Pinewood Derby Times Newsletter Volume 8 Issue 3

Pinewood Derby Times
Volume 8, Issue 3
October 29, 2008
In this Edition:

- Editor's Notes

- Feature Article - Top Fuel Cars: Direct Drive

- Humor

- Product Showcase

- Car Showcase

- Q&A

Editor's Notes

Two-Wheeled Car Results
In Volume 7, Issue 14 - April 2, 2008 I mentioned that I would be racing a two-wheeled car on April 18, 2007.

The car took 1st in Design, and 2nd in Speed. The winner was our Bolt design with our 4040 Outlaw Wheels. So, I was certainly satisfied with the outcome of the race.

Maximum Velocity Car Kits If you are planning a race and are not required to use a specific kit type, our MV Basic Car Kit is just what you need. These attractively priced kits are equipped with:

Quality Block - Unlike the blocks provided by some organizations, our blocks are soft, northwestern pine blocks, cut precisely to 7 inches long, 1-3/4 inches wide, and 1-1/4 inches tall. These dimensions, as well as the axle slots accurately duplicate the dimensions of standard pinewood derby blocks from BSA and PineCar.

Simple Axle Preparation - Don't worry about filing off flaws, or losing hub caps. Our Speed Axles have no burrs or crimp marks, and install without hub caps. With or without polishing, they are ready to go. We supply five, so you have a spare.

Quality Wheels - Forget cheap, out of round wheels. We supply top- quality, PineCar-brand wheels to give great performance.

So, if your organization does not mandate a particular kit type, consider our Maximum Velocity Car Kits.

Do You Have a Pinewood Derby Memory to Share?
We are out of memories to share with our readers, but I am sure that many of you have a story to share. So, please type up your humorous, unusual, sad, or heart-warming pinewood derby tale and send it to info@maximum-velocity.com

If your memory is used, you will receive a $10 coupon in May of 2009. Don't worry about literary polish. We will edit as needed. Also, please read our Submission Policy

Upcoming Raingutter Regatta or Space Derby?

If you have an upcoming Raingutter Regatta and would like some speed tips, decals, or extra kits, please visit us at Raingutter Regatta - World Class Boats. Our booklet, "World Class Boats", provides many techniques and tips for getting the most speed out of the standard BSA design, and also shows how to build the super fast Catamaran and Hydrofoil. These boats are so fast, they have been banned from some races!

We also can help with your Space Derby project at Spaceship Derby - Soar to the Finish!. Our booklet, "Soar to the Finish", provides you with all the speed tips you need to build a super fast space ship.

Can We Help? If we can help you in any way with your pinewood derby project, or if you have any feedback regarding this newsletter, please contact us at: info@maximum-velocity.com

Feature Article

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 (.pdf file).

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 (.mov extension) Video 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.

Humor

One summer evening during a violent thunderstorm a mother was tucking her small boy into bed. She was about to turn off the light when he asked with a tremor in his voice, "Mommy, will you sleep with me tonight?" The mother smiled and gave him a reassuring hug. "I can't dear," she said. "I have to sleep in Daddy's room."

A long silence was broken at last by a shaken little voice saying, "The big sissy."

Product Showcase

Propeller Car Kit

Create a super fast, propeller assisted kit for an outlaw race or just for fun!

The Propeller Car uses a ducted fan for additional propulsion. The car is powered by a 9 volt battery, and is started by a front-mounted switch. It also has a "kill" switch to turn off the car when not in use. The kit includes a pre-cut and drilled pine block, ducted fan, switches, battery holder, and the other parts needed to assemble the car. Wheels and axles are not included. Any pine derby wheels can be used, but for best speed we recommend our 4040-Outlaw Wheels & Nickel Speed Axles.

On a typical track, this Propeller Car will generally beat a standard, gravity-powered car by 8 feet or more.

Propeller Car Kit - $5.00 off

Until November 11, 2008, you can purchase a Propeller Car Kit for $5.00 off the regular price. To take advantage of this limited time offer, Click Here.

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.
Editor's Note: This car is based on the "Fast Talker" design by T. Dean White Creative.

Share your car with our readers!
Do you have a car you would like to 'show off' to our readers? If so, send us a photo of your car along with a brief description of any special features. Also, please include your full name. If selected, we will include the photo and description in this newsletter.Please e-mail photos to:
info@maximum-velocity.com.

Photos must be sent by e-mail in JPG format (minimum size of 640x480, maximum size of 1280 x 960). Please shoot photos from the front left of the car, similar to the orientation of this car:

Send only one photo per car, unless an additional photo is needed to adequately show a feature. Also, only one car per subscriber per year please. Thanks!

Q&A

Our Pack rules state that new axle holes can be drilled but the spacing between the front and back wheels must be kept at 4.40 inches. Given this constraint, how far back should I place the rear axle? I am afraid that placing the rear axle to far back will cause the car to be unstable.

Generally, you can place the rear axles at 5/8 inch from the rear, and then place the front axles at 4.40 inches in front of the rear. As long as the weight is placed such that the final balance point is 1 to 1-1/4 inches in front of the rear axle, the car will be stable.

I was thinking about using 3/32 (.0937) inch music wire for a rear axle with BSA wheels. I plan on pushing the wire all the way through the car to create a solid rear axle. Do you think that 3/32 inch music wire will be too big?

If you are using DerbyWorx wheels (or similar) that have been reamed, then they will fine. But if you use wheels with the original bore size, some of the wheels may not work well, as the bore would be too small.

Do You Have Questions that Need Answers? Do you have a pinewood derby-related question? If so, send your question to: info@maximum-velocity.com. We answer all questions by e-mail, but not every question will appear in the Q&A section of the newsletter.

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Volume 8

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Volume 7

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Volume 7, Issue 4

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Volume 7, Issue 6

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Volume 6

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Volume 6, Issue 14

Volume 6, Issue 15

Volume 5

Volume 5, Issue 1

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Volume 5, Issue 3

Volume 5, Issue 4

Volume 5, Issue 5

Volume 5, Issue 6

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Volume 5, Issue 9

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Volume 5, Issue 14

Volume 5, Issue 15

Volume 4 is available as a PDF file, ready for immediate download.

Volume 3 is available as a PDF file, ready for immediate download.

Volume 2 is available as a PDF file, ready for immediate download.

Volume 1 is available as a PDF file, ready for immediate download.

Newsletter Contributions

We welcome your contributions! If you would like to contribute an article, a web site review, or a speed tip, please send it to: info@maximum-velocity.com.

Please read our submission policy.

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Randy Davis, Editor, Pinewood Derby Times
E-Mail: info@maximum-velocity.com

Copyright ©2008, Randy Davis. All rights reserved. Please do not reprint or place this newsletter on your web site without explicit permission. However, if you like this newsletter we grant permission, and encourage you to e-mail it to a friend.

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