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Pinewood Derby Tips?
PizzaFace asks: "My son and I have to start building his first Pinewood Derby racer, and I'm looking for tips. I've found conflicting advice online about even the basic science (e.g. high vs. low centers of gravity) so I'm hoping to tap into some of Slashdot's expertise." Might someone have some pictures of cool designs that might useful as a starting point?"
(e.g. high vs. low centers of gravity)
Remember gravity isnt instantaneous, it travels at between 0.7 and 1.2 times the speed of light. This may affect your plans.
Since the last pinewood derby I had the pleasure to attend was over a decade ago, my memory is a little hazy. However, I do clearly recall all of the fastest cars having one common feature: They were almost planes. And I don't mean the flying vehicle kind. Plenty of people made very carefully crafted, glossy cars with carefully painted details, but they never won. All of the cars I saw do well were basically shells whose purpose was to hold the weights (which were always measured out to be barely below the upper limit) and the wheels together. Further, I recall many taking great trouble to rub some lubricant on their axels prior to every run. I can't speculate on the usefulness of such a thing.
Overall, I think the process is more fun if a lot of effort is taken in designing the car to look nice more so than making it fast, due to the blandness of competition stated above. That's not to say I didn't see a couple of nicely decorated planes, but when you got right down to it, it was still 2-dimensional.
You like splinters in your crotch? -Jon Caldara
1st place, cub scout pinewood derby, 1980
Slashdot readers will look at a pine derby car and wonder if they can cut a window in the side and add neon lighting.
- billn
Let's see. my body was no thicker then my pinky in the front of the car which came to a rounded point in the front. The back was no thicker then my thumb.
;^)
:^)
I put wood puddy (putty? hrm, it's late) in the middle where most of the fishing weights and lead were hidden. It looked like a cockpit/bubble like thing on the top middle. But I also had a door for access to a small amount of loose wieghts on the bottom for find tuning.
I even put a spoiler over the back wheels for kicks. With 2 wood dollies holding up a trianglar piece of wood on top. Hey, it looked cool
But after all is said and done, it is all about the wheels. I have seen people take 3rd with an un carved square block with weights.
Sand the wheels with some of the finest sand paper you can get (220grit at least, but the last of the sand papers was almost like paper it was so smooth...dont remember the grit on that one, though). I remember sanding the wheels for more hours then builing the thing. Also, I used graphite powder on the wheel nails for lubrication.
I won two 1st places in cub scouts with this design and one 2rd place later racing against the adults as a cubmaster.
Have fun
Graphite on the axles. I did very little to the thing other than that. No fancy slick low-drag paintjob. Put some weights in the bottom of the car to meet the maximum weight allowed, and graphite on the axles. That's all you'll likely need. But a low-drag paintjob wouldn't hurt. That's really about all you're allowed to do, anyway. And what else is necessary? Low-friction for the axles, low friction paintjob, and enough weight to maximize the 'thrust'.
:)
:)
:)
You don't need to worry about center of gravity - all you're doing is running a car down a straight track. No turning or anything like that - center of gravity has no effect on the type of performance you're looking for whatsoever.
Oh, don't forget the racing stripes - that's critical. Plus it should be red.
For a sweet low-friction paintjob, here's my advice:
Carve the thing into a blob shape - remove as little as you can get away with, as you'll just have to replace with weight later on (melt some lead into some holes till you get what you need). Once you have your shape, wet the thing down a bit and sand it smooth. Let it dry. Wet it down again and sand again with a smoother grit sandpaper. Repeat the process until you get a sweet, sweet shine. Using pine, you'll eventually be able to get the wood so smooth you can see reflections in it (no exaggeration). Once you've got it to that point, you're ready for painting. Enamel paint, for sure.
Put the weight in after painting, and get it up to the maximum weight allowed.
Graphite the axles before each run, of course, and whack your opponents on the knee before competition.
Weight tips: pretty simple. Make everything symmetrical. Putting more weight on the front, or more weight on the back, will simply screw it up - you want the wheels to have equal weight on them.
Good luck, and don't forget to be a geek and put pix of the whole build process online somewhere for us to Slashdot.
What's this about wheel nails? Are American rules differerent from the UK?
I would recommend...
1. Rubber tyres
2. Bearing and axle
3. Keep the wheel base fairly wide compared to the buggy height, this will about any dangerous tips at speed.
4. Keep steering simple
5. Make sure EVERYTHING is tight, real belt and braces. Don't screw when you can screw and glue, don't nail when you can bolt. Most crashes are caused when racers can't take the strain and start to disintergrate. You need to be Robust.
1) weight won't make your car go faster. See Galileo.
2) Weight might be useful in overcoming wheel friction, helping your car to keep it's speed on the level straightaway. So make your car as heavy as allowed.
3) Weight distribution: You can put all the weight in the front, or the back, or in the middle. It won't matter too much. Probably best to put it in the middle, as it's easiest.
4) Make sure the wheel nails are absolutely straight. If they're crooked, that's added drag. Test your car on a flat floor. It should track absolutely straight. If you have access to fancy tools to measure wheel or nail angle, use them to make those nails straight.
5) Don't make the wheel holes larger than the nail. That means no spinning the wheels without lubrication. No dropping the car on the wheels - that will move the nails too.
6) Always use a graphite lubricant before every run. Lubricate the inside of the wheel holes. Lubricate the outside of the wheels too. They rub against the track as the car goes down.
7) An ugly car will be just as fast as a pretty one. So no reason not to make it pretty.
8) Make sure that the wheels cannot move from side to side or slide on the axle. The nails shouldn't bind the wheels up.
9) It might help to polish the nails and the inside of the wheels to make them smooth. You can do this with a very very fine grit with just a *little* bit of rubbing. You don't want to remove material, just smooth what's there to a fine finish.
10) Polish the sides of the car where the wheels will rub. Or, if it's allowed, put a spacer on the axle that will prevent the wheels from touching the car body at all.
That's all I can think of. When I was in Cub Scouts my car took 2nd place. I didn't follow any of these rules except for the graphite lubrication though. I just got lucky.
If tits were wings it'd be flying around.
Er, am I revealing woeful ignorance or are there a lot of other people out there who haven't the faintest idea what the heck this is? Couldn't an informative link have been provided?
OK, 5 minutes with Google later, it appears to be something coming from the Scouting movement; kids build cars out of a basic kit of a block of wood and wheels, and then race them down an inclined track. So you get competition, woodworking skills, and parent/child bonding as Grandad shows you how to work a lathe etc. (OK, you don;t use a lathe to make a wooden car but obviously since I don;t know what it is I have no woodworking skills)
~~~~~ BigLig2? You mean there's another one of me?
Take a high cfm 12v fan, drop it onto the car, glue it, run it at 9v or whatever.
Put all your weight in the middle, and as low as possible. If you put it up front, your rear wheels end up being a drag. Max out the weight as everybody suggested, it does help it run more smoothly. Just hollow out the shell as much as you dare, melt lead fishing weights into it, and goo the whole thing over with silicone to make it stay in place. I have a shoebox in a closet that I just happened to open a few months ago that has 25 year old cars in which the siliconed weights are still securely in place. The nice thing about lead is that you can actually re-melt it and experiment with distribution prior to siliconing it into the final location. For testing we'd just temporarily tape it in place using something strong like electrical tape.
