Pinewood Derby Car Showcase – May 29, 2015

The Hive – Scott Morrill

We held a derby as the main event at our family reunion this past summer. My grandfather was a beekeeper, so in his honor I created “The Hive”. The hive itself is an empty shell of balsa which also hides the tungsten weight. The bees were individually created with beads and wire to form the wings and stingers.

Wayne – Bob Kirmis

I am not a scout but rather a mid-forties guy who is part of an annual pinewood derby race at my place of employment. This “car” is a City of Fargo, North Dakota “Wayne” street sweeper. As you can probably guess, I am from Fargo. The guy driving the street sweeper is my dad (who is coincidentally named Wayne).

The two back wheels are glued together to create one wide wheel. The car is elevated about a quarter inch so that it would fit on our track. As you can guess, the car didn’t do real well in the speed category.

From Pinewood Derby Times Volume 8, Issue 11

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Raising the Pinewood Derby Performance Bar

Most people have a sense of fair play. When two mismatched teams or individuals compete with each other, interest usually wanes, and from a sense of sympathy oftentimes the underdog is the crowd favorite. But when inferior equipment, questionable coaching, or unawareness of the rules disadvantages one competitor, most people hardly consider the
event to be a truly fair contest.

People generally prefer to watch an event where the teams or individuals are evenly matched. When skills, equipment, coaching, and officiating are all relatively even, then a sense of fairness prevails and — because the outcome of the event is uncertain — the interest level of the spectators remains high.

Similarly in pinewood derby racing the most exciting events are those in which many of the cars are closely matched in performance. Since the outcome is uncertain, everyone will be on the edge of their seats until the races are concluded.

Due to mistakes, inexperience, shoddy work, etc., there will always be some cars that are out-classed. But the goal of the race organizer should be to give each entrant a full opportunity to perform at a high level.

How is this done? In today’s article I will share several ideas for leveling the playing field, not by penalizing the best cars, but instead by raising the performance bar.

The first way to level the playing field is to provide clear and complete rules for the event. The rules should clearly state what is, and what is not allowed. Rules that require interpretation will result in entries using performance-improving techniques that others had assumed were disallowed. This can only result in disappointment or disillusionment.

Please note that I am not advocating highly restrictive rules. On the contrary, I prefer to allow car designers to use their creativity and ingenuity to increase performance. But to do this, the rules must clearly state what is in bounds, and what is out of bounds.

Another kind of information to distribute is performance tips. Although veterans of your event will likely know the tips already, this information will most certainly be an eye opener to newcomers.

Equal access to performance tips could consist of distributing:

– a list of the better pinewood derby-related web sites,
– a locally-developed tip sheet, a tip sheet from a web site, or
– a commercially available speed tip booklet.

In any case, all participants should receive the race rules and the performance information at the time when the car kits are distributed.

To raise the performance bar, participants should have equal access to the required tools. In every organization there are some folks with an extensive workshop and with skills to match. Others may not even own a hand saw. Clearly, this leads to lopsided events.

A simple way to provide equal access to tools (and skills) is to hold one or more workshops prior to the event. Of course workshops are more than just an opportunity to share tools. These events provide opportunities for comparing/learning techniques, collaborating on design ideas, and in general becoming more competent in car building. In recent years, we have held a workshop for our group on two consecutive Saturdays at Maximum Velocity. Kids and parents use the tools, seek advice, test cars on the track, and collaborate with the other participants. For those with little pinewood derby experience, attending a workshop can make a big difference in car performance.

In particular I remember two boys and their single mom who attended a workshop for some assistance. I helped them add weight to the car, prepare the wheels and axles, and loaned them some graphite. They ended up taking first and second in their age category — not bad for their first event!

Another way to raise the performance bar is to allow practice time on a derby track. This gives participants the opportunity to test their cars, and thus recognize if changes are needed.

