Pinewood Derby Tips? 139
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?"
Gravity (Score:2, Funny)
Remember gravity isnt instantaneous, it travels at between 0.7 and 1.2 times the speed of light. This may affect your plans.
Bad memory (Score:2, Insightful)
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.
Re:Bad memory (Score:4, Informative)
When it's all lubricated and assembled, try spinning the wheels with your hand. I remember we'd all have competitions: spin all four wheels at once as fast as you could, and time whose wheels would spin the longest.
Re:Bad memory (Score:2)
Weight is everything (Score:5, Interesting)
1st place, cub scout pinewood derby, 1980
Re:Weight is everything (Score:2, Informative)
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.
Re:Weight is everything (Score:3, Interesting)
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.
Assuming you can manage without unbalancing the car, it's useful to raise one wheel up a millimeter or two, so that your car runs with only three wheels touching the track. Ideally, this reduces the wheel friction with both body and track by almost 25%. Make sure the car still rolls straight, though, and make sure it doesn't wobble. Wasting energy bouncing up and down or -- even worse -- bouncing off the sides of the track will kill you.
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.
Which, unfortunately, means you should absolutely never allow a Cub Scout to touch it. The biggest problem with Pinewood Derbies, IMO, is that you have to choose: will it be Dad's car and have a shot at winning, or will it be the boy's car and lose badly? Next time around, we're going to make two cars, one mine and one his, so that he can have some fun building and racing his own but we can also have a real shot at winning.
Friction (Score:3, Interesting)
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!
Re:Friction (Score:2)
I'd also recommend you give him sanding sealer to use before the paint. Makes for a much glossier finish. Apply sanding sealer, sand, repeat, sand with 000 steel wool, and then spray a high gloss paint.
Remember, the kids want the cars to do two things: win the race AND look cool. Your goal should be to raise the excitement, get the kids to want to get involved. Not every kid can win the race, but all of them can make their cars look cool. Our pack always had a separate trophy for coolest looking car, judging was by the parents and grandparents in the audience.
Have fun!
Wobbly Wheels Killed Me (Score:2)
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.
Moderators -- Please Read (Score:2)
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.
Immitation is the most sincere form of inadequacy (Score:2)
Strange, isn't it? I mean, just look: Compare this [slashdot.org] to this [slashdot.org]. 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?
Re:Weight is everything (Score:3, Informative)
BTW, we learned this by finishing last place the first year, third place the second year, and second place last year. Just two more races to go before Boy Scouts. I raced back in the good old days of the early 70s and got two first place trophys myself.
Re:Weight is everything (Score:3, Informative)
Also, mount the wheels in your drill and run them over some 220 grit sandpaper for a fraction of a second and then graphite the nails before you attach the wheels to the car. (I've heard of using oil like the parent mentions, but I had great luck with graphite).
As for cutting the wood, the fastest design I ever made was just to pass the block through the table saw with a tapering jig so it was almost full height at the rear and a sharp point at the front. The weight was 3/4 of the way back. I built the whole thing in an hour.
Re:Weight is everything (Score:2)
I know this is a "duh" posting, but it needs to be repeated, and especially when there are kids involved.
Scout stores and hobby stores sell prescored "pinewood derby weight kits" that come with predrilled plates, some doublestick tape, and a couple of screws. They're nontoxic, and you can easily break off excess amounts of weight during the weigh-in. (Personally, I think they're a bit overkill, but hey, they're non-toxic.) If you don't want to go that route, I had my son use thick steel bolts or threaded rod glued into predrilled holes. You only need 5 oz max. Just about any metal will work. It doesn't have to be lead.
If you must use lead (because fishing sinkers always seem to be at hand) make sure the kids (and you!) wash your hands thoroughly after handling the lead, and most definitely before eating anything or even touching your faces. (And if you're a smoker, wash before touching a cigarette.) Apply a thick layer of white glue over the lead as soon as possible to reduce the amount of time your kids will be exposed to it. You can tell your kids that it's filler to make it more aerodynamic. And when you're all done racing, you still need to be concerned that your kids will contact the lead when playing with the car.
Finally, don't forget that the addition of lead will make the car a hazardous waste. Please don't throw the dead cars containing lead in the garbage. If they're trash, at least remove the lead before disposal.