I'll go counter to everything everybody else said: Aerodynamics didn't seem to matter at all. Many decades ago I consistently won with *everything* I built -- specifically, that included a big boxy "fire truck" design festooned with all sorts of plastic "equipment". I never took anything less than first place in the 20 or 25 cars I built and ran over a period of several years. I doubt the cars go fast enough or run far enough for aero to matter -- it's all weight distribution and free rotation of your wheels.
That said, most of my car bodies still followed a basic low-wedge shape, with a wide rounded-bottom groove down the middle. This was easy to build, sort of looked aerodynamic, and removed as much high-riding wood weight as possible, leaving as much low-riding lead weight available as possible. I've tried shaving weight off EVERYWHERE, in some cases even trimming wheels down to flat discs (leading to new rules in our group requiring the use of specific wheels from a kit).
"Real" car designs are boring, everybody does those. Go for the abstract. Confuse your opponents. :)
Slashdot quality declines as the number of hot grits posts decreases. - Provolt's Law, Apr-09-2005
It's not too hard. As others have pointed out, center of gravity means nothing, except that a lower center would tend to have less cross-sectional area (which is good). All you have to worry about is friction and weight.
.001g over, use a sharp knife and remove a sliver of tape to finish the tuning. You'd be amazed how much a bit of vinyl electrical tape can weigh...
Friction is the hard part, and you've got two kinds to deal with: Friction with the air, and friction between the wheels and their axles.
For wind resistance, just start slicing the car down as much as you feel you can without sacrificing strength, or capacity for added weight. Round off both ends of the block into something that looks reasonably aerodynamic - I used a bench-mounted belt sander. You want it low, and flat, so as to displace as little air as possible as it moves down the track. Using similar curves to a high-speed train will yield better results than mimicking an F14 or Lamborghini. That the resultant form is rather boring is not an accident.
Friction against paint is probably not a big deal. My finish was a hand-brushed yellow-and-black flame paint job, and was nowhere near smooth. But it certainly wouldn't hurt to make it as mirror-like as possible with careful painting and sanding, along with a coat of well-buffed wax.
One trick I used which I've never seen repeated: A small circle of electrical tape, placed over the outside of each wheel, to further reduce drag. They were cut with a ball peen hammer and a coin of appropriate diameter, and fit precisely. It should be flat or slightly convex, but not concave, when applied to the wheel. This will increase rotational inertia (==bad) somewhat, but it seems like a beneficial thing to do.
To reduce friction between wheel and axle, I first removed the burr on the supplied axles using progressively fine sandpaper - there were two axial burrs, along with one across the back of the head. I also removed burrs on the inside of the wheels, and slightly rounded the flat part near the middle, inside of the wheels where it can touch the body, to reduce contact area.
Use graphite on the wheels and bearings, and use it as much as a polish as you do a lubricant. Work it into the microscopic texture of the axles, the inside of the wheels, and the bearing surfaces between the axle and the body by whatever means you can find, and then add some more and roll the car around a bit.
I used feeler stock (thinner-than-hair bits of flat metal) to get each wheel to within a thousandth-or-so of an inch of being on the same plane, such that they'd all be in contact with the track surface. I don't know if this helped, but it seemed like a good idea.
At least, try to keep your axles as straight and square as possible with eachother and the body. You do not want any pressure on the points where the wheel contacts the body, or the head of the axle.
And adjust the axles so that there is as little play in them as possible. The wheel should not move appreciably side-to-side, nor should it forcably rub on any point. Slop here translates to lost energy. It may take several iterations of gentle tapping on the axle and even-more-gentle pulling on the wheel to get this right.
Weighting is a science. You want the car to be as heavy as it possibly can be. Remember that you won't be immediately disqualified for having a very slightly heavy car, and that you'll get at least a couple of chances to bring the weight down.
Drill holes in the bottom of the car, and pour lead into them. I used an antique balance I had at home and added weight until I measured it being just -over- specification, and so the lead was protruding slightly below the bottom of the car. This allowed me to use the official scales to tune the car at the event, removing a bit of lead with a file and re-weighing several times before nailing it precisely, while in the process filing the lead flat and reducing drag.
Place a strip or two of electrical tape over the lead, to further reduce drag and add the nth degree of tuning: If you file a bit of lead off and the car still measures
If your track levels out toward the bottom, put the weight as far toward the back of the car as you can. You'll get a few more inches of "thrust" by doing this, vs. your front-weighted opponent.
The devil's in the details. When it's all done, handle the car as if it were full of nitroglycerine - don't even look at it funny, or all of the precarious work you've put into it will begin to undo itself. Never let others handle it, and absolutely never leave it unattended at the event. It's a finely-tuned, very delicate instrument, and is deserving of respect.
Kid-proof tablet..
for some really nice pinewood derby timers, that can even be hooked up to computers, check out www.microwizard.com
The rules are quite strict about size and wieght. The wheels cannot be modified from the state they come in the kit. You can lube the axles, which are also supplied in the box.
Of course my car wasn't flat.
Guy I work with who has 3 boys gave me this odd tip. Even if you're required to use all 4 wheels, just set them up so that only 3 touch the ground. He said he gets surprisingly good results without the extra friction/drag from the unneeded wheel. I would expect that he weights heavily to the middle/front so that the car's not constantly shifting its weight down onto the extra wheel.
www.HearMySoulSpeak.com
I had the slick aero car that had a sorta wing profile to it, painted nice and silver, I made it to the finals but that damn slugmobile...
I guess that was a pretty significant event for me because I think back on it often, overengineering got beat by brute force.
The car straddles a wood strip as it drops down the track. If it has a tendency to turn it will repeatedly turn into the strip as it drops, generating much friction as the inside of the wheel rubs the strip. Insure that it runs true.
Regarding friction on the wheels, the head of the nail (you may be required to use them) will contact the wheel as will the wood on the inside of the wheel. You may want to address these areas, tapering the nail head and inside to minimize contact area.
OK, I ran a den for a few years. Our pack alternated between Pinewood Derby, Rocket Derby, and Raingutter Regatta.
Pinewood Derby - Race little wood cars down a track.
Rocket Derby - Race little rubber-band propeller-driven "rockets" down a piece of fishline; you go for distance, not speed.
Raingutter Regatta - Race little sailboats down a length of raingutter, powered by Cub Scout breath.
The biggest challenge to all three of these is to make sure the boys, not the fathers, do the bulk of the work. For most hand tools this isn't too hard, though the boys usually want the slicker looks that Dads can produce. You also want the boys to be able to have win-capable racers, without stepping in too much. We built the Pinewood Derby racers in den meetings, and I insisted that fathers (where available, a sad story in itself) attend with their boys. We settled on a basic design, and each boy got two cuts on the radial arm saw with me, while the fathers supervised other work like polishing axles. My hands were on top of theirs, the cars were clamped, but they got to run the saw back and forth, and learned a little about power tools, safety glasses, and hearing protection.
Oh, a tip, speaking of polishing the axles. Those little nails they give you for axles often have a burr on the inside of the head. You want to chuck the nail into a drill, and polish that burr off. It's also a good idea to tilt the angle of the inside of the head a little obtuse from the shaft, so that the inside of the wheel rides on a slight cone - less area for friction.
Of course my son didn't win, so maybe you should ignore this. But I will second any vote for graphite.
The living have better things to do than to continue hating the dead.
My Dad and I, after getting the car to within a couple of ounces of the target weight, rounded out the rest with nickels hot glued to the bottom. Then at competition time, just pry off a coin or two if things are too heavy. Worked great, and won a couple for us.
