Chassis
At the fear of boring to tears the non builders and
the builders, the hobby is a multifaceted experience that can
be delved as deeply as you get an urge to, or just be kept to
the lets buy plastic track and set it up when and where we can
and play till we drop. None of which is wrong or right. Many
start the plastic track way and then let it go
from there or not. The old timers like myself had to start building
our own if we wanted something that appealed to us. I was going
to Community college in 1963 and found a small store in a small
shopping center that was starting to carry slot car parts and
was building small routed track layout in a small alcove shop
right across the hall. This guy had nothing but parts for cars,
some wheels, tires, axles, bearings and some bodies in clear vacuum
form hanging on the wall. He had some music wire, and brass tubing
and some pictures of cars from the LA area he came from. (We were
basically out in the sticks) I used Ho gauge train motors I swiped
out of locos I had in storage, mostly Pittmans or Lindsay's. That
first Porsche 904 body in 1/24th scale did me in, I had to have
it. A couple of the locals were attempting to get some cars built
and they were pretty crude as most knew nothing about soldering.
So I said I had done some were I had worked and would help out.
In a couple weeks we had 6 guys with cars that ran pretty good
and the racing started from there in the area. I learned what
I needed for a car and helped others learn how to cut the metal,
clean it and how to solder it together. From there it took off
and I have been doing it that way for 39 years. Hard to stop now
:) But my background was as a tool and die maker apprentice before
the Army got me. Depends on your skills and ability to use them
or learn to use them. It
can be just learning to cut plastic in a straight line and how
to glue it all together or soldering hunks of metal together.
Many skills are needed you just have to decide how far you want
to jump in. Some build great chassis and can't paint or detail
a body worth a dang. Others paint and detail bodies that you would
not want to put on the track, takes all kinds and most are happy
with what they like to do. After a while, the competition part
if it began to creep in, as more and more drivers became competitive.
Winning became too important for a while till I decided that that
was not fun anymore. (15 years later) And many now, like us old
Pharts just like to tool around and threaten to beat each others
creations to smithereens in a match race. Ain't gonna happen.
Still having fun and making new friends almost every
day online or in person, like at the convention in Las Vegas in
April.Join in, the waters warm and fun. It's only as deep as you
want it to be.
SIot Car Chassis
by Larry Shepard
(Notes by Rockland F. Russo)
For the purpose of this article certain details of
chassis construction are assumed to be obvious.
1.1 The chassis must be flat and true. . . this cannot be emphasized
enough!
2.] The rear wheels and axles must be aligned to track straight
and true. Any untrue tracking or twisting, will cause problems
with the car swinging from side to side under acceleration or
behaving erratically in corners.
3.] Front wheels should be just slightly, evenly spaced off the
track surface so as to not cause drag on the straights.
4.] The front wheels should be free to spin if body weight transference
causes them to touch in the corners.
Most of the art of slot car handling and tuning is
trial and error. This article will attempt to explain some of
the theory and reasoning covering the basics of tuning and setting
up the cars. These assume we are beginning with an excessively
rigid chassis/body package. Such a condition will limit a car's
ability to flex during cornering. A full-size racing automobile
relies upon an infinitely adjustable chassis that can be changed
for differing or changing track conditions, types and surfaces.
This is accomplished with changes to suspension, shocks, springs,
torsion bars and tire pressures, etc. These same changes are difficult
and, depending on the starting point, may be impossible to duplicate
on a smaller scale such as applies to slot cars.
(rfr - NOTE: Actually, if you are serious, you can
do a lot of subtle tuning from track to track based on the stiffness
of the main rail section, literally changing the diameter of the
rails on a wire frame, along with the hardness of the tires AND
the dimensions of the rear tread. Gary Gerding, the year he was
national champ, thought it was particularly important to dial
in the track in such a way as to use a different width/height/shortness
tire ON EACH LANE.)
However, these same basic adjustments which apply to
full-size cars are also applicable to slot cars - there are just
different methods of achieving these changes and settings. Cornering
forces on 1/32nd scale tracks are greater in comparison to the
big cars and the more movement you can allow a slot car body/chassis
to have, the more it can be adapted to varying conditions. A laser-cut
or brass/wire chassis has built-in provisions in the design for
adjusting most types of chassis movement to allow for the various
forces at work on a slot car in the corners. One major theory
relating to slot car handling is that the cars are really tripods
based upon the placement of the rear drive axle and the guide
shoe pin. This theory further states that the front wheels assist
only in an outrigger fashion during hard cornering. The longer
the effective distance between the centerline of the rear axle
to the pivot point of the guide pin can be, the smoother the car
will handle.
