Pinewood Derby Tracks and Their Construction

  Pinewood Derby Track Design 101

The Track can be the most important element in whole derby event. However, all too often its the last thing dragged out of storage and dusted off.  Its been there since last year's race and you forgot all about that broken release gate. While much attention has been given to car construction and racing techniques all too often winning or losing came down to who was unlucky enough to be assigned to the "fast" or "slow lane.

Its true, too many times despite how carefully or randomly the lanes were assigned the track itself was all too often the beast to beat. To compensate we have designed complicated charts, computer programs that perform automated lane rotation, statistical analysis and other techniques to the end of compensating for the shortcomings of the tracks. Would it not be easier to build a better track? You might think so, but its not all that easy. If nothing else, we'd like to be able to reduce the factor the track plays in influencing the race outcome.

Think about it, how times have you looked at your group's track and wish you had something better? The typical track was built on a budget using plywood or other donated materials and is probably many years old having been passed along from garage to garage over time. Minor repairs are done just before the derby and make it just usable. The number two lane has always been slow and the seasoned racer knows to avoid it. Sounds familiar huh?

First, let's state for the record that no matter how much effort you put into it, no two pinewood derby track lanes will be the absolutely identical. It is technically impossible. You can only get close. In reality, the best test for comparing two or more cars is to have them run on the same lane and electronically record the elapsed time. If you want to have fun, though, there's no replacing the side-by-side, multi-lane race. So. . . what do we do? What makes the lanes on our tracks slow or fast and how can we do better?

How serious are you? After all, its only a single event for a group of 10 year-old boys, right? At risk of sounding a little presumptuous I would tell you - don't attempt to build a 'good' track unless you're prepared to spend a fair amount of time and money to complete it. If you can, rent or borrow a good track before you build one unless you're really handy in the shop.

  Determine the Track Size

If you're Really Serious then ... What size of track do you need? Most tracks will fall into the two, three and four lane categories and are often 32 feet long. The track length is usually a result of the use of 96" x 48" plywood. With the average standing height of most Cub Scouts being no more than 5 feet a track with a 4 foot top-end height provides acceleration adequate for around 30 feet. Four lengthwise strips of plywood end-to-end provides the 32 foot length. The newer aluminum surfaces require longer track lengths because of their super-smooth and harder finish offers less rolling resistance. Instead of 32 feet aluminum-surface tracks are more often over 45 feet long.

So if 32 feet is usually adequate for length how many lanes do you need? Larger groups will benefit from a track with a larger number of lanes. There's no hard and fast guidelines but if you're running a good race it should provide lots of racing for everyone and that means either a longer race or more lanes. If you're going to provide side-by-side racing with officials at the end of the track calling the finish order then any more than two lanes is more of a challenge for your judges. Tracks with more than 4 lanes may be built but they are really best for groups larger than 60 racers.

The last preliminary consideration is portability and storage. Where will the track be stored when not in use (which is most of the time) and how will it transported when needed? Most pickups and vans can carry an eight foot load. If you make it longer you will make it difficult to carry in most vans.

  Track Building Materials

The Running Surface. The type of running (rolling) surface you select will influence the base construction of the track, so let's look at that first. The rolling friction of the plastic pinewood derby car wheel and the flat surface of the track can be vary considerably. The microscopic obstructions of a wood-surfaced track can really slow down a low-mass car when compared to a smooth plastic laminate or metallic surface. Sanding, staining and finishing a beautiful wood gain can create a very nice looking track but there can still be a noticeable difference in lane performance.  Whatever material you choose, even if its a "slow" surface, the key goal is lane-to-lane consistency.

Wood. The most obvious materials for construction give us the most problems. Even after it has been varnished or painted wood has a tendency to have grain patterns that effect the speed and tracking of the cars that zoom down the guided path. Paint and varnish have a texture that effects the way the cars run. Nearly invisible brush marks can influence the tracking of a car.

Masonite® surfaced tracks provide a better starting basis. Masonite™ brand panels are fine-particles of wood byproducts laid up  with a bonding agent and pressed into sheet forms of 1/8" and 1/4" thickness.  Plans published by the company have been circulating in Pow Wow books for many years. When buying this material be sure to select tempered Masonite. The tempered Masonite panels are fairly smooth and provide a reasonably consistent running surface but they are also subject to the effects of raised fibers and surface irregularities created by the application of paint and other finish coatings. Use a sanding sealer on the surface then sand with a 240 grit for finer sand paper.

