A bit of a different topic… My son and I e-mailed Click and Clack for some advice on Pinewood Derby car creation. The cub scouts and their parents use a kit to design and build small cars that are raced down an inclined plane that’s about 25 feet long.
Thinking that the Car Talk community might be able to chip in their wise advice on car shapes, aerodynamics, tips for smooth rolling wheels, how to distribute the weight of the car for maximum speed, etc., we thought we’re write in. Click and Clack passed the buck on to their learned listeners. We’d welcome any helpful suggestions! Thanks in advance.
Any way you could (concisely) list the regulations that affect these things? I imagine there are lots of limitations to prevent $20,000 Derby cars. I know this from the so-called ‘kids’ pinewood derby cars we’d get at our den’s races…
Here’s an idea - have a couple of different ‘classes’, one for 100% kid-made cars, maybe build them at den meetings. There are always the ones that dad ‘helps’ on, they’re fun to see, too.
As for smooth rolling, graphite powder seemed to work well.
- Make sure the car is at right at the weight limit
- Make sure that the weight isn’t too far forward.
- Make the car aerodymanically clean as possible
- Make sure to “Break-in” the wheels and pins and use graphite as a lubricant
I won my pack’s derby three years in a row, and finish in the top 3 in the coucil all three years I entered as well. Two 2nds and a 3rd.
One really big factor is getting the axles PERFECTLY straight.
Here is one tool and on the site are lots of tips. Enjoy.
http://www.pinewoodpro.com/pinewood-derby-wheel-axle-alignment-tool.htm
Also, the last couple of races I went to, the fastest cars had the most weight on the rear.
Right On FoDaddy. My Son Retired Undefeated (small town). One Strong Competetor Went For “Best Of Show” The Following Years After He Was Eliminated From Winning The Speed Events.
I like your list. We chucked the pins in my drill and spun them inside the wheels for break-in, before adding graphite. We were right at maximum at weigh-in with the weight almost centered in the chassis.
We’ve had Snoopy and Charlie Brown driving rear engine V-8 (eight straight pipes) cars, rear spoilers, roll bars, etcetera. It was a blast and my son has some pretty tall trophies.
CSA
Graphite lubricant on the axels where the wheels roll is defiantly the way to go. I won this event when I was like 12. Add weight using lead slugs (bring a drill with you to the race incase you are over weight).
Let me add a couple more tips.
Pick your favorite high performance sporty car and saw the car to look like it, but keep it only about 3/4 inch tall.
Chuck up the wheels carefully in a drill and smooth the bottoms of the wheels.
Remove the flashing from the heads of the “axles” or at least remove the rough edges from the flashing.
Use a soft #2 pencil lead and go over the portions of the “axles” that the wheels touch before using the graphite.
Put the weight as far back as possible. The car starts down an incline, putting the weight as far back as possible means it starts out further up. Since about half the track is flat, the weight ends up at the same height no matter where it is in the car, but starting out at a higher height means that it falls further, developing more energy along the way.
You can also consider shaving the center of the wheels out (doesn’t take much) so they will be slightly concave as viewed from end on.
This will essentially make knife edges out of the sides of each wheel and will greatly reduce rolling friction.
When my son was in Cub Scouts, it was definitely a dad project. The kids who had a dad who wasn’t a machinist were really humiliated. I didn’t like it much.
Irlandes said it. People who have access to machine tools and dads who are technically able have it over those kids that don’t. There is a better, commonly available lubricant than graphite but I won’t say what it is. If you want to be super competitive, build your own track at home so that you can experiment. Cars must track straight and CG as far back as possible is good, short of making the front wheels too easy to lose control.
A very difficult situation that I encountered was weight. I had access to a precise, calibrated scale in an engineering laboratory to weigh the car. One of the proctors at a race had a garbage piece of junk scale that was grossly in error and we found ourselves frantically carving weight from the car in order to qualify to run the race. We should have objected and walked away from that debacle.
We won most years and I used to do a tip sheet for the pack each year.
- Precise weight right up to the limit-After pouring in lead in the back, we used brass screws for the final adjustment and would have it within one half brass screw. If its over weight for the scale used at weigh in, you just take a screw out.
- Polished axles
- True up the wheels to flatten them and take the wobble out.
- Lube the axles with a mixture of alcohol and graphite before each race.
- Only three wheels on the ground to reduce friction.
- Shape doesn’t really matter much but we always went with a wedge.
Its supposed to be fun so don’t get too serious.
The first thing you need to do is to find out what the Pack rules are.
There are many tricks you can use like one front wheel off the track or negative camber on all of the wheels but the Pack can set the rules for the race and some of these tricks can be illegal.
Other rules are… you can only sand off the casting mark on the wheel, you can only sand off the burr on the axle and nothing else, only graphite is allowed no alcohol or lithium.
I’m going counter here. You don’t have to have access to a machine shop or a lot of money. When my son was in the Cub Scouts, I was a young enlisted man in the Navy living in Va Beach. We had almost no money after paying for housing and utilities. All I had for machinery was an old drill.
The Den Mothers husband had access to a band saw and he cut out all the kids cars to the profile they drew on the block of wood. After that, we used sandpaper, a points file and the drill. I bought the Pinewood derby car kit, a can of paint, some lead fishing weights, the graphite and sandpaper. The first year, we sanded the car to the profile of a Ford GT40 (my choice), drilled holes in the back about where the tail lights would be, filled them with lead until the kitchen scale said 5 oz and painted the body.
I did the things listed in my previous post. I forgot to mention that I not only rubbed the pencil lead all over the axles, but on the surfaces of the wheels that touch the body and the axle heads. We also rubbed it on the inside edge of the outer circumference of the wheels in case they contacted the center channel that was used to guide the cars down the track. The pencil lead actually qualifies as graphite and you don’t really need the powder. We used it anyway but I really suspect the car might have been faster without it, but we used very little.
Since the track is made from plywood and has a rough surface, we left the bottoms (tread) of the wheels flat so they wouldn’t get caught up in the surface irregularities. My wife took it to the post office and got it weighed to make sure we weren’t overweight.
There were plenty of Fathers who had access to machine shops and professional help, but they all lost, my Son’s car beat every competitor by at least two feet.
The next year, my son used the profile of a Trans Am, he was a fan of the show Knight Rider. I was out to sea at the time so he did everything himself just the way we did the year before, and again, there was no one even close. It got ugly that year, wish I’d have been there but one or more of the other kids father’s tried every trick in the rule book to get his car disqualified, but it passed every test.
It doesn’t take much to make a fast pinewood derby car. Just avoid the mistakes that the other guys make. A lot of good tips for building your pinewood derby car are at http://www.abc-pinewood-derby.com/basic-guide.php
Shotgun Shot…an EZ way to get right up to…but not over the weight limit.
Won the pack races with that method.