Jim wrote:
My son competed in his second Pinewood Derby a couple of weeks ago.
Last year he finished dead last. This year he finished 3rd from dead
last. I would like to ask for some diagnostic help from more
experienced Pinewood Derby racers.

First my credentials: My son's cars won first place at the pack level
3 years in a row. One of those years he raced against more than 90
other cars in a double elimination tournament such as you describe.
The other two years he raced against probably 40 cars. Perhaps
coincidentally, I have an engineering degree.

Assuming your weight is close to the maximum 5 ounces, I think only one
thing can cause a car to run that slow - friction at the wheels and
axles.

Forget about aerodynamics. The car is going less than 12 miles per
hour and aerodynamics plays a small part at that speed. It may make a
difference between first and second, but not between first and last.


Forget about fine-tuning weight placement. It may get to be an issue
among the fastest 2 or 3 cars, but not among the slowest. You don't
want the front end to be so light that it leaves the ground at the
track joints. You don't want it so heavy that the car can't steer
itself easily. Other than those issues, I don't think it's very
important.

Spend your time and energy on wheels and axles. Look closely at the
nail that comes in your kit. It has a spur under the head that wants
to dig into the plastic wheel and stop it from turning. The part of
the axle that the wheel rides on needs to be soooo smooth it shines
like a mirror. There are lots of ways to get there. I chucked the
axle up in a cordless drill and had my boy run the drill while I
applied:
1. A small file to the offending spurs under the head.
2. Narrow strips of sandpaper starting with 300 grit and progressing
to 800 grit.
3. Jeweler's rouge applied on a felt wheel spun by a Dremel Tool while
the axle was spinning in the drill.
We probably spent 30 minutes on each axle. If the axle is a little
smaller in diameter where the wheel runs on it, that's a good thing.

Don''t ignore the wheels. The running surface of the wheel needs to be
as smooth as a baby's bottom. Chuck the wheel hub in a drill and sand,
then polish the plastic. It will take a high gloss if you polish it.
Find a way to polish the inside of the hub where it runs on the axle.
I found that the shank of a Dremel bit is just the right size, but
DON'T spin the bit in the hub, you'll get it out of round. Instead,
put a little grinding compound or jeweler's rouge on the shank and spin
the wheel on the shank. I used an air blower to spin the wheel at high
speed. Wash the wheel with lots of hot water to be sure you get all
the abrasives out.

Adjust the tracking by bending axles as needed so that the car rolls
straight when pushed across the floor. You don't want the car to scrub
of speed by hugging the center rail all the way down the track.

Lube the axles with graphite lubricant.

If you do all those things, I can't promise a win, but you shouldn't be
embarassed.

DonkeyHody
"Even an old blind hog finds an acorn every now and then."