The Bolt

The Bolt

Pinewood Derby Times
Volume 5, Issue 10
February 8, 2006

In this Edition:

- Editor's Notes

- Feature Article - Weight: Place it Carefully

- Newsletter Subscriber Specials

- Car Showcase

- Memory - 90 Percent

- Q&A




Editor's Notes

Reader Feedback
"Several years ago our Cub Scout pack used to host a pinewood derby invitational race. We would invite the Girl Scout troop that was also sponsored by our school to make cars and then race us. We did it three years in a row and each year the girls took all first place trophies and quite a few seconds. After the last defeat of our fastest racers, the boys decided that this was not such a good idea and we have not had any more invitational races." - Scott Wheeler

"Here at Pack 1020 (Houston, TX), we have used your newsletters as long as I have been leading the Pinewood Derby (I think I am into year 5). We had another very successful pinewood derby race (over 100 cars entered by the Scouts). Several of the designs were modeled after the pictures from your newsletter. For the Scouts, the pictures are probably the most important part of the newsletter. I keep the pictures in a book available to all to scan for ideas (shapes, colors, and themes). Keep up the good work. We look forward to each issue." - Gordon G. Start


Back Issues
Are you a new subscriber? Have you missed a few issues? You can start reading all of the back issues of the Pinewood Derby Times today by Clicking Here.


Questions
If you have any questions about the Pinewood Derby Times, Maximum Velocity, or about building a pinewood derby car, please contact me at: info@maximum-velocity.com


Digital Calipers
Once you use digital calipers, you'll find 101 uses for them!

- Digital Calipers are a precision measuring device to easily and accurately measure objects. It is especially useful for measuring round objects such as wheels and axles.

Digital Calipers are featured as a Newsletter Special this month.




DerbyDome
- The DerbyDome is a high-quality case for safely displaying pinewood derby cars. It uses a patent-pending mounting system to keep the cars in place. The DerbyDome works with standard wheelbase cars (BSA and PineCar) with unmodified wheels. A custom label is available from the manufacturer.

The DerbyDome is featured as a Newsletter Special this month.


Feature Article

Weight: Place it Carefully

Over the past few years I have written several articles, speed tips, and answers to questions that relate to weight position. Today, Iíd like to bring this information together into one article. I realize that some of this information is a repeat, but I hope that each of you will find a few nuggets of information that you can put to good use.

Terms

First, letís get some terms defined:

COG: Center of gravity - the location at which an object balances in all three dimensions. In this article it will strictly refer to the lengthwise and height-wise point at which the car balances (also known as the horizontal COG and vertical COG).


Weight Position: the location on the car where the added ballast weight is placed. Note that weight position affects, but is not the same as the COG,


Wheelbase: the distance between the front and back axles.
Locating the COG

The horizontal COG of a pinewood derby car can be easily located as follows: (1) set a balance stand (or a ruler on its long edge) on a table and (2) lay the car (with wheels and axles in place) on the device as shown in Figure 1. Move the car forward or backward until it balances on the ruler. This point at which the car balances is the horizontal COG.


Figure 1 - Locating the COG


Horizontal COG - Front to Back

Due to track differences there is no one best horizontal COG. In fact, the horizontal COG that produces best results on one track will likely not produce the best results on another track.

There are three track types in use today (see Figure 2), with type 2 being the most predominant:

  1. Continuous-slope - One continuous slope from the starting line to the finish line.


  2. Ramp-flat - Starts on a slope, then transitions to a long flat section.


  3. S-shaped - Starts on a slope, transitions to a steeper slope, and then transitions to a flat section).

Figure 2 - Track Types


For the continuous-slope track, the horizontal COG of the car has only a minor effect on car performance (due to uneven weight distribution on the wheels), but it is best to locate the COG near the middle of the car body.

For the ramp-flat track, best performance is obtained offsetting the horizontal COG towards the rear of the car. The actual location varies from track to track, but a good rule of thumb is 1 to 1-1/4 inches in front of the rear axle. This location should be adjusted based on the following track features:

Why is the horizontal COG offset to the rear on this type of track. With an offset horizontal COG, the car will have a longer fall distance and will thus achieve a faster speed at the bottom of the hill (see Figure 3).

Figure 3 - Fall Distance Based on COG Position


For the S-shaped track, the best location of the COG depends on the length of each section. But, in the absence of track testing (see below) it is best to locate the COG similar to the ramp-flat track.

Testing The Track For Horizontal Cog

Testing for the best horizontal COG location for a given track is fairly easy if you have a track timer. Build a lightweight car without added weight, but with three dowel rod pieces sticking up out of the car (one in front, one in back, and one in the middle). Using steel washers weight the car in the front, back, and middle and compare the results. Mix and match to find the best COG for the track.

I ran time trials with this type of test car on a 32 foot ramp-flat track and found that rear-weighted cars outperformed front-weighted cars by up to one car length. Other testing results show similar results.

