dearby car _ 02

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Scotten W. Jones

8/12/2019 Dearby Car _ 02


Start with the official BSA

pinewood derby car kit

Finish with a fast pinewood

derby car

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• Buildin a inewood derb car re uires tools ossibl

including power tools.• Your son should be as involved in building the car as

poss e u you nee o use goo u gmen n erms o

what he can safely do.

• Do not let our son use tools he isn’t read to use safel .

You will likely have to do some of the work yourself.

• Wear appropriate safety gear at all times.

• Each boy is different, only you know what your son cansafely do.

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• Ph sicist with almost 30 ears of en ineerin ex erience.

• Bought and read all the guides.• Searched the internet and read hundreds of articles.

• Built and tested 37 cars on our own track with ten

thousandth of a second timing.• .

• First place pack fifty, four of the last four years.

•

smashed, 2007 and 2008 he won districts. 2009 no

district race was held, third at council.

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• Race long enough and you will see something go wrong.

• The races are run by volunteers doing their best for free, notpaid professionals. They are trying to be fair but mistakeshappen.

• I have seen:• Our car smashed

• The track contaminated

• Cars fly off the track and or handled roughly

• Our car raced in the wrong lane and our first place credited tosomeone else

• Politely and privately bring up your concerns to the raceofficials.

• The race officials decisions are final, my experience is they willfix what they can if they understand the issue.

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• Read the official pack rules, they are final. This is just a

sampling.• Car must be built during the scouting year.

• , .

• You cannot move the pre cut axle slots in the wood block (this

is a common reason for not being allowed to race).

• The inspector must be able to see the nail points in the axle

slots (another common problem area).

• ” - ” ,

ounces.

• Wheel treatment has specific limits (more later)

• You can add weights but they must be secure.

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• The old “standard” for a track was 32’ long made of wood.

• Even years ago there was no real “standard”.• Pack fifty uses a 40’ wooden track and has for at least ten

ears.

• Districts used to use 32’ wooden tracks (until 2007), now theyare using 40’ aluminum tracks.

4’

Finishline

Approximately 28’

32’

Standard track

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• At the be innin of the race the car has otential ener .

• This is the most energy the car will ever have!• Once the starting gate opens the potential energy begins

o conver o ne c energy spee an ea ue o

friction.

• Heat due to friction is ener lost bad and no lon er

available.

• Maximize the potential energy and minimize the friction is

a you ave o o o ma e a as car.• Sounds simple, right?

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• Potential ener is

determined by twothings:

• e we g o e car.

• How far the center of

ravit will fall. AB

• The heavier the car and

the father the center of

Approximately 30 o

grav y w a e g erthe potential energy.

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• Kinetic ener for a

given weight isproportional to

0.60

0.70

0.80

.

12.00

14.00

16.00

.

s 2 )

2 )

Acceleration

due to gravity

Friction

.

• Without friction 100%

of the potential 0.30

0.40

0.50

6.00

8.00

10.00

e c c e

l e r a t i o n ( f t /

c c e l e r a t i o n ( f t /

energy will be

converted to kinetic0.00

0.10

0.20

0.00

2.00

4.00

0 10 20 30

Air resistance

accelerates down the

ramp.

Distance

Forces acting on a well

desi ned car.

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• Rolling resistance due to wheel and axle friction is the most important. .

• Air resistance is less important and mostly effects the car once itreaches top speed at the bottom of the ramp, but it does matter.

12.0

14.0

16.0

)12.0

14.0

16.0

)

6.0

8.0

10.0

V e l o c i t y ( f t / s

Bottom of

the ramp

6.0

8.0

10.0

V e l o c i t y ( f t / s

Bottom of

the ramp

0.0

2.0

.

0.0 5.0 10.0 15.0 20.0 25.0 30.0

Feet from the start

0.0005 ‐> 0.005 ‐> 0.01

0.0

2.0

.

0.0 10.0 20.0 30.0

0.1131 ‐> 0.2262 ‐> 0.3393

Air resistance

Rolling resistance

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• Weight and weight distribution

• Aerodynamics

• Do these three things well and you will have a

.• The rest of this presentation will cover practical

.

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• Some testin I have done

indicates the car is fasterif the weight is more to2.620

Elapsed time versus center o f mass (side-to-side)

.

• I don’t understand why

this would help. 2.560

2.580

.

( s e

c s )

• It could be bad test data

but….2.520

2.540 T i m

2.500

3.50 center 3.75 off-center 4.00 center

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• The maximum allowable Tun sten

Sectional

weight

car weight is 5 ounces.

• Weights can be built into

the body or added on

y n er

weight

plates

later, internal is better for

aerodynamics.

• Some people use thesectional weights on the

top or bottom of a car.

This is easy to do but not

very aero ynam c. eweight is on the bottom

make sure it doesn’t hang

.

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• The car sits over a 1-5/8” wide b ¼” hi h lane uide ou

must leave enough clearance.• Extra space is needed for the curved section of the track.

Car

Wheels

Lane guideTrack

”

1/4”

-

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• This design uses the cylinder weights inserted into 3/8” holes

3” deep.

• The weight has to be filed down to fit and slides in tightallowing you to push it in until you get the center of gravity youwant.

Top view

Rear viewWeights

e vew

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• Tun sten is more Chiseling out space for

dense than lead andthin plates can be

the plates

thin car.

• You can’t cut theweights and so you

have to snap them The finished car

hammer if you need

fractional plates.

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• Rid es and rou hness.

• You must smooth out the axles for a competitive car.

Ridges

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• Mount the axle in a drill or drill press, start the axle spinning

and use a fine file to remove the ridges.

