View Full Version : pinewood derby
My son joined Cub Scouts this year, and this will be his first ever derby. He picked a design this week (top), and he gets to start cutting this weekend. A few of the dads bought extra kits so we could have some fun too :cool:
http://i910.photobucket.com/albums/ac306/lindertw/2010_pinewood_derby.jpg?t=1261173145
Anyone else building cars over Christmas break?
South Park has an episode about pinewood derby that might help. :D
(I still have my racer)
Yes, Baby Farqs McGeezaks can help you out on that one... ;) It's been about 25 years ago here, but we still have the car. It's a great father / son project, have fun.
My girlfriend's son has this project almost complete for a pre-derby race their pack held. If I see him playing with it at her house I will offer my services, as I think it still needs some weights added to it. I'm trying not to step on his dad's toes though.
decodeddiesel
12-18-09, 16:35
I still have my racers too. In fact my last year in Cub Scouts my dad and I won 1st place at the state level competition.
The secrets?
Polish the heck out of the "axles". You want to remove flashing and burs and get them as shinny as possible. My Dad and I chucked them up in a dremel at low speed and used cotton cloth and mild polishing compound, this was 20+ years ago though and they may have changed the rules.
Ensure the "wheels" are true and round. A lathe works well for this, or you can do as my Dad and I did and chuck them up in a drill and lightly hit them with some 220 grit sand paper.
If you can, use a graphite based lube on the wheel/axle bearing surface.
Get the car absolutely as close to the max weight as possible. If you don't have access to an accurate balance use the scale at the post office.
Wedges are typically the fastest body shapes, however they are the most boring.
Most of all have fun with it!
landrvrnut22
12-18-09, 17:10
I still have my racers too. In fact my last year in Cub Scouts my dad and I won 1st place at the state level competition.
The secrets?
Polish the heck out of the "axles". You want to remove flashing and burs and get them as shinny as possible. My Dad and I chucked them up in a dremel at low speed and used cotton cloth and mild polishing compound, this was 20+ years ago though and they may have changed the rules.
Ensure the "wheels" are true and round. A lathe works well for this, or you can do as my Dad and I did and chuck them up in a drill and lightly hit them with some 220 grit sand paper.
If you can, use a graphite based lube on the wheel/axle bearing surface.
Get the car absolutely as close to the max weight as possible. If you don't have access to an accurate balance use the scale at the post office.
Wedges are typically the fastest body shapes, however they are the most boring.
Most of all have fun with it!
This is spot on what we used to do to mine. Having a machinist as a dad was a big help too. I remember using a scale that cost more than my first car, and was accurate to .0001. However, my dad made me do 90% of the work, and only gave a guiding hand. Good memories.
Demel tools make this an easy project. My son and I did a "hot dog" (bun and weiner) quite fun! Enjoy, don't forget to document so Mom can scrapbook it...
Mine were always slow, but normally some of the neatest looking. Mine kinda followed the scheme of a furmula 1 car, but I got those little lead ZOOMIE headers and lead blower manifold to glue on the front. Once I painted and flamed them, they were good to go. Slow, but sweet looking...LOL!
Definitely get the weight as close to the upper limit as you can. We use a kitchen scale to fine tune it. You can get screw-on weight kits at just about any hobby/craft shop, or you can stick things like washers, pennies, ceiling fan balancing weights, etc to the underside of the car. One year we drilled holes and dropped some fishing weights in, then filled the holes with wood putty. My son is a Bear scout this year, so this is our 3rd derby. We're planning to do our car between Christmas and New Year's.
Make sure you let your son do as much of the work as he can safely do (if he's a Tiger that may be limited to "design", painting and maybe sanding).
In any event, Pinewood is a great father-son project, and brings back a lot of memories for me from building these cars with my dad. Good luck and have fun!
I still have my racers too. In fact my last year in Cub Scouts my dad and I won 1st place at the state level competition.
The secrets?
Polish the heck out of the "axles". You want to remove flashing and burs and get them as shinny as possible. My Dad and I chucked them up in a dremel at low speed and used cotton cloth and mild polishing compound, this was 20+ years ago though and they may have changed the rules.
