Saturday, January 23, 2010

Pinewood Derby 2010


3rd Time's a Charm

Our first Cub Scout Pinewood Derby (PD) was when my eldest son (ES) was a Tiger Cub in 2008 and he wanted to make a humvee.

Last year, ES was a Wolf Cub for the 2009 derby and wanted to make a bullet train.

This year is the first time we've made two cars. ES is a Bear Cub, and although his younger brother (YB) isn't old enough yet, the pack is having a "sibling" race category.

Step 1. Concept

YB wanted to make an old-fashioned train locomotive, and I said sure. That's easy enough.

ES originally wanted to make a Halo Warthog, and I'm thankful for a friend who shared his Warthog template, but I decided it was too complicated, too detailed, and would require too much effort on my part.

Call me lazy if you will, but I try to be realistic about making PD cars. No, the boys couldn't make the cars all on their own. They certainly need help and supervision. However, I do try to have them participate in each stage, hold the tools themselves, and let them do whatever parts they can. So I had the boys choose some simpler designs that each boy could help cut out and sand.

ES and I decided to incorporate lessons we've learned from the previous two derbies and try to make a race car with a chance of winning. That means low-profile (in other words low-cross section to the wind), maximum weight allowed (5.0 ounces), and polished axles.

Step 2. Template / Design. I made a template on paper by tracing the outline of the top, side, and front of the block of wood onto a sheet of paper. Then I made several copies of the blank template for them to work with and had them draw what they want their car to look like.

Step 3. Draw the cut-lines onto the block of wood. Once the boys had drawn for me what they wanted, I drew onto their blocks of wood which parts we would cut off.

Step 4. Off to the wood shop. We have an awesome friend from church who very graciously allowed us to come over one Saturday and use the tools in his professional wood shop. Man, having the right tools makes things like pinewood derby cars a breeze!

Showing ES how to use the band-saw.

YB learns how to adjust the height of the table saw blade.

ES sanding his race car.

All done at the wood shop.


Step 5. Painting phase one. I had each of the boys spray and initial coat of the color they chose for their cars.

ES lays down the first coat of orange spray paint.

Me helping YB put the first coat of black on his train.

Step 6. Installing the weights. In previous years, our cars have ended up looking sorta odd with quarters hot-glued to the outside to get the weight up to 5.0 ounces. That was in addition to having the standard screw-on weights screwed to the bottom of the car.

Aside 1. Tool Time. As I mentioned earlier, this was our third PD, and with YB joining Tiger Cubs next year we're going to have several more PDs in the future. I finally gave-in and bought a Dremel tool this year, and WOW what a difference it makes. If you foresee building PD cars in your future, then I highly recommend purchasing a Dremel tool.

Aside 2. Learning Process. At our first PD, the humvee didn't do so well (came in dead last as a matter of fact), and I thought it was due to aerodynamics. At our second PD, we made a very aero-dynamic bullet train, but it still didn't do well. This time around, we did a bit more research first. The two most important things I learned this year was that cross-section (not necessarily shape) and polished axles are key to a fast PD car. I found the following two videos on YouTube especially useful:

Wind Resistance


Polishing Axles


Back to our preparations...


Based on the first video above, we decided to make the car as low-profile as possible. We basically cut the wood block in half horizontally. Then we did a preliminary weigh-in and discovered we needed to add a LOT of weight to our low-profile car to get it up to the desired 5.0 ounce maximum. The half-block of wood plus the four axles and wheels came to a whopping 2.2 ounces.

It took BOTH the full screw-on weight AND the full tungsten puddy weight to get the car up to 5.0 ounces.

We used our new Dremel tool to carve out a space underneath the car for the weights. This way the weights are recessed under the car and not adding to the cross-section of wind-resistance like in the first video above.

ES using the Dremel tool with a router bit and guide.

Recessed Weights

One of the other cub scout dad's told me that putting weight toward the rear of the car helps make the car faster. You DON'T want it so far aft of the rear axle that it will cause the nose to tilt up, so put it somewhere close to or above the rear axle. So we used the Dremel tool to dig out a hole on the top back side above the rear axle, and filled the hole with a tungsten puddy weight.

Hole for the puddy weight

They sell these at the hobby shop along with all the other PD kits, decals, weights, etc.

Based on some reading and watching the second video above, we also polished the axles. We put each axle in the Dremel tool to spin the axle like a lathe, then held strips of sand-paper up to each spinning axle. First we used some 150 to get the main burs and rough spots out. Then we used 320 to polish it.

ES polishing an axle in the Dremel tool.

A word of caution: I heard more than one horror-story from other dad's saying they tried polishing the axles NOT by spinning the axle (i.e. not in a Dremel tool or drill press). The result is they sanded the axle out-of-round leaving flat spots and bumps and having disastrous effects on their race times. They would have been better off not even trying to polish the axles.

Race Day

When we weighed-in, we discovered cutting out the wood to recess the weights took 0.2 ounces off our weight, so we glued two dimes on top to bring the weight back up to 5.0 ounces. Then, ES decided he wanted to decorate his car some more. The car was originally orange with yellow polka dots. He used Sharpie markers to draw stripes on his car.

This is technique actually worked pretty well, and I would recommend others consider spray painting a base color on and then have your child do the rest of the decoration with Sharpie markers.

Then he wrote this on the bottom.

Last but not least, we used dry graphite lubricant on the axles before turning the car in for registration. Note: We used the same dry graphite lubricant last year and didn't do well in the race, so the lubricant in and of itself doesn't help - the cross section and polishing of the axles are key.

The Results?

Well, I sure hope you don't think I wrote all that up above just to tell you that we lost. On the contrary, we were very pleased with the results.


This morning, ES's car took 1st place in every race, and his car won second place overall amongst the Bear Dens - missing first place by 0.008 seconds! That sure felt good. We went back for the overall pack championship in the afternoon, and his car came in 4th place out of 90 cars.

It was good to see ES smiling at the end of this year's race.

Here were some of the cool designs in our pack this year:





My two favorites were:
Beaver on a Log

Crack-a-Lackin'

When we got home, the boys made a bee-line to the playground to have their own sibling-finale.


Well, if you've actually read this far, thank you for sticking with me to the end. I hope the pointers here will help others looking for ideas or gouge on how to make a winning PD car.

Update...


6 comments:

Tabor said...

These traditions are always such good memories for kids when they have grown. Glad you did so well as you deserved it!

Hilary said...

Great job. Congrats to ES.. and his Dad. :)

divrchk said...
This comment has been removed by a blog administrator.
Sagey said...

ES did a fantastic job designing, creating and decorating his car! I am so proud of the hard work he put into it and so pleased with how pleased with himself he is! With all you are teaching him he will be making his own without any supervision soon! :-)

SamanthaSimons said...

This was a fun post to read, especially since it was our first year experiencing PD with J.

Congrats...he did an excellent job and that is one smoothing looking car...love the stripes. You guys really went a long way to getting them involved and enlisting top notch advisement!

Erin Howarth said...

I really like your train design. It's the best I've seen. I'm going to give it a try, but I don't have the tools you had. I'm not sure how I will pull it off, but I sure appreciate your photos.