In addition, Michael Lastufka used a computer model to generate data and reached similar results at:
www.lastufka.net/lab/cars/why/qplace.htm - 0.025 second improvement

(One or more of these sites may not be available during pinewood derby season due to bandwidth limitations)

Vertical COG - Up And Down

Letís now move on to the vertical position of the weight. Is it better to have a high center of gravity (HCG) or a low center of gravity (LCG)? A LCG car will tend to be more stable, but it would seem that a HCG would impart more speed to the car. But is this really true?

In fact, it isn't. Given two cars with the center of gravity at the same lengthwise location, but with one having the center of gravity low on the car, while the other has the center of gravity high on the car, the LCG car will fall a greater distance. Referring to Figure 4, note that because of the starting ramp angle, the fall distance for the HCG car is actually less than the fall distance of the LCG car. The actual difference is based on the slope angle. But on this hypothetical track, the HCG car falls only 96.6% of LCG car's fall distance.

Figure 4 - Effect of Vertical Weight Position on Fall Distance


Although the LCG car will attain a higher speed, due to a pendulum effect the HCG car will traverse the curved portion of the track slightly faster than the low center of gravity car. But unless the flat section of the track is very short, the LCG car will overtake the HCG car on the flat section.

Other Considerations

Here are several other factors to consider when locating the weight

Type of Weight - The actual weight type does not affect the speed of the car, but does affect how easily the COG can be placed as desired. Denser weight (such as tungsten) allows much greater flexibility in weight placement than does less dense weight (such as zinc).


Length of Car - Longer cars allow the horizontal COG to be moved further to the rear (it also allows a longer wheelbase which aids in stability and alignment). So it is generally best to maintain the longest possible car body.


Raised Wheel - A raised front wheel necessitates a rearward adjusted horizontal COG.


Wheel Type - The horizontal COG must be measured with the wheels and axles installed. So, lighter wheels (such as our Outlaw Wheels) allow more flexibility in horizontal COG placement.


Wheelbase - The location of the axles affects the location of the COG. Specifically, the position of the rear axle sets a limit on rearward placement of the horizontal COG. As noted in Figure 5, simply using the axle slot closest to the end of the block as the rear axle allows a 5/8 inch rearward movement of the horizontal COG.


Figure 5 - Effect of Block Orientation on the Horizontal COG
Conclusion

The COG has a significant effect on the performance of the car. If possible, find out the specifics of the target track and design your car for optimal performance.




Special Offers for Newsletter Subscribers



DerbyDome: $1.00 off

The DerbyDome is a high-quality case for safely displaying pinewood derby cars. It uses a patent-pending mounting system to keep the cars in place. A custom label is available from the manufacturer.

For more information about the DerbyDome, Click Here.

but make sure to Purchase Here.


Digital Calipers: $2.00 off

Once you use digital calipers, you'll find 101 uses for them!

Digital Calipers is a precision measuring device to easily and accurately measure objects. It is especially useful for measuring round objects such as wheels and axles.

Features include:

  • Outside, inside, and step dimensions measured with jaws,

  • Hole/pocket depth measured with depth blade,

  • Inches / millimeters can be changed at any time.
For more information about Digital Calipers, Click Here.

but make sure to Purchase Here.

These specials are valid through February 21, 2006.



Car Showcase

Mean Green Machine: Bob Babich


Here is a picture of my son's car from 2005. Robby did a lot of the work himself with my guidance. His goal was to have a cool design (he designed the car) and he wanted to use a skin along with paint. At the end of the day, he finished second in his den and second in the Pack. Yes, the boys car that won our den, won the pack. Actually, places 1 - 6 in our Pack came from our Den and we had over 100 cars in the PWD race. Pretty competitive Den to say the least. Robby lost to a car that set 3 track records in 4 heats and still only lost by a few thousandths of a second. At the end of the day, my son was happy, and said, "Dad, next year I want to WIN."

Flintstone Coupe: Scott Wheeler


I make a pace car every year for my pack. One year a mom told me that her son could not make a car because she didn't have a saw. So prior to handing out all of the kits I took a kit and just carved on it with my scout knife. I shaved off all of the corners and pointed it like you sharpen a pencil. I then took a hand drill and drilled a few holes. I prepared a mixture of wood shavings and white glue and wiped it all over the car to make it look like bark. Then I went into the back yard and pulled a twig off of the tree to make the canopy. A small piece of brown construction paper cut with scissors and glued to the canopy frame made the covering.

The wheels are standard BSA that have just been sanded down until all of the design is gone. I then painted them to look like stones with different shades of flat gray model paint.

After I showed it to the mother she said that maybe he could build one after all. Her son got some help from a neighbor and he did real well in the race if I correctly recall.


Dollar Car: Kevin & Kyle WhiteCorron


My son had always wanted to build a 'dollar' car,' so we needed a flat car design to make it look like he wanted. We designed the dollar bill - which included his name and age - and we wanted the wheels to block the design as little as possible. The Extended Wing kit was perfect for the task, and it went together easily and quickly. The tungsten weights were a must to get the weight toward the rear. How did it do? It never lost a race


Share Your Pinewood Derby Car Creation
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. Please include your name, city and state. If selected, we will include the photo and description in this Car Showcase section. 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 the cars shown above.

