[Kartbuilding] Chassis Building

[Stephen Burke]

Hi Robert,

Building a kart that runs on hydrogen sounds like a very interesting and 
challengine project! Im sure you will have lots more concerns once you 
have the chassis built!
Anyways - to answer your query regarding chassis design:
Chassis without suspension need to be able to flex a certain amount. If 
you have suspension planned for your kart - then maybe it might be better 
to have a rigid chassis.

On all karts - there is a steering setup/geometry to be followed. This 
is especially so where there is a "Live Rear Axle" where both rear 
wheels spin together. The correct setup involves the Ackerman, Castor and 
Camber angles. With these angles and if 
there is no suspension, the chassis NEEDS to be able to flex - albeit a 
small amount, for correct and responsive steering. As a result - depending 
on the total weight of the kart - a chassis can be designed using a light 
a tubing as possible. Some people also "braze" the chassis members 
together (instead of welding) as it provides for better torsion and will 
not result in cracking around welds (which can happen if the chassis 
flexes a lot).

There are a few types of chassis design - 1. The ladder type (which I use 
in my kart plans) 2. The box type and 3. The space type. The ladder type 
takes the form of a ladder and can twist/flex easily. The box and space 
types are NOT flat - but have vertical members also. This makes them rigid 
and solid - making them very suitable for karts with suspension.

So - with a "Live Rear Axle" and "No Suspension" then your chassis needs 
to be able to flex and twist in order to corner correctly. A combination 
of the correct Steering Geometry AND a Chassis which can flex is required. 
The steering geometry is what forces the chassis to flex, in particular 
the camber and castor angles.
When turing left, the inside rear wheel *MUST* slip or spin, as the 
outside wheel must go faster. If the inside wheel does not slip - the kart 
will propel in a straight line even if the front wheels are pointing to 
the left! To help the inside rear wheel lift off the ground - allowing the 
kart to corner effectively, the camber angle is used. Normally the camber 
angle in cars etc. is to keep the tyre FLAT on the ground and reduce 
excessive tyre wear. On a kart - it plays a further role of raising the 
chassis on the front (called a jacking effect). When turning left - it 
raises the front of the chassis - and this causes the chassis to twist 
about its corners. Therefore (if the weight balance and steering is 
correct) the inside rear wheel will ever-so-slightly lift off the ground. 
Ideally the rear wheel will not come off the ground - but the weight on 
the chassis will be transferred to the other wheels allowing it to spin 
when it needs to.

I cant offer any more of a description. I suggest you make a small scale 
model and test it out. Note: it is possible to adjust the camber and 
castor angles AFTER the chassis is made - so all is not lost if its not 
fully correct from the beginning. Fixing the angles would involve grinding 
off and re-welding the King-Pins (pivot pieces where the front stub axles 
mount onto the chassis).

I hope this helps you a little robert. Im sure there are books out there 
on the subject. I have included 2 photographed images out of a karting 
book called: "The NatSKA guide to karts and karting / authors: Brian Lord, 
Colin Fenwick and Ian Paddy" Castrol Ltd., 1984, 1984, 2nd ed.
The links are:
http://www.kartbuilding.net/chassis_design_book_1.jpg
http://www.kartbuilding.net/chassis_design_book_2.jpg
I have also attached them to this email.

I hope you find this information useful and that you manage to design and 
fabricate a good chassis for your promising hydrogen kart.

Best of Luck,
-Steve


On Wed, 7 Mar 2007, Robert House wrote:

> Hello,
>  My name is Robert House and I am a mechanical engineering student
> at Lawrence Technological University in Southfield, Michigan.  For my senior
> project I am part of a team trying to build a kart that runs on hydrogen.
> Next week we are building our first mock up of the chassis. In doing
> research for this build I found your page on chassis building.  I wanted to
> thank you for posting your paragraph about allowing some flex in the
> frame to enhance cornering; this was an element that our design was
> lacking.  If you have more insight about frame design and how it can improve
> handling performance I would be quite interested to hear from you.  Thank
> you again for your help.  Take care.
>
>
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