One concern with allowing practice time is that some competitors may become disillusioned if they are continually bested during practice. To avoid this issue, disallow racing between competitors during the practice time. Instead, each entrant may run their car alone (sufficient if the track has a timer), against the entrant’s car from a previous year, or against a “benchmark” car. This minimizes comparing cars during the practice time, but still allows the entrants to ascertain how their car is performing.

Would you consider it a true competition if the New York Yankees were pitted against a college baseball team? Not likely. But a similar mismatch does occur in some pinewood derby events. If your derby has rather flexible car design rules (e.g., allows modified wheel bases, machined wheels, or similar), then likely the event will end up with some high-performance cars leaving the more traditional cars in the dust.

Obviously, the rules could be tightened to disallow certain modifications, but I suggest an alternative. Instead of reducing design options, consider offering different entry classes. How about a “Stock” class race for cars with standard wheel bases, unmodified wheels, etc., and an “Open” class race for cars with extended wheel bases, modified wheels, etc? This will require more awards, and a little more time. However, I believe you will find the increased competition and excitement will more than compensate for the additional cost.

Raising the performance bar can help to make for a more memorable pinewood derby event. By providing equal access to information, tools, and practice time, and by possibly having multiple event classes, the races will be closer and more exciting.

By the way, what I have included in this article certainly does not exhaust the possibilities for raising the performance bar. If you have other ways to raise the level of competition, please share them with me. Thanks!

From Pinewood Derby Times Volume 8, Issue 11

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Pinewood Derby Car Showcase – May 15, 2015

Modified Detonator – John Cerrone

This car was one my son and I built, slightly modifying the Detonator design. The only rules for this particular derby were to use the wheels and block supplied with the BSA kit and not exceed five ounces. So we extended the wheel base and rear weighted with tungsten to achieve a COG at 3/4 inch. We cut down and used a dome to cover the rear cylinder weights, and molded the sides and rear of the car to conform to the outside edges of the dome. We painted the inside of the dome black and then used epoxy to fill in the gaps between the dome and the car body, then finishing it with a fine pin stripping around the dome. The car took first in class, second overall in the pack race, and took first in class at districts. We also received the Best and Fastest looking car awards at both the Pack and District event.

Iwo Jima – Scott Morrill

My son enjoyed helping with this car which was created for an adult race. We used Tannin’s army men, and cut the bases off the feet then used heat to allow us to bend their legs and arms. The rocks are Styrofoam, and the large rock which holds the base of the flag pole hides the weight. The flag is a miniature fabric flag that was starched to hold the shape. Due to the height, the flag was just for display and not in place during the race.

From Pinewood Derby Times Volume 8, Issue 10

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Pinewood Derby Lubricant Testing

If you have done any pinewood derby research on Google, or looked at derby products for sale on eBay, then I’m sure you have run across statements such as:

– “Tungsten Disulfide (WS2) has an extremely low coefficient of friction of 0.03 — lower than that of Teflon, Graphite, or Molybdenum Disulfide”

– “Molybdenum Disulfide (MoS2) has a lower coefficient of friction than graphite. This means (brand name removed) is a better lubricant than graphite.”

If you are looking for better derby performance, then statements such as these are quite intriguing, especially when accompanied by a graph comparing the coefficient of friction of each substance (see Figure 1).

Figure 1 – Lubricant Comparison from BryCoat, Inc.
Graphic from BryCoat, Inc. web site

When viewing statements and graphs such as these, it pays to take a careful look at the details. In Figure 1, the range of the data is between one and three hundred thousand PSI. This is an extremely high pressure condition. Most importantly, note how the coefficient of friction of the three materials appears to be the same at the low end of the data.

An important question to ask oneself at this point is, “What happens as the pressure reduces further, especially at a pressure that would occur in a pinewood derby car?” Clearly, for MoS2 or TS2 (or any other lube for that matter) to be of value, it must have a lower coefficient of friction than graphite at the pressure found in pinewood derby cars. So, let’s test these lubes in that pressure range.