But more important than weight, as others have said, is the wheel setup. Do like the instructions say, and but all the wheels on a nail, and buff them all smooth on a drill press or lathe. Then make sure your alignment is dead-on-balls-accurate. And then graphite the wheels - I suppose you could oil them, but there must be some reason everyone uses dry lubricants (and it's not ease of use!!) Make sure you don't mix dry and wet lubricants.
Not that an un touched block of wood weighted right with perfect wheel setup will handily beat the slickest looking aredynamic beast that did a shoddy "powertrain" job.
And remember, most important is that you and your son have a good time doing it. My dad once helped my brother carve his into a perfect looking banana with wheels. Wasn't the fastest, but it was loads of fun, and won the best looks competition.
_sig_ is away
Ours had many categories apart from speed. I won a couple prizes for "fanciest" for cars that didn't run that fast.
My father made a truly geek car. He took a matchbox mercedes ambulance and made a beautiful model of it. Of course he added a couple flashing LEDs and a siren in it.... He built it 25 years ago, but I found it at their house last weekend -- half way around the world from where he built it!
Our entire school was eligible to enter, and there was a category for "over 15" where custom axle systems were allowed. Those cars flew! The traditional "fast" axle system was to install plates along both sides of the car. A pair of wheels was on a common axle with points on the outer ends. These ends fit into concave bolt ends threaded through the plates.
So to sum up: Speed is all in the wheels and axles. A block of wood with good wheels will beat anything.
You'll find experianced Scouters and Scouts on rec.scouting.usa. Be sure to read the charter before posting.
Help us build a better map!
1. Scuff the wheels up the stock wheels are to smooth and sometimes have a ridge...this helps alot...tip put them all on a long nail put the nail in a drill as a bit...spin drill...hold wheels against sandpaper...scuffing takes about 20 seconds and comes out very even if done right.
2. Put all weight on the bottom of the car. Put even amounts near each axle...and the remaining amount dead center of the car.
3. Lots of powder graphite on the inside of the wheel and the axles...but do not apply to the axles till they have been mounted...maybe that mistake one year..wheels came flying off mid run...
4. Different districts seem to apply rules on axle attachment differently so your YMMV on this one. Dont use the slots on the bottom of the block
the axles can slip out...if your allowed drill a pilot channel directly through the body from side to side...just make sure the front and back are at even hieghts....this should be done carefully as it must be no more than a 1 -1 1/2 centimeters from the bottom of the car, otherwise the car might not clear the track guide.
a. if you must use the channels they might let you glue the axles into them do this if you can...I have seen lots of wheels fall off mid run.
b. make sure the wheels are as close to the body as possible without restricting movement
c. if allowed use a copper bushing again well graphited, between the body and the wheel, this will allow for maximum stability of the car and maximum wheel turn rate.
5. I have seen conflicting evidence in my time on car shape, and aero dynamics...all I can say for sure is I have seen more cars win that where shaped like airplane wings...and sanded very smooth with a high gloss paint...Hint: nail polish and clear nail top coat.
6. This is supposed to be a fun event don't go overboard concentrate on the fun aspect of building the cars, and having a good time as a father son activity. Winning is good, but not the point. My den was one of 20+ in the troop, there were probably 100+ of us at every derby, and only one person can win...if your in a similar situation, the odds are horendous.
PS. Anyone remeber the Balsa wood hanging rocket races...with the huge propller on the front...I liked that one even better than pine wood...of course that was probably because I won everytime. My designs were consistently the only ones that made it to the end of the hanging track!
Power Corrupts,Absolute Power Corrupts Absolutely, leaving one person(group)in charge is absolutely corrupt.
I dont know if your pack is anything like mine was, but we only had the pinewood derby every 3 years, the other 2 years we'd have the Space Derby and the Raingutter Rigotta(sp?). The the Raingutter Rigotta was always fun, you build a little boat and have to blow it down the length of an endcapped gutter full of water, the trick was a good keel. The spacederby was ok, but heres a tip. Never spray paint your rocket! It'll partially disolve the styrofoam weakening the rocket to the point when you wind up the rubber band (rubber band and propeller power) the rocket would fall apart. It was a failue, but at least it was a spectacular failure, obscuring the other rockets in a cloud of foam particles. :D
"Sic Semper Tyrannosaurus Rex."
1) Make sure they are round. Put them in a drill and sand the outside (tread) area to make them round.
:-) Scouts raced one Saturday, the next Saturday was the parent race. Living in DuPont country had some pretty flashy paint jobs and some very fast cars.
2) You want to be at the 5 oz limit. Put the weight in before you paint and assemble.
Cut the body out and weigh all the parts. Add lead weights to the pile to get it to slightly above 5 oz. Now drill out the body to hold the weights.
Buy a small cast iron pan at the local $1 store and melt lead weights into it. Pour the molten lead into the car. It keeps it from shifting / falling off. You can us a 1/32" drill to trim the weight exactly. BTW the best scales are at the post office, make friends with the Postmaster to weigh your car before hand. The winning cars are all within micrograms of the weight limit.
3) If you look at the car there are two bearing surfaces, the side of the car and the head of the nail. You want these two surfaces to be as smooth and even as possible. When you sand the nail, you want to also sand the inner face of the head.
When you assemble you want to reduce the wheel wobble to zero and make sure the car tracks cleanly down the track. I've built cars that run on three wheels touching, they are slightly faster than those with four touching. The key is the tracking. (Two fronts touch, only one back one touches). The other magic is EPOXY. You don't want the wheels to move once they are in. The car will get banged around during the race. White / yellow glue is good, but is not as strong / hard as a good epoxy.
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Memory flashback - When I was Cubmaster there were a lot of overachiever dads. (Slashdot readers?). The deal was each scout had to swear that they built over 1/2 of the car. To help out we had a "Parent Only" race. Rule was car was to be 100% parent built, no help from the scout
And yes, we raced the winning scout cars against the winning parent cars and about 50% of the time the scout car won.
Good luck.
Carve and paint it to look like a shoe, and be satisfied for winning "Most Unusual" in the design competition.
Of course, a lot has changed since the mid-70's. Perhaps tricking it out as a ricer might be a more contemporary option. A spoiler and stickers would be easy enough. But how about carving out a place for some button batteries to power some LED "neon" running strips? Cram in one of those boy-band keychains you can find at Toys-R-Us, and it can even be a boomcar. Real riceboys would be pissed at the music choice, but the adult judges will never know the difference.
In a related story, the IRS has recently ruled that the cost of Windows upgrades can NOT be deducted as a gambling loss.
Speaking as one who served as Cubmaster for five years (my son graduated to Boy Scouts a year ago) I have some observations from running several derbies.
Graphite on the axles and check the axles for burrs (they are stamped nails, there is usually a ridge under the head).
Get the weight to be as close to the max allowed as possible. My Pack did weigh in the night before the race -- makes for less confusion before the derby. We had glue, drills, and extra weight on hand to find tune the cars to as close as our scale could get to the weight.
It helps if the car runs straight - bouncing off the guide slows things down.
From my observations, in most cases areodynamics has little to do with the performance of the car. We have had the last minute, painted block o' wood car finish in the top 5 (of 50).
And a comment aimed more at the Pack leadership - Let the boys handle their cars! I have seen several packs run their derbies where the scouts deposit their cars in the staging area, and that is the last the boy gets to touch his car until it the race is over. (Boring!) Our Pack the scout was the only person who could touch his car.
It does not hurt that our track electronics only records the first car across the finish - we have a 8 lane track, and take each den and use the den heat to sort the cars by speed (first one with 2 wins is fastest and is removed, then repeat until all the cars are placed in speed order). We then repeat this for each den. Once all the dens have raced, we start with slowest cars (the ones that placed 8th in the den heats) and race them against each other - the fastest of these cars fill the 7th place heat to 8 tracks. Repeat until racing the 1st place heat.
