Correlation is low! (0.3) F F W –mass should be less a factorW –mass should be less a factor Data suggests in practice this is more significant Data suggests in practice this is more significant

with a power function of 2.0with a power function of 2.0 Correlation is almost twice as high (0.5)Correlation is almost twice as high (0.5) Interpretation? Students assemble long vehicles Interpretation? Students assemble long vehicles

from kits without thinking?from kits without thinking? Students who modify for mass acquire and apply Students who modify for mass acquire and apply

design skills?design skills?

The Mantra:The Mantra: Smaller!Smaller! Lighter! Lighter! Farther!Farther!

Say it again!Say it again!

Do the Math…Do the Math…

Rubber BandsRubber Bands All shapes and sizes All shapes and sizes

Experiment!Experiment!

Component DesignComponent Design

Low inertia and light weightLow inertia and light weight

Wheel and Axle DesignWheel and Axle Design Minimize friction lossMinimize friction loss

LubricationLubrication Graphite powder Graphite powder

Silicone spray (WD-40 is not Silicone spray (WD-40 is not recommended)recommended)

Creative thinkingCreative thinking

What advantage is there to winding a What advantage is there to winding a rubber band compared to stretching it?rubber band compared to stretching it?

Are there other ways to use a rubber Are there other ways to use a rubber band that is wound up?band that is wound up?

Iterative DesignIterative Design

PrototypePrototype Measure and record performanceMeasure and record performance Tweak the design (smaller, lighter, Tweak the design (smaller, lighter,

farther)farther) IterateIterate ReplicateReplicate CalculateCalculate CelebrateCelebrate

Design optimizationDesign optimization

Frictionless bearingFrictionless bearing Frictionless unwinding of the rubber Frictionless unwinding of the rubber

bandband Thick or thin rubber bandThick or thin rubber band Length of the lever armLength of the lever arm How many wheelsHow many wheels Wheel materials for low inertiaWheel materials for low inertia

Microsoft Excel

Worksheet

The Mantra:The Mantra: Smaller!Smaller! Lighter! Lighter! Farther!Farther!

Say it again!Say it again!

Do the Math…Do the Math…

Most importantMost important

Have Fun!Have Fun!