There are five steps to making a simple frame. First of
all the following steps are:
1. Engine And Passenger Layout
2. Drive Train System
3. Steering System
4. Brake System
5. Throttle System
Let's get into it now....
Engine And Passenger Layout
First of all the assumption, whether this go-kart is
made out of wood or is made out of steel is that you have
some sort of layout in mind. Typically the engine is
behind, and the person sits in front of the engine. A good
safe layout is to have a seat protect the passenger from
the engine.
So a structure of some sort is needed to hold the seat
in place. You can use a seat off of a chair, but a more
protective seat is a ½ piece of plywood angled back and
supported. Covering the piece of wood is optional, but it
is more comfortable with basically a piece of heavy cloth
covering a cushion. The cloth is stapled typically into the
board (on the backside).
The structure supporting the seat can be wood, or
steel.
The frame work can be wood or steel as well. If using
wood, use two by fours placed vertically, so that the
strength of the wood is optimized. (I strongly do not like
wood because of the "carriage wheel steering system." It is
hard to control and very unstable. If however you are using
a combo of wood and Ackermann style steering, then I am not
so upset...)
If you are using steel, use a tubing that is at least
.070 wall or thicker. The length of the frame is really
dictated by how big the person is. Have a person sit
comfortably in the leaned back position with a steering
wheel in their hands. That is the person compartment.
Measure this length.
Add the engine drive section and the person compartment
lengths together and that is the length of the gokart. Cut
your frame tubes (or tack tubes together) to this length.
You will need at least two parallel lengths of tubing.
Space the tubes apart the width of the seat you made (20
inches is a good width).
Cut at least four (4) tubes to the 20 inch length. Lay
all the pieces on the floor. Place the 20 inchers at the
following locations: Engine Plate area, seat back section,
seat forward section, front main bumper tube, and rear main
bumper tube. (The bumper tubes can be wider than the frame
by 12 inches (6 inches per side).)
Tack the tubes in place using a welder. If you do not
have a welder, then you can fasten them together using
plates and bolts. (Trust me, buy a $100 welder and save
yourself wood chips and drill bits, busted knuckles and
exasperation!)
What you have put together now is what I term a "flat-go
kart." You will soon find out that flat gokart frames are
weak and require extra stiffening. You may want to put some
struts into the system to bolster the frame design.
Typically what I use is the seat back as reference. This
works very well as an integral frame support, side seat
holder, and engine protector.
2. Drive Train System
The next sequence is to place your engine and drive
train system in place. At the same time put your seat in
position to make sure the seat and engine are not hitting
each other. Be sure to make the seat removable so that you
can actually work on the engine system when needed.
When placing your engine typically a plate is needed to
hold the engine onto the frame. Some designers use tubes
with holes drilled in them for engine placement. I prefer
the plate option, because it gives me greater options as
far as engine choices in the future.
For example on the Phi-Alpha-10 and the Phi-Alpha-9 (go
karts I designed) the engine plate served well in allowing
me to use different engines, whether Briggs and Stratton,
Tecumseh or even Honda. All engine types could be easily
mounted just by drilling the holes in the motor mount
plate.
Most go karts use a slot system to keep the chain tight.
In other words, the engine is mounted not using holes but
slots. That works, but honestly, drilling slots is
intensive works and requires some patience and thought. So
I prefer tensioning the chain, it works better on multiple
fronts. (I can go on and on about engines, drive trains and
such...but we have got to keep moving here...)
A word about drive systems: A live axle system is really
the way to go. All you have to do is mount two bearing
brackets and away you go. On a one wheel drive system, you
need to have special rims that contain bearings, special
drive sprockets that connect to the tires, and the axle if
it gets bent, you have to cut it out of the frame and start
over....so use a live axle...
3. Steering System
So after having mounted the rear axle (with brake disc
(or brake drum) and sprocket), and having placed the engine
and chain system in place, proceed to mounting the front
steering system.
Before you did some measurements of the person sitting
in the comfortable position, make sure you remember the
measurement (relative to the go kart frame) of the steering
wheel. That is the target point for the steering wheel.
The actual position of the front wheels is a bit more
involved though. You will need a scale. Place the scale
first of all under the rear wheels. I typically use a board
placed across the rear frame rails underneath the wheel
area. Have someone sit in the gokart. (Be sure to a have
the front wheels, steering wheel and steering structure on
the go kart when you weigh it)
Now proceed to the front of the go kart and place the
board in the general area that you want the steering
system. Again weigh the go kart.
Take the two weights and add them together. That is the
total weight. The front weight ideally should be with-in 5
to ten pounds of the rear weight. This is called 50/50
weight distribution. The more weight you have on the rear,
the more the go kart will under-steer. Meaning, when you
turn the wheel the go kart will tend to keep going
straight. The more weight you have on the front wheels, the
more the go kart will over steer. Most drivers are used to
under-steer, it is easier to recover from.
But I digress...
Once you have placed the front wheels in place then fix
the front steering system in place there. I typically use
plates, so that I can move the steering system back or
forward. So I weld mating plates on the frame and the
steering system, then bolt them together.
A word on steering systems: You can purchase from the
store steering assemblies that you tack onto tubes. These
work real well, with one acception, they typically come in
.750 inch diameter shafts, where most high speed bearings
use .625 diameter shafts. The shafts may need replacement.
Look for .625 shafts... Additionally, there are ways to
make the steering more tractable and more user friendly,
these involve geometric relationships such as camber,
caster, Ackerman and so forth.
4. Brake System
Now that you have the steering system in position, you
can button up the hole project by covering the bottom of
the go kart. Sheet metal (like furnace guys use) is the
best option. Buy some tech screws (the ones with drills on
their ends) and zip through the sheet metal into the
tubing. Once you have that in place, you don't have to
worry about your feet hitting the ground!
Now it is time to place the brake system. You notice we
placed the brakes in place on the live axle, now the actual
braking mechanism needs to be mounted to the frame work.
You can either weld it, or bolt it to the frame. I prefer
bolting, it is more forgiving and easier to repair.
A word on brake float: The brake system should float.
What that means is that the disc either needs to be mounted
freely on the shaft, or the brake caliper needs to float.
If the neither is floating, you will get a binding, and
prematurely worn out brakes, and fast! So keep that in
mind. Something has to float, the disc or the brake caliper
(1 of the 5!)
For your brakes it is important to have the brake off
while driving. A good spring is needed to keep the pedal
back when the brake is not being used.
5. Throttle System
This seems like the most inane or over looked system on
the go kart. It shouldn't be though. A good connection
between the throttle and the pedal is needed and a good
range of motion is needed too. Most pedals give you
different holes to work with, allowing your several options
in throttle actuation.
Again, like the brake, a good spring is needed. Do not
use a spring on the carburetor, but use the spring in the
pedal, or pedal system.
A word about throttles: most engines come with
governors. It is a good idea to use the governor system,
because it helps keep the engine at even speeds and from
over revving.