The main thing this did was cause the slowest cars to race the most... And occasionally we would have a car that would 'come from behind' in the pack heats to win or place.
1) Sand the wheels. Often the wheels that come with the kit have a little seam on them from when they came out of the mold. Use fine sandpaper to smooth out the surface of the wheel.
2) Contrary to many people's posts, center of gravity can make a difference. Since your car starts out sloped downwards, if you put the weight towards the back, it has farther to fall, and imparts more speed on the car. Just make sure you put the center of gravity ahead of the rear axle.
I used to bulls-eye womp-rats in my pants
Here's my advice.
Ask your son to draw some pictures of what he wants it to look like. Go over them with him. Pay particular attention to any pictures that go on the sides -- that will tell you his interests in a way conversation can't.
When it comes time to begin actually carving the block of wood, take a dummy piece of wood and make sure he knows how to cut. Then let him cut the dummy piece. Then let him cut the car.
Use a scale and some lead shot (or whatever), break out a piece of paper for a real application of subtraction. How much lead shot do you add to get to the maximum allowed 5oz? (Wow, subtraction is useful in real life, dad?) Ask him how best to attach your weight. Perhaps he can think of other materials just as good? (Paint will add some, so it may be helpful to keep it possible to remove a little.)
Now, start painting. Maybe you sand first, maybe you don't. Chances are, he's getting tired of this project and just wants to see the final shiny piece. High gloss enamel spray paint in the color of his choice. Anybody older than the Tiger Scouts (if they're still around) is old enough to handle spray paint with supervision. Try to coach, not lecture. Help, not instruct. Ask the boy how best to apply the artwork from the first paragraph.
Overall, the goal is to spend quality time with the boy. Sure, the boy says he wants to win. You or I may have won when we were kids, but do we remember? I don't. All I remember is how little help I got. My first car started out as a team project but it ended up as the metaphorical "Team of One". For my second car, I was told that I knew where the table saw was. These are the times he'll remember. And the times you will wish you had back. Try to imagine what'll happen to your son when he's 18. What will you wish you had done? What will you wish him to remember? Does a trophy really matter?
In the end, which would have more value to a boy like yours: winning first prize in the Pinewood Derby Competition, or his dad taking him and his den out for pizza? My money's on pizza. Judging from the winners in my pack, the pizza would have been cheaper.
Have fun. I wish I was in your place.
As a 2nd Eagle Scout in the family we spent may days building those early cars. It has been about 15 years since out last car so things have changed but
1)Small car like a triangle shape
2)Lubricate with dry lube all the time
3)As close to max weight as possible
4)The biggest thing to remeber is that this is a family event.
I knew a few fathers that forgot that and brought the car to the MMM labs and build the best car ever. The problem is that the kid was not allowed to touch his car. Of course that car did well, but the family idea was lost. Also there was a kid that the father did not touch it. The kid took a butcher knife and carved it himself and threw on the wheels. We felt sorry for him so we helped him get his wheels running, but after that took a top place with a simple car. The car I remeber the most of others was that simple car because the kid built it all by himself.
Don't forget rolling friction!
Ideally, you want to stick the wheels on a lathe to minimize the amount of wheel surface touching the track. This should have more impact than any tweaking of aerodynamics!
1:Graphite
2:Use molten lead to make weight. That way you can carve out miniscule amounts to make it perfect.
2:graphite
3:make sure the wheels are on perfectly straight.
4:graphite
5:car body shape helps, thin and small is etter, unless youre going for best looking car.
5:more graphite.
All Troll + "offtopic" mods are meta moderated as "Unfair", because you abused the system.
I'm in charge of our Pack's Derby this year, and many of the suggestions I've seen posted would disqualify our cars! Obviously - each Pack is going to have a different set of rules so the customizations you can make are going to be minimized by that.
:-)
;-)
Our Pack disallows any lubircant except graphite. You are required to use only the car parts that come with the kit, except for the addition of weights and decorations. We also encourage the boys to build the cars (yeah - right..
Now with all that out of the way
The things I've seen that seem to be important are:
1) True up the wheels so they are all touching the ground and the same diameter. To get the same diameter you can put them on a nail into a drill and sand them some till they are all the same diameter.
2) File down the little attachement wings between the body of the nails and the head of the nail. The wheels can bind there.
3) Bring the car up to exactly the competition weight limit. We use a diet food meter to do this, and it served quite well.
4) Lubricate the wheels with graphite. It's cleaner than WD40 anyway.
Just about everything else I've heard or seen doesn't seem to make a bit of difference. The first year we raced, the car that won was a TRUCK! It had a larger face area than ANY of the other cars, yet it consistantly won - oh and it was from my TIGER den!! So I discount the aerodynamic affect at this size.
Have you compiled your kernel today??
My pinewood derby car was heavy and had polished axles but that wasn't enough to win.
The killer for me was that the wheels were too wobbly on the nail axle, which effectively added more friction.
I'm wondering if evenly distributed weight on the outer surface of the wheels might have helped stabilize them from wobbling. Either do that, or somehow add some filler to insure your axle-wheel gap is not too sloppy, and then add the lubricant.
"Provided by the management for your protection."
The kits are fairly cheap as I recall. Buy several and make your boy tear into the first one the day you get them home. Don't let him procastinate. Let him do all of the crazy things he wants to do, let him run it down the driveway, carve it into different shapes .. experiment with the wheels and axles - let him PROTOTYPE it.
:
After a week or two, take two other kits, one for you and one for him. Make suggestions, demonstrate on yours but let him do it on his. At the end of the day if you have not even touched his - you win. You still get to make one, you just don't submit it with his name on it.
Race day results
Lose badly - he learns a lesson in humility, lesson in pine derby that he can apply next year.
Runs mid pack - hopefully he had a good time doing it.
Wins (places in top three) - your kid just beat someone else's dad. Now THAT is something to be proud of.
Glonoinha the MebiByte Slayer
Graphite on the axels is definitely a big plus.
My car looked horrible, I never had the knack for painting as a kid. The car actually got the "Most Humorous" award before the races - a pity award, I think.
However, the car everyone made fun of ended up beating the rest of the troop.
I still have the medal and ribbons somewhere.
Geez, that was 20 years ago....
I won first place my first year in my pack, and second place my second year, but that's not the point of my post :)
The funniest item I ever saw in our races was, one year, one of the kids brought in a three-wheeled car. It had two back wheels and one center-mounted front wheel. This kid cut a section out of the front of the car and put the wheel there.
Anyway, the thing was a speed demon on the short (~6 ft) test/weigh-in track. Everyone else was *sure* the race was over before it started.
Race night came, and that car was in one of the later first-round heats. Everyone lines up, places their car, and...
The three-wheeler bounced back and forth down its track. Hilarity ensued.
It wasn't centered enough to go straight down the real track. Everyone else had a chance to go pick up their car before this one made it to the end. I felt so bad for the kid.
I just weighed in my son's car last night, now it is "impounded" until the trial on Saturday.
I think most people know about graphite, etc. so it may not give an advantage (but of course is needed!). One thing you should do is hold the car on its side so the wheel is resting on the end of the axle/nail. Then spin the wheel. It should spin pretty freely. Then do the same with the car flipped so the wheel is resting on the body of the car. If it doesn't spin freely in both those situations, then smooth it out, more graphite, etc.