Ensure the "wheels" are true and round. A lathe works well for this, or you can do as my Dad and I did and chuck them up in a drill and lightly hit them with some 220 grit sand paper.
If you can, use a graphite based lube on the wheel/axle bearing surface.
Get the car absolutely as close to the max weight as possible. If you don't have access to an accurate balance use the scale at the post office.
Wedges are typically the fastest body shapes, however they are the most boring.
Most of all have fun with it!
Those are all still legal and we encourage the dads to HELP their sons do these steps. A word of advice, be very careful about buying aftermarket parts (axels, wheels, etc..) We ran the district and council derbies here and we had to sadly DQ quite a few boys. So make sure you are using BSA sanctioned parts.
Another tip, some folks put all the weight in the back, or will be 1/3rd in the front and 2/3rds of the weight in the back. It's due to the physics of coming out of the incline and going horizontal.
Oh and your pack should have an outlaw division for parents and siblings. Over Christmas break my son and my daughter and I will be working on our cars.
Make sure you let your son do as much of the work as he can safely do (if he's a Tiger that may be limited to "design", painting and maybe sanding).
As the assistant cub master for my troop I cannot emphasize the above enough. This is an event for the boys to learn from and bond with their father and mother.
Great advice so far. I was going to add the thing about having the weight in the back, but it's been covered.
Other hints:
- Reduce rolling resistance by crowning the wheels so that there is only a minimal line-to-line contact patch in the middle of the wheel.
- You only need three wheels to be stable with the weight balanced right. This reduces rolling resistance and axle friction by 25%. Install the 4th wheel, but make sure it sits higher and doesn't touch the track
- Polish the ID of the axle hole in the wheel.
- Make sure the three wheels you are actually using are in perfect alignment.
FromMyColdDeadHand
12-18-09, 23:58
- Reduce rolling resistance by crowning the wheels so that there is only a minimal line-to-line contact patch in the middle of the wheel.
- You only need three wheels to be stable with the weight balanced right. This reduces rolling resistance and axle friction by 25%. Install the 4th wheel, but make sure it sits higher and doesn't touch the track
- Make sure the three wheels you are actually using are in perfect alignment.
Now that is some sneaky bastard stuff!
Any boundry layer effects on the bottom of the car?
ZeroFail'd axles be legal?
i finished 2nd in my pinewood derby when i was a kid.(still have the trophy) I look forward to enjoying that time with my son when he is old enough. My dad helped me with mine, we used a dry graphite on the wheels don't know if you can find it anymore.
Thanks all for the great advice! It's amazing what I found while googling, and even more amazing how far some kids-at-heart take it :p
Those are all still legal and we encourage the dads to HELP their sons do these steps... As the assistant cub master for my troop I cannot emphasize the above enough. This is an event for the boys to learn from and bond with their father and mother.
My boy is a Tiger Cub, but he gets to do all the work himself. He cut out the back half of his car last night with a coping saw (I helped get the blade started). He's super excited to do the work on his own which I why I bought a separate kit for me :D
I'll let him decide if he wants to do the extra stuff (axle/wheel polishing, three wheel setup, etc.). In the meantime, it's fun just hanging out at the workbench...
I drilled some holes on the top rear of my sons one year and put 9mm bullets in for weights. Looked kinda cool.
Romeo Foxtrot
12-19-09, 14:28
http://www.southparkstudios.com/clips/224681
The weight should be as far back as possible (and still be stable). It has nothing to do with coming out of the incline and into the horizontal. It has everything to do with potential energy and having more potential energy with the back of the car heavier since almost every track I have seen starts the cars at the top of the incline with the cars also at an incline. The further up the track the center of mass the car is the more potential energy it will have. This potential energy will get turned into kinetic and rotational energy. (more on energy in a moment)
If your Pack allows it move the wheels out to both ends. The longer the wheelbase the more stable the car is. It is not against BSA rules (or was not last I checked) but some packs say you have to use the slots cut in the woodblock and some let you cut new slots.
