Introduction: Pinewood Derby Car Weight Compartment

Picture of Pinewood Derby Car Weight Compartment

This instructable will show you how to create a "pocket" underneath your son's deby car for easy weight addition/removal.
Get the closest possible to the maximum5.0 oz.

Step 1: Acquire All the Parts

Picture of Acquire All the Parts

1 Ea. Pinewood Derby boxed set.
Wooden block
4 Plastic wheels
4 Metal "axles" (nails)
Set of fishing weights
1 Ea. 35mm Film Canister with lid
Fast Setting Epoxy or Hot Melt Glue

Drill Press
2 Forstener bits (1 the size of the cannister, and the other slightly larger than the lid)
Dremel Tool with sanding drum attachment
(You can forgo the drill press and bits, but you won't get the tight fit that looks good.)

Step 2: Drill a Hole in the Car Body

Picture of Drill a Hole in the Car Body

Find a position to drill on the car body as close to the back end as possible.

1) Flip the car over on its back.
2) Using the drill press and the larger Forstener bit, Drill a hole slightly deeper than the thickness of the film canister cap.
3) Replace the bit with the smaller bit and drill a second hole, this time drill as deep into the car body as you can without protruding on the other side.
4) With the Dremel tool, sand a notch on one side of the canister so you can get your finger under the cap to remove it.
5) Test fit the canister and lid to the hole.

Step 3: Glue the Canister to the Car Body

Picture of Glue the Canister to the Car Body

1) Cut the canister in half.
2) Add some glue to the inside wall of the smaller hole that you just drilled in the car body. Use just enough glue to attach the canister to the wood. You don't want it to dribble all over the place, specially between the cap and the canister.
3) With the cap on the canister, slowly insert the canister into the car body until the top of the canister lid is flush with the bottom of the car.
4) Turn the car over and sit it on a flat surface.
5) Put a heavy weight on the car so the glue dries with the lid sitting flush.

Step 4: Weigh the Car and Add Lead Weights As Needed

Picture of Weigh the Car and Add Lead Weights As Needed

1) Using a popsicle stick, or screwdriver, carefully pry the lid off the now securely attached canister.
2) Flip the car upside down on a postage scale, and weigh the complete car, with the lid on the scale as well.
3) Add weights into the canister until the scale shows the regulation 5oz.
4) Close the lid tightly.

Step 5: Gentlemen, Start Your Engines.

You are ready to race.

During the day of the race cars, and owners, will go through registration where the cars will be weighed. This is where this project pays for itself. Invariably, your scale, and the judges scale, will show different weights due to manufacturer, curvature of the earth, distance from your home to the Earth's core vs distance of the race location to the Earth's core, relative humidity, low battery, high tide, low tide, Sun spots, Van Allen Belts, etc., etc. Simply pop the lid off, and add or subtract weights until 5oz is achieved once more.



debi.s.ansley (author)2015-03-05

Also, I've used Shoe Goo, Wood Putty, Hot Glue, Gorilla Glue, and Epoxy to keep weights in place so they don't move. You can mix fishing weights/BBs/ball bearings with putty, Shoe Goo, or Hot Glue in a compartment to keep the weights still has required my most rules.

debi.s.ansley (author)2015-03-05

Here's why the weight in the back is better. When you start your car is in the starting block at an angle with the back of the car higher. You want as much as far back because the back of the car is then higher then the rest of the car. That gives you as much potential energy as possible. When the car reaches the level part of the track your weights have fallen farther then if the weights are in the middle or back. Therefore you have more energy when the car reaches the flat section which translates into extra speed. Assuming you have good axles and straight wheels you're car will be about as fast as possible. Good smooth polished axles combined with rear weighting is the best combo for a fast car. Wind resistance helps but almost negligible for such a short distance and slow speeds. Good lubrication helps, wheels must move freely with no binding. Another trick is to not paint the wood where the wheels might touch and rub dry graphite into the wood in those spots.

DayBowBow (author)2015-01-07

Did you have any issues with the container opening during arun?

