Wednesday, August 23, 2006

The Übercar!

I wasn't able to attend game night last night so I can't tell you what went on there but I can tell you what I was up to instead.

Several years back my oldest son was just beginning cub scouts. Now every spring the cub scout packs in our area (like most areas throughout the United States) hold a pinewood derby. Unfortunately, the track that my son's pack had available to them at the time was in a horrible state of disrepair. My wife and I, realizing we had five sons who would all be cub scouts at one time or another, wondered if perhaps it wouldn't make sense for us to buy a new track. That way we could contribute to the local community and ensure that our boys would always have a good track on which to run year in and year out. After a bit of searching, we found a place back east that made excellent tracks for a reasonable cost and placed an order. Since then, we've been happy to rent our track out for a small fee to any group in the area provided they let us run it. (Our own pack gets free use of course.)

Most of the time our track is rented to cub scout packs but every now and then a few fathers get jealous and decide they want to run a race of their own. Last night was just such a night. A group of dads from a church in Kirkland rented the track and I had a great time running it.

One thing that's particularly fun for me is that now every time I run the track I get to show off "The Übercar!" I made this car a few months back for a father's race that our own church held. After running this track for several years and seeing all of the great designs, I've picked up a few ideas about what goes in to a truly high performance pinewood derby car. The Übercar was the result of all of that experience. In its first race it barely came in second. The time difference was measured in thousandths of a second over three heats. Since then it's undergone a little more fine tuning and it has yet to lose a race. I'm sure that record won't last forever but either way, it's a pretty darn fast car. More importantly, it incorporates a few really neat design ideas and it always turns some heads.

So here, without further ado, I am proud to present the Übercar!

Let me walk you through its features.

First of all, this car is 100% BSA legal. The axles and wheels are straight from a BSA kit. The measurements are all completely within spec. The axles have been polished of course and the wheels have been sanded perfectly smooth and completely coated with graphite to reduce friction, but they haven't been "doctored" in any other way.

The trick to building a fast pinewood derby car is to build a car that converts as much potential energy as possible into kinetic energy as quickly as possible and then make sure that energy stays in the system. That means putting the weight as far back as possible and then doing whatever you can to eliminate friction. Most of the special features in this car are an attempt to apply these principles.

The most obvious "odd" feature on the car, and the one that draws the most comments, is the large turnbuckle that runs the length of the car. That is the car's primary secret weapon. It's an ultra-light aluminum and plastic turnbuckle that would normally be used on a radio-controlled model airplane. Its purpose is to flex the car's frame and thereby allow extremely high precision adjustments to the car's steering. If I lengthen the turnbuckle, the axles flex apart and the car steers just a bit more to the left. If I shorten the turnbuckle, the car steers a bit more to the right. By carefully adjusting the steering over multiple trial runs, I can "dial in" the car so that it tracks as straight as possible down the track, thereby reducing friction and ensuring a straight and fast course.

The wooden frame has been trimmed to the barest minimum. I've removed almost all wood except for the two axles and a thin strip connecting them. The axles are located very far apart to encourage straight tracking. The front axle has been carefully drilled so that only the left wheel actually touches the track. The right wheel never touches the track at all, ensuring that only three sets of wheels and axles are adding friction. The rear axle is as close to the back of car as possible to try and get the weight as far back on the car as possible. Almost directly over the back axle is a small bolt that rises from the bottom of the car. On either side of the bolt's shaft are permanent lead weights. On the bolt itself are a number of heavy flat washers secured with a nut. This enables me to put approximately 90% of the car's weight almost directly over the rear axle. Furthermore, the washers allow me to finely adjust the weight of the car so that I can quickly add or remove weight to ensure that no matter whose scale is being used, my car will always weigh in at exactly five ounces.

The only other feature of note is the boom at the front of the car. This is the only really "sneaky" part of the car. Over the years I've noticed that cars with a raised nose tended to get a slight advantage at the start. The reason for this is quite obvious once you think about it. The starting gate on most tracks (including mine) is a set of posts that rise up from underneath the track. The cars rest against these posts until the starter simultaneously drops all of the posts, releasing the cars. Because the posts drop down under the track, cars with a raised nose tend to be released a fraction of a second sooner, particularly if the starter is a bit slow on the release. This is a definite advantage with a slow starter as it can put my car a full inch ahead of the other cars. It's also an advantage which I've always been very careful to completely negate whenever I run the starter by being sure I drop the starter faster than the cars can move.

At this point, I'm convinced that the only thing I could do to make this car faster (without violating the rules) would be to improve the wheels themselves. While I spent a fair amount of time on the current set of wheels, I would love to get a precision lathe and balance a new set of wheels that roll even straighter. Still, I'm pretty happy with this car since it's consistently been the fastest car I've ever run on my track.


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