Pinewood Derby Car Weight Compartment


Introduction: Pinewood Derby Car Weight Compartment

About: "Better to have it and not need it than to need it and not have it."

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

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

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

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

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.




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    55 Discussions

    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.

    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.

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


    4 years ago

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

    1 reply

    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?

    3 replies

    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.

    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.

    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.

    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.

    1 reply

    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.

    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.

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

    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.

    1 reply

    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.

    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.