CementTruck (author)DayBowBow2015-01-07

The film container lid snaps closed and takes quite a bit of effort to open so it's very secure.

dkrall (author)2013-11-07

I like your idea. but after you have the hole a fender washer and a screw would have been my lid.

CementTruck (author)dkrall2013-11-07

Not a bad idea. Easier to remove.

wanna beco (author)2011-11-13

Kholle, do you have any links to verify this info.

And to the OP, is the rear of the car the best spot for the weights? I thought that having them nearest the nose was most beneficial?

CementTruck (author)wanna beco2011-11-14

You might want to reply to kholle1 using the reply button beneath his comment.

I read this somewhere, but can't remember where. I am just paraphrasing from memory:
In the past people have cheated by using some sort of mechanism that rolled a ball bearing from the back of the car to the front. The mechanisms were hidden inside the car. The act of the bearing striking the front of the car after the launch gave the car an added boost of speed. The car's owners were disqualified after someone got suspicious and checked the car.

In regards to the weight placement, right in front of the rear axle is considered the best placement. If it is behind the rear axle it makes the front too light and makes the nose want to hop every time the front wheels roll over the track joints. You want the center mass (weights) positioned as high up as possible on a slope because once the car is level the center mass's momentum can no longer be affected by gravity. Since the rear of the car is the last portion that makes it to the flat track gravity is pulling the center mass down until that point in time.

wanna beco (author)CementTruck2011-11-14

Great, thanks for that info... I can't wait to race!!

jgderuvo (author)2011-07-20


CementTruck (author)2010-04-29

I embedded the BBs in play dough/clay the first time I tried this. The clay also added some weight while keeping the BBs (and itself) immobile. The consecutive races later I used hot melt glue and dropped BBs in the hot melt before it cooled. Both ways worked fine.

Thanks for the comment.

kholle1 (author)2010-04-29

Great idea.  However, I must point out under many group's rules all parts including the weights must be fixed to the car.  That is they are not allowed to move relative to the car.  BB's and fishing weights are allowed but must be glued or fixed in place.

quesoman (author)2009-02-15

Im still a teen and i love doing pinewood derby... my car this year is too thin but this will be and idea ill propose to my dads webelos den and will probably do this on my car next year.

CementTruck (author)quesoman2009-02-16

Before you spend your time doing this make sure your Pack and council allow it. I would hate for you to do all the work and end up being disqualified because of this instructable. Regards.

chinchymork (author)2009-01-27

Thats a really good idea!! I remember when I did pine wood derby. It was a lot of fun I made it to state my last year but I couldn't go because we were out of town.

bruno13069 (author)2009-01-26

My Derby cars had lead weights counterbored into the underside. Dad could drill them out slightly to adjust the weight.

zeke34 (author)2009-01-24

I remember pinewood derby cars. I made a T.V. remote. I was going for Art but got a silver medal in Speed. Went to the district finals and got 16th place.

CementTruck (author)zeke342009-01-25

My son's 2009 race was last weekend. We made a "Batman" themed car. Our times were much improved from previous years, but did not win any heats. His car was consistently 2nd place in any heat he ran, so we were pretty competitive. He brought home the "Best Design" trophy.

MajikMan (author)2007-12-24

This is an interesting idea. My dad and I just used the standard, xylophone-shaped weights, and brought a file to the weigh in. We always planned to come in just under-weight, then added screws after painting - those kinds of weights are nice because they can be attached with 2-6 (or so) screws. That kind of flexibility made it easier to get up to exactly the max weight. We had one second and one first place in the pack - great times. I can still remember standing in the basement polishing wheels and axles. I think this instructable has inspired me to go dig out the boxes that my old cars are in.

Pumpkin$ (author)MajikMan2008-09-16

a few years back (like 7 years ago) me and my dad built one and we just put quarters on the bottom. I still have mine "the Hotwire"

CementTruck (author)MajikMan2007-12-24

I have every confidence in this stealthy weight compartment. I have seen many beautiful derby cars whose aesthetics were ruined ruined by add on weights. What I don't have confidence in is my ability to polish axles and smooth out wheel surfaces.

mrmath (author)2007-01-18

Did you smooth out the axels? Got to put them in a drill and file them smooth to get rid of the burrs, then polish them up.

jridley (author)mrmath2007-12-06

Not allowed in our area. You're allowed to remove the burs and apply graphite, but NOT to polish. They do check, and cars have been banned.