The reason the 3 wheels on the track works better (as long as it is stable) has to do with energy.
Most tracks have an incline and then a short flat section at the bottom before the finish line. So you want to maximize kinetic energy and minimize rotational energy. You only start out with a certain amount of potential energy at the start and you want to convert that energy into kinetic (forward motion) energy and not waste it on rotational energy (energy spent to rotate the wheels).
IF (IFF) your track has a very long flat section at the end (1/2 the track or more is the flat after the incline -- yes, some tracks do work like this) then you actually want to have lots of energy locked up in the wheels since once you hit the bottom your car bleeds kinetic energy and energy locked up in the wheels will keep them spinning and "push" your car forward.
But most tracks are not like that and only have a short flat section at the end so you want to minimize the energy lost to rotating the wheels. One way to do this is to make them have as less mass as possible (less weight). The less mass the less energy it takes to rotate them. So lighten the wheels as much as possible.
The 3 wheel thing works because you are only rotating 3 wheels instead of 4 so have less energy being put into rotational energy.
(BSA used to sell extra official wheels as well -- buy a bunch so if you screw one up you have replacements -- you can also find the best made ones).
Rounding the wheel profile etc also removes mass and also very lightly reduces the friction of the wheel on the track. Make sure that you will not get in trouble doing that. Some cub leaders are stupid and anal about the "rules". This company claims that the rules they show are the ones most people use: http://www.hobbymasters.com/pinewoodderbyrules.aspx . Make sure you get your packs rules and make sure whatever you do to the wheels is kosher according to your rules.
Make sure the axles are exactly perpendicular to the body. I used a brass tube inset into the block of wood into which the nails were pushed to help make the wheels be exactly parallel and it helped make them perpendicular as well.
Polishing nails etc and using lots of powdered graphite is a good idea. No reason to waste energy as heat energy from friction. You don't want the wheel rubbing the car if you can avoid it. Use lots of graphite so that you get a graphite film between the car and wheel as well as on the axle.
I use monokote to cover my car instead of painting. (The shrink film used by RC people). You get a nice shiny finish...
Again, it is all about potential energy and converting it to kinetic and not other forms of energy.
I am not a ME but I did win a college engineering pinewood derby (using mostly BSA rules) in 1991 at BYU when I went back to school to finish up my CS degree. Was satisfying to win the engineering college pinewood derby as a software guy. My brother came in 3rd and he was in physics then (later software), again not an engineering college guy. Actually an ME professor's car beat everyone but he disqualified himself form winning since he was a professor. He gave a small lecture after the race to explain the stuff that is really important in a pinewood derby (air resistance is not one of them -- the cars do not go fast enough). That is where I learned it all revolves around energy.
A few years later I was back at BYU as a grad student in CS and they had another pinewood derby sponsored by the college of engineering. This one was anything goes. The winner had razor thing tires that had almost no mass. However, one guy with huge tires (lots of mass) was always last at the bottom of the incline but would shoot ahead at the flat on the bottom when the razor thing guys car (and others with less mass tires) would start to slow down. Unfortunately the flat at the bottom was not long enough to let his stored energy in the wheels really bear fruit.
Chad
- Reduce rolling resistance by crowning the wheels so that there is only a minimal line-to-line contact patch in the middle of the wheel.
This is a good idea. Unfortunately many packs will disqualify cars that do this... Check your pack's rules.
The biggest reason this is a good idea is that it reduces the mass of the wheels which reduces the loss of potential energy into rotational energy. Less friction on the track etc is also nice.
I remember doing that back in the day. Was always fun.
I had hoped to have my child involved when I had one, but alas it is not to be.
Hope he does well :)
I am a Bear cub den leader and a couple of my boys don't have dads or access to tools so we will be having a den meeting at my house so we all can do our derby cars. Everything I do is listed already except I put a stack of quarters superglued to the back (on the top) of the car to bring it up to weight. My son almost always comes in the top 3 at our pack derby and came in 8th out of over 200 in our regional. I would have to say sanding down the mold marks on the tires and polishing the axles produced the biggest speed difference for us. If we do nothing else to the car we always do that.