One thing I did was put a bit of paint on the body right where the wheel touched it, then sprinkled graphite on the paint when it was still wet. We'll see if that helps. Excuse me, I meant to say MY SON did that.
- adam
First place the axle nails in a drill and using very fine wet/dry sandpaper buff the axles while spinning the drill. Then, using a rag apply some graphite to the axle in the same way.
Third mount the wheels themselves in the drill and lightly sand the outsides of them, as there is ussually a ridge of plastic left from molding. Now mount the wheels on the axle and the axle in the drill. Spin it up again and apply some more graphite to the spinning wheel. The idea is that a small amount of lapping takes place and smoothes the wheel's spin on the axle.
When mounting make sure to mount the wheels so that they spin freely but yet don't wobble on the axle.
Finally, yes bulbus shapes (think falling water droplet cut in half) are the most streamlined but I felt that keeping the weight in the back was more important as it gave gravity a split second longer to act on the car. in which case a wedge shape is best.
Just my thoughts and three first place trophies talking so take it with a grain of graphite!!!
My father ran for several years a council-wide competition as well as the pack-level races. Just to try out different things, he made a test car that had different styles of wheels, solid axle vs. nails, etc.
WRT the wheels, he milled perfectly flat across (maximizing contact area), a very small sliver on the inside or outside of the car, and a v shaped wheels. It ended up that multiple runs ended up with near identical times. Wheel shape really didn't come into play. Didn't matter because altering the wheel shape was against the rules.
Weighting does come into play, but not the position of the weight. Just get it close to 5 oz (the limit at the time). If you have races over multiple days, remember that scales sometimes do change slightly over time, so it may be better to be a tad under.
Solid axles did nothing once you cleaned up the nails and put graphite on them.
Some other things that we found out with test cars and through observing the races that really don't affect times:
-Paint jobs. Smooth, polished, waxed. Didn't matter. Have fun with it, put stripes on it or flames, but don't go crazy trying to get the perfectly smooth finish to minimize microflaws in the paint. Regular ol' Krylon works fine.
-Percise "aerodynamic" shape. The winner was almost always a flat car about 3/4 of an inch think. Pointed, rounded, or angled noses didn't matter, but they usually had some type of "areodynamics" to them just for looks. A square nose ran just as fast.
-Drag, turbulance around the wheels, etc really don't come into play. They are light, start off slow, and reach the bottom quickly that it dosn't come into play significanly.
Things that did help with the car:
-Not buying the premium "pine car" accessories like the weights, "better" wheels, axles, etc. Any weight will do. We used old brass hardware. Lead shot also works. Feel free to have fun with model car parts like windshields, tailpipes, etc. Keep in mind overall dimension limitations.
-As someone else pointed out, polish the supplied nails to remove the burrs or whatever they are from both the head and shaft. You want a very smooth nail. Easiest way is put them in a drill press, get some fine sandpaper and some water. Turn the press on and just polish away.
-Pop the wheels into a lathe or drill press and wet sand down the surface of the wheel to remove any moulding lines.
-Graphite, graphite, graphite. Don't use WD-40, oil, etc. graphite is the key. Put it on till everything is covered where a wheel may even rub (side of car, nail head, shaft) I think liquids or grease might even be against the rules (drips on tracks) as well as spacers.
-Getting a fast lane. This is just a chance. Some lanes run faster the others. They may be smoother at the joints or have a better finish or something.
Some other advice:
-Have fun.
-Take your time. Work with your son to figure out what you want to do before hand on paper. Have him draw out a couple of ideas and talk to him about the design qualities (aerodynamics, liitations of the wood, available tools to make it).
-Don't do it all. This is your son's project that you are helping. Give him some tips/help, but don't do it all for him. I remember when I was a scout seeing these wonderful looking cars magnificantly created and a flawless paintjob. It's very obvious when Dad does it all and the kid has didn't do anything. Son will get more value in the long run from spending time with you working then if you did it all and he wins. Looking back, I didn't win 1st, but I usually ranked high and I remember working with my Dad more then anything about the race.
-Both of you should remember it is only a race. It doesn't mean anything in the grand scheme of life. I remember kids crying because they lost. I'm sure some dad has gotten "track rage". It isn't worth it.
As a former Cubmaster, I used to hate Pinewood derbies. It was the fastest way to take 50 kids, (and their fathers) who were proud and excited about their works of art, and turn them into 49 loosers and 1 winner. Only one kid would go home happy.
After building ten different cars, I learned to focus on having fun. Make a unique car that you can be proud of. Make a car that will make you smile or laugh (a fire truck, a bananna or hot dog on weels). But JUST HAVE FUN!!!!
Rather than web search and determine optimal physics and materials for your Pinewood Derby racer, why don't you just make one? It's about making something cool with your son and crossing your fingers. My dad and I lost the speed race every year, and had a great time doing it.
My dad actually drilled through his hand while trying to make a hole for some fishing sinker weights in our second year. I remember mom driving us to the hospital, and the drill bit still sticking out of the back of his hand. No real damage done, and that was the year we came in second in the appearance trophy, but the little whorl in the center of his palm was the real prize: memories.
It's possible to overthink anything. And even in my small hometown, twenty years ago, the Pinewood Derby competition was fairly ruthless. It was the one thing we did in Scouting that wasn't at all about cooperation and fun. More like a bunch of aggro, little-league dads working out their frustrations through their sons' competitions. Take a step back from that, and you'll enjoy it more.
Common sense stuff here, but.....
1. Molten lead is hot, very hot. ADULT use only.
2. Molten lead puts off poisonous fumes (from the lead, and from impurities in the lead). Melt lead only in a well ventilated area (outside), and keep the kids away from it.
3. Above all, let the kids dictate the overall design of their cars. Suggest all you want, but if they want to build the coolest looking, slowest car around, let them. It's their race, not yours, and they need to be the ones who enjoy it for their own reasons.
Lead makes great Pinewood Derby weight (dense, cheap, & easy to work), but be careful with it:
-Lead is poisonous, especially to kids. It causes brain damage. Infants, children, & pets are at greatest risk, but adults are not immune. Fine particles produced by sanding lead are perfect for getting into the body through the lungs, mouth, etc.
-Molten lead is damn hot. Have you ever enjoyed a 3rd degree burn or house fire? Molten lead also gives off lead fumes to breathe in and contaminate your work area.
-Any Pinewood Derby car containing lead is a hidden toxic waste issue. Where will it wind up? Burned with rubbish (producing lots of lead fumes & contaminated ash)? In a dump (with rainwater slowly leaching the lead into the soil)? Where? I'd bet that less than 1 lead-laced car in 1000 gets proper disposal.
Do a Google search on "lead poisoning" before you play with the stuff. Better yet, do that search together with your little Cub Scout.
Want an alternative to lead? Try iron or steel. They've got about 2/3 of the density, are cheaply available in many convenient shapes, and are effectively non-toxic.
It's easy to make up & spread cool- and credible-sounding stuff. Finding & checking hard facts is hard work.
Just add to your racer a huge freakin' spoiler, lowered front and rear bumpers, low profile tires, and open the exhaust. Then give it a multi-color paint job, preferably using at least one neon color. Finally, write something in chinese or using a kung-fu font across the top of the windshield. It may not win, and it may scrape it's bottom on the ground, but it will surely impress everyone who sees it. I know I'm impressed when I see those fast 'n furious four-bangers that sound like big go-karts zooming from McDonalds to Dairy Queen and Back.
How are you going to keep them down on the farm once they've seen Karl Hungus?