(rfr - NOTE: This concept is a ‘sorta true'. There
are two problems to consider here -
1 .]The longer the car, the SLOWER it is in the corners. It is
slower because the rear swings out and covers a longer ARC through
the corner than the guide does in the Slot. The longer the car,
the longer the arc, the more time in the corner, the slower the
lap time. This defines why NASCARS are usually slower than GTPs
on a given track. Ironically, if built to correct scale, most
modern Fls and Sports cars would have 4.5" wheelbases in
1/24th scale, but everyone runs them at 4" for this reason.
2.]The second problem is FEEL. When I build for someone, I like
to watch them drive. John Cukras doesn't count - he can drive
anything! One old pro I have built a lot of cars for likes hard
nervous cars, because they FEEL fast. However, he cannot drive
that kind of car. I have to be a tyrant with him and insist on
the softer car. This is the car he can dial in and run perfect
heats with. On the other hand, another pro I build for NEEDS a
short nervous car. He cannot seem to stay focussed if the car
is easy. And loses all the heats. If I give him the short nervous
car, he concentrates beautifully and for 20 minutes will run with
anyone. But he usually loses at the end.
Due to its momentum, a slot car's tendency is to go
straight upon entering a corner. If the chassis is too stiff,
it will react stiffly and resist the change in direction. If you
can soften the initial pressure of the wall of the slot against
to the guide shoe blade during cornering and allow the car to
react in a ‘softer' manner to the change in direction, it
can be kept in place in the slot more efficiently. That is why
certain chassis have what some drivers call rear steering. The
theory of three point chassis construction states that the guide
pin is attached to the rear wheels by a center section that should
have some flex in relation to the rest of the chassis and allow
a slight springing away from the wall of the slot by the guide
blade. The rest of the chassis and body are then allowed to swing
out slightly and are pulled back into line in a shock absorber
type movement. Within that tripod center section there can also
be a built- in torsion bar effect. Such a device, when successful,
resists the twisting of the chassis in the corner, but also allows
absorption of some of the cornering forces. Up until now this
article has dealt with the placement of the guide shoe, the rear
end, the center section and the rest of the chassis. The body,
whether injected or vacuum-formed, must be dealt with separately.
If rigidly mounted to the chassis, any body will restrict the
movements of the chassis and hinder them. Most builders want to
float the body to some small extent, either loosening the body
mount screws a small amount, or building body mounts that float
separately from the chassis movements and help isolate the body
from the frame as much as possible and still keep it on the car.
Bat pan floppies are hinged to allow some weight transference
(lifting) of the body from one side of the chassis to the other
in a corner. If weight is transferred to the outside wheel, it
will give more traction on the wheel and the car is able to resist
excessive sliding to the outside of the corner. At the front,
this same weight transference puts some weight on the outside
front wheel to cause it to act as an outrigger and so prevent
the tipping out of the slot of the guide shoe. Weight transfer
is as important to the handling of a slot car as it is to a full-size
car for three reasons:
1.]at rest
2.]while in motion
3.]in a change of direction either fore and aft or side to side.
Most slot cars have too much weight on their rear wheels because
of construction limitations. (inline or sidewinder drives) The
best place for weight or the transfer of weight under braking
is to the front onto the guide shoe, pickup brushes and (minimally)
to the outside drive wheels. The more weight on the shoe in cornering,
the harder it is for the guide to come out of the slot.
A ‘plumber' type chassis allows the transfer of
weight to the front under braking and, with appropriate hinging,
also allows the rear of the chassis/body to lift slightly and
thereby cause even more weight to be transferred to the front.
This keeps the guide shoe planted in the slot and provides a better
power pick-up for braking. Some chassis are designed with built-
in sliding motion of the body and chassis, to move for and aft
in relation to the center section, guide and rear wheels. This
has the effect, under braking, of transferring weight to the front
and then, under acceleration, the weight can move back and help
with traction to get up the car up to speed quicker. This movement
should be minimal and only experimentation will determine what
is correct for any given car/chassis on a given track. Most of
the preceding particulars apply to scratch or custom-built cars.
But the principles apply to the home set car as well. Bent or
twisted injected frames are difficult to true and make run correctly.
A miscast frame without true axle alignment can hurt as well.
Freeing up the body as much as possible will help and maybe some
small rubber washers between the body and the chassis mounts can
isolate the vibrations that upset the cars handling. Use of traction
magnets masks many of these problems, but does not eliminate them.
A magnet car will run much better when the basic principles are
applied to them as well.
Pete Sardella -
There are a few basic principles that we must acknowledge before
building a frame:
1) The 3 Point Principle;
2) The Weight of a Frame;
3) The Frequency and Cross-flex of a Frame.
