Thursday, August 28, 2014

PINEWOOD DERBY CAR SHOWCASE

I would share our 2007 cars (not shown is the original prototype of the Velocinator, which was included in Volume 7, Issue 4).

Speeder - Stephen Davis

My youngest son, Stephen, has always liked the Speeder (I do too). This is the second Speeder he has made (the first was in 2002). It was quite fast, taking 3rd place, but not fast enough to catch his sister's 1st Place car.

Detonator - Janel Davis

My youngest daughter built this Detonator. It was extremely fast, easily taking first place.

Wedge SE - Elisa Davis

The extended wheelbase Wedge SE is weighted with tungsten, and is equipped with Outlaw wheels. It was nosed into 2nd Place, behind an extended wheelbase Bolt equipped with Outlaw wheels (built in our shop by a friend).

From Pinewood Derby Times Volume 8, Issue 4

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Thursday, August 21, 2014

PINEWOOD DERBY CAR SHOWCASE

Big Wheel - John White

I pushed the design envelope this year; after two years of mulling over an idea this is what I came up with. The two front wheels sit just off the track and are there to keep the car going straight. The center wheel rides down the middle of the track and works the kid's legs. My goal was to make everyone at the race laugh. I wasn't sure what was going to happen: would I qualify, would it make it down the track, run into another car, or just plain fall apart? Well -- mission accomplished! He was just a peddlin'. It wasn't fast by any means, but everyone enjoyed watching it race. And it won "Funniest Car".

Awana Tractor - Doug Kile


I'm a leader with our local Awana program at Valley Community Church in Salinas California. Since Salinas is the "Salad Capital" of the world, you see many of these tractors in the fields around here.

Fast Talker - Frank Tonra

I made this car as the Pace Car for Pack 57 in Toms River. I found the idea for this one online and could not resist making it. Someone else came up with idea but it did not matter, they lined up to see the car and laughed all afternoon. I sent the car to the Districts and got the same result. What a joy to see their faces! It was well, worth the hours of sanding.

From Pinewood Derby Times Volume 8, Issue 3

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Thursday, August 14, 2014

Top Fuel Cars - Direct Drive

(The fifth in a series of articles on cars that "stretch the rules")

Last summer I was searching the web for articles and Blogs relating to pinewood derby racing. Most of what I find is not particularly interesting, but occasionally I come across a real gem.

One of these gems was an article written by Eldon Goates, owner of Synthesis Engineering Services. Eldon decided to use PRO/Engineer design software to design a top-performing, direct-drive pinewood derby car for an outlaw race. After designing and building the car, he wrote an article describing the process for Pro/E magazine. You can find the entire article Here

Although I do not have the sophisticated equipment available to Mr. Goates, I decided to make my own version of the car using a pinewood derby block. I do have a lathe to make a few of the key parts, but otherwise, the car was made with basic shop tools.


Figure 1 - My Direct Drive Car

CAR DESIGN
The basic premise of the car is that a string is wound around the rear axle and is attached to a spool mounted onto a motor. When the motor is turned on, the string is wound onto the spool, causing the rear axle to rotate. The length of the string is set such that it runs out just as the car crosses the finish line. So, if the car was used on a track of a different length, the string would need to be adjusted.

The unique feature of this car design is the axle "transmission". To understand how this works, think of a ten speed bicycle. When in a low gear (more torque, less speed), a smaller front "motor" sprocket (the motor is a pedaling human) and a larger rear "drive" sprocket (attached to the rear wheel) is used. But in a high gear (less torque, more speed), a larger front sprocket and a smaller rear sprocket are used.

Now adapting this concept to the direct drive car, at the starting line a low gear is wanted. This means that a smaller motor sprocket and a larger drive sprocket are needed. The smaller motor sprocket is simple; it is just the empty spool attached to the motor. The larger drive sprocket is accomplished by creating a larger rear axle (the right side of the transmission seen in Figure 4). Conversely, near the finish line, a high gear is desired - a larger motor sprocket and a smaller drive sprocket. This corresponds to the nearly full spool on the motor, and a smaller rear axle (left side of the transmission).

To make this work, the string is first wound around the smaller (left) portion of the transmission. Next, the middle portion is filled, followed by the larger portion. When in motion, these are, of course, unwind in the reverse order. The only trick is to make sure to rotate the rear wheel in reverse when winding. Otherwise the car will go backward!

PARTS
First I needed to collect and/or manufacture the various parts. These included:

- Basic block: This was drilled and milled to hold the parts.

- Starting Pin Switch: I used a contact switch (part #275-016 at Radio Shack). It is normally on. When the car rests against the starting pin, the weight of the car closes the switch turning the motor off. Thus, when the pin drops, away it goes. This switch can be seen in Figure 2.

- Kill Switch: A small toggle switch (part #275-624 at Radio Shack) that is used to turn the motor off when not in use. Just make sure to turn it on at the starting gate!

- Batteries, 9V clips and cover: Two standard 9V batteries with 9V clips are located in the bottom of the car, hidden by a cover plate of styrene plastic (see Figure 4).