• I use Maximum Velocities Axle Polishing kit to polish the axle.

• Wet the sand a er with WD40 wra the sand a er around awooden block and hold against the spinning axle.

• 30 seconds using 30 micron paper, buff with a clean cloth to remove the grit.

• , .




• 30 seconds using Mother’s aluminum polish on a cloth, buff with a clean cloth toremove the grit.

• The axle should look like a mirror.

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• Use a file to form a roove in the axle underneath where

the wheel will rotate. This minimizes axle wheel contactarea.

Drill chuck Drill chuck

Axle AxleTop of the woodblock is aligned

4” wood block

with the inside of

the nail head

4-1/8” wood block

File

Drill press table Drill press tableCar body

Axle

Axle narrowed

Cut-away ofthe wheel

x e eaangled to onlytouch the wheelat the wheels

center

to minimizecontact with

the wheel

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• An le the axle head so it

only contact the wheelclose to the center. Slightangle

• se an ang e p ece o

wood during polishing to

polis the angle.

Drill chuck

Axle

Wood block

Sandpaper

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• Axle ress to insure it is strai ht.

• New axle press allows the head to beangled but I don’t like the shape of the

ea a resu s.

• Harden the axle before polishing

•

• Plunge it into cold water

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• Wheels as received

have mold marks thatneed to be removed.

• e o s on e e ge

of the wheel must be

left so don’t removetoo much material.

• The wheel tread must

cannot be narrowed. H wheel –

illegal under

ack 50 and

district rules

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• Mount the wheel in a Maximum

Velocity pro wheel mandrel.

• Start the wheel spinning in a drill ordrill press.

Drill chuck

• Wrap the sandpaper around awooden block and hold against the

wheel.

Collet

Wheel

Wood blockSandpaper

• Use 60 grit paper to sand out moldmarks.

• Polish the wheel with 600 rit 1000

grit and 1500 grit sand paper insequence. The paper should be wetwith water before polishing the wheel

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• Lathin the wheel to Lathing tool

insure it is round.• Balancing the wheel.

to insure

roundness

• Coning the inside of

the wheel hub so it

onl contact the body near the axle. Wheel

balancing

Wheel

coning

tool

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• Standard wheels Wheel Car Elapsed

are approximately0.45 ounces per set

(ozs)

(ozs)

(secs)

0.45 5.00 2.5581

0.30 4.85 2.4772

.

• 0.30 and 0.15

ounce Cub Scout

0.15 4.70 2.4677

0.15 5.00 2.4424

cut down wheels

are available.

• .

don’t meet the

current district

rules.0.45 untouched wheels 0.15 cut down wheels

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–• Oils – Kr tox Su er

Z and NyOil areillegal under pack

.

• Only dry powder

lubricants areallowed but there

are still a lot of

.

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• Seven ears of Time

lubricant testing

head to head with

Lubricant (secs)

Pine Pro 2.4768G/M 2.4834

NyOil II 2.4934

preparation.

• Shorter times are

Super Z + Oil 2.4959

Max-V Lube (Preliminary ranking) 2.5137

Tube-O Lube 2.5140

-

better. .

Hob-E Lube Teflon 3.1947

• Pine Pro is the best but it is touchy. Put it on, spin it in and leave it. It isgood for about 10 to 15 races before it starts to slow down!

• I put it on and run it down the track 5 times to run it in and then leave it

• Graphite lubricants generally “warm up” and get faster.

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• Put some ra hite on a i e cleaner mount it in a drill

and run it inside the wheel bore to polish the bore.

• Bore polish is available but how do you get the grit out afterwards?

• e w ee ore w grap e an en s e e ax e n.

• Spin the axle in the wheel bore with a drill and keep

addin ra hite to run it in.

• Apply graphite to the car body where the wheel will touch

and on the outside and inside of the wheel where it will hit

e car o y an ax e ea .• Mount the wheel and axle on the car, turn side ways, add

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• Minimize the car cross section in the direction of travel.

• The car surface should be as smooth and possible andtaper at both ends so the air can flow smoothly over it.

2.6200

Elapsed time versus cross sectionalarea

2.5700

2.5800

2.5900

2.6000

.

e ( s e c s )

2.5400

2.5500

2.5600

0.0 1.0 2.0 3.0

T i

Cross sectional area (square-inches)

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• Put nails in the axle holes before aintin to rotect the

slots

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• When the startin ate o ens

the higher up on the pin your

car hits the sooner it starts to

.

• Only matters if the gate opens

slowly enough for the car tomove with it.

• Beware of how the finish is

.

that sticks up and if your front

is too high you may take longer

to trigger it.

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2007 – 2.4597 avera e

2008 – 2.4603 average

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• Use Cub Scout s acer tool to

set wheel to body gap

(~1/16”)

• ar s ou no roc on a a

surface

• “One wheel lifted is faster” is amyth based on my testing

• Roll forward and back,

“ ”

and not move in or out.

• Good alignment makes a

huge difference!

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• Maximum Velocit

body tool and axle

guide.

ro

bodytool

• e o y oo r s

out the axle slots to

be perfectly squareto the body.

• The axle guide helps Axle

straight and gaps the

wheel.

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• The ke items:

• Polish the axles

• Smooth the wheels

•

• Make the car weight as close to 5 ounces as possible

• Alignment• Secondary items

• Aerodynamics

•

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• htt ://www.maximum-velocit .com/ tools and su lies

• http://www.shopatron.com/products/productdetail/part_number=PIN10010/164.0 the source for Pine Pro Graphite

• There are lots more but these are the ones I use based

on seven years of testing and racing.

dearby car _ 02

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