[Kartbuilding] Chassis Building

[Stephen Burke]

---------- Forwarded message ----------
Date: Wed, 7 Mar 2007 13:41:34 -0500
From: Robert House 
To: Stephen Burke 
Subject: Re: Chassis Building

Thank you very much!

On 3/7/07, Stephen Burke wrote:
>
> 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.