Again, this may seem silly but lead is an insidious toxin. It never leaves the environment. And it seems to affect developing children even more than adults.
Re:Weight is everything (Score:2)
Besides, unless you pay extra, "lead" for stained glass isn't really 100% lead anymore. It's mostly tin. Same goes for fishing weights, which kids have been closing onto the line with their teeth for centuries. Don't swallow it and you'll have no trouble.
You can tell your kids that it's filler to make it more aerodynamic.
Lying to children is dispicible and counter productive. Be honest to your kids. They'll understand more than you give them credit for. If you tell them the truth about whay you're sealing it up, they'll remember it in the future, but if you lie to them they may think that melting lead is something fun to do when you're not around. Besides, they can tell when you're lying. They might not figure it out right away, but they will eventually. Then later you'll wonder why you have a defiant teenager.
While you're at it, don't lie to your kids about sex or drugs either. When you tell them (or the DARE office tells them) that smoking pot will kill you they'll know you're lying, and may not belive you when you tell them that heroin or crack will kill them. It certainly won't stop them from smoking pot.
Children (and teenagers) may lack wisdom and experience, but they don't lack intelligence. They depend on adults to help them gain wisdom and experience without having to learn the hard way. You're not protecting them by interfering with the process.
Finally, don't forget that the addition of lead will make the car a hazardous waste. Please don't throw the dead cars containing lead in the garbage. If they're trash, at least remove the lead before disposal.
I still have all three pinewood derby cars that I made (even the first one that lost miserably). If your son puts a significant amount of effort into building the car, it'll probably be something he saves for his whole life and brings out to show to the kids and grandkids when their pinewood derby comes around. I don't think you have to worry too much about them getting thrown out.
Re:Weight is everything (Score:2)
[ I'm sorry, but I just want to scream when I hear people talk like this. "It won't hurt my kids; we did that all the time when I was a kid; I never got sick from it." You sound like my father-in-law, who would be very lucky to make it to age 70 after all his occupational exposures to various chemicals. He has certainly been crippled by them. ]
Lead is toxic in any quantity. It doesn't change toxicity just because you have less of it. The real issue is "at what quantity does this toxicity pose an unacceptable risk to me or my child?" Do you know how much lead you or your child can safely tolerate? Did you look it up? I'll save you the trouble. According to the CDC [cdc.gov] the current action level for lead is 10 micrograms/dL. That's been reduced about 10 micrograms/dL per decade since the 1960s, when they first decided 40 micrograms/dL was too much.
An average adult has about 5.6 liters of blood. Figure a child under 12 as having about half of that. That means you should be concerned if your child's blood contains more than 280 micrograms of lead. .00028 grams. A 1-ounce fishing sinker contains one million times this amount. If you can see the gray smears on your hands and fingers after handling the lead, you probably have more than that right there on your hands. Wash it off.
Children also have a much higher absorption rate of ingested lead -- adults absorb about 11% of the lead that reaches the digestive tract, while children absorb about 35%. For this fact, others, and a listing of the damage lead can do to a human, read this FDA report. [fda.gov]
Keep in mind that lead does not exit the body. Lead builds up over time. If your child acquires .0001 grams of lead this year, .0001 grams next year and .0001 grams the year after, he will exceeded the actionable amount of lead.
The CDC and other federal agencies have been lowering the acceptable limit of lead dramatically every decade since the sixties, and not just for children. They lower it because they know the dangers of lead poisoning are real, and the studies keep showing neurological damage occurs at lower and lower levels. They don't know at what level (other than zero) it's safe.
And regarding telling the kids about "aerodynamic glue", I didn't know if you were the sort of person who would feel the need to have a cover story to hide behind. As you may have guessed, I certainly told my son the truth about the lead sinkers we were using, and we washed our hands carefully afterwards. Hell, I made our whole family wash our hands after working with the Christmas tree light strings this year, because I discovered they use lead-based pigment in the green electrical insulation!
Lead exposure is a serious health problem, and one that you can help avoid every time you avoid exposure. And this is an easy one to avoid -- use an alternate substance. If your car is .1 gram overweight at the official scale, use a drill and remove wood instead of lead.
But don't go telling people stuff like "it's OK, that's not enough lead to hurt you or your kid." That's irresponsible in the extreme.
