Copyright © 2009 by Stan Pope Page 1 Pinewood Derby Performance Design An introduction to making a...

Pinewood Derby Performance

DesignAn introduction to

making a high performance

Pinewood Derby car

Part of this presentation is oriented around this idea ...

Regardless of the lane in which you race, you should race in:

The steepest lane, The shortest lane, The smoothest lane, and The slickest lane

Then, you will be racing in ... The fastest lane!

But if you don't get to pick the lane, how do you make sure to get the fastest lane?

By what you do to your car!

That is why this presentation exists.

Modern Track

Starting Line

Finish Line

Race in the

Steepest Lane

Which car wins?

Which car is fastest at the bottom?

Why? Gravity!

Gravity and the mass of the car create a force along the line of the track.

If the track is steeper then more of the gravity force goes to pull the car forward.

Car A has farther to fall,

so it has more potential energy to turn into speed.

How do I make my lane steeper?

Physics says that “my lane” is the path followed by my car's center of mass.

Center of Mass

It isn't about weight in the back pushing the car down the track...

Or about weight in the front pulling the car down the track.

It is about how far the car drops as it goes down the track.

The amount of drop determines the amount of “potential energy” that can be turned into speed.

With modern tracks, drop increases as center of mass is moved farther back in the car.

Make your car as long as rules allow.

Locate the center of mass (balance point) as far back as stability allows. “Stability” includes “sticking to the track” and not sliding sideways.

This applies to modern tracks which start on a slope and flatten out toward the finish line.

This does not apply to older style tracks which have constant slope or which have both increasing slope near the starting line.

Race in the

Shortest Lane

Which car wins?

Set axles so that car runs straight and level.

Align as required.

You may analyze the track and find that raising the CM reduces the distance that it must travel. Right!

But this usually fails because the CM is so far from the wheels. You must be on a very smooth track, and your wheels must create very little oscillation.

Race in the

Smoothest Lane

Which car wins?

How does the car's center of mass move as these wheels roll?

Which car handles bumps best?

Wheels roundBore centered and smoothTread smooth Wheelbase extended (but not too much!)

Race in the

Slickest Lane

Identify the frictions and losses.

Eliminate losses, if possible.

Make frictions as small as possible.

Move friction to where it hurts least.

Eliminate Loss

If allowed, lift a front wheel.

If allowed to lift a front wheel, avoid ever spinning it up.

Keep most heavily loaded wheels off the rail.

Are these criteria always true?

Well, no, they aren't. There are some exceptions. However, the exceptions are very few.

When aren't these criteria true?

Different track stylesCM too far backFront wheel too far forward

Some Key Steps

Preparing Axles

To hold nail while filing sholders near nail point

Then chuck in drill and clean under nail head.

Preparing Wheels

A drill press can work as a lathe.

Wheel is held in a mandrel and rotated as it is moved past a cutter.

Here, the cutter is held in a piece of wood.

The cutter assembly is held, by hand, against a guide bar.

The cutter is moved gradually closer to a stop block on the guide bar.

Of course, sandpaper against ablock of wood can also be used.

Make sure the block is square!

Body Preparation

Drilling Axle Holes

Here is a homemade drill guideto help keep the holes perpendicular to the car body.

Layout car body plan on block.

Locate holes.

Drill first!

Here is a tool that is supposedto produce perpendicular holes even with a hand drill!

Good Racing!

Use of This Presentation

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You may use the presentation as-is within your organization.

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Technical Note

This presentation was prepared using the “Impress” feature of OpenOffice.org 2.4.

OpenOffice is free for individual use through a project supported by Sun Microsystems, Inc.

Software is available at http://www.openoffice.org

Copyright © 2009 by Stan Pope Page 1 Pinewood Derby Performance Design An introduction to making a...

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