Larry Geddes: 2002 Marconi Proxy Race Entry
A while back, Larry Geddes sent me these pictures of his 2002 Marconi Proxy Race entry. Wow, these modern
flexing chassis are getting quite complex! Thanks for sending this along, Larry.
Larry Geddes writes:
"Attached are a couple pictures that may interest you. The car is my entry in the 2002 Marconi Proxy race.
It is 1/32 scale, and was built for one of the non traction magnet classes.
It is based upon the car I built for the 2001 Marconi, using the same central spine chassis design.
I saw some cars of Russell Sheldon's that used this "flexi-board" design and thought I would give it a try.
The 2001 car worked so well I stuck with the same basic design for this car the following year.
The explanation for this design (as far as I can tell anyway) is to allow the rear half of the chassis
to twist easily enough to let the inboard tire lose some traction and the outboard tire to gain some
traction. Since there is no differential in the typical slot car, getting the natural weight shift to
alter the traction is the only way a live axle can negotaite turns. If both tires maintain a high degree
of traction, the car will tend to roll in a straight line. Building in some flex to encourage the outer
tire to do most of the work and the inner tire to slip is beneficial, I feel.
I think this type of chassis works best when the rear chassis half is kept fairly light and the front half
is kept fairly heavy (and low). I also think that the car should be set up with all 4 tires supporting weight,
with just a few grams on the guide. If the two "torsion springs" that tie the front and rear together are
made flexible enough, the front and rear halves begin to behave as two separate bodies, each with
its own center of gravity. I believe the centrifugal force the car undergoes will more easily affect
the (higher) CG of the rear half while leaving the (lower) CG of the front half relatively stable.
This chassis uses 1/32 piano wire for these springs, with a free length of 1.200". The 2001 car had
even "softer" springs, 1/32 diameter x 1.500" long.
This car weighed in at about 101 grams, while the 2001 car was a slightly heftier 116 grams.
The rear tires carried about 55-60 percent of the total weight in both cases.
Scratchbuilding was (and still is) the best part of slot racing for me. Scratchbuilding is more
than just assembly, since it not only involves soldering, but also actually cutting the parts
themselves from raw metals. Today's laser-cut or wire EDM chassis may require soldering, but
all the parts are already made, so it is nothing more than just assembly with solder instead
of nuts and bolts. The assembled chassis is just like everyone else's, just as a bolt-together chassis would be.
Building your own chassis delivers a great deal of satisfaction, and lets you try out any design
you can think of. Each chassis is completely unique and building them provides an outlet for
your creative urges."
Regards ----- Larry G
