[Kartbuilding] GO-kaRt

[Stephen Burke]

Hi,

There are a few options for the drive for a kart. The most simplest is a 
sprocket on the engine, a sprocket on the rear axle and a chain connecting 
the two. This is called Direct-Drive. The engine is directly linked to the 
rear axle. Therefore to stop the kart, one must stop the engine also.

To make the above Direct-Drive transmission far superior, one can use a 
"Centerfugal Clutch". This is an automatic clutch, which dis-engages the 
drive when the engine slows to idle, allowing the kart to be stationary 
while the engine remains on running. These types of clutches are found on 
chainsaws. An example photo of a centerfugal clutch can be found here:
http://www.kartbuilding.net/gallery/v/Kart_Clearance_and_Memories/DSC01103.JPG.html
http://www.kartbuilding.net/gallery/v/Kart_Clearance_and_Memories/DSC01111.JPG.html
http://www.kartbuilding.net/gallery/v/Kart_Clearance_and_Memories/DSC01162.JPG.html

The bell housing part of the clutch has a sprocket already attached, and 
typically has 12 teeth. The inside part of the centerfugal clutch is 
bolted to the engine, and also has a keyway to make sure the center piece 
rotates with the engine.

Choosing Sprockets:
When choosing sprockets you need to take the following things into 
consideration:
Size of Engine: 70cc
Size of Wheels: ?? (The smaller = the slower the kart goes, but the more 
torque/power is produced)
Weight of the Kart and Driver: ??

A general estimate is to have a ratio of 5:1, so the rear axle will spin 5 
times slower than the engine.
Therefore