An Open Source Pinewood Derby Track

There are a lot of reasons to consider reproducing. Tax breaks are near the top of the list, and a bizarre obligation to ensure the survival of the species following closely behind. The pinewood derby, though… Where else are you going to get a chance to spend hours polishing axles and weighing down bits of wood so they can roll faster?

The Lansing Makers Network has cub scouts around the shop, most likely goofing off while their fathers spend hours building their son’s pinewood derby racers. Where there’s a pinewood derby manufactory, there’s a need for a track to test these racers out.

blurry-scoreboard-gutsThe four-lane, 38-foot run was made out of five sections of cabinet plywood attached with 4″ lap joints. That’s the way to do it if you want a smooth running surface. The lanes are 1/4″ strips of maple plywood, and the last four feet of the track – after the finish line, of course – are a ramp that raises the lanes another 1/2″ above the ground. There’s very little need for a bunch of pillows or foam at the end of the track.

This is the 21st century, and no pinewood derby track would be complete without a few bits of electronics. The starting gate is activated with a push button. A solenoid keeps a quartet of pins in place until the race is started. When the start button is pressed, the solenoid releases, sending the cars on their way.

On their way down the ramp, the cars pass over an IR object sensor which records their starting time. Thanks to some more sensors at the finish line, the track records each car’s position in the race on a few seven-segment displays.

34 thoughts on “An Open Source Pinewood Derby Track

  1. The last step of any derby track build should be a controlled experiment to determine whether there’s any bias in the lanes. My troop’s track favored one particular lane, and we kids quickly figured it out even though the adults acted as if they hadn’t.

  2. Designing a “fair” race is a standard interview question for me.
    Here are the high points that should be considered:

    1) Run every car on every lane and record the time. Then rank based upon the sum of the times ( NOT THE AVERAGE )
    2) Be prepared to show a live scoreboard. I had a child who saw his car “win” every race but he simply had not raced the fastest cars. The raw data showed that he did not win but the his eyes told him otherwise.
    3) Use some per-heat post processing to reorganize the cars between races. So long as every car runs once in each lane, you will collect the necessary data. But with careful processing, you can ensure “close” races to increase excitement. I simply did a left-shift with my races but with cell phones for your helpers, it is not unreasonable to have a completely new lineup for every race.
    4) Use ambient light sensors and visible “green” LED’s for the lane timer. This dramatically simplifies setup as it is difficult to see IR.
    5) Use a single micro switch to start the timer when the start gate falls. Then only one set of sensors is required.
    6) Using a timer to poll a port is an easy way to fairly collect all the lane data. Putting all the sensors on a single port and reading in a single operation ensures fairness to the nanosecond.
    7) If you do poll with a timer, the polling interval should be approximately 500uS. I used 1msec and had 2 ties. Summing the data over 4 races in 4 lanes resolved the ties, but a little more resolution would have been nice. The top two cars where typically within 10msecs of each other on my track.

    Never forget that you are making a bunch of 6-10 year olds happy. Simply getting the raw data and giving them a trophy can easily create a boring race day. Design the race so it is not as important that the lines be identical. NEVER EVER do a bracket race. The sterns method is interesting but I had boys show up a little late and the entire method is toast. Recording the time for each race is the only way to go. Display a running leaderboard so there are no surprises at the end. And use the data to increase the excitement with “close” races whenever possible.
    Of course lasers, fog machines and a photo finish camera can only help.

    1. While you have some good ideas, I would like to bring up a couple of points based on the fact you are working with “a bunch of 6-10 year olds” and the size of some Cub Scout packs.

      As an example let’s say there are 25 ‘racers’ overall, including the cub scouts and (as in the case of our pack) the ‘family class’ where all the other family members can participate. We used a 3 lane track, and the average time we tried to keep each heat at around 7 minutes each given that 6-10 year olds will run around and may not necessarily be ready right then.

      To run each car on each lane of our track would take about 21 minutes per set (3 cars at 7 minutes each). For 25 people this would take 8.3 heats (Rounded) to run all cars on all lanes. This will take 175 minutes. (8.3 heats at 21 minutes for each heat set). If you do the math this takes almost 3 hours, and considering that most of our meetings would start around 7PM and go for maybe 2 hours including the opening and closing ceremonies for the entire pack meeting, just the racing part would put almost every kid past their bedtime by almost an hour.

