Pinewood Derby Gallery
After a half dozen years with one boy or another in the Cub Scouts, we have collected quite a few pinewood derby cars. To keep the Dads from putting too much effort into their kid's cars, we would hold another event for the Dads. For the Dad's event, the only rule was to keep below 5 oz. and be gravity powered, about anything else you could do was legal. We even had an unlimited weight class, the only rule being that the car had to be gravity powered, and it couldn't hurt the track (or anyone) if it got out of control.. The Gravity Go went undefeated 4 years in a row.. it still has never been beat..
Most people hold their pinewood derby car secrets close, or even try to sell them. I prefer to share freely any ideas I have and hope others will share their ideas with me. Send them to firstname.lastname@example.org It's all in good fun.
Click on photos to enlarge
BatMobile - Has there ever been a pinewood derby without at least one Batmobile? This was my entry for the 1st year Dad's event. I put most of the work into the body and paint job (it had about 6 coats of lacquer), not enough into the wheels and I didn't know about the best graphites (don't ever use standard door-hinge graphite!)
BitMobile - Being a tech kind of guy, the next year made the BitMobile. Note the wheels now have hub-caps, which keep the wheels away from the car body. These are made from photographic paper with the shiny side in, glued on with super glue with graphite inside the hub. Just the rounded head of the axle(nail) rubs on the inside of the hub cap - very little friction. Think about the theory and you'll get it. This car was much faster than the BatMobile. Notice the front of the car is sloped downward from top to bottom - this makes it so the top-most part of the car is the only thing in contact with the starting gate. The starting gate is usually a wooden or metal peg which comes up through the track, and holds the cars in place until it pivots down toward the finish line and disappears under the surface of the track. As the starting gate is lowered, the top of the gate moves faster than the bottom (think of a lever) and since that is the part the car is in contact with, it gets off to a faster start. Think about it..
Silver Bullet - This had the same high-tech wheels as BitMobile, along with highly polished axles (done in drill press). I found the best graphite to be Hob-E-Lube. It's graphite with Molybdenum, and available at most hobby stores (but is always sold out during pinewood derby season so plan ahead). I found it faster than the white teflon variety but this is endlessly debatable amongst derby-car enthusiasts. Another trick to add to polished axles is to put a small pipe cleaner in a drill motor, coat it plentifully with Hob-E-Lube and run it through the wheel bearing at slow speed for awhile to polish and coat in inside well. Don't go fast as heat will melt and warp the hole. All these cars have a drilled 3/8" hole through the body for added weight. I pick up the cylindrical weights from the hobby shop - much better than using toxic lead - and they fit perfectly in the 3/8" holes.
Gravity Go - This car weighs almost a full 1 pound, but is purely gravity powered so met the rules of our "unlimited" class. It takes a little work to prepare it for launch, but then boy does it GO. This car has a 21", 1/8" diameter piano-wire rod attached to the car leaning 15 degrees rearward of perpendicular to the ground. The rod has a 1/2 inch washer welded to the bottom end, is embedded into a hole in the car and glued in place with PL Premium construction adhesive (available at home depot, but only in chalking tube amounts). The 8 ounce ball weight (standard fishing gear) has a hole drilled in it and slides freely along the rod. It is raised to the top of rod to prepare for launch. The angle of the rod is really important and matched to the track I was racing on, so that the rod is vertical while in the starting gate. Otherwise, the car would fall over with all that weight up so high. A strong thread, attached to the ball weight - the attached thread goes around the top pulley and back down to the rear axle. The thread is wound around the "gear" on the rear axle. Notice that this car has a rear axle, connecting the rear wheels together and keeping them perpendicular to track. Axles are generally illegal for cub scout pine wood derbys, but not in this special class. Wheel bearings were made from a couple of derby car wheels, sacrificed to a Dremel moto-tool. Look at the close-up of the axle to see that the "gear" is made from a narrow strip of double-sided tape wound around the axle until the right diameter (gearing) was achieved through trial and error doing test runs down a track. The "gear" is glued on it's sides to the axle with PL Premium The diameter of the gear is crucial to performance: too small and gearing will be too tall and acceleration off the line is too slow; too large and power to the rear wheels is so great that the wheels either lose traction and spin, or the car wheelies off to a start and falls over backward. Fast acceleration off the line is the trick to best performance down the track, so additional weights were added to the car to improve traction of rear wheels to the track, and to keep the front end down (avoid wheelies even though they look cool). Two 2 ounce pyramid shaped weights are placed as far back as possible and above the rear wheels - these help get power to the ground, without wheel spin. Their shape helps reduce air resistance. Another 2 ounce flat weight is added to the front end of the car, cantilevered out tot he front getting the weight as far forward as possible to help avoid wheelying. It also raises the contact point to starting gate as high as possible (see theory in BitMobile description). The front wheels are the standard hub-cap style design. When the starting gate falls, the weight falls all the way down within about 6 feet of track, propelling the car at impressive speed. By the time the track levels out, the ball weight is already down low so at this point it doesn't matter that the rod is mounted with a rearward lean. If you know anything about physics, there is a relatively huge amount of potential energy stored in the car, with the ball weight so high at the start, that is converted to other energy, much of it kinetic, as the ball drops and the car drops in elevation down the track. This car has never been beaten, but I'm sure there are creative people out there that can do much better. I'd be happy to hear your ideas. Send them to email@example.com. :-)
Here are some of my kid's cars. They build their own..
The Turtle - and it sure was..
Tyler's Black Lightning
Craig's Shark Attack - This was a really good car - took 2nd or 3rd place.
Tyler's Green Alien
Tyler's Lizard - This was my boy's first car that ever took the overall win. It is faster than any car, that met rules, that I ever made too. The only difference I could tell was he put his wheels farther apart, not using the stock "grooves" for the axle nails.