02 03 Pinewood Derby Stories and Photos from Maximum Velocity 04 05 15 16 19 20 21 22 23 24 25 26 27 28 31 32 33

34
5 Keys to Performance

I can't count how many times I have been asked, "How do I make my
pinewood derby car go fast?" If you have been involved in pinewood
derby racing for any time at all, or if you have been a subscriber to
this newsletter, then you understand that there is no simple formula for
success, and thus no simple answer to this question. But since I am
asked the question, I provide five keys to unlock the performance of
pinewood derby cars.

Key 1 - WEIGHTING
Maximum weight; Balance point 1 to 1-1/4 inch in front of rear axle

Best speed is achieved at maximum weight, so clearly weight must be
added to the car to reach that weight. In addition, the location of the
added weight is an important factor. Tests show that best performance
is generally achieved when the balance point of the car (the center of
gravity) is located about 1 to 1-1/4 inches in front of the rear axle
(see Volume 2, Issue 4 - "The Big Debates - Part 1").

Does the type of weight matter? The maximum weight can be achieved with
any type of weight; however, the type of weight does affect how easily
the balance point can be located. Denser weights (such as lead or
tungsten) take up less space on the car, so there is more freedom to
place the weights such that that the desired balance point is achieved.
The amount of added weight also affects the next key: aerodynamics.
Since denser weights require a smaller volume of space, they enable the
creation of more aerodynamic cars (See Volume 1, Issue 6 - "Weighting
Materials: So many choices").

Key 2 - AERODYNAMICS
Profile and body features minimized to improve air flow

If you asked me a year ago, "How do I make my pinewood derby car go
fast?" I would not have included aerodynamics as a key. However, since
that time I have read one study and performed another, both of which
showed that the effect of aerodynamics on pinewood derby car performance
is not trivial (see Volume 3, Issue 9 - "The Big Debates -
Aerodynamics").

There are many elaborate ways to perfect aerodynamics, but for our
purposes, I suggest the following:

1. Low-profile cars (smaller surface area as viewed from the front of
the car) will tend to outperform higher-profile cars.

2. Cars should taper from a smaller surface area in the front to a
(possibly) larger surface area in the rear.

3. Edges running across the car should be rounding or tapered.

4. Wings, sails, flags, pennants, etc. add to the surface area, thus
they tend to decrease performance.

5. Unfilled (major) holes can catch air and slow down a car.


INTERLUDE
Another question I am regularly asked is, "Which of your car designs is
the fastest?"

I answer, "All of them are fast, since they will achieve maximum weight
with the proper balance point, and have a reasonably good profile."

The follow-up question is then, "Okay, but which is faster?"

I usually then list a few cars and the person is satisfied. But in
reality, the body of the car is only a small part of creating a fast
car. Note that the previous two keys relate to the body of the car,
while the next three keys relate to the wheels and axles. Thus, to
create a fast car a lot of work must go into the wheels and axles.

(See Volume 1, Issues 5 and 6 for more information on designing the body
for speed.)

Key 3 - WHEEL/AXLE PREPARATION
Axles - no flaws, straight, polished; Wheels - no flaws, polished

All of the frictional losses in a pinewood derby car come from the
wheels and axles. Start by inspecting the parts in your kit to make
sure they are usable. If a part has a serious flaw, replace it.

Next, prepare the nails. This topic was covered in detail in Volume 1,
Issue 8 - "Axles: Nails or Precision Parts?". But in summary, for
nail-type axles use the Pro-Axle Press to ensure that the nails are
straight and round and use a file to remove the flashing under the nail
head and minimize the ridges on the shaft. Beveling the nail head
slightly is also a good idea. Finally, polish the axles until they are
bright and shiny.

To prepare the wheels, use the Pro-Hub tool to square the wheel hub.
Then polish the wheels. If allowed by your local rules (and the
configuration of your wheels), use the Pro-Hub tool to cone the inside
wheel hubs.

(Wheel preparation was covered in detail in Volume 2, Issue 1 - "Where
the Plastic Meets the Road")

Key 4 - LUBRICATION
Quality lubricant applied properly.

Lubrication is an extremely important factor. The difference in time
between a well-lubricated car and a car without lubrication can be
one-half second or more (this translates into several feet on the
track).

If you use graphite-molybdenum, take the time to work it in thoroughly;
a casual puff before the race is not sufficient. After lubricating,
make a few test runs to break in the lubricant (or free spin the wheels
several times). Since graphite works best after a break-in period, don't
relube between heats.

If you use a liquid lube (such as Krytox 100), make sure to follow the
recommended application procedure. With liquid lubes, less is best.

(A comparison of lubricant performance can be found in Volume 3, Issues
1 and 4.)

Key 5 - ALIGNMENT
Car goes straight

In order for the car to get to finish line as quickly as possible, it
needs to go straight. If it zigzags down the track, it will travel a
longer distance, but worse it will continually lose speed as it bumps
and rubs against the guide rail.

To minimize the amount of alignment adjustment needed, make sure that
the axle slots/holes are perfectly parallel to each other and the axles
are straight. Also, when using axle slots, make sure that the axles are
inserted perfectly straight. The Pro-Axle Press and the Pro-Body Tool
are good tools to help minimize the need to align the wheels. In
addition, the Wheel Alignment tool can help get the wheels mostly
aligned.

There are many different alignment procedures, and they vary depending
on the use of axle slots or holes. For fine adjustments, shims made
from wax paper can be insert into the holes or slots, in front of or
behind an axle. For a more coarse adjustment the axle bending method
can be used.

1. Determine which of the front axles appears to be the most out of
alignment (or with a raised wheel, adjust the wheel/axle that is on the
ground).
2. Make a mark on that axle where it comes out of the car body.
3. Remove the axle from the car and remove the wheel.
4. Using a vise, pliers, etc. very slightly bend the front axle at the
point marked in step 2 (the Pro-Axle Press works well as an axle
holder).
5. Replace the wheel and re-insert the axle.
6. Roll the car on a smooth and level surface.
7. If it does not roll straight, slightly rotate the bent axle by
grasping the axle head with a pair of pliers.
8. Repeat steps 6 and 7 until the car rolls straight.

CONCLUSION

Anyone can create a competitive pinewood derby car, as long as they
don't lose their keys!

From Pinewood Derby Times Volume 3, Issue 12

To subscribe to this free e-newsletter, please visit:
www.maximum-velocity.com/subscribe.htm

(C)2012, Maximum Velocity, Inc. All rights reserved.
www.maximum-velocity.com
35 36 37 38