CO2 Powered Pinewood Derby Car Is Definitely Cheating

The Pinewood Derby is a classic Cub Scout competition where dads and sons come together to build a small-scale race car. You start with a kit that includes a block of wood for the body, as well as four plastic wheels and four nails to act as axles. Most innovations in the ‘sport’ center around reducing friction between the wheels and the axles, and making the body as aerodynamic as possible.

This year [Sliptronic] grabbed an extra kit and threw the rules out the window by powering the car with compressed carbon dioxide. He used a 3D printer to make a housing for two CO2 cartridges that mounts on the center of the chassis. An official Pinewood Derby race track is on an incline and has a wooden gate that keeps each car in place until it is dropped to start the race. [Sliptronic] is using this gate as the triggering mechanism. Springs on either side of the car pull against an arm at the back of the vehicle. This arm is held in place by a rod protruding out the front of the vehicle. When the start gate is dropped that rod releases the trigger, which is pulled up by the springs to pierce the CO2 cartridges. You can see an overview of how that mechanism works in the video after the break.

37 thoughts on “CO2 Powered Pinewood Derby Car Is Definitely Cheating

  1. My old middle school had a CO2 powered derby every year. We’d spend 6 weeks designing, building, testing, and then racing our cars. Each car was attached to a cable as it went down the track, to prevent it from flying off the table. I always enjoyed it, because you had to put some real thought into building a car as light as possible, while still being strong enough to withstand the force from the CO2 cartridge. Our cars always ended up looking more like drag racers than your normal pinewood derby cars.

  2. We made C)2 racers in middle school shop class in 1981. The teacher had a rig to mount both cars in that he hit with a hammer to launch them. Fishing line for a guide wire and a pile of blankets to stop them at the end of the hallway. It was a lot of fun, no one got hurt, and I don’t believe I ever saw a pair of safety glasses once in the whole year in there. His idea of safety was “Don’t cut your finger off!!”

  3. I’ve seen both cub scouts and high school shop classes do this. For safety they typically have a guide line attached to the car by an eye screw so the car doesn’t go completely ballistic.

  4. The best (legal) pine derby cars were always cut to about 1/4 inch thick (just enough to get the wheel axles/nails in). Slim little cars with weights on top of them always whupped the fancy cars.

    This one’s pretty cool — too bad no judge would let you near a track with one. ;)

  5. i did the same thing in middle school. but just like a few others who posted we had a track with a guide wire and and a sort of nozzle that forced the car down the track. i got a little clever and got some rc car gas shock lube and lubed up my axle’s.

  6. I remember doing this in an engineering class in high school. I took a cardboard box outside on a breezy day with sticks shoved in its side, lit them where they would smolder, and conducted crude wind tunnel tests. I won by roughly .5 seconds over everybody else.

  7. We also did the CO2 powered cars in my middle school. We also had a mini wind tunnel in the shop for testing our designs. Mine ended up being the most aerodynamic the teacher has ever measured and the lightest weight in the current class. The shop teacher didn’t follow the standard rules and set up a reaction-based drag system which I false started on and was disqualified in the single elimination tournament :(

    1. In my junior high in 8th and 9th grade I did co2 races. 8th grade I build a relatively simple hollowed out car. I cut my model in half hollowed i out, fiberglassed the top and only had it half fiberglass. I won that year. 9th grade I went overkill. I build a fiberglass one athirst, then I designed one in solid works, cnc machined it, and build it out of carbon fiber. The teacher let me race both, but he disqualified my first one for being “too flexible” It weighed 13grams and you could fold it in two.

  8. Heh, looks good. :) I suspect the design won’t be too prone to tipping or flailing because of the way the CO2 tanks are oriented, but if I was doing a CO2 car event with kids I’d be sure to use the guide line too because with kids you never know…

  9. As a side note, I absolutely hated pinewood derby races in cub scouts, because my dad and I were the only people who actually did it the right way where I built the car and he assisted. I always ended up in last place for not having my dad build the car for me.

  10. Same thing as a lot of posters – we did this in middle school shop class in ’88/’89. Only one cartridge though. In fact the blank came pre-drilled with the hole for the cartridge, so I don’t think “cheating” is quite the right term, just a different set of rules.