Sheet metal including Aluminum, plated steel and even stainless steel can be used as the primary rolling surface. A metal surface tends to be faster than wood surfaces as are plastic laminates. Aluminum sheets in a 0.020" thickness are not terribly expensive and are easy enough to form over a plywood base. The biggest concern with sheet metal is the sharp edges. Try to cover edges with wood trim after filing them to remove any burring. Metal surfaces are fast and less trouble in the long-run but more expensive than plain wood. Try to fabricate a metal lane guide to mate with this type track.

Formica®, Wilsonart®, Nevamar ® and other brands of plastic laminates cemented over a wood base remove most of the rolling surface irregularities. Tracks constructed from this class of material will tend to result in more consistent races, they're easier to clean, look nicer and last longer. The rolling surface doesn't need to be painted either. On the down side however, they are more expensive to build and the laminate requires more skill and patience to cut, position and cement in place. At $50 dollars per sheet (typical cost in many areas) these thin, brittle plastic sheets have caused more than a few inpatient novices a fair amount of trouble. This is likely the best compromise of cost, quality and long lasting surfacing material.

The Base Material. The base material for the construction will in most cases be plywood. Half inch thickness (nominal) are the most common in track construction and provide a natural flex that is ideal for obtaining a natural slope. Most plywood is now glued up as exterior grade but you would do well to verify that you're using a good grade of wood to reduce the risks of voids, high warpage, splitting and cracking. It is highly recommended that the wood be sealed with a varnish or sealer to avoid moisture problems later. Shop grade plywood will have only one "good side" and may be marginal for use in some applications.

  The Lane Guide

The cars are routed down-track by lane guide strips, one for each car. While a few tracks may use strips on the outside of the lane boundary most tracks are designed to use a single strip that the car wheels straddle. The guide is sized to fit between the wheels, under the car. The dimensions of the guide are specified as 0.25" (1/4") in height and 1.625" (1 5/8") wide. This permits horizontal clearance between the wheels and vertical clearance to the car bottom. For those using the BSA track plating the lane guide is a part of the single-piece aluminum extrusion.

Problems in some designs are caused by the guide strip. It is the friction from the inside of the wheels on the cars as they roll against the guide. The cars with poor alignment, of course, suffer the most. The guide strip is most often made from wood but could be fabricated from any workable material. This should be the only other surface that the car wheels will contact during the run. Each guide strip must be uniform to give the lanes consistency. They must be installed so that they are straight down the track and parallel to the other guides. Alternate materials include ABS, Acrylic and other types of plastic, aluminum, fiberglass and other cast materials.

While the base of the strip should be 1 5/8" wide the top is sometimes tapered and/or rounded to reduce the influence of a sharp corner. This rounding or taper process can be accomplished with a router, shaper or stationary saw.

  Support Structure

The top end of the track will be supported by legs, braces and cross-braces. Solid woods like Fir are best because of price and strength tradeoffs. The supports for the track can be built into the track and hinge or they can be separate assemblies on which the track is positioned.

Wood Finishes

The track will look better, last longer and clean up easier with a well applied coat of paint, stain/clear finish or other coating. If you employ a wood running surface paint it with coats of sprayed hard enamel. Use a smooth, high-gloss enamel finish in a color that doesn't easily show the graphite that will certainly appear with each race. It takes quite a while for most paints to completely cure after it dries to the touch. Paint the track many weeks or months before the race. When storing the track, avoid putting painted surfaces next to each other as they can stick together. Clean the track after each use and try to cover it to keep off the dust.

  Design Considerations

Lane Spacing. It is not usually obvious until you start laying out the design on plywood that you discover that the spacing between the lanes has required you use more plywood than you had planned. Each car should not exceed 2.75 inches in width and allowing .375 of additional space for each car to wander side-to-side you end up with a 3.5 inch minimum lane width.

Most tracks will vary from 3.5 to 4.0 inches of width for each lane. Does this make a difference? Maybe. If you're using an electronic lane judge check the sensor spacing. Are the sensors adjustable? Are you on a budget and undecided whether to build a three lane or four lane track? The three lane (32 foot) track can be built using just one sheet of plywood at 3.75" spacing. A 4" spacing wouldn't leave room for the saw blade kerf.