As a tiger he told me the general shape and painted the car.
As a wolf he designed the shape, sanded everything and did all the wheel/axle work by himself as well.
This year he does it all, I'm anxious to see what he comes up with.
Good luck to ya
Merry Christmas to all
My son finished his car tonight!
http://i910.photobucket.com/albums/ac306/lindertw/derby_1.jpg
http://i910.photobucket.com/albums/ac306/lindertw/derby_2.jpg
Mine, however, is still looking pretty rough :p
This is a good idea. Unfortunately many packs will disqualify cars that do this... Check your pack's rules.
The biggest reason this is a good idea is that it reduces the mass of the wheels which reduces the loss of potential energy into rotational energy. Less friction on the track etc is also nice.
if you can not crown the wheels you can put the axles in at an angle (caster) so just the edge of the wheel is on the ground. I miss cub scouts, had great times helping my sons build cars, probably got a dozen of them in the house.
Also put your axles in a ziplock bag with graphite and let them soak in it.
My son finished his car tonight!
...
Mine, however, is still looking pretty rough :p
Nice work! I helped my son with the cuts on his car on Sunday, and he finished sanding it last night. We should be painting and finishing it up this weekend.
My son is getting ready to get his started and I'll be suggesting some of the tips for him to try out.
Local rules say:
1. Cars must be constructed of materials provided in the official BSA Pinewood Derby kit. This includes the wood block, axles and wheels.
2. Non-BSA wheels are not allowed, including performance wheels that may be sold at local hobby shops for Pine Car models.
3. Wheels cannot be sanded or crowned on the surface.
4. Cars must not weigh more than 5 ounces as measured ON THE OFFICIAL REGISTRATION SCALE. Other scales, including those in the garage area, are not official.
5. Cars must not exceed 7 inches in length or be wider than 2/3/4 inches or taller than 3 inches. An underside clearance of 3/8 inch is recommended.
6. Car axles may be placed at locations other than the pre-drilled locations as long as the overall length of the car, including the wheels, does not exceed 7 inches.
7. Weights and other car details must be securely fastened to the car body and cannot be loose or movable.
8. Cubs may use approved lubricants – dry white or graphite is permitted.
9. Cubs must be present to enter the race. Cars must be built in the current year and cannot be re-used from previous years.
10. Cars passing inspection will be given a sticker with an entry number which will be placed on the car in a location clearly visible by judges.
On #3 I can't tell if they mean the wheel in it's entirety cannot be sanded, or just the crown. And as far as the camber, would you bend the axle to get the wheels set up like that?
I never knew there was so much that went into these little cars. First year for me, 2nd for my son.
The_War_Wagon
01-21-10, 16:44
Workin' on my son's car right now! Well, another coat of paint is drying, anyways. ;)
He's a Bear, but my twin boys will be Tigers later this year - we'll be building Pinewood Derby cars 'til the end of time! :eek:
Here's our car "Jaws". My son was able to do a lot more of the work this year (he's a Bear) than in previous years, and he really enjoyed that aspect of it. Weighs in right at 141 grams, and we will be racing Saturday morning. Good times!
awesome work, and thanks for posting pics Argus. I showed it to my son and his friend/fellow cub scout and they liked it a lot!
Mine is finished (on the right), but I don't think I'm going to paint it by this weekend...
http://i910.photobucket.com/albums/ac306/lindertw/derby_update.jpg
The 'dad' race at the end should be fun :cool:
The derby is awesome. My son is now a Bear (just finished his badge requirements). They suckered me into being Committee Chair so I wrangle adults which I'm pretty certain is harder then wrangling the boys.
This we will be our third derby coming up in April. We haven't won yet, but we've had fun with the cars.
His first car he wanted just like the truck his Uncle Tom drove in Iraq so we made a Humvee. Came out very similar to the drawing he showed me when I asked him to design it. Won the most creative award and placed 3rd in the races. The tooth pick bumper actually held up.