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



Pinewood Derby Memory

90 Percent

I do a lot of hands-on work in the garage with my three sons around. Drilling, cutting, sanding. You name it, they have done it with my supervision. My oldest son (a Life Scout) never had the advantage of me using your site for tips when he was racing and never did better than 10th place in our Pack Pinewood Derby. But he did his best!

My 2nd son, now a 1st year Webelo, has taken 1st place at the Pack and 2nd place at the District two years in a row, with him doing 90 percent of the work. Being the Cubmaster I hear smart remarks about "his dad must be doing the work". So this year I stressed to the parents that yes, my son has won 2 years in a row and all the information we used was found on the internet. You just have to look for it like I did!

So this year, like I always have, I asked my son, "Get a Hotwheels car that you like and we will try to duplicate it; but it still has to be your design."

He responded back, "I already know I want a low flat car because they have less wind resistance!". So I told him "The whole idea is to do your best and if you win that's great!"

So we transferred the lines from the slots to the other side of the block, and marked the block for drilling holes (3 wheels to touch the ground). Then he drilled the holes with a drill press. I then laid out the weight placement for him to drill out. He then used my scroll saw to cut out the body, and then sanded it by hand. Next he chamfered the axle heads and removed the burrs. Then he sanded and polished the wheels.

Spray paint was next, followed by lubricating the wheels. Now I stepped back into the action and helped him install the wheels onto the car, and then align them. I thought to myself, "Yes he did 90 percent of the work."

On race day he came home again taking 1st Place. After the race I said to him, "You know we even forgot to polish the axles! Next year why don't we shoot for another category like best of show, or most original, and give someone else a chance to win the race?" He replied, "Yeah, let's do it!"

Bill Whittaker


Do You Have a Pinewood Derby Memory to Share?

Now that many races have been completed, I am sure there are many stories to share. Please jot down your humorous, unusual, sad, or heart-warming pinewood derby tale and send it to:
info@maximum-velocity.com

If your story is used, you will receive a free copy of Volume 5 of the Pinewood Derby Times when it is compiled during the summer.

Don't worry about literary polish. We will edit as needed, and review it with you before publishing. Also, please read our Submission Policy




Q&A

I can never seem to get the paint to come out right. I can never get a good shine on the paint. It always look dull. What is the best way to apply paint?

The trick is to use a good quality paint, to apply multiple coats (lightly sanding between coats), and then finish with a clear coat. I recommend avoiding enamel paints, as they are a pain to work with.

I use Krylon brand paints (Michael's Crafts and Ace Hardware carry this brand). Apply two coats of primer, then 2 or 3 coats of color, lightly sanding with 600 or 800 grit paper between coats. I then use Kylon "Crystal Clear" acrylic spray for the clear coat.

Another way to get a shine is to apply auto polish to the car body after painting. It will tend to shine up dull paint.

If you use a brand other than Krylon, make sure to check the dry and recoat times. Some paints have strange rules for recoating, and you don't want to break them!

For even more information on painting, refer to the article "The Ultimate Finish", in volume 3, issue 8.

Once I have primed, sanded, painted and re-sanded our car, will applying a car polish or wax to the body help with speed and reduce friction?

A clear coat generally works best. But as long as the product gives a nice hard, smooth finish, that doesn't get soft or sticky when friction is applied, then it should be fine. This is important at the areas where the wheel hubs contact the car body. When the spinning wheels contact the area, the area heats up.

Car polishes are usually okay as they smooth the surface of the paint to improve the sheen. Waxes leave a layer of material that could soften with friction.

We just completed my son's derby car using all of your great advice and products. I was wondering if you know what to use to remove excess graphite from the body without ruining the paint job?

I haven't personally tried this, but several people have told me that you can put a little vegetable oil on a soft rag and wipe the car. Then go back over the car with a clean rag. For some reason, the vegetable oil picks up the graphite.


Do You Have a Question?

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.



Back Issues

Are you a new subscriber, or have you missed some of the previous newsletters? Don't miss out! All of the issues for Volume 5 are posted on our web site:

  1. Volume 5, Issue 1


  2. Volume 5, Issue 2


  3. Volume 5, Issue 3


  4. Volume 5, Issue 4


  5. Volume 5, Issue 5


  6. Volume 5, Issue 6


  7. Volume 5, Issue 7


  8. Volume 5, Issue 8


  9. Volume 5, Issue 9


  10. Volume 5, Issue 10
Issues from the four previous seasons are available in four formatted volumes, ready for immediate download. To find out more, Click Here.





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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The Pinewood Derby Times is a free e-newsletter focused on the Pinewood Derby. It is published biweekly from October through April.

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


Copyright © 2006, 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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The Pinewood Derby Times is not specific to, and is not affiliated with the Boy Scouts, YMCA, Awana, or any other organization.


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