Downhill Acceleration slope. There is no standard for the acceleration slope on a pinewood derby track. Some tracks allow the cars to plummet nearly straight down for the first few feet with an extremely long roll-out while others have a slope for more than half the track distance while the fall distance remains the same. Many tracks use rigid sections that transition from a sloped section to flat section at a single joint while other rigid-section deigns incorporate a curved splicing section that provides a smooth transition between the sections. Flexible section tracks use fewer supports and permit the natural flex of the track span to achieve the transition from downhill to flat.

It is recommended that you avoid the abrupt slope to flat transition. Especially the 45-60 degree transitions to the flat run out. This is hard on the cars rolling down the track and can cause them to bounce out of their lane and sometimes even pop the axle out of the body.

The Release Device

The car release used at the top of the track could be as simple as a hand held yardstick pulled away at the drop of a hat. More often it is a mechanism consisting of nails, wood dowels or metal bars that mechanically slide below the track surface. There are similar restraints that rotate up and away from the cars.

The better mechanisms now in use include several variations of rotating restraints that rapidly move away from the cars and rest beneath the track surface. Here are some do's and don'ts for release devices:

 Don't use ferrous metal in the car restraint. Use wood or Aluminum instead. Some racers (or more likely, devious dads) have been known to place super magnets in the nose of their cars as a launch gimmick

 Avoid designs that drop the restraint straight down. This vertical dropping action drags on the nose of the car and can give some cars a small advantage over others depending on their nose height. The friction of the sliding restraint can also change the initial direction of the car.

 Use a restraint that holds the cars at the same point along the nose where they will be sensed at the end of the track. This is usually at the center of the lane which is also the car's nose.

 The release device must very quickly move away from the cars and not make any contact with car after the release.

 Make sure that your restraint is taller than the highest point allowed on the car. The nose of the car should never come over the top of the restraint.

 The restraints should be vertical and consistent with each car when in the "LOAD" position.

The above illustration shows a typical car restraint in the "load" position. The release is normally spring-loaded to quickly swing away from the car path and rest under the track rolling surface.

Track-Section Joints

Section Joints. The joining of the track sections end-to-end is very important as it will determine how easy the track is to assemble and how smoothly the cars will run as they pass over the seams. There are several issues to consider when designing the joint.

 Aligning the lanes and guide strips. The lanes must continue with no direction change and misalignment of the lane guides.

 Track section level changes must be avoided. The rolling surface must transition from one section surface to the next smoothly. If anything, the change could be a slight drop but never a bump up to the next section.

 Section joints need to be strong enough to maintain a rigid/continuing surface. No droop!

 Easy assembly. It shouldn't take long to set up and break down the track.

The illustration below shows examples of several joint types.

The first joint show uses three additional cuts of plywood. The two on the left form a receiver for the single attached piece on the right. The single piece may be sanded to reduce the thickness for the best fit. Brass table pins may be used to align the two top track sections. The pins are not shown. The second joint uses "U" shaped wood or metal brackets and a slats to secure the two sections together. The track plywood sections are aligned with a sheet of aluminum that is fitted into a slot on either section and joined at the two end sections.

There many variations of these joints and they are commonly drawn together by over-center latches, bolts and wing-nuts, and other similar devices.

Car Catchers, Stops and Other Arresting Gear

Just after that fancy red car passes the finish line in a blur and gets the checkered flag it . . .   (Pick the best answer)

    a. is splintered into a hundred pieces by a stack of bricks.

    b. rolls into a tank of water to prevent it from getting scratched.

    c. keeps on rolling across the floor until hits the far wall.

    d. Is slowed to a controlled stop in a padded skid box

While it might fun to try some these more drastic measures to stop the cars most of the racers aren't going to see the humor. We might make an exception for some the cars that a Dad built and didn't even allow the youth to touch until the race . . . but that's another subject.

The car arresting gear is often an afterthought but that's okay since its something that is generally attached to the end of the track anyway. It isn't enough to just provide more track for the car to eventually stop. That would be awkward, wasteful and wouldn't always stop every car anyway. First inclinations would suggest a thick padded stop across the end of the track. Our experience with this solution has been some combination of cars bouncing half way back up the track while others were flipped end-over-end off the end of the track.

Here are several workable solutions for a car-catcher.