Re:Weight is everything (Score:2)
You, sir, have a problem. All I said was that having it on your hands isn't dangerous it you wash it off afterward. I don't see why you have a problem with this. I don't disagree that lead is as toxic as you say. I simply disagree that it is sufficient reason not to use it. Besides. You won't see any lead smeared on your hands after touching the rod. It's soft, but not that soft. Though it seems like a small number,
If you swallowed a fishing weight, only the lead on the surface of the weight would be harmful to you. You would not absorb 35% of that lead into your blood stream because 99.9+% of it would come out the other end before it disolved. Again, before you flip out, I'm not advocating you do this, but you are being misleading. You wouldn't end up with 1 million times more lead in your bloodstream.
But don't go telling people stuff like "it's OK, that's not enough lead to hurt you or your kid." That's irresponsible in the extreme.
All that matters is if it's true of not. What I said was true since all I said was that the lead will not harm you or your child as long as you take the most basic of precautions. It is okay to use lead as weight in your car. It can be safer than drinking out of a public water fountain (Which may be old enough to have trace amounts of lead in the pipe solder), or eating vegetables from the garden next to your house (which may have lead paint chips in the soil).
If your car is
Well, first off you should be able to get closer than this at home, but if you are overweight I also advocate removing wood. Simply from the technical perspective, it's too easy to remove too much lead. Besides, your lead will be sealed up, remember?
Wacky source of advice, all things considered. (Score:5, Funny)
hmmm long term memory kicks in ... (Score:3, Informative)
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
how I won my pinewood derby (Score:4, Informative)
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.
Re:how I won my pinewood derby (Score:2)
If it's allowed by the rules - cut the hell out of the wheels till they're nothing more than razor blade sharp on the edges. That might make enough of a difference to win. Maybe not.
About the wheels - make sure they don't wobble. Do whatever you have to, within the rules, that you can to make sure they don't wobble - that's a killer right there.
re: drag
Okay, aerodynamic tip - this thing is going substantially less than the speed of sound, so bulbous shapes are best (not pointy like jets). Think of the wheel fairing on a slow airplane and you'll get the right idea.
Re:how I won my pinewood derby (Score:2)
And max out the weight.
I remember a winning design (not mine though) was a long pencil-shaped body, just thick enough to provide solid mounting for the axle cross members. They drilled the center of the body out and filled it with lead shot up to the weight limit. A 747-looking rudder capped it off on the ass end (more for intimidation than effect, I'm sure).
And don't forget the stripes! Use this site [beaterz.com] for inspiration!
Re:how I won my pinewood derby (Score:2)
Charlie
Re:how I won my pinewood derby (Score:2)
> high or low it is, but how far back it is.
> Consider that the track is curved.
The track is either flat all the way down, or curved downward.
If the track is completely straight all the way down, it'll make no difference.
If the track is curved on the way down, the downward vector is higher at the top of the track than at the bottom. It depends on the nature of the curve, of course, as to what point a rear-weighted car will be more than the forward vector of the car, but either way, it'll switch over at some point. During the entire trip, though, there will be both downward and forward vectors moving the car.
The thing is, to overcome the resistance of the friction of the wheels to start with, you need a higher forward vector rather than a higher downward vector, otherwise your car will get off to a slower start, thus making it more desireable to have a greater forward vector and less of a downward one.
I'd say the physics here is most likely a net 0 as to which is more important, especially considering the scale of the 'vehicles' involved.
I'd say you flunked your physics 101 problem. We studied that kind of thing in _high school_ physics, btw.
UK Design (Score:1, Offtopic)
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.
Re:UK Design (Score:1)
Nothing quite so fancy as what you had; I don't even recall having bearings between the wheel and axel. Also, there really wasn't anything at all to screw or glue; just cut your pattern into the wood, lubricate everything, add lead weights, and go.
Re:UK Design (Score:1)
Pinewood Derby is when you cut a car out of an approximately 15cm by 4cm by 4cm block of pine wood (hence the name). The cars run on a track with ruts cut into it. You line all the cars up in their respective ruts and let them go, and it's pretty much a straight shot down to the finish line. The track is only 3-5m long.
The race is just as much an excersize in arts-and-crafts and woodworking skills, since there are awards for the best looking cars. It's also kind of a "father-son" event, where the dads are supposed to help their kids build their cars. Of course some dads did all the work and got way too competetive.... Ah... the memories
Re:UK Design (Score:1)
Pinewood Derby (Score:2)
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.
