Friday, January 30, 2015

Graphite Questions
The Two Most Popular Questions of the 2013-14 Season

By Randy Davis

Each pinewood derby season, there are always a few questions that get asked more than any others. Some years the questions are about weighting, while other years the questions are about alignment. But during the past season, there were two popular questions about lubricating with graphite. So let's discuss these in detail.

Question 1: How do you get graphite to stick to the axles?


The short answer is, "You don't want graphite to stick to the axles", but let's go a little deeper. Graphite is carbon in a unique molecular structure; the carbon atoms are formed into a layered structure. These layers allow the molecules to slide on each other, thus giving dry powered graphite a natural lubrication ability.

Dry graphite does not typically stick to metal or any non-porous surface. So, it does not stick to pinewood derby axles. However, it does stick to porous surfaces, specifically polystyrene, which is the plastic from which most pinewood derby wheels are made.

So, when lubricating pinewood derby wheels and axles, the graphite adheres to the inner bore of the wheel, and the axle slides on the graphite (and the graphite slides on itself). If the layer of graphite on the bore is sufficiently thick, then all contact between the metal axle and the plastic wheel is eliminated, resulting in a significant reduction in friction. Building this layer of graphite can be done in many ways, but all involve repeatedly adding graphite and rotating the wheel on the axle.(1)

There is a way to make graphite stick to an axle. This involves making a graphite paste by adding isopropyl alcohol. The axle is then dipped in the mixture and allowed to dry. Unfortunately, the resulting coating does not lubricate as well as dry graphite because the molecular structure is modified in the process. For this reason, Maximum Velocity does not offer graphite-coated axles. In all of our performance tests, graphite-coated axles were inferior to polished
axles.

Question 2: What do you think of that graphite packing video on YouTube?

There are a lot of videos about graphite packing. These can be divided into two categories: wet packing and dry packing.

Wet Packing
Wet-packing involves making a graphite paste as described above. The axle is inserted into the wheel and the paste is pressed into the bore around the axle. After the graphite dries, the axle can be removed leaving a thick ring of hard graphite on the bore of the wheel.

There are two significant issues with this process:

1) There is no guarantee that the graphite ring is concentric with the bore of the wheel. In fact, it would take precision equipment to make a truly concentric ring (see Figure 1).


Figure 1 - Non-concentric Graphite Ring

In one video, after the ring is created the producer of the video spins the wheel on the axle. He states: "This wheel isn't balanced at all; you can see how it wobbles." Almost certainly, the real problem is not the wheel; the wobble is because the graphite ring is not concentric.

2) The ring does not lubricate as well as dry graphite. As described previously, in our testing, graphite with alcohol was always slower than dry graphite. In fact, if you watch the video mentioned above you will note that there is no comparison test between a dry-lubed and a wet-packed wheel/axle. In fact, there is no claim that the wet-packing method is effective other than "it might help you knock off a few thousandths of a second".

Dry Packing
Dry packing involves creating a ring of dry graphite in the bore of the wheel. As previously mentioned, it involves repeated applications of graphite, followed by spinning the wheels on the axles. The purpose of the spinning is to incrementally build up the graphite ring.

There are videos showing many ways to this. I am sure that many of the methods are effective, but I want to provide a few cautions.

1. Be leery of any method where the wheel is rotated at a high speed for an extended period of time. Many people advocate using a Dremel-like tool and a buffing wheel to rotate the wheel. Recognize that on a typical track, the average RPM of the wheel is about 2200. Dremel-like tools generally have settings as high as 30,000 RPM. If a wheel is spun up to 30,000 RPM, the graphite will wear off very quickly, and the wheel will overheat. Remember that the point of spinning is to build up the graphite ring, not wear it off.

So, if you use a Dremel-like tool to spin wheels, set the RPM to the lowest speed (on my tool this is still 5,000 RPM) and just briefly touch the wheel to the buffing wheel, letting it spin down to a standstill.

2. Some videos recommend using a treadmill to spin the wheels. That is, the lubed wheels and axles are installed on the car, the car is placed on a treadmill with a string from the front of the car attached to a stationary object so that the car stays on the treadmill. The treadmill is then started, and at intervals graphite is applied to the wheels.

Again, the wheel spinning is to build up the graphite, not wear it down. So if you use a treadmill, limit the runtime between graphite applications to about ten seconds. This simulates four heats on a standard track.