Skid Ramp. The skid ramp approach to stopping the car involves maintaining a guide strip under the car as it leaves the end of the track but the rolling surface either drops away or the guide strip is elevated. The result is a controlled skid between the bottom of the car and the guide. Experience has shown that this is great for most cars. However for those racers that have weight attached to the bottom of the car the car will often roll to its side and crash into an adjacent car. To avoid the collisions, place a carpeted barrier between the lanes. To increase the friction and shorten the stop distance you can apply a coat of rubber cement on the last part of the lane guide. When dry, it will provide a more positive stop for the really fast cars. There many variations of the skid ramp.

Carpet Trap. The fact that a wheeled object doesn't roll well on carpet creates the basis for the carpet trap. The car rolls off the track into a carpeted open channel or tunnel that will quickly slow it to a stop. Allow two to three feet of roll-out on these surfaces and end the path with a padded barrier. One the many variations of this approach is to use either terry cloth towels or carpet and direct the cars into a "V" wedge. This method of arrestment can damage loosely fastened characters and car trim.

Bells and Whistles - The More Sophisticated Track

How much can you do to add helpful bells and whistles? What's really necessary and when do add-ons become unnecessary frills? Typically, the larger the race the easier it is to justify the cost and complication of more technology. A new 8 lane elevated track with electrical lane set-release mechanisms and complete car and 18-wheeler truck detection systems can easily cost $1500-$2000 before the lane judge system is added. This isn't realistic for a 20 boy Cub Scout Pack or small church organization where there really isn't a budget for a track at all. Pick and choose the from the entries below for expanded capabilities that are in concert with your requirements and interest.

The Aluminum Track Plating. The BSA retail catalog offer an extruded aluminum plating material for constructing new tracks or refurbishing old ones. The product is also available directly from Betacrafts. (see the address in the links section) This product is no longer being offered as single sections through the catalog. Each piece measures 4 x 93 inches. A package of 6 (part number A7696A) lists for $137.00 in the 2003 catalog. It's a mystery why they didn't make them a full 8 feet long instead of 3 inches shorter. The edge of one lane actually fits into the next lane forming what appears to be a continuous width resulting in lane separations of 3.775 inches. While you can use this plating to resurface your old track it may be smarter to start building from scratch when you consider the unusual length and center to center spacing.

The track plating sections are an all-in-one running surface and track guide with a tongue and grove interface to adjacent lanes. Its actually works pretty slick. The best features of this track material are the speed and consistency. Since all the pieces are identically produced they have the same hardness, shape, profile and dimensions. This is probably about as close as we've seen yet to having a "perfect track". And fast, whoa, you won't believe it! These tracks are so fast that the cars don't get much separation for quite a ways down the track. Its this the reason that they are sold in sets of six. It takes a track that long (46+ feet minimum) to make a fair race. Their instructions suggest either 6 or 7 sections which is around 46 1/2 or 54 1/4 feet in length respectively. If you build one of these "bad boys" be prepared to find a really long hall to run your race and use an electronic finish sensor.

The BSA catalog offers a design kit for building a track using this plating. "The Challenger" track design uses frames to which the plating is fastened. This is a detailed plan that gives you a complete material list with dimensions for a variety of tracks. This is one the most complete plans we've seen for a pinewood derby track. Look for free plans from the BSA web site. http://www.scoutstuff.org/

With all the benefits of this plating there is a down side. Its the cost! The plating alone for a four lane track will cost over $500 by the time you've paid tax and shipping. You then still have to build the rest of track (frames, support, release device etc.) lane judge or timer. Even still, if you afford it, its great!

The Pinewood Derby Trucks - RIP

In the 1997 catalog season BSA supply introduced eighteen wheel truck kits. Alas, after they were removed from the BSA supply system in 2001. Yes, the kits were dumped by the supply division. While they were fun to build they were a harder to race and in many cases the tracks just couldn't handle them. Too bad!

Four-Lane Track Plans

This set of 4-lane track plans have been developed to produce a rugged, high-quality track that sets up quickly and provides years of service with just a little care. It features a simple but effective release mechanism, plastic laminate racing surface with tongue and groove section alignment.

Specifications:

Track and Race-Related Ideas

Classify these ideas under the categories of cool, unusual, odd, outlandish and unbelievable but they've been done, suggested or at least stories we've been told. Who knows?