jrz

I have been involved in many forms of racing where interpretation of rules separates the winner from second place. I have our tooling / machine shop currently involved (3 D milling,Balancing,Turning,CMM) how far should I go.

Breathe Later

I appreciate your predicament. I was at the same point with my boys several years ago. What woke me up was my son's statement "Dad, are we going to be able to see the car before the race?" The body was CNC machined, wheels turned true, weight to within .001 g, etc. We placed 2nd. to a car that was built entirely by a 10 yr old! IMHO, help them get the weight right, but let them do most of the work.

robyw1

I know this is off subject but it reminds me of many years ago when we had to make those mousetrap cars for a science project. Well I was 11 at the time and already knew how to weld. I took a rattrap spring, narrowed, welded together and mounted it to a mousetrap board. I even engineered a 2-speed differential to carry it the long distance. Well I won the contest by 150 feet over second place. However the School Principle took my mousetrap car to the science lab and measured the spring thickness with a caliper. I was disqualified, received an F for the project and was removed from honor roll. I had by far the most sophisticated mousetrap car ever and I was booted out. What a CROCK. To this day I’m still bitter about it.

Roby

Ron P

I'm a past Soap Box derby champ and I can tell you that all the CNC work in the world won't help unless you get the weight dead on to the max and contour the leading edge properly to maximize air flow. This doesn't necessarily mean a sharp nose. Depending up speed and length of the track a blunt nose may have a lower drag coefficient.

If you can, study last years winning car.

robyw1

As close to a tear drop shape as you can make it would work best.

Roby

mr_velocity

We've set track records the last 3 years with our cars. Even though I do most of the cutting and polishing, my son understands all the principles of what we are trying to accomplish. The most import thing is where the location of the most mass. It's simple physics. Before adding weight to the car we had the wood block down to 1.2 oz so we were able to add the weight where we wanted it. Much like building a race boat, build it light then put the weight where you want it to make it fast.
We focus most on the weight, then polish the wheels and axles, then make sure that it runs straight, watching each wheel to make sure it tracks perfectly.

Here is last years winning car.

Frequency

jrz,

Both my sons raced pinewood derby. mr_velocity gave you good info. The first car we built was at the specified weight with even weight distribution. I did an engineering study of the body to develop an "ideal" aerodynamic shape. We watched our car lose every time!

After we got smart we placed in the top three at regionals three years running. If you're racing to win you'll want a flat car. Pay attention to the wheels and weight distribution.

Our best running car was under weight at the scales for the regional race. We glued a penny to the top of the car at the right location. Blew everyone away.....

Let your kid do most of the work, while you concentrate on the important "areas"

PhantomChaos

What great fun!!! I did my car with my dad. We made the front a wedge shape and tapered the back in a tear drop.....but I think most of the speed gain was from perfecting the axles and wheels, plus getting as close to the MAX weight possible.

I came in second when all was said and done. I would have come in first except for one mistake. We painted the bottom. After it was all over, there were many scrapes in the paint on the bottom.


DON'T PAINT THE BOTTOM!!! Good Luck!

jrz

This project is actually being done with my 11 year old daughter. She designed the body (F 1 issue of rececar engineering helped), polished the axel's (after slight machine work), picked the colors, and above all seems to have an understanding of everything that happened to the car. She thinks she wants to be a teacher but maybe I can get her to start building headers.

Ron P

Let us know how you make out.

Check out the Soap Box Derby too. It was the highlight of my youth.