CementTruck (author)mrmath2007-01-18

Done, and done! The Geezer race I mentioned earlier has lax rules, so I'll be making speed axles for my car. My son and I de-burred, and polished his axles. Races are on Jan 21st. Cross your fingers.

mrmath (author)CementTruck2007-01-19

Good luck! My (son's) weigh-in is next Wednesday, and then we get to race on Sunday. Lots of preasure. He was first place last year for his den. Won 5 out of 6 heats. This year, due to low membership, we're only getting 1st place and partipation trophies. So he REALLY wants to win again. But, we've had fun making it, and that's what really matters. Win or lose, we've had fun.

StepsoftheSun (author)2007-01-18

I really admire the idea, execution, and write-up of this Instructable. Having said that, I really dislike the phrase "create a 'pocket' underneath your son's derby car." Being fairly young myself and having recently left behind various high school building competitions, I still twitch when I find out a parent's meddling hands were all over their son's or daughter's project. A lot of scenarios are floating through my head about why it might be acceptable in your case, but I'd honestly like to hear your defense of this modification of your son's car. "Living vicariously through my children" cannot be one of them.

jridley (author)StepsoftheSun2007-12-06

Pinewood derby is ALWAYS a joint father-son activity. That's what it's INTENDED to be. In fact that's what CUB scouts is all about. As long as the kid is taking an active hand, it's all good. My son picked the design and paint scheme, and did a good portion of the rough carving and final sanding and painting and fixing up the axles. I did the power tool stuff, the fine carving, and in the case of one car with fine (breakable) detail like spoilers and front wings, I drilled and placed some reinforcing nails. From talking to other dads, there were some there that were doing a LOT more than I was. When the cubs cross over to BOY scouts, then they're on their own. But Pinewood is a cub event, at least around here.

The pinewood derby was never intended to be for the kids anyway. :P

Fenwick (author)vatosupreme2007-02-14

Haha so true...

mrmath (author)StepsoftheSun2007-01-23

Mine would be (I know it wasn't directed at me) that my son is 7 and couldn't do it himself.

There are 2 entrys in his Cub Scout troop. The Cub's and the "Geezers". The vehicle depicted is my son's. I cut the shape he chose because he's too young to use the bandsaw. He sanded it. He and I sanded the wheels and spindles 50-50. I spray painted, he decorated, as far as the weight goes, I did not want to "destroy" the shape of the vehicle he designed by installing all the lead weight ingots, sold at craft stores, all over his vehicle. I chose the discrete method for his sake. My son just turned 7, and the older he gets, the more he'll get to do. The Geezer race was created to channel the vicarious behavior, which it has done well. This is my son's first race, and when he gets his feet wet, I hope the spirit of competition will finally stir within. Getting him to sand this damn thing was chore. These "meddling hands" oozed guidance and tutelage for future events. When you hatch your own kid you'll see what I mean. Regarding the damage to the design, see Mikesty's comment about adding weight at the last minute.

Oh, I thought the implementation was great--a very discreet technique. The "Geezers" group is a great idea! I wish there could be such things for all manner of father-son activities. I agree, a seven year old should probably not be using a bandsaw but I'm sure he'll be taught well!

mrmath (author)2007-01-23

MAN! I just found out that our derby race doesn't allow this:

Note the last rule. "No loose materials of any kind are allowed in the car."

Be sure to check the rules for your Pack before using this method.

jridley (author)mrmath2007-12-06

That's why I pour in melted lead to bring it up close, then I epoxy in lead shot to finish up the last 10 grams or so. If I'm overweight, I just pop out a few balls of shot at a time until I'm on the mark. I also always overshoot by several grams on my scale, so that if their scale is reading low, I can take advantage of that.