      So while I applaud your attention to detail and accuracy for absolute fairness, this is not exactly a practical approach for what is simply supposed to be a fun if slightly competitive evening for the above mentioned 6-10 year olds, especially when we are trying not to push ‘winning’ so much as ‘have fun’.

      I will however allow that this attention to detail and competiveness would go quite well for the Hack-a-Day community as well as the adults at the above mentioned pack meeting AFTER the kids are in bed….

      1. As the cub master for 5 years I did operate a 5 different races. The first time was on a bored track and the stearns method. This was the least successful.

        When we ran the electronic system, we had 30 kids and it took 4 hours to judge, race every car 4 times and hand out the awards. We were always done by lunch. Sometimes we had a lunch after the racing and let the kids run their cars on their own.

        Each race was 2.5-4 seconds long. The data recording was a serial port from to a terminal on my laptop. Unfortunately I did have to manually transfer the times from the serial display to a spreadsheet and this took a few seconds.

        There were 4 lane helpers who took the cars from the stage and placed them. Each helper was responsible for 1 lane. The cars were lined up on the stage in the sequence they were judged. 2 helpers walked the cars from the finish line to the stage and replaced them in the correct order on the stage.

        No boys handled their cars once they were turned in for judging.

        Each heat took 2 minutes to reset the track, setup the cars and run the race. With 30 cars and 4 lanes, 30/4 == 7.5 (call it 8). 8 heats * 4x = 32 races * 2 minutes = 64 minutes for the racing.

        While the numbers were being crunched (sort the list on my laptop) we held a race for all the family members. This was the no-holds-barred race just don’t damage the track or spectators. Offering this class of race hopefully kept the dads from “helping” the kids. We had a Dad and Daughter who consistent won this race.

        We used the SUM instead of the AVERAGE because that provides a sort of oversampling. Of course given a sufficient resolution in the computation there is no difference but by summing the result you don’t need to decide the races on fractions of a sec. Instead the races are decided on a dozen msecs or so. Besides, I did not even try to ensure that the lanes were the same since every car would run on every lane. Therefore the average is not that meaningful.

        1. OK, I can see being able to run that many heats on a weekend, our pack meetings usually got held on a weekday night when I was that young for various reasons usually because everyone had other activities that would conflict (such as little league for example). We also had a slightly more relaxed approach to let everyone have more fun that evening. Had we been able to have the meeting on Saturday then yes, we probably would have been able to take your approach to a longer meet.

          Our system was that each racer was responsible for bringing their car to the track, and the cubmaster was the starter and would place them on the track. Generally we tried to have everyone race on a different track each time, but if a racer was ‘late’ getting his car to the track he got what was left.

          For the cub scouts themselves, it was the ‘regulation’ race requirements with inspection and weigh in. If you didn’t meet the requirements, you could either try and adjust your car or you could only race in the ‘unlimited’ class with the parents. For everyone besides the scouts we had the ‘unlimited’ class, where pretty much anything went so long as it fit on the track. A few of those each race would fail to stop so we usually had a ‘safety crew’ to catch those after they departed the race course.

    2. > 1) Run every car on every lane and record the time. Then rank based upon the sum of the times ( NOT THE AVERAGE )

      When would ranking by sum ever get a different order than ranking by average? Average is going to be sum/Constant.

    3. A bracket “race” is not a race. A race is a contest to see who or what can cover a set distance in the least time, or cover the most distance in a set time. Any speed/distance competition where you can lose by going too fast is not a race! TSD rallies (Time Speed Distance) are called that because they are not races. A rally where the competitors don’t have to match a time as close as they can for their vehicle’s class *is* a race.

      Remember “Pinks: All Out”? At most of the events, as the contest ran into the evening, at least one car would pick up a bit of extra speed due to the cooler, denser air and would run just a bit too fast and be disqualified. They never compensated for that, which they should have. Such a slight change in temperature and density has little effect on most normally aspirated engines but with power adders like nitrous, super chargers, turbos and exotic fuels a small increase in air density can cause a significant amount more of air and fuel to be drawn/stuffed into the engine.

      A solution to that would have been a sensor to attach to the throttle linkage at wide open position and a green light to put somewhere on the car. If the driver lifted off the throttle (turning the light off) before passing the trap, disqualified.

    1. Yep. At a garage sale I once found a book called “secrets of pinewood derby racing” or something along those lines. Looked like it was maybe a special issue of a woodworking magazine. I picked it up for 50 cents cause I thought it might have good tips for precision woodworking. Only sort of met that requirement, but I clearly remember one particular line in the article about polishing “axles” (nails) with 1000-grit sandpaper for minimum friction: “this is a great chance for your child to help out.”

