Pinewood Derby Car Design Tips
The Pinewood Derby has been drawing Cub Scouts together for a day of competition since 1953. The noble goal of the derby is to foster a stronger relationship between the Cub Scout and his parent by working together to create a personalized, custom, one-of-a-kind car from a basic BSA kit. It is hoped that a scout feels pride in his work, enjoys the competition of racing against other scouts, and demonstrates good sportsmanship whether he wins or not.
I've been through 6 years of Pinewood Derbies with my sons. The first year was a rude awakening to the reality of Pinewood Derbies. These are the few truths I discovered:
- Some dads do all the building of the car and the scout carries the trophy home. There is no way to prevent this.
- Some cars are purchased ready to race rather than built. There is no way to prevent this.
- Some fathers will teach their sons that cheating is ok.
- Most scouts prefer to roll their cars around on the gym floor after the race rather than care about who won.
After the first derby, I sat down with my sons and we talked about the various levels of craftmanship and speed we had seen. They decided that next year they would try to win the Most Creative award instead of the Fastest Car because the scouts all voted on the Most Creative. They recognized that some scouts did very little work on their car because the scouts told them. They also didn't care about not being fastest. They were already talking about cool designs for next year and asking me if I would do the sawing again - that's all I ever did on their cars. Every year, I also made my own car on which I could demonstrate my creative abilities.
I believe the Pinewood Derby is a wonderful opportunity for a son and parent to have a great time working with wood, learning about friction and gravity, being creative, and just having an excellent time together. As long as the parent emphasizes that they are participating together and does not take over the project, the derby is great. I think the team needs to set a few goals and guidelines before the derby car kit is even opened:
- Enjoy the process and the event, win or lose
- Do our best within the rules
- Hope for the best
- Congratulate the rest
While my scouts were not too concerned about speed, I was very interested. Some of those cars just flew down the track and I wanted to know how. After hours of research, I learned all the tricks for a fast car and I learned the Pinewood Derby is Big Business with a myriad selection of tools, templates, plans, and designs for a dad to purchase in an effort to help his scout bring home a trophy. I decided to try some of the free speed tricks myself - I won the pack's adult competition. The following tips tell you the most important pinewood derby car design concepts. Doing just the first few will make a huge impact on your performance.
Pinewood Derby Car Design TipsThese tips are in order of the most important first. If you have wheels as smooth as glass on axles that are misaligned, it will do no good.
- Heavier is Faster - Pinewood derby cars are gravity driven. Make your car as close to the 5 ounce weight limit as possible. When the car reaches the flat end part of the track, its extra weight means more momentum to continue moving fast.
- Axle Alignment - Absolutely straight, perpendicular axles mean a straight-running car with no drift. Every time your car drifts to the side and touches the lane boundaries, it slows down. The predrilled axle holes may not be true and straight.
- Graphite Lubricant - dry graphite where the wheels and axles meet reduces friction and results in longer, faster runs.
- Longer is Faster - if your rules allow you to move the axle locations, move the front and back axles as far apart as possible. The longer wheelbase results in less car wobble.
- Weight in Back - by moving weight towards the rear of the car, it moves further up the track at the starting point. That means it falls further and propels the car longer. If the weight is too far back, the front of the car will wobble so finding the best location takes trials.
- Polish Axles - the standard axles have imperfections that will increase friction with the wheels. Grinding the ridges off and polishing reduces friction.
- Smooth Wheels - The standard wheels have ridges and bumps. Sand and smooth them to reduce friction.
In a bid to make superfast cars, some folks have modified the design in ways that are often outside the rulebook. These modifications also tend to be outside the skill level of a cub scout. I don't recommend doing these unless you have an unlimited category for adults.
- Thin Wheels - shave down the wheel width so they look like bicycle tires. This causes a very thin track contact point for less friction. It also has less mass in the wheels meaning less inertia and less energy to get the wheels spinning at the start.
- Wheel Grinding - the cap on the axle touches the plastic wheel across its surface. This means for friction to slow down the wheel. Grind away the outter side of the wheel so a thin circle around the axle hole is higher than the surrounding wheel. This causes the wheel to touch the axle cap close to the center where there is less energy wasted.
- Hub Caps - similar to the Wheel Grinding, but better. Make a round paper hub cap to glue onto the wheel after final assembly of the wheels and axles. When the wheel moves towards the car body, the hub cap contacts with the axle cap before the wheel can touch the car body. The spinning wheel and hub cap just touch in the very center of the axle cap resulting in minimal friction. Even better if you put a bit of graphite in the hubcap before final glue-down.
- Raised Wheels - position the axles and balance the car so that one of the front wheels does not touch the track. Three wheels mean less friction. Just make sure the car runs straight on the three wheels. I've also heard of cars being balanced on opposite front and rear wheels with the other front and rear wheels only occasionally touching the track in an effort to further reduce friction.
- Suspension - It is possible to cut your pinewood block in a long zig-zag manner so that the entire piece of wood acts as a suspension. This absorbs more bumps and keeps the mass moving evenly down the track, resulting in less lost energy.
- Track Bumpers - Running down the track, a car will eventually touch the raised center of its lane. This raised center keeps the car in the lane but most cars will touch it with their rotating wheels which slows down the wheels. At the front and rear of the car, add four small brad nails under the car body way out by the sides. These will touch the center rail before the wheels, reducing the friction to the wheel rotation. Another enhancement is to place a smooth bead on the brad nail so it touches the center rail and spins easily, reducing friction a bit more.
For many Pinewood Resources, check out my Pinewood Links page.
Feb 20, 2012 - Branden Griffin
We were thinking of just rounding the front/back of the block to save weight and keep it aerodynamic. Would trying to keep most weight to the rear (potential energy) by having the axles closer to the front make sense?
Moving the axles wouldn't make much difference, probably cause more steering problems. Aerodynamics of a block of wood versus a slightly rounded block of wood is miniscule. Trying to keep as much weight on as possible would help.
But, really, it's a dumb rule to add to the process because everyone else uses the 5 ounce rule. Some wood blocks will weigh less than others, so your den's rule is unfair.
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