Boy's Life had an article about a scout and his Physics prof dad who studied the problem extensively. The conclusion they came to is that the critical factor is the alignment of the brads that hold the wheels on. They were by far the largest factor. Google can't find the article, does anyone have a reference?
Envy my 5 digit Slashdot User ID!
Though this guy is rather crass, I do agree with what he says. No matter what you put into your car, be sure not to take over and make it YOUR car. Remember, this is your son's project. Have fun helping him, but don't do it yourself and then use the guise of "my son's racer."
How are you going to keep them down on the farm once they've seen Karl Hungus?
If the timing system you use is anything like what we had as kids, there is a piece of metal sticking out of the track that registers when the car crosses teh finish line. If you run multiple races, your car is going to whack that metal several times and beat up the front of your car.
Might help to place a thin strip of metal on the front (not too much, you want most of the weight in the back) to keep the wood together. You still want a car at the end of the day, right?
I killed my den, and tied for 2nd in the regionals, or whatever they were. So here's my tips...
1) Polish. Polish everything. Use pumice powder on the axels. Take a 1cm strip of old t-shirt and get it wet, then put some wet pumice powder on it. Use a drill to hold the axel and spin it while using the cloth strip to polish the axel. Thread the same strips through the wheel to polish the inside. Use 000 steel wool to polish the wood.
2) Shape the wheels. This might be illegal now, but if you can shape the wheels so that the wheel edge it slopes in and is not perpendicular to the axel then the car will run just on the outside edge, drastically reducing friction.
3) Use small weight adjusters. I found some screw-in types at the hardware store and had stable weight adjustment.
4) shape doesn't really matter, but make it thin.
5) Graphite lubricant. the way to go.
ok, hope it helps. One more thing though: make your kid do all the work. I did it all and it was fun, even if my dad helped with the ideas.
We have a Pinewood Derby for adults here at work, with proceeds going to the local Boy Scout chapter. It's fun.
/. isn't very useful. :)
In our rules (which I believe are standard PWD rules), you must use the wheels and axle that come in the derby kit. And tests have been done proving that aerodynamics do not matter at all -- by far, the biggest contributors are center of mass and wheel friction. With these things in mind, you can see that most of the advice on
Use powdered graphite on your wheels. Raise one wheel slightly above the track, so that your car is racing on only three...but make certain that the racer rolls straight without wobbling. Make the center of gravity one inch in front of the rear wheels. Get as close as you can to the maximum weight. And build your car with a 'nose up' design -- have the front of your car touch the starting pole as high as possible, with nothing below. When the starting pole drops, a nose-up racer starts downhill a fraction of a second before a racer with a low nose.
The above is what you'll want to do if you want to win. My advice, especially if you're doing this with your child, is to build a neat design and go to have fun.
Genocide Man -- Life is funny. Death is funnier. Mass murder can be hilarious.
Modifying the wheels or axles in any way is also not allowed, nor is the use of lubricants (though most packs don't have a problem with graphite powder.)
Here's what I've learned from running derbys for the past five years:
Add weights until the car is exactly the limit (5 ounces), no less.
The car must run absolutely straight. Push it across a smooth floor; if it veers to either side than it will wind up rubbing on the center strip of the track, slowing it down
Put a tiny blob of glue on the body just next to each axle, then sprinkle some graphite powder onto the glue before it dries. This will create a very small, smooth surface area for the wheel hub to rub against, rather than the side of the wood body.
General consensus is that it's better to have most of the weight in the rear of the car. The rear sits higher than the front when the car is on the starting line, which gives it a little more potential energy. Most will carve the wood block as small as possible, then add weights to the rear of the car to bring it back up to 5 ounces.
At the speeds that these cars run, air resistance can be pretty much ignored, so don't worry about an aerodynamic surface for anything beyond just making it look cool.
Also, remember to have fun, that's why you're doing this. Have awards for best paint job, funniest design, best muscle car, most space-age looking car, etc.
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
Look, I know you're terribly smart and you can build a car that will beat the other cars, and this is just the kind of Pinewood Derby experience I had in Cubs - lead weights, sanded wheels, graphite on the axles, etc.
It's a contest among the Dads.
That's not the point. It's supposed to be a contest among the boys. Don't live vicariously through your son. Yeah, other Dads are going to do it too, but take a principled stand, this is important.
I recommend having a Dads' race and a Sons' race if your Cubmaster has any sense of fairness. Go ahead, trick out your car with depleted uranium inside the body and aluminum-oxide-polished wheels with Buckyball lube on the PTFE-coated axles.
But let you son be a kid who has a sense of accomplishment in building something himself.
My God, it's Full of Source!
OUTSIDE_IP=$(dig +short my.ip @outsideip.net)
Big R-type sticker and a spoiler. That'll make it mad fast.
- A.P.
"Remember when the U.S. had a drug problem, and then we declared a War On Drugs, and now you can't buy drugs anymore?"
I grew up near Detroit, and while my dad worked for a car company, he wasn't an engineer. He figured, correctly, that many of the cars in our Pack would actually be built at the GM Tech Center by engineer fathers. We went with looks, adding fins and (at the time, unusual) flouresent orange and green paint and won second place in looks. (1st place went to a fantastic rendition of Mr. Rourke's open-air station wagon from Fantasy Island.)
Dude, I think I can see my house from here.
Just a few tips that I found helpful:
1. Use graphite on the axels
2. Make the tires smooth by sanding down the seem in the middle
3. Add weight in two places -- about and inch behind the font wheels and in the absolute back of the car.
4. Make the car as aerodynamic as possible.
Ok, so some of us adults got tired of sitting on the sidelines and have had a few of our own "Adult Pinewood Derbies" to battle it out amoung parent couples teams (lots of fun). The following tips are from my experiences as an adult PWD car racer.
Important considerations that I haven't seen mentioned (or were not stressed):
1)Wheelbase - The longer the wheelbase the more stable the car will be and the less likely it is to rattle back and forth against the track guide. Don't use the nail slots that come pre-cut on the car. Cut your own very near the ends of the car to exend wheelbase and reduce "overhang". (for more on wheelbase and overhang issues do a google search for the "physics of racing" documents that are floating around on the net)
2) Get longer wheel nails. The ones supplied with the kit are short and easily dislodged by bumps and falls.
3) Polish the wheel nails (axles). Use jewlers rouge impregnated in a strip of cloth. Grip the nail in a vice and polish the running surface by doing the "shoe shine stroke" with the strip of cloth. Keep it up until it shines like a National guitar.
4) Use graphite only as your lubricant. Any liquid lubricant will increase drag.
4) de-burr the plastic wheels. Use the drill technique others have mentioned, but do it all carefully. The inside running surface of the wheels may need attention too, but that would be easy to mess up. Spin them on your polished axles to identify any burrs or flashing that needs to be removed. The wheels do not provide traction, so I see no reason to "rough them up". Ever seen train wheels? Smooth as glass = lowest rolling resistance.
5) Drive shims into the nail grooves to align the wheels so the car sits flat and tracks straight. This is critical. A car that pulls to one side grinds against the track guide and will lose every race. Do this carefully.
6) Use a weighting method that is adjustable. You want to be able to take your car to exactly 5.0 oz. and that means you are going to need to adjust your weights right to the limit at the weigh-in. Another racer and I tested and found that 0.2oz reduction in weight was all that was needed to change which of our two cars was consistantly faster. Remember, 5.0oz on your scale might be 5.1oz on the scale at the races so make your weighting adjustable and get it spot on 5.0oz on at the races.