  11. @Brennan — I’m with you on that one… my dad would point me to the workshop and say “Don’t cut off any fingers, or your mom will get pissed with the mess.” That would be the extent of his involvement.

    As a side note of my own… isn’t the objective to limit friction, wind resistance, and zero-velocity inertia as much as possible? Why is it, then, that every guide to making these things recommends getting the car’s weight as close as possible to the legal limit?

  12. In my area there’s an Outlaw face after the main derby race, there are very few rules. We raced against a Dual C02 car, that thing was dangerous and shouldn’t have been allowed on the track. It didn’t trigger properly and hurdled off the track more often than not. My kid an I won with a car with most of the body built from thin balsa, an electric ducted fan engine, and a couple of Air Hog Lipos I got on clearance.

  13. C’mon, it’s not rocket scie… oh wait yeah it is!

    Win :)

    I’m wondering if it might be better to have a single gas capsule mounted centrally. The thrust would be less but it would be a bit easier to manage. I reckon the twin canister model would suffer because the thrust would be off-centre on average and would cause instability. A single can would save some weight too.

    Man I wish I had the gear to do this myself, looks like huge fun. And there’s not a bloody Arduino to be seen, bonus!

  14. This Post reminds me of my youth, My friend’s dad was a Aero space engineer. so when the Raingutter Regatta came around he designed a boat with a very fancy well designed hull. although for the record they lost.

  15. thrust-to weight. plastic bottle from whatever comes in pet bottle fits in the hole.fill with enough liquid co2/dry ice plug? Frangible tipped, glass? tubefrozen in dry ice @ thrust end. darwinbait yeah, but certain to be memorable if survived.

    art requires danger? sometimes i do show a bit of old school bet yer fingers hackart.


    if anyone’s suicidal enough to attempt my “joke” they may be a hacker.

    and this is stupidly risky, don’t EVER try it ok ?

  16. In HS I was part of an organization called TSA (Technology Student Association, Montana. There was a yearly meeting for competitions between the enrolled students from schools across the state, including CO2 car racing.

    You were given a regulation block of balsa with a hole cut in the back for the cartridge, two axles and four wheels. Then you had to shape it down to the car you wanted, by whatever means you had. Well our school was one of the only in the state with CNC mills, and I’m pretty sure the only one with the jig that held and rotated the block, allowing a perfect cut on both sides.

    Unsurprisingly, our CAD designed streamline designs won all the top spots every year.

    But also because we were able to get our cars so light while still maintaining structural integrity they would often turn from cars into planes, destroying themselves on the blockade at the end of the track

    Fun times all around

  17. @asheets

    The reason you want the car as close to the weight limit as possible is because the track isn’t strictly downhill. The large flat section at the bottom requires inertia to keep the car moving at a reasonable speed.

    The best option that I’ve found is to put as much weight as you can on the BACK of the car, because this weight will stay on the incline for the longest time, maximizing your acceleration time. Also, wear in each wheel/axle combination with a power drill and graphite lube and leave them together as matched sets. If you’re being really crazy, wear them in in the direction they’re going to travel on the car. Also be sure to de-burr all surfaces of the wheel that come into contact with the track, so the outer rim and the inside edge that keeps the car centered.

    When setting the wheels, try to make the car run on only three. If you’re feeling ambitious try to balance it across two, but I find that its easier to just get one of the front wheels lifted off the ground a little bit. No sense dragging it along behind you. Also make sure that the wheels are pointed completely straight ahead (even if the car body is crooked relative to them, make sure all the wheels are dead straight relative to each other) so that way you won’t be bouncing from one side of the containment rail to another.

    Believe it or not there are actually websites that will sell you lightened and balanced wheels, polished/plated axles and all sorts of other questionably legal (and by that I kinda mean fun) stuff. Just remember folks, stepping up the level of competition is fun, just make sure you aren’t being the cheating asshat. Get everyone in on the fun, or play by the (letter and spirit of the) rules haha.

    As far as air resistance goes, I agree it can be important, BUT, you have to make sure you have your wheels and axles in good standing first. You could have a CD of 0.01 and crap for wheels and you’re gonna lose.


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