      Pretty much says it all, doesn’t it?

      1. My father handed me the kit and a knife and said “go for it”. Didn’t offer me a bit of help other than carrying the trophy to the car.

        Every book/article I’ve ever read since on PWD cars says I built my car wrong, too… Go figure.

  3. Have just ran the district pinewood derby, we raced 24-29 kids in each group, a;; boys ran in all 6 lanes and each group took less than an hour each, We race in a lane rotation, which save time as 5 of the 6 boys already have their cars loading or loaded in to the track with a new racer taking the place of the one that just rotated out. The difference between 2 and 3 was .001 secs or .006″ of an inch. We use a Fast Track compute timer that send the results to a laptop or desktop and we have a projector that displays all the results. And the computer software has a track record popup on the screen so the boys know if they are a fast car.

  4. This is great. My sons pack inherited another packs race track this year, but they didn’t use the electronics, they thought they were broken. I brought everything home and tested it, it turned out to be OE, which was really disappointing, there is some room for improvement in the COTS solutions.

    1. When I was a boyscout, I found some sort of teflon paint(?) at the hardware store while buying stuff for my derby car with my dad. I then proceeded to spray the nails down with it before I hammered the wheels on. It wasn’t banned at the time I built my car, but boy, was it banned to hell when I beat all the scoutmaster’s kids with my ugly-looking shitpile. :)

        1. apparently some races say “no lubricants allowed” nowadays.

          Polishing the axle nails and running dry graphite was basic to almost everyone’s car back when I was young. Of course, in those days, packs had REAL wolves, and we kept cub scout pack size down by leaving a few behind on campouts…

          who the hell are you? get off mah lawn! :)

    1. wood is the finest natural composite. Unless your printer is carbon fiber capable, you’d be hard pressed to get something demonstrably better than good ol’ wood. Now looking cooler/more fantastic/outrageous is another story altogether.

    2. It is difficult enough to keep some parents from buying pre-build car bodies. With 3d printing kids would not build at all, but download. There is more need now in the 21st century to have our kids work with their hands and make something.

    1. yep. because you actually build them, instead of assembling a kit. And races start slow but get close-and technology doesn’t improve much so race times stay close for years. Whizzzing around in circles/figure 8s with not even slot car control, where the outcome of a race (and a car’s entire expense and competitiveness) is determinable in a few seconds) tends to appeal more to the Pokemon/constant allowance spending crowd.

      I know because I got into the tamiya thing for a short time at 16 and what of my part time minimum wage didn’t get spent on fuel and car insurance for my work/school commuter, went into more bearings, new motors, chassis, side rollers, more boxes of obsolete and broken parts. I switched to a “race team” of 4 of my friends who all got together to race 1/10 RC by 17 and had a lot more fun with a second hand Grasshopper (also tamiya, natch) than I did with the half dozen 4wd chassis I owned.

      Pinewood however, was all about showing you could figure out a saw and a drill press, using dad’s old dangerous power tools in the basement. Our pack spent as much time judging cars for appearance as racing them. You could tell when fathers got too involved, mostly because young kids get bored with sanding LOL

      Now that I’m old, I’m trying to get a coworker to do the “unlimited” class in his cub scout race so I can build another car. I don’t have cub scout age kids that I can “help” :(

  5. This is cool. I prefer the variation where you are given a bunch of craft supplies and have free reign to create your vehicle. Pipe cleaners through drinking straws as bearings or 6 bobbins as wheels to try and make the bloody thing go in a straight line.

    Based on the comments here, do cubs and scouts not include girls in the US?
    UK cubs/scouts was about 50:50 boys:girls when I was one over a decade ago… Though I believe guides is mostly girls still.

  6. Mathematically Averaging times is no different than summing the times as far a ranking them. I have calculated the results both ways for the last three years and they have always been the same.

    We have a two lane track that was build by scouts over 40 years ago. The starting line is 6ft above the finish line level. It is fast!

    We do a trials and finals format. After all cars have their 4 runs, the 3rd and 4th fastest run off for 3rd place and the first two fastest cars run off for first and second. A coin flip determines lane assignments for the finals.

    Everyone gets to enjoy their car going down the track and there is the excitement of the finals at the end.

    Our biggest year was 42 cars each getting two runs down each lane. We had 82 heats + 10 finals races, awards and pictures in less than 3 hours.

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