Good luck and have fun. Make sure your son has the lead role in construction and racing. You are the consulting engineer there to give him the technology edge. He's the builder/racer. This can be a great father/son experience. My childhood PWD cars did ok (always placed, never won - until I was an adult), but my father and brother went all-out on my younger brothers regata boat. Razor-eged keel, baked/polished/waxed enamel paint, and a sail design that involved research, matterials testing, and calculus. It was so much faster than any of the other boats that 15 years later the two of them still laugh about it together.
Have fun!
-=-=-=-=- osjedi uses Debian GNU/Linux. -=-=-=-=-
Has anyone tried letting their kids build the car?
just cut the block into a wedge, tape some silver dollars to the bottom to the max weight, and put graphite on the wheels.
this got me first place back in the day and only took me about 15 mins. of work. looked like shit but moved, and it was fun watching it romp on cars that people took days to make.
now to add even more speed to your ghetto looking mini ride. put a miniature powerd by honda sticker on it or perhaps a Type-R sticker and attach a thimble to the back for your coffee can exhaust tip. this should easily knock off a few 10ths...at least that is what the honda guys tell me.
I'm assuming these are what we call Cub Cars in Canada, correct? (States don't have cubs before scouts do they?)
;-)
We always had 2 categories for ours, race winner and best design. I won the first year with an ugly piece of shit that followed many of the design principles suggested here (graphite, careful filing of rubbing parts, simple blunt rounded design, MAX OUT THE WEIGHT). I won the second year for design. Beautiful model of a Jeep that came in last over and over again in the heats
No Comment.
When I was in boy scouts, 15 years ago or so, we never had any pinewood derby races - full scale, anyway. What we did have were little 1/20th scale 5-inch pinewood racers with pre-made everything. In fact, all I recall doing for the event is marking a block of pinewood with a pencil, and handing it off to one of the dad's who cut the slope and drilled the holes.
I blame this rather banal memory on trial lawyers:P
- James
The parent post is a copy of this post. Note that the parent post is #5038962, but the linked post is #5038841. The parent obviously plagiarized the linked post's text.
Yet the parent is currently +5 insightful, while the original has yet to be moderated. Please moderate the parent down, and the original up instead.
When I was a Scout, the winning design was the same at every Derby: a wedge. I don't know why; it doesn't seem particularly aerodynamic or anything. It just was.
That said, I had two designs that nearly won. Both were destroyed (while in the lead) by poor construction before crossing the line. But here's the idea, in any case.
Design #1: Flexible body. When they come off the inclined slope, rigid cars lose a lot of energy in the sharp transition to nearly-level. Some of this energy can be detected as noise. To counteract this problem, I built my racer with a vertically flexible body. This was accomplished by sawing slits from the pine block until it could flex. Then I embedded fishing sinkers until the body weighed as much as possible. This was less than the max, because I didn't have much space left.
Performance of Design #1: slow off the line, due to its lightweight nature. Smooth through the transition, leaping into the lead. Broke in two halfway to the finish line. Build yours a little stronger than I did.
Design #2: Take advantage of rotational inertia. Because the wheels are rotating so quickly, they contain a lot of energy. The more mass, the more energy. I built a wing-shaped body out of the lightest wood I could obtain: balsa. I packed the wheels, roughly equally, with soldering wire and glue until the entire assembly reached the max weight.
Performance of Design #2: Neck-and-neck off the line. Even to the transition. Then my opponent's wedge simply coasted, while the inertially enhanced wheels of my design pushed my car to a substantial lead. Three car-lengths short of the finish line, a nail axle came loose. The wheel finished in first place. The car flipped off the track. I recommend super-gluing your axles in place.
Good luck!
For geek dads: Contraction Timer
IAAP (I am a physicst)
From a conservation of energy standpoint, you should try to put as much mass as possible over the back wheels. If I remeber from my Boy Scouting days, the derby cars started out sort of pointing downwards. Having more mass "higher up" the starting ramp means that it will have slightly more gravitational potetntial energy than a car built with mass in the nose once the cars hit the flat part of the ramp near the finish line.
Of course, I think that it would only be a few % difference at most. Something like (length of car)/(height of ramp).
From an engineering standpoint, I think just having the maximum mass (and excellent wheel lubrication) is the most beneficial, so as to reduce the percentage of energy lost to drag.
Remember Galileo dropping the large stone and small stone from the tower of Pisa? (ok, an apocryphal story, but anyway...) The both hit the ground at the same time since they were dropped from the same height. If we negleted friction & drag from the Derby, which is actually a MAJOR concern, all cars would fall equally fast, EXCEPT those with more mass at the back of the car, and therefor furthere up the ramp, and therefore with more potential energy.
Quando Omni Flunkus Moritati
How odd that your dissertation looks just like the comment that I posted myself on these pages, an hour before you.
Strange, isn't it? I mean, just look: Compare this to this. The similarity is striking, isn't it?
Tell me, if you would, which of the following explanations is most applicable to this deceitful prose: A database error, some sort of maligned human oops, or just good old-fashioned plagiarism?
If it were a database error, the entire comment would have been duplicated verbatim, but it was not: the tags I used to italicize "nth degree" are absent, for example.
If it were some sort of human oops, I imagine that the such a hastily-construed cut-and-paste job would have included my sig, not to mention chunks of headers, leading and trailing stories, etc. In other words, by the time you'd reached a sufficient level of intoxication that your brain would permit you to accidentally duplicate a comment of such length, other mistakes would be apparent.
Therefore, I deduce plagiarism to be the cause.
Which leads me to be curious: How much code do you intend to steal for inclusion in your upcoming PDK product?
Kid-proof tablet..
As I'm reading these stories, I am amazed at all of you that won first place (almost like every woman who was reincarnated was Cleopatra). Me, well, I used to come in near the bottom of the pack (pun intended). My "Dad" was no help. I still have a couple of 30 year old cars tucked away in the basement somewhere. The Lemon. Bright yellow, with a dribble of lead that I slopped out the back of the car sticking up as an antenna (ooh, that helped). It was still fun. Sure, I would get killed on the track by other kids dads, but I took pride in building them myself.
on both of my cars, i was well in the running and made the championships, then the car "broke" at the wheels during each champ run. In one, they cracked down by the axels, the other the wheels got loose and so there was too much side-to-side movement increasing friction against the runner.
"But remember, most lynch mobs aren't this nice." (H.Simpson)
-- Joe
Of course, I was in the runnings for several years and only won once. So that should work a little better with the odds of winning. Anyway, my car had no scientific basis at the time, although I see now why it probably worked so well. I have always loved whales, particularly Orcas (Killer Whales) and that's what my car was shaped like (for the most part). The heavy front end (the head) vs. the very lite back end (the tail). I think helped immensely. In other words, you want to get as much weight as you can in the front of the car, without it skidding on it's nose (or bumper, whatever the case may be) the whole way down. I recommend good aerodynamic wedge, that's what mine was for the most part, and Fins just make it look cool. Fritz
Spooooon!!!!!
I loved the pinewood derby, it was a lot of fun. I lost horribly the first year with basically a wedge car. It would have been great, but the wheels were not on as straight as they could have been, and we didn't lube the axles (graphite works well). Anyway, the next years I created good looking cars and won every year except for the last. I tied the last year with my friend who created a model T or something like that. In my opinion, it's more fun to create something that makes people go "thats really cool" than something that goes fast for 20 feet or whatever. Now if your car could be motorized...
