Rubber Band Car
Student Seminar
Brad Nunn
BSIE Purdue University
Program Manager - Citrix
Feb 25, 2006
Today’s Activities

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Typical rubber band cars
Propeller based designs
Review competition rules
Component design
Other designs
Build a kit
Typical Rubber Band
Cars
Typical Rubber Band
Cars
Typical Rubber Band
Cars
Typical Rubber Band
Cars
Propeller Rubber Band
Cars
Propeller Rubber Band
Kit
Propeller Rubber Band
Cars
Propeller Rubber Band
Cars
Propeller Rubber Band
Kit
Review Rules

Refer to Go Cart
Competition
Construction and
Operating 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 =
F
D
=
=
L
=
W
=
1
W
D
L
2
Final Score
Longest single distance traveled in a straight line.
D = 2500 if Go-Cart traveled 2500 centimeters or more.
Longest dimension in any direction (length, width, height) in
centimeters.
Weight of the Go-Cart in grams.
11
Review Scoring
F
=
1
D
2
*
W
L
•Consider tradeoffs - (D+L squared)
Terminology

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Potential to kinetic
energy transfer
Torque
Acceleration
Speed
Momentum
Friction
Desired Outcomes
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

A small car that travels 2500 cm and
doesn’t weigh much
A gradual transfer of energy that has
just enough torque to establish
motion
A sustained transfer of energy that
delivers sufficient momentum to
cover the distance
Competitive Benchmarks
•2004-5:
T E A M IN F O
2 0 0 5 S C O R IN G S U M M A R Y
2 0 0 5 O P E R A T IO N
1
g
cm
ft
School N am e
R a n k L o c a l P o n ts
P e rf
B e n S h e p p a rd
1
100
406
J o e lla C . G o o d
2
95
175
R . R . M o to n
3
90
70
N o rth D a d e C e n te r M o d e rn L a n g u4a g e s
85
29
E a rlin g to n H e ig h ts
5
80
22
B a rb a ra H a w k in s
6
75
15
L a k e S te v e n s
7
70
15
B u n c h e P a rk
8
65
6
W . A. C hapm an
9
60
1
H u b e rt O . S ib le y
10
55
1
Irv in g a n d B e a tric e P e s k o e
11
50
0
ft
w
W
L
D1
1
2 0 .6
13
2 5 .2
1
5 2 .7
26
5 7 .8
1
6 9 .2
28
6 4 .1
1
123
4 1 .6
0
1
8 4 .5
29
4 0 .8
1
1 0 8 .6
4 2 .2
0
1
1 0 0 .8
4 2 .6
2 7 .2
1
1 1 1 .3
43
3 6 .6
1
9 8 .9
4 1 .4
5 .5
1
1 8 5 .5
2 8 .6
9 .4
1
2 4 1 .5
1 6 0 0 .2
9 3 .4
1
0
1
0
P e s k o e u s e d a "s lin g s h o t" ru b b e r b a n d th a t m a d e th e e ffe c tiv e le n g th o f th e ir c a r 1 6 0 0 .2 c m ra th e r th a n th e
cm
D2
39
90
5 9 .2
93
29
5 5 .4
5 4 .6
9 .6
12
cm
D1
D2
768
1189
1762
2743
1954
1804
0
2835
1244
884
0
1689
829
1664
1116
293
168
366
287
0
2847
0
0
0
0
0
c a r o n ly le n g th o f 2 3 .6 c m
c a lc
c a lc
c a lc
B e s t (D )
1189
2743
1954
2835
1244
1689
1664
1116
366
287
2847
0
0
M a x (D )
1189
2500
1954
2500
1244
1689
1664
1116
366
287
2500
0
0
F
406
175
70
29
22
15
15
6
1
1
0
0
0
•2003-4:
TEAM INFO
School Name
Ben Sheppard
Rainbow Park
Ernest R. Graham
Joella C. Good
R. R. Moton
Lakeview
Hialeah Gardens
Phyllis Ruth Miller
W. A. Chapman
Eugenia B. Thomas
SCORING SUMMARY
OPERATION
1
g
Rank Perf
w
W
1
1
40.1
607
2
1
47.9
317
3
1
60.5
67
4
1
144.1
38
5
1
71.7
30
6
1
97.6
29
7
1
219.3
23
8
1
50
22
9
1
50.5
11
10
1
161.2
6
cm
L
13.5
20.3
39.4
22.5
22.5
30.6
35
18.7
18.5
22.2
ft
D1
69.1
72.5
82.4
52.6
22.77
46.23
83.85
20.55
14.08
22.4
ft
D2
65.45
84.85
83.82
54.35
34.1
53.5
77.5
15.63
10.47
12.47
cm
D1
2106.168
2209.8
2511.552
1603.248
694.0296
1409.09
2555.748
626.364
429.1584
682.752
cm
calc
D2
Best (D)
1994.916 2106.168
2586.228 2586.228
2554.834 2554.8336
1656.588 1656.588
1039.368 1039.368
1630.68
1630.68
2362.2
2555.748
476.4024 626.364
319.1256 429.1584
380.0856 682.752
calc
Max (D)
2106
2500
2500
1657
1039
1631
2500
626
429
683
calc
F
607
317
67
38
30
29
23
22
11
6
Propeller Design
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Airscrew - push or pull
Left hand or right hand when facing air flow
Airfoil shape like a wing
Rubber Bands
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All shapes and sizes
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Experiment!
Component Design
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Low inertia and light weight
Wheel and Axle Design
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Minimize friction loss
Lubrication
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Graphite powder
Silicone spray (WD-40 is not
recommended)
Creative thinking
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What advantage is there to winding a
rubber band compared to stretching it?
Are there other ways to use a rubber
band that is wound up?
KNEX Kit – Rubber Band Roller
Dixie Roller
Dixie Roller
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Dixie cup Axles
Rubber Band
Construction tool – fishing line
CD Wheels
Washer, grommet, bead bearing
Drive Lever
Driven nail or paper clip
Tape
Design Challenges
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How do you make one wheel drive
and the other one follow?
How do you nest the rubber band
inside the axle so it doesn’t rub?
Little torque so the friction in the
bearing must be kept to a minimum
Little torque so the car must be light
Construction tool
Iterative Design
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Prototype
Measure and record performance
Tweak the design (farther, shorter,
lighter)
Iterate
Replicate
Calculate
Celebrate
Design optimization
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Frictionless bearing
Frictionless unwinding of the rubber
band
Thick or thin rubber band
Length of the lever arm
How many wheels
Wheel materials for low inertia
Today’s Kit
Tools for cutting, drilling,
and assembly
Aligning the Frame
• Align the axle holes before gluing rails
• Not the ends of the side rails
Gluing the Frame
• Use Gel Control Super
Glue - NOT the Liquid
(too watery)
• Less is more…
Problems / Solutions
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What problems were encountered?
What solutions were effective?
What can be done for further
improvement?
Optimization
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Enough torque to get moving?
Multiple propellers?
Travel straight?
How many winds?
Too many winds?
Smaller?
Farther?
Lighter?
Most important
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Have Fun!
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