Here's how to do it (Score:2, Informative)
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.
Re:Here's how to do it (Score:1)
This is only true if the car is falling vertically in free space, with negligible air resistance. However, since the car is travelling down an inclined plane, or ramp, mass does make a difference. Remember - F=mg, *but* the extra mass increases momentum. So two objects of dissimilar mass will fall at the same speed. However, it's not falling freely but sliding down a slope so there's a bit more involved. I can't remember the exact equation though, but it's something to do with F=mg sin theta. It's been about 15 years since I did physics at school.
Re:Here's how to do it (Score:1)
I never got to put this into practice, as my father never permitted me to touch my car until time to carry it to the starting line (he always finished slowest or next to it), but it's only logical.
Re:Here's how to do it (Score:2)
Tim
Re:Here's how to do it (Score:2)
You want to convert energy of position -- being higher in the gravity well -- into kinetic energy. Given that velocity gain down the slope due to the acceleration of gravity is identical (which is what you're saying in #1), then total kinetic energy at the bottom of the ramp will be higher if there's more mass (e=0.5*m*v**2). Quick sanity check -- does it take more energy to lift 1 unit of mass into position at the top of the ramp versus 2 units?
If frictional losses are the same, the heavier vehicle should win on the flat portion of the track.
Re:Here's how to do it (Score:2)
In reality, every year you see races where a car is behind at the bottom of the ramp but "catches up" on the flat portion. This is exactly the behavior you should see if the design has exchanged a small loss in maximum velocity (caused by very slightly greater friction due to increased mass) for a sufficiently bigger gain in kinetic energy.
Re:Here's how to do it (Score:1)
Re:Here's how to do it (Score:1)
Remember these are cars running down an incline, not freefalling. And the cars sit on wheels that (1) make contact with the wood track, and (2) rub against their bearing-less axels. So the way to win was to (1) minimize friction, and (2) make your car as heavy as absolutely possible.
At these speeds, starting from 0 and going to maybe just a few miles an hour, the total force of the drag is small compared to say, an airplane, but it is still very significant.
Question (Score:4, Insightful)
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)
Woodworking with kids (Score:4, Informative)
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.
Re:Woodworking with kids (Score:2, Funny)
I finished last.
But my time was accurate to 1/100 second.
Re:Woodworking with kids (Score:1)
Seemed like they needed to emphasize the parental guidance factor over actual labor.
You could always tell the kids whose fathers didn't help, had no woodworking skills, or as you point out, weren't available, and they'd get totally hosed.
I wish I could say you saw more mothers involved in this aspect too, but again, sadly not. Kids' fathers whom you'd never seen before would materialize for this one glory-hogging event, then disappear back into the woodwork, leaving the mom to attend all the less-glamorous meetings. This was 20+ years back, though. Hopefully it's improved.
Add a fan and some batteries (Score:1)
A few points (Score:4, Interesting)
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. :)
Re:A few points (Score:1)
Makes sense, but unfortunately the rules about what you can and cannot do to your car are pretty strict (at least in my Cub Scout Pack and District -- actually, I think the rules were nationally standardized). Everyone built their cars out of the exact same block of wood and used the exact same wheel nails and plastic wheels.
Re:A few points (Score:2)
Use the stock wheels, and the stock wheel nails - no problem - In fact, we going to GLUE the wheel onto the nail!
Of course, that nail will be inserted into a nice micro ball bearing
Think OUTSIDE the box
Re:A few points (Score:2)
Personally, I would like to see a Unlimited Class of pinewoods for Webelos. Still keep some of the rules, but allow them to do things like get craxy with the wheels. You have not seen anything til you had your dad grind the polish our wheels down until they come to a point...low friction then!
1. The car must have been made this current scouting year.
2. The car should meet all racing specifications:
Car must be made from official kit provided.
Width cannot exceed 2-3/4 inches. Width between wheels must be 1-3/4 inches.
Length cannot exceed 7 inches.
Bottom clearance between the car and the track must be at least 3/8 inch.
Weight cannot exceed 5 ounces. Scales vary slightly -- be prepared to make adjustments.
No loose materials, no taping weight down to car.