'My' car won everything, consistently, year after year, as did my older brother's (This was sometime in the 1960's). ...based on a two rail dragster, (the rails were arched for strength) with a slab of lead in the 'seat' where the (in real life) cars' driver would be. A piece of cloth was glued to the lead as a 'seat cover' for looks. At the weigh-in, holes would be drilled in the lead 'seat' to bring the car just to the weight limit.
...it was really my dad's car, but I walked away with the trophy year after year ...the 'race' was pretty much just a formality when that car showed up :)
...but couldn't find it to take a picture ...sorry :)
The design was the same
As stated elsewhere, much attention was paid to getting the wheels 'just right', removing burrs on the wheels/nails, etc.
Of course, I did very little of the work
My parents just mailed me one of the cars within the past five years, as they moved from the family homestead, and found it as they were packing stuff up for the move. It's now out in my garage somewhere, I looked
and make sure you get a smooth lane. try to watch other heats first before your son is required to pick a lane.
I did pinewood derby a long time ago and took 2nd place. My car was very smooth and thin, even to the paint job. Furthermore, I routed out a hole in the bottom, added just enough lead to get the weight up, and put wood putty over it. I fixed the burr in the nail axle and actually drilled a new hole for it up more so the car was closer to the track. I dont if that helped, but I dont think it hurt at all. What I didn't do was sand the wheels at all. The person who took first.... well did. He actually sanded his wheels, so that the minimum serface area touched the track. There was a ridge in the center of the wheel that he sanded down. It semms like that should work better, but I am Just a high school student.
My son usually won this race because I taught him about Newton's 2nd law of rotary motion; viz, angular acceleration equals applied torque divided by moment of inertia. Since the torque applied to the wheels is constant (it depends on the inclination angle of the track), their angular acceleration will be greater when their moment of inertia is smaller. So the fastest racers always have wheels with minimal moment of inertia. This means keep the majority of each wheel's total weight as close to the axle as you can. They could be spoked wheels with light weight rims and tires or disk wheels made of balsa glued to a pine hub.
Several posters have stated that the position of the center of gravity doesn't matter. I respectfully must disagree. Since the car begins on an incline and ends horizontal, the higher your center of gravity at the begining, the more potential energy you have to work with, and the faster your car goes. You make the CG higher by putting the weight in the back of the car.
I not only know this because I am a career physicist, but because when I was in the scounts many years ago, I built my own test track with an integrated electronic timing system in my back yard and built an array of cars to empirically determine the best design, and I have several pack and state derby championship trophies to show for it. The sweet spot is to have the CG between the rear axle and about 1cm forward from that place. If the CG gets behind the rear axle the car becomes unstable and you'll waste energy on friction between the insides of the wheels and the guide strip that the cars run on.
The best way, as opposed to drilling holes and filling them with lead shot, is to sand cast the rear portion of the car out of molten lead. Use of an oxy-acetylene torch to melt lead and make precision casts may be beyond the reach of most cub scouts. I was fortunate enough to have a dad who thought welding was a very important skill to have and taught me at a very early age.
Anyway, best of luck to you.
I had a great time making pinewood derby cars when i was a kid (70s). One looked like a corvette, sparkly red paint.
My dad worked at a food plant, so he'd bring one of their food scales home to weight the car when we were done, less trimming on race day. Nowadays, i'd get one of those digital diet scales.
As far as speed, what we'd do is put each nail into a drill and polish it with very fine emery cloth, then string all of the wheels together on a thin screw and sand/polish the outside so the running surface was smooth and round. Then we'd douse the thing regularly with graphite.
For weight, we did different things. One year, we epoxied a bunch of bbs into the bottom for the weight, and we gouged out one or two at the final weighing to get just under the max. My brother once made a car with a giant fishing lead weight sticking up in the middle, painted like a driver. I think we carved pieces off the back of his head when it was too heavy.
What would really make me lose a race every time: i'd drop the damn thing. Or, it would roll right off the table. Once you crack off part on one of those plastic wheel hubs, you're screwed.
After years of electronic timed (our own high quality track)testing. The following are the definitive results
1. Areo not important
2. number of wheels on ground, 3 good, 2 best
3. proper axel location (drill jig setup for
drilling 3/8 inch basswood "plank car"
4. perfect balance with weight as far "up the
hill" as possible (remember not a 4 wheeler)
5. axel finish,precision ground,
flashcrome, teflon or moly
coating optional
6. wheel OD consistancy,balance and center
trueness
7. wheel mass, lighter the better
I know it's not the same event but one trick I learned in the box car land is that they have a metal bar that they drop when you're allowed to start. If you can secretly put a tiny but powerful magnet in the nose of the vehicle when that bar drops it pulls you forward. A few years back that was what made the difference. Unfortunately the fascists that run the box car races think of it as "cheating" rather than innovating and overcoming challenges.
A previous poster already mentioned the correct position of your weights. At rear of car just in front of the rear axle. Porsche makes mid-engine (which isn't truly middle of the car as you are seated in the middle of the car) cars for that same reason the poster illustrated (center of gravity near rear of car provides the greatest potential energy and minimizes the amount of friction on wheels). So I won't beat a dead horse.
As for the car design, I recommend the simple wedge shape. The lowest profile and smallest acute angle (as measured from the front of the car) you can acheive will provide you the most return.
To know is to have knowledge....to understand is to be enlightened.
Having raised two sons form cub scouts through Eagle scouts I have seen a few races in my time. The most amazing winner was simply a block of woon right from the box. The wheels were added and it won! After all the streamlining, painting, adding graphite to the axels it seems the most importnat factor was the weight.
The best advice anyone can give you, is to let your child do most of the work. Let them design it and let them paint it and apply graphite to the wheels. Sure it might not be the best looking car and it might not be the fastest, but 10 years down the line, your child will remember making the car with dad although they probably won't even care how well they did in the race.
1st year: obsessed and built the slowest car out there. 2nd year: grumbled, but kids insisted on building cars. I helped at the last minute: hollowed out undersides, polished wheels and axles, installed max weight. Took home 3 first place trophies. 3rd year: became more involved. built three cars, took home 1st & 3rd and 1st place trophies. daughter and i were in same category and double elimination unfairly hurt her. subsequent years were more fair since we used times instead. 4th year: got serious. took home 1st, 2nd, 3rd and 1st place trophies. 5th year: everyone was out to get me. took home three 1st place trophies. One car won for design instead of speed. it was too tall to test and was slow.
Lessons learned: wheels and axles are most important. Polish with fanaticism. avoid grit, dust, sawdust contamination. Keep cars in zip-lock bags. If your kids want to play with the cars, build a second car for them to screw up but not race.
Testing is important. cars must run straight (use a pingpong table's stripe). Make a test track from a pair of rain gutters pop-riveted together. use an opto sensor for timing. the 2nd lane was a waste, use a single lane and an opto sensor timer.
Weight placement is a religious argument. You want your car to run stable down track. I minimize angular moment in hopes that rattles down the track will be easily corrected. Ideally, I want a 5oz point mass payload centered in a zero-mass car. others maximize angular moment to prevent rattling. that means a dumbbell mass distribution. Check it out for yourself. I place weight just in front of and above rear axle. I remove all material possible from everything else in the car. Since car sits on a slope, rearward weight is located higher on the track. This gives you epsilon more potential energy. Probably not significant. I think locating weight on & just before the rear axle makes the car more stable.
Everybody you talk to has his pet ideas. Nod, smile and wait to see if their cars go faster.
People with the fastest cars do the least talking.
Me? I'm not racing this year.