3. Some videos recommend pressing the graphite into the bore of the wheel (truly packing it). This is probably fine as long as the wheels/axles are spun many times to loosen up the system and shed the excess graphite. If this is not done, the wheels will not spin well.

At Maximum Velocity, we recommend spinning the wheels by hand before they are mounted on the car. This is a safe method, and a "tried and true" method. To make this method easier for kids (and their parents), you can make a simple tool to allow all four wheels to be spun at one time. This speeds up the process and minimizes the risk of dropping the wheels.


Figure 2 - Wheel Spinning Tool
(Not pretty, but it works)

CONCLUSION
I hope you found this information useful. I certainly didn't mean to disparage any of the folks that post videos on YouTube. But recognize that like any information found on the Internet, it needs to be filtered with careful thought and good judgment.

(1) Our procedure for lubricating with Max-V-Lube Graphite can be found Here.

From Pinewood Derby Times Volume 14, Issue 9

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Friday, January 23, 2015

PINEWOOD DERBY CAR SHOWCASE

Smaug - Holt Family

Smaug was raced at our local race. It is made from light-weight
modeling clay.

Stanley 220 Block Plane - Dennis Bjorn

I built this car 16 years ago out of pallet wood that held granite
blocks from India. My weights are hidden under the lever cap. The
blade adjuster on the back is from a Stanley block plane.

From Pinewood Derby Times Volume 14, Issue 8

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Thursday, January 15, 2015

FEATURE ARTICLE
Shop Talk: The Best Pinewood Derby Rule


Although you can get away with using a cheap plastic ruler for an occasional pinewood derby car, having a nice, accurate rule (not ruler) is a must for any serious craftsman. But like any tool, there is a large variety of rules available on the market. Today, I want to share with you my favorite rule. In my opinion, this rule is a must have for pinewood derby enthusiasts.

The rule I am referring to is the Incra Six Inch Precision Bend Rule. Although this rule wasn't specifically designed for pinewood derby use, I have to believe that the designer was a pinewood derby parent.


Photo 1
Incra Six Inch Bend Rule


The obvious feature of the Incra Bend Rule is the shape. The rule is specifically designed to fit over the edge of a block or board in order to make precise measurement with ease. The rule is marked in 1/32 inch increments, and at each increment is a hole and a slot that allows insertion of a 5mm pencil (standard mechanical pencil size). These holes and slots eliminate the inaccuracy that comes with trying to make a pencil mark along the side of a regular ruler.


Photo 2
Making a Measurement


This feature in itself makes this a nice tool, but there's more. On one end of the Incra Bend Rule you will find measurements that are perpendicular to the rule. These are used to mark offsets from the edge of a block. For pinewood derby cars, the obvious use is marking axle locations, weight hole positions, car thickness, etc.


Photo 3
Marking a 1/8 inch Offset for Axle Holes


But this offset measurement feature is not just to make a tiny dot, but it can also be used for drawing horizontal lines. Just insert the pencil at the desired location, and slide the rule along the edge of the block. Sweet!


Photo 4
Drawing a Horizontal Line


Now the "pièce de résistance". Do you want to locate the center of your block? One half of the Incra Bend Rule is 3/4 inch wide, while the other is 7/8 inch wide. 7/8 inch is a familiar number - it is one-half of the width of a standard block. So to find the center of a block, lay the rule with the wide portion on the top or bottom of the block, and strike a line. Since blocks are not consistent, put the rule on the other side, and draw another line. "Voilà!" The center of the block will be between the two lines (or coincident with the two lines if the block is exactly 1-3/4 inches wide).



Photos 5 & 6
Finding the Center of the Block


I am confident that you will enjoy this rule as much as I do. You can find it on our Web Site or in our Product Showcase.

From Pinewood Derby Times Volume 14, Issue 8

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Friday, January 09, 2015

PINEWOOD DERBY CAR SHOWCASE

Arrow of Lightening - Scott & Derek Bobbitt

For his final foray in pinewood derby racing, my son Derek opted to showcase Scout Spirit and go for the "Lord Baden Powell" award for most Cub Spirit. His entry, the "Arrow of Lightening" succeeded. He won the Cub Spirit award and placed first out the 30 entries in the pack. At the district finals, five cars from each Pack were invited to participate. The "Arrow of Lightening" won every heat and placed second overall by just 0.007 seconds! Most importantly, though, his car won the District award for "Best-In-Show". He was one elated Webelos!

Triangulator - Gerald Scotting

After seeing the unusual triangular tungsten canopy I knew i wanted to design a car around it. The canopy made up most of the weight for the car, but due to the super slim design I was still too light. I ended up using a bunch of the 3/16" tungsten beads. The body was cut out as a side profile, then a rough top profile. All other shaping was done with either a round file or sandpaper, and lots of patience.

From Pinewood Derby Times Volume 14, Issue 7

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Friday, January 02, 2015

Height of Ballast Weight Vs. Performance - Part 2
By Randy Davis


Last season, I ran an experiment and published an article on the effect of the height of the ballast weight on performance (see Volume 13, Issue 9 - "Height of Ballast Weight Versus Performance"). You can read the article Here.

That experiment showed that for a reasonable (9/16 inch) variance in the height of the ballast weight, there was no measurable effect on performance.

After the article was published, I received quite a bit of feedback claiming that the experiment was under ideal conditions so it could not be applied to real racing.

Truly, the test was done under as ideal conditions as possible, as I wanted to ensure that any variance in performance was due to the height of the weight and not some other factor. For example, outlaw (disk) wheels were used to minimize friction, and the track was very smooth.

So, to address the feedback I determined to run the test again with the following changes:

1. BSA Wheels and Axles instead of Outlaw Wheels - these wheels have more track surface contact, and the wheel/axle fit is sloppy.

2. Rougher track

EXPERIMENT SETUP
The same car was used as in the original experiment (see Figures 1 and 2). Of course the wheels/axles were swapped out; Pro-Stock BSA Speed Wheels and BSA Speed Axles were used and lubed with Krytox 100 lube.


Figure 1 - Top of Test Car


Figure 2 - Bottom of Car with Weight and Spacers Inset

As a recap, the car has a 1-3/8 inch hole drilled completely through the car, and a medicine bottle cap with a 1-3/8 inch internal diameter is glued over the hole. The resulting cavity can hold a 3.25 ounce tungsten round (9/32 inch thick) and two hollow plastic spacers (same OD and thickness), and a thin plastic shim to prevent rattling. On the bottom of the car, the hole is covered with a removable plate (shown in Figure 2). Additional ballast weight was added to bring the car up to five ounces.

To add "roughness" to the track, strips of Post-it material was applied to the track. At each track joint, a strip was placed on both sides of the center guide rail. At the half-way point of each track section, a strip was placed on one side of the rail (alternating sides down the track). When the car raced, it made a pleasing clickety-clack train track sound.


Figure 3 - Post-it Strips on Track

The experiment started with the tungsten round at the bottom and the two spacers on the top. Three heats were run with this configuration. Then the plate was removed, the round placed between the spacers, and the plate replaced. After three heats with this configuration, the round was placed above the two spacers, and six heats were run. Then the configuration was changed back to the round in the middle for three heats, followed by the round at the bottom for the final three heats. Thus, six heats were run for each configuration.

EXPERIMENTAL RESULTS
Other than the car being a little slower than in the original experiment, nothing else changed. The car was still very consistent, and performed the same regardless of the height of the weight.

2.5308 Sec - Low COG Average
2.5297 Sec - Middle COG Average
2.5305 Sec - High COG Average
.00156 Sec - Standard Deviation

The greatest difference in average times (between the low and middle COG was 1.1 milliseconds which was less than the standard deviation of the data, so the difference is statistically insignificant.

CONCLUSION

Thus, the same conclusion can be drawn as in the original experiment: within reason (9/16 inch for this experiment) don't worry about the height of the COG. Certainly get the COG towards the back, keep your car aerodynamically sleek, and have fun designing your car. If you want to use a tungsten canopy, certainly don't be afraid to do so.

From Pinewood Derby Times Volume 14, Issue 7

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Friday, December 26, 2014

PINEWOOD DERBY CAR SHOWCASE

Here are some cars from the "Wood and Wheels" race held in Australia (Maximum Velocity supplies the wheels and axles for the race). The photos were submitted by Matthew Webb.







Also, a Formula One Awana car built by Matthew:



From Pinewood Derby Times Volume 14, Issue 6

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Friday, December 19, 2014

Runoffs - When and Why to Run Them
By Randy Davis


Years ago, virtually every pinewood derby race used an elimination method (usually double elimination) for running a pinewood derby race. This method was relatively easy to implement and easy to understand, but did have issues including:

1. Slowest racers ran a few heats and were then eliminated (and likely lost interest in the event.

2. Possible unfair trophy assignment (third fastest car is eliminated early due to repeated pairing with the fastest two cars).

3. Cars did not always run on all lanes, so some cars had an advantage if they were assigned to a fast lane.

With the advent of Race Management software, many events have transitioned to a chart-based racing method, whereby all cars run the same number of heats, race in all lanes and are paired against a broad selection of other cars. These methods are much fairer, and are more accurate in assigning trophies.

But when using a chart-based method, the scoring method must be selected: time or points. I won't get into a full comparison of time vs. points in this article.(1) Time-based scoring is certainly popular and is really the best choice for large events. But for smaller events, I prefer point-based scoring. I believe this method keeps the audience more engaged, keeps each heat exciting, and makes the finish order of each heat important.

But with point scoring, the final trophy assignment may not be accurate after the heats are complete. Like elimination methods, random heat assignments can result in the third fastest car being relegated to fourth place.(2) So, to ensure that trophies are assigned properly, another round for the fastest cars may be needed. Let's look at when a second round is needed, and how many cars to select for the second round.

WHEN IS A SECOND ROUND REQUIRED?
To answer this question, we must first understand the terms "Perfect-N" and "Partial Perfect-N" (PPN) as they apply to race charts.

A Perfect-N race chart is one in which every car races the same number of times in each lane, and races against every other car the same number of times.

The simplest case is 4 cars on a four lane track, racing one time per lane. Each car races one time in each lane, and in each heat races against the other 3 cars. Other cases of Perfect-N charts will be described below.

A PPN chart is one in which each car races the same number of times in each lane, and heat assignment is optimized so that no one car races against any other car more or less than one time greater than the average.

An example of a PPN chart is one with 8 cars on a four lane track, racing one time per lane. Since the example car will need to race against 12 other cars (3 per heat), and since seven (the original 8 cars minus the example car) doesn't divide into 12 evenly, the example car will race against 7 cars one time and 5 cars a second time.

For a four lane track, Perfect-N charts exist for the following numbers of cars(3):

4 - Yes
5 - Yes
6 - Yes - Bye required(4)
7 - Yes
8 - No
9 - No
10 - No
11 - No
12 - Yes - Bye required
13 - Yes

For all car counts greater than 13, only PPN charts exist.

When a race has a Perfect-N chart the race is perfectly fair and a run-off is not needed (except in the case of tie). But if the race has a PPN chart, it is possible that a trophy may be incorrectly assigned. In this case, a run-off race is required.

HOW MANY CARS SHOULD BE IN THE SECOND ROUND?
From the above discussion, the answer is clearly that a number must be selected that has a Perfect-N chart. In no case should a second round use a PPN chart.

Typically, we select the top seven cars, except when there are ties that would drive the number beyond seven. Then we select the top five or six cars.

IMPLEMENTATION / CONCLUSION
I grant that a time-based race is easier to implement, as the need for a second round is not necessary. But with a modern race management application, such as Grand Prix Race Manager, creating a second round is quite easy. In our race, we typically have the second round ready to go in two minutes from the completion of the final heat of round 1. Our emcee fills the time with a few kid-friendly jokes, so the excitement of the event continues during this slight delay. Then during the second round (seven cars typically take less than ten minutes), the excitement level (and sound level) reaches its peak.

If you are currently using a time-based method for your small race, consider switching to a point-based method. I believe you will generate greater interest and excitement, for just a few extra minutes of event time.

(1) For a comparison of these two methods, please refer to:
Points or Times: Which Method Should I Use?

(2) For example, if the third fastest car races the two fastest cars resulting in two second place finishes, and the fourth fastest car only races against one of the top three cars resulting in one second place finish, then the fourth fastest car would be incorrectly assigned the third place trophy.

(3) If you have a track with more or less than four lanes, you can use Grand Prix Race Manager (GPRM) to determine the Perfect-N charts.

(4) A phantom car is inserted into the schedule. When it races, the lane is left empty. GPRM automatically takes care of byes.

From Pinewood Derby Times Volume 14, Issue 6

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