"tillius" wrote in message
ups.com...
Why would you want to weight the wheels of a Pinewood Derby car? Adding
weight at their periphery will increase the rotational inertial of the
wheels, and they will accelerate more SLOWLY than unweighted wheels.
Just
the opposite of what you want. But I may be missing something...

Because the track we run on has a very long runout at the bottom of the
slope. I was thinking that the rotational inertia would cause the
wheel's RMP's to decay slower on the straight away. That, and moving
the weight from the body to the wheels would decrease the friction
between the wheel axels and the wheels.


I think you could mix lead shot with epoxy and fill each cavity. To balance
you could just subtract from the heavy side.


I may be wrong, but since we've got another year to prepare, I was
thinking we could set up a small test track in the basement and try
different configurations. It would make a great science project for the
kids as well.

BTW, while I'm on the subject, is there a better lube than graphite
powder? We tried teflon and graphite this year and the graphite
definitely outperformed the teflon by a HUGE margin.

Why not buy mechanical pencil leads and then use them as the needles for a
needle bearing setup. I have never checked, but they appear to be nice and
smooth and very straight. That way all you would have to do would be to
ream and polish the inside of the tube to the proper diameter. It wouldn't
last forever, but you would probably eliminate most of your friction, and it
should last long enough to win the race.

Another option would be to get some solid graphite scrap from an EDM shop.
Turn round slugs with an accurately centered hole and use some nice ground
and polished drill rod for the axels.

--

__
Roger Shoaf

Important factors in selecting a mate:
1] Depth of gene pool
2] Position on the food chain.