He drew the outline, final sanding, and paint job. We dug some parts out of an old plastic model to top it off.
http://i87.photobucket.com/albums/k158/mrbieler/derby_1.jpg
http://i87.photobucket.com/albums/k158/mrbieler/derby_3.jpg
Last year I made a wedge of swiss cheese with a mouse and he made a coke bottle, but I can't find pics. He was more involved with the hand tools the 2nd time and will do even more this year.
I have no idea what design he'll come up with next.
My son is getting ready to get his started and I'll be suggesting some of the tips for him to try out.
Local rules say:
On #3 I can't tell if they mean the wheel in it's entirety cannot be sanded, or just the crown. And as far as the camber, would you bend the axle to get the wheels set up like that?
I never knew there was so much that went into these little cars. First year for me, 2nd for my son.
you can just angle the axle instead of making it perpendicular to the side of the car.
6. Car axles may be placed at locations other than the pre-drilled locations as long as the overall length of the car, including the wheels, does not exceed 7 inches.
Your car will be more stable if you can lengthen the wheelbase as much as possible. Make the front of the car and the front wheels be in line and the same on the rear.
I don't know if I would angle the axles. Makes it harder to keep it stable I think.
If you can make it reliably go straight and be stable, making one wheel not touch the track is your biggest gain. A full 1/4 of your potential energy loss to tire rotation is eliminated which leaves more energy for forward motion.
Remove as much material from the tires as you can without making it look like it. Think inside the tire to remove material. The less material in the tires, the less energy is lost in making them rotate and the more energy going to kinetic energy for forward motion.
Shift the center of balance as far back as you can and still be stable and straight running. More potential energy.
Did I mention lightening the wheels as much as possible (without making it obvious so you don't get disqualified)? This rotational energy / kinetic energy thing is the biggest thing you can do on your car.
They suckered me into being Committee Chair...
HA HA!!! Sorry but I would rather run the district and council events (and I am) than chair the pack pinewood derby. Talk about an aneurysm inducing experience.
6. Car axles may be placed at locations other than the pre-drilled locations as long as the overall length of the car, including the wheels, does not exceed 7 inches.
yep and I have given up on that. I suck and putting the wheels in. So I looked for the axel jig and couldnt find it anywhere. So I bought a block of wood with the axle holes pre-drilled
HA HA!!! Sorry but I would rather run the district and council events (and I am) than chair the pack pinewood derby. Talk about an aneurysm inducing experience.
Not just the derby, I'm the Pack Committee Chair. :eek:
Pulling teeth to get parents to step up and help instead of using Scouts as a drop off day care.
just got back from the derby and it was loads of fun! We think my son placed in the top three in his Tiger Cub den, but we won't know the final results until the Blue & Gold dinner in two weeks. Each kid walked away with a pinewood derby medal and a certificate for their car!
Our derby was today. This is my stepsons first year and he is a Bear. I did all the power tool work and he did the design, the paint and some of the sanding. We didn't win but we had a excelent showing. The way the brackets fell we didnt even get in the top three, but in the grudge matches after we beat the third place car 3 times running.
Our track has a LONG flat and one of the cars had the stock wheels filled with epoxy. It was behind down the ramp, but faster in the flats and made a pretty good showing. Something I'm might do next year. Also going to put most of the weight in the rear above the rear axle.
We did win the prettiest car award. Guess my 5 coats of paint and wet sanding paid off...
Awesome:) Can't wait for ours in April.
Blue and Gold will be a hoot. Ours is on 2/23.
Ww're doing our derby at the Blue and Gold. I cut my sons car yesterday and today he will be sanding, sanding, sanding
Our track has a LONG flat and one of the cars had the stock wheels filled with epoxy. It was behind down the ramp, but faster in the flats and made a pretty good showing. Something I'm might do next year. Also going to put most of the weight in the rear above the rear axle.
Yep. This illustrates exactly what I was saying about the kinetic vs rotational energy. Going down the slope it was behind since the wheels were soaking up available energy to go forward into rotational energy instead to get the wheels turning... So the cars with lighter wheels were ahead. But you get to the bottom and all that energy in the wheels comes into play.