The coefficient of friction is the ratio between the mass of an object and the amount of force required to move the object. Normally, the coefficient of friction is indicated by the Greek letter “µ”. So the mathematical formula is:

F = µM or µ = F/M

Where F is the force required to move the object, µ is the coefficient of friction, and M is the mass (weight) of the object(1).

As an example, if you were to push a heavy box on a rough road (asphalt) and then on smooth sidewalk, pushing it on the sidewalk will be easier because the µ of the sidewalk is lower. If you then pour oil on either surface, it will be easier to slide the box because the oil has lowered the µ.

The coefficient of friction can be measured in any of several ways. For our purposes, we are going to use the “Tilted Plane” method. In this method, an object will be placed on a smooth surface which can be incrementally tilted. At some point, the object will slide on the surface. The angle at which the object slides is called the “friction angle”, and is notated as ø. We can then calculate µ as follows:

µ = tan(ø) (2)

The main piece of equipment for the experiment is a tilting apparatus (Figure 2). It consists of a piece of glass on a tilting frame, which is moved when the crank winds the string around a rod. An angle measuring device shows the current tilt angle.

Figure 2 – Tilted Plane Apparatus

The sliding blocks are also critical components. Eight blocks of Delrin (3) were machined to the same dimensions, and provided with two smooth surfaces. Delrin is not as consistent in density as some other plastics, so there was a slight weight variance between the blocks. So, the lightest block was found, and then small holes were drilled in the sides of the other seven blocks until all of the blocks weighed the same.
The resulting weight of each block was 2.05 ounces. This is the typical load for one of the rear wheels on a pinewood derby car.

Three lubes were tested: TS2, MoS2, and Max-V-Lube Graphite. Two blocks were used for each lube, and the last two blocks were used without lube as a control.

The glass plate on the tilting apparatus was first cleaned thoroughly with a glass cleaner. This cleaning was repeated each time the lubricant was changed.

A quantity of each lubricant was placed on a sheet of clean newsprint. One side of a block was then rubbed on the lubricant until thoroughly coated (Figure 3). The block was then placed on the glass and slid back and forth to distribute some of the lube onto the glass. The block was then re-coated with the lube and placed on the uphill side of the glass. The glass was then slowly tilted until the block slid to the downhill side of the glass. The tilt angle was then recorded. This test was repeated five times for each block.

Figure 3 – Lubricant Application

After all of the tests, the high and low angle measurements were removed and the remaining three were averaged. µ was then calculated for each of the lubricants and for the control test. The results are shown in Figure 4.

Figure 4 – Coefficient of Friction for Pinewood Derby Lubricants

As shown by the data, both MoS2 and TS2 have a higher coefficient of friction than Max-V-Lube graphite at 2.0 ounces.(4) Thus, these lubricants will be less effective than graphite as a pinewood derby lubricant.

(1) Oftentimes, F(normal) is used instead of M in the equation. These are essentially the same.

(2) If you are interested in why this is true, there are several good discussions of this on the Internet. Just search for “measure friction angle” on Google.

(3) A brand name of an engineered plastic.

(4) In a previous test using this apparatus, I compared many of the top graphite brands with MoS2 and TS2. In all cases, graphite had a lower µ than MoS2 or TS2. At that time I also tested “Dry White” Teflon lube. Not surprisingly, the µ of “Dry White” was higher than MoS2 or TS2. Note also that spin tests were performed on all of these lubes with
compatible results.

From Pinewood Derby Times Volume 8, Issue 10

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Pinewood Derby Car Showcase – May 1, 2015

Guitar Car – Mark Robison

This is one of the more recent cars I have made. I downloaded a picture of a Fender guitar, worked it into a pattern, used a little intuition, and voila… a Fender guitar car! This will surely be a hit among the kids (especially Guitar Hero fans — like my wife).

Cobra – Mike McBride

I always try to do a theme car every year that I don’t intend to race. I’ve got many interesting pieces of art on wheels, like this fluorescent cobra car that I did for a Halloween race this year.

From Pinewood Derby Times Volume 8, Issue 9

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