Wheel bearings, washers, & bushings not allowed
Wheels and axles may not be modified in any way.
No springs allowed.
Detailing is allowed as long as it fits dimensions and other above rules.
Car must be free-wheeling, with no starting devices.
The only lubricant to be used will be dry graphite. It must be applied before weigh-in.
Car must pass inspection committee. If you fail to follow the rules, your car could be disqualified.
3. No test runs before the event.
4. Once a car has been through weight inspection and passed, it will go to the holding area and must not be touched.
5. Only members of the race committee will be able to handle the cars during racing.
6. Each heat will be announced. Viewing must be done from behind taped areas. Let the den whose heat it is get up front.
Re:A few points (Score:2)
Hmmmm, maybe THAT's why my big boxy fire engine won. :)
I won. (Score:5, Informative)
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.
A real geek car (Score:2)
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.
Re:I won. (Score:2)
I say "mostly" because I had some help from my dad: the design was the result of much groupthink. Most of the work, however, I did myself, including the shaping. Dad did the initial rip down the length of the car with a radial arm saw, did most of the handling of molten lead, and other potentially-hazardous things. I also had a friend of mine help paint the flames.
I consider it a perfect example of what a father-son project is supposed to be -- we both learned a lot, and had fun.
Conflicting advice? (Score:5, Funny)
Pinewood derby timers (Score:1)
Three Wheels (Score:2)
I had the aero car, and lost... (Score:1)
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.
Make it run straight (Score:1)
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.
We used Nickels... (Score:2)
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.
Re:We used Nickels... (Score:1)
Re:We used Nickels... (Score:1)
Of course, if a dry lubricant gets wet, you'll have the same problem.
Ask on newsgroups, too! (Score:1)
Car Tips (Score:2)
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!
Slghtly OT, but still Cub Scouts (Score:2)
Re:Slghtly OT, but still Cub Scouts (Score:2)
Wheels, weight, wobble (Score:1, Informative)
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.
------
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.
What I did: (Score:2)
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 [riceboypage.com] 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.
Some Tips -- (Score:1)
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.
A couple of points that haven't been mentioned. (Score:2)
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.
My advice. (Score:5, Insightful)
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.
Re:My advice. (Score:2)
Kids need your time more than anything else. They ultimately don't care about money or things. They want your attention and approval.
Regards,
Anomaly
WHat i learned in the cub scouts. (Score:2)
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.
Follow the rules... (Score:2)
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.
Buy several kits. (Score:1)
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.
Graphite (Score:1)
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....
Bad design (Score:1)
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.
results of some experiments... (Score:2)
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
Wheel and axle tuning (Score:3, Informative)
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!!!
Some advice on what to do and not to worry about (Score:4, Insightful)
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.
Bad Memory, Bad Idea and Good approach. (Score:1, Insightful)
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!!!!
Time to chill. (Score:1)
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.
Be careful meltin glead into these... (Score:3, Interesting)
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.
Re:Be careful meltin glead into these... (Score:3, Insightful)
Far less dangerous.
Re:Be careful meltin glead into these... (Score:3, Informative)
body kit (Score:2, Funny)
It's the alignment, stupid. (Score:2)
What I did, and things I haven't seen here yet (Score:1)
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.
Nose up, and/or have fun. (Score:3, Interesting)
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.
There are rules... (Score:2, Informative)
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.
Let your son build it (Score:2)
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.
Do what the riceboys do. (Score:2)
- A.P.
forget speed, go with style (Score:2)
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.)
Kids (Score:2)
They still do this? (Score:2)
I blame this rather banal memory on trial lawyers:P
Winning Designs (Score:2)
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!
Center of gravity (Score:3, Interesting)
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.
Wow, you all won first place? (Score:2)
find some way to stablize the wheels (Score:2)
Center of Gravity does matter (Score:2, Informative)
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.
the best advice.. (Score:2)
Re:why? (Score:1)
Re:Careful with the lead, guys! (Score:1)
And not to dismiss the issue, but there's plenty of other 'everyday' lead crap out there that people don't think twice about, without covering the relatively rare occurance of discarded pinewood derby cars. How many forests are full of lead shot, or lakes with lead sinkers?
But good points about safety and lead alternatives. I don't even know where you'd find bulk lead these days...