CementTruck (author)mrmath2007-01-23

Hot melt glue in layers. It works. I did it.

mrmath (author)CementTruck2007-01-23

Yes, but that adds to the weight, so you'd hvae to do that on the scale, wouldn't you?

CementTruck (author)mrmath2007-01-23

Correct. I did not think that hot melt glue was so heavy, but I actually had to reduce the about of lead that I used. My wife brought home the postal scale from her office. While on that scale I got the car up to 4.8 oz. and closed the lid. While at the actual scouting weigh in, I opened the lid and weighed the car upside down with the lid still on the scale. I proceeded to add a couple of small weights to get the car up to 5 oz. The judges didn't care about the 2 little weights rolling around. You could do most of these tips, but to top the car off you could probably use playdoh. It mashes up nice, and won't roll around. Anyway, good luck to you! Now that I got the weight solution licked I have to figure out how to reduce friction. I did the axle sanding and polishing, but it didn't do much good. Although the car was not left in the dust, there were definitely faster cars.

mrmath (author)CementTruck2007-01-23

Did you use graphite to lube the wheels? Did you make sure there were no burrs on the tires?

CementTruck (author)mrmath2007-01-24

Yes I did. I de-burred the shaft and inner shoulders of the axel, and I polished and lubbed it with graphite. I also smoothed out the wheel surface, polished the axel hole and smoothed the area where the wheel makes contact with the car body.

mrmath (author)CementTruck2007-01-28

Just got back from my sons race. He took first for his den, and first overall for the pack. It's a small pack. We only had 12 cars total for our pack, so we had to race with, but not against, another pack.

eyeblack42 (author)2007-01-20

when I was in cub scouts I just bored out a compartment filled it with pennies and hot gued it down till i had the right weight plus it was eay to drill out the glue if the car was a little overweight

eyeblack42 (author)2007-01-20

The whole idea of the pinewood derby is to get kids to spend time father-son or mother-son in some cases and if a kids dad has done it all so what

CementTruck (author)2007-01-20

21 Jan - hours after the race Well, my son's car, "The Cosmic Cowabunga", didn't win anything. There were defintely cars there that were not built by kids, and they placed. My son got the "Best Sportsmanship" award. Oh well. We had fun. Maybe next time.

0.775volts (author)2007-01-18

What my dad and I always did was to drill 3/8" holes in the bottom of the car and fill them with solder (or lead wire, if you have it), then to remove weight, you just drill out the solder with smaller bits, by doing this and refilling the voids you leave, you can quickly get very close to the max. weight (4.99oz was the closest we got). also, graphite powder on the nails, makes that thing faster than hell.

LasVegas (author)0.775volts2007-01-19

This is exactly the process my dad and I used for our cars. The three holes were exactly between the front and back axles to balance the weight too. He also designed a test jig to pass the cars through testing height width and wheel spacing.

HamO (author)2007-01-19

Very well done and informative Instructable!!

Sinner3k (author)2007-01-19

I've got to finish up my son's car tonight (race is tomorrow). I've tried to make sure that he did as much of the work as possible, but in areas where a little more skill was required, I had to employ a heavier hand. This is our first year, so I know the last-minute weight add-ons will turn out ugly. -Sinner

dizzydave (author)2007-01-19

my dad and i would hollow out a compartment like you did, and then melt the lead down and poured it into the cavity. We always made it over-weight, and then brought a cordless drill with us to the competition. We would have the car weighed, and then drill out tiny bits of lead until we were right at the limit. We won four years in a row. (two cars each dad alway won the father division too). Graphite on the axles is also key...The location of the weight looks to be about right too...

ranex (author)2007-01-18

when i did pine wood derby with my dad he just drilled alot of holes the diameter of the fishing weights and then just cut the right amount out of the fishing weights (he had some kind of fishing weights that come on a stick that you break up) and then put them into the hole and put some sort of putty over it to seal it then before a race he'd put graphite lube on the axles- my dads a mechanical engineer so he went crazy with the pine wood races he was in charge of the maintenance of the track

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