Most tracks don't have that long of a flat compared to the sloped part. But for those of you with quite long flats after the slope, you need to balance the need to get down the slope with the need to cover the flat. MORE weight (actually mass) in the wheels helps you do that, but you start from behind once you hit the flat and have to catch up, which you can do. It is amazing to watch actually.
and now I am in uber deep shit with my 10 yr old son. He has done great so far with his car. I had to cut it out on the scroll saw, but I did an intentional rough cut to make him spend plenty of time sanding it. Well that is all well and good until he says he wants to use sinkers for weight. Problem is that we have made a really light and think racer. So dad gets the sinkers, takes the drill to the car.......and disaster. Right now the entire rear end is covered in wood putty. I have a feeling that we will be sanding and refilling all night long. Yeah Im in the dog house. Looks like Im just going to go with the bar weights. This really pisses me off because we both believed in our hearts that we got a winning design this year. But my dumbass has to use a drill bit way to large for the job. God I could kick my self in the ass up one side of the street and down the other at this point.
HES,
if there's a Michaels (http://hosted.where2getit.com/michaels/) near you, they carry PWD stuff. IIRC you can get a replacement block for ~$3.
Good luck!
HelloLarry
01-28-10, 21:43
Michael's has weights too.
I used a mill on my son's car to make a groove in the bottom of the car. Tape-a-weight wheel weights fit in it. A router could make the same cut.
and we're off to the races in a few minutes
My son's car
http://img.photobucket.com/albums/v234/frontline_01/scouting/pinewood1small.jpg
http://img.photobucket.com/albums/v234/frontline_01/scouting/pinewood2small.jpg
That thing is all weight in the back. The car came in at 1.5 oz and we put the rest of the weight in the back using bullet weights that were both drilled into the body or krazy glued to the outside and then covered with paint. It ought to fly like lightning.
and my youngest daughter's car for the siblings / outlaw category
http://img.photobucket.com/albums/v234/frontline_01/scouting/pinewood5small.jpg
and we're off to the races in a few minutes
My son's car
http://img.photobucket.com/albums/v234/frontline_01/scouting/pinewood1small.jpg
http://img.photobucket.com/albums/v234/frontline_01/scouting/pinewood2small.jpg
Looks good!! The only thing I would have done was shift the rear axle as far back as possible for stability. (And remove mass from the wheels)
Let us know how it turns out
If you look at the bottom pic behind the rear wheel you can possibly make out where I had originally drilled out the hole for the rear axles. Even then I probably should have pushed them back even further. However since we won Council last year my pack is running it this year and my cub master made up this rule. So he made a the rule about no extended wheel bases, which pissed me off to no end. He and I (asst. cubmaster) went round and round on this one. So I re-drilled and yeah the results were predictable. The car was popping wheelies all down the track. :mad: Had the axles been allowed to be pushed back as intended it would have flown. Still he finished in the top 10 out of pack of 100 boys.
If you look at the bottom pic behind the rear wheel you can possibly make out where I had originally drilled out the hole for the rear axles. Even then I probably should have pushed them back even further. However since we won Council last year my pack is running it this year and my cub master made up this rule. So he made a the rule about no extended wheel bases, which pissed me off to no end. He and I (asst. cubmaster) went round and round on this one. So I re-drilled and yeah the results were predictable. The car was popping wheelies all down the track. :mad: Had the axles been allowed to be pushed back as intended it would have flown. Still he finished in the top 10 out of pack of 100 boys.
Good for him. Kind of a dumb rule. The model cub scout rules allow you to move the axles as long as the overall length remains the same. Anyway, next year, turn the block of wood around if you have the same dumb rules so that the rear axel is the slot closest to the end. That will allow you to have as much weight as far back as possible and still have the center of gravity ahead of the rear axle.
Powered by vBulletin® Version 4.2.5 Copyright © 2024 vBulletin Solutions, Inc. All rights reserved.