The 3 Point (Triangle) Principle
Frames work on a three-point principal. The center of the guide
pivot and the rear tires make up the ‘triangle'. The smaller
the angle created at the guide pivot the deeper your car will
go into a turn; the angle at the guide pivot is inversely related
to the distance between the guide pivot and the rear axle -- the
angle gets smaller as the distance increases. The ‘increased'
distance enables your car, aside from going deeper into a turn,
to be less responsive to your trigger, which is a welcomed trait
on a small tight track. The ‘triangle' principle works best
when the front wheels are able to ‘float' on the track surface.
The ‘float' effect can be attained by incorporating an iso-fulcrum
(hinged front axle tube), or an oversized axle hole in the front
wheels, or an oversized axle tube.
The Weight of a Frame
The next issue in building a frame is its weight. Here we must
look at the variables that determine the weight of a car. The
variables are weight of body, weight and strength of motor, track
size and tightness of turns, track surface texture and finally
the material being used to make the frame.
Body weight: The heavier the body the heavier the frame. The frame
must counter the tilt factor of the body; as you increase the
body weight you will need to also increase the frame weight.
Motor weight and strength: The heavier the motor the heavier the
frame. Heavier motors will need more weight up front in order
to maintain the proper front to back balance. Keeping the weight
of the motor the same (same setup) but installing a more powerful
armature will necessitate extra weight to be added to the frame.
Track size and turn tightness: The larger the track the lighter
the car. The increased running surface of a large track allows
the body to generate and transfer more downforce to the frame;
therefore your frame can be lighter. With the limited downforce
attainable on a short tight track a heavier frame is needed. Smooth
track surfaces offer more ‘bite' therefore a lighter frame
can be used; bumpy track surfaces require a heavier frame to obtain
better traction.
Materials: The stronger the frame material the lighter the frame.
Brass frames are heavier than steel frames since brass is a softer
yet heavier material than steel. A thicker brass plate is needed
in order to attain the strength of steel. The ‘new' frame
material, 6160 aluminum, used in wing car frames, is lighter and
as strong as steel. It has become the modern lightweight frame
material.
The Frequency and Cross-flex of a Frame:
A slot car frame is like a rolling tuning fork. The vibrations
induced by the motor (starting, topping out and braking), out
of round tires, bad bearings, and bumpy track surfaces, etc. can
send the frame into chaos causing you to de-slot. To control these
unwanted vibrations a frame must be built very stiff in the front
to back direction; adding a reinforcing rail atop the center rail
or pan generally does the trick. A frame should not flex when
downward pressure is applied between its guide flag and rear end!
The stiffness raises the frequency point of a frame; the terminal
velocity of a frame increases as the stiffness increases. Note:
this does not apply to one-piece wing frames.
Cross-flex is the side-to-side flex of the rear end while keeping
the front end stationary. The tightness of the turns on a track
and the power of the motor determine the amount of cross-flex.
Too much cross-flex will cause your car not to straighten out
fast enough exiting a turn in order to accelerate up the straightaway.
Too little cross-flex will cause your car to chatter and de-slot
through the turns. It is best to start out with too much cross-flex
and gradually stiffen the main rails by soldering piano wire on
top of them. Start from the front of the rail and work your way
back with longer pieces until the desired amount of flex is attained.
This method is preferred to adding lead.
"Ok but then what is this WOMP I see referred
to?"
In the late 1960's, an American slot car company by
the name of "Riggen" (from its founder Al Riggen) devised
and built a 1/32 scale car with a one-piece in-line stamped brass
chassis. After they sold to Gayla Industries in 1972, the tooling
for this chassis was used to produce aluminum cheaper versions
(brass is a more expensive metal) using the seemingly inexhaustible
stock of leftover Mabuchi FT16 end bell-drive motors from the
1960's "heydays". The Gayla bailed out of the slot stuff
and by 1977, REH inherited most of it, while Parma got the chassis
tooling. From this, they expanded the tool and created a new,
low-cost RTR series called poetically "Womp-Womp" (don't
even ask why). The Womps as they are familiarly known, are as
basic as it gets, but as long as the tires are fresh, they do
work decently. Bodies ranged from Porsche 911 in flared-fender
varieties to the wildest and ugliest beast that the moldmakers-on-drugs
of the late 1970's to the mid 1990's could devise. Parma sold
thousands of them worldwide, and they are still in their catalogues
today. The Parma Womps can without doubt be called the anti-scale"
slot car, as in "anti-Christ".
Regards,
Philippe
Well, I think we're on our way toward the FAQ! just
copy and paste these responses. If possible a photo of the subject
matter would help greatly. (now I know what a WOMP is, but wouldn't
know it if it bit me in the butt!
Thanks for the info all...
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