One of my most humiliating times in my life happened when I was a Cub at the Pinewood derby. We built our cars during the den meetings with no help from the parents. None of us kids had any idea how to build the cars or make them fast. Even the Den Master (a mom) had no experience.
My car would not even make it down the ramp. :o :(
When my boys joined the scouts, there was no way that I was going to let this happen to them! It took us several attempts to make a good showing. We finally got a second place in the over-all, and the red one recieved Best of Show.
My advice would be to help your son with his car, letting him do as much as possible (with your supervision).
It's great to have a sharp looking car, but in the end it all boils down to who wins the race.
Here are some things I picked up along the way ...
1. Axles and wheels. Chuck up the axles (nails) in a lathe or drill chuck and smooth and polish the area where the hubs will run. Try to not take too much off the diameter of the axle. Be sure to polish the underside of the head, but keep it flat. Once you have the axles smooth, burn in the wheels by sliding them on the axle and spinning the axle in the lathe or drill. Apply graphite to the axle and using some small amount of pressure against the wheel, burnish the hubs to the axel while rotating the wheels. This will actually embed some of the graphite into the hub and really make them slick! You'll know you're finished when you can get a one minute spin of the wheel when you spin it with your finger. Make sure the hub sticks out further than the wheel on the inside so that you won't be rubbing the body other than at the hub. You might also want to round the outer running surface of the wheel to cut down surface contact and runout. We did this using a tight fitting mandrel in the hub and spinning it a lathe. We took a light cut across the tread area to assure roundness, then beveled the outer edges to leave a small contact area. You don't want wide slicks and traction here!
2. Weight. Make sure you are at the weight limit. Gravity and momentum are your engine. Balance is up for debate, but I tried to keep the bulk of the weight to the rear. The balance point we used was about one inch in front of the rear wheel. If the front end is too light, it will jump around a lot on the track, and cause erratic behaviour. We used cast lead bullets pushed into holes drilled on the underside for the weights, and empty holes for fine tuning the balance. (see pics)
3. Assembly. Make sure axles are set in straight, parallel, and tight. Some people glue them in, however this makes last minute wheel work more difficult. Check your car to make sure it tracks straight and does not wobble or show erratic behaviour. You don't want to discover these things at the race!
4. When you are finished, don't play with the car, or allow your son to. The day of the races is most crucial as all the kids will want to handle the car and push it thru the dirt, and see if it will take flight, or crash well. Save that for after the race.
5. Fun! That is what it's all about. But don't think for an instant that it won't be competitive.
Here's some pics of our better cars. The stacks and exhausts on the red car are .177 pellets! The silver one was the fastest.
The stacks and exhausts on the red car are .177 pellets!
Good luck! ;)