- Motor: 12 VDC motor, I drove the motor at 18V for more power. This would eventually burn out the motor, but the on-time is so short that the motor doesn't get a chance to overheat.

- Motor Harness: The motor is mounted on a piece of brass, fastened to the block, and held down by a piece of styrene.

- Axles: Front axles are our 4095-Speed Axles. The rear axle (one piece) is a piece of 3/32 steel rod.

- Bearings: Two bearings are attached to the side of the car in the rear (I used small screws to catch the flange of the bearing). Thus, the entire rear assembly (wheels, axle, and axle transmission) rotate as a unit, supported by the bearings.

- Bushings: The axle was a bit loose on the bearings, so I inserted two short pieces of copper tubing between the wheels and the bearings to keep the axle assembly from shifting left or right.

- Wheels: The front wheels are white RS wheels from DerbyWorx. The rear wheels are two inch servo wheels from Pitsco. This larger size was needed so that the string spool would clear the center guide rail (it also helped performance). I had to make bushings of black Delrin so that the 3/32 inch axle rod would press fit into the wheels. You can see one of the bushings in Figure 1.

- String Spool: This piece presses onto the shaft of the motor (Figures 3 and 4). It was machined from Delrin. A hole is drilled through the spool. The string is threaded through the hole, and then tied in place.

- Axle Transmission: This piece was machined from Delrin (see Figure 4). It was then slid onto the rear axle and permanently attached with epoxy. There is a hole drilled into the transmission into which the tip of the string is inserted before winding.

- Wiring: Light gage electronics wire. Positive side of the battery goes to the Kill Switch, then to the Starting Pin Switch, then to the motor. The negative wire goes to the motor. Batteries are wired in series.

- String: I used some strong kite string. It tends to fray, so dental floss, or another type of non-fraying string would be better.


Figure 2 - Front of Car


Figure 3 - Back of Car


Figure 4 - Bottom of Car
Left Photo - String is wound and car is ready to go
Right Photo - At end of run, string is wound around the motor spool

PERFORMANCE
I ran this car on our 32 foot aluminum track, and it was faster than all of my propeller cars (see Pinewood Derby Times Volume 6, Issue 15 - April 18, 2007).

Unfortunately, the car sat a little too high, so it would not go under the timer.

Against a fast gravity-powered car, it wins by nearly two track sections (about 14 feet). Here is a Quick Time Video (.mov extension) of the direct-drive car racing against a fast gravity car.

CONCLUSION
This was a fun and challenging project. Certainly my car is not elegant like Eldon's, but it got a lot of attention at our race in April 2007 - it confounded kids and parents alike. "How does it go so fast?," was a common response.

By the way, if you build a direct drive car based on this design, or a different design, please send me an e-mail with a description and photos.

From Pinewood Derby Times Volume 8, Issue 3

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Thursday, August 07, 2014

PINEWOOD DERBY CAR SHOWCASE

Ski Racer - Tom Bybee

My 8-year-old daughter took skiing lessons this year and was wildly
enthusiastic about the sport. Her first car design was a natural
expression of her new-found passion. She placed second in the siblings
race at our Pack.

NASCAR COT: Caterpillar Toyota - Brent Whitlow

My father and I take pride in creating full-bodied NASCAR style
pinewood derby cars. Since the COT (Car of Tomorrow) made its debut
last year in the Nextel Cup, we have been trying to create a pinewood
derby version. This year we were able to debut our first ever COT at our
local SAPCAR pinewood derby racing event.

Pink Ghost - Brian & Brianna Fenech

This car is my daughter's submission from her April 2008 Awana Grand
Prix race with Adamsville Baptist Church. The paint is a bright pink with
ghost Lemans stripes. The car features an extended wheelbase wedge
design, offset front wheels, and raised right front wheel. We used flat
black under the nose to ensure instant timing light trigger. All the
tungsten weight is located near the rear axle, precisely at 5.0 ounces.
The wheels are race-ready, graphite-coated slicks. The axles were
smoothed and grooved to reduce friction and utilized Krytox oil rather
than graphite lube. The car raced a total of eight class heats. It sped to
1st Place - Top Speed in Class, then Top Speed Overall to beat all
competition, including parents. The car also garnered 2nd place in class
for design. We're looking forward to starting our 2009 Awana Grand Prix
racer. By the way, Brianna was also the reining 2007 Top Speed Overall,
(See Car Showcase in Volume 7 - Issue 9).

From Pinewood Derby Times Volume 8, Issue 2

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Thursday, July 31, 2014

Graphite on the Tread

Graphite on the Tread

Do you put graphite on the tread surface of your wheels? Come on, you can admit it. I started rubbing graphite onto the tread surface about eight years ago. It seemed like a good thing to do, and it made the tires look nice and shiny. But honestly, during this time I didn't know whether it did anything to improve the speed of the car.

So I decided to test whether applying graphite to the tread surface has any effect on speed. While doing this, I also tested the benefit of applying graphite to the inside edge of the wheel (the part of the wheel
that touches the center guide rail).

EXPERIMENT EQUIPMENT
The experiment used the following equipment:

- Extended wheelbase Wedge Body(1), weighing 5 ounces, with the balance point at one inch in front of the rear axle, and a raised front-left wheel.

- Pro-Stock Speed Wheels from DerbyWorx(2) - These official BSA wheels are accurately trued, but are not weight reduced.

- Speed Axles from Maximum Velocity(3), polished with Brasso.

- A 32 foot anodized aluminum Freedom Track with a Judge Timer. For each run the car was staged in the left lane.

EXPERIMENT SET UP
Before mounting on the car, the wheels were thoroughly lubricated with Max-V-Lube(4). To prevent the graphite from getting onto the tread surface or inside edge, the wheels were wrapped in paper (Figure 1).


Figure 1 - Wheel Wrapped in Paper

After lubrication, the paper was removed and the wheels were mounted on the car. The car was then aligned, and given a few break-in runs.

EXPERIMENT PROCEDURE
1. The car was run six times, the high and low runs were removed, and the heats were averaged.

2. Graphite was applied to the tread surface of each wheel. This was done without removing the wheels. To prevent graphite from getting on the inside edge of the wheel, a piece of cardboard was pressed against the inside edge of the wheel.

3. Again, six heats were run, the high and low runs were removed, and the heats were averaged.

4. Without removing the wheels, graphite was applied to the inside edge of each wheel.

5. A final set of six heats were run, the high and low runs were removed, and the heats were averaged.

EXPERIMENT RESULTS
The following chart shows the results of the test. As you can see there was a slight improvement in performance when graphite was added to the tread surface, and then again when it was applied to the inner edge.

Note that the amount of overall improvement is only four thousandths of a second. However, the heat times were very consistent; the standard deviation (amount of deviation of the heat times from the average) is quite small (ranges from 0.0005 to 0.0017). Thus, the improvement, albeit small, cannot be completely attributed to statistical noise.


Figure 2 - Experimental Results

CONCLUSIONS
Although the small improvement could be important in a tight race, lubricating the tread surface and inside edge is an extremely small factor in overall performance. If allowed in your race, I would certainly do it, but you would not suffer a significant performance penalty if you choose to not lubricate the tread.

Another factor to consider is that the anodized aluminum track on which the experiment was run is extremely smooth. It is possible that if the experiment was run on a rougher track, there could be a larger performance improvement. However, rougher tracks do not generally provide consistent heat times. So the standard deviation of the heats would likely be much higher, and any improvement could be buried in the statistical noise.

(1) Part 5622

(2) Part 4080

(3) Part 4095

(4) Part 5104

From Pinewood Derby Times Volume 8, Issue 2

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Thursday, July 24, 2014

PINEWOOD DERBY MEMORY
Proud Grandpa


My grandson, Leo received his first pinewood derby kit in December 2007. His first reaction was, "Grandpapa, let's build it now!" I told him that we needed to do some research and planning before we could build.

His pinewood derby was scheduled for January 12th, 2008. So we had time to do the research and planning. As part of the research, I talked to several cub scout leaders whose sons had won first place. They all provided me with great advice, and even showed me one of their son's cars. They also suggested that I go to your web site and read your newsletters.

So we started building the kit. My grandson did the cutting, sanding and painting. I only drew the template on the block of wood and provided guidance throughout. He helped with polishing the axles and the wheels, and I did the drilling for the weight and axles.

Race time came, and my grandson was pretty excited. When we got to the event, he said to the Cubmaster, "I'm going to win!" He was the only Tiger in the Pack, so he had to race with the Bears and Wolves. They had to race three heats. He won all three heats, taking first place by a foot margin.

Next he had to race in the grand finals. There again, he had to race three heats. The race was very tight, and he ended up in third place overall . He was very excited at taking third, and I was a very proud Grandpa.

Donald J. Judeikis

From Pinewood Derby Times Volume 8, Issue 1

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Wednesday, July 16, 2014

PINEWOOD DERBY CAR SHOWCASE

Camping Tent - Jack Long

Camping Tent was a car I made just for fun for the 2006 pinewood derby. The tent is canvas, the poles are toothpicks, the feet are from a doll, and the fire has a red light bulb that lights up.

Old #25 - Robert Mareches

I wanted to share my car with all the fine young racers. This car is probably 40 years old. My Dad and I made this car together when I was seven or eight years old. We didn't know anything about weights or polished axles. With lots of guidance from Dad, I learned how to use a wood rasp, file, and sandpaper. The big decision was what color to paint it! He did find out that sanding the wheel diameter made it run smoother. I thought that this would be the clincher for me to win the race. Well, our car lost, but I still have fond memories of building a derby car with my Dad. The memory means more to me than winning a race; my trophy is this car. Good luck to all you fine young men in building your trophy racer.

Ghost Rider - David & Davey Sides

My 9 year old son, Davey, is very proud of the car we built. He is very enthusiastic about anything regarding Marvel Superheros and loves this particular character. Next year, he wants to made a "Wolverine" car.

From Pinewood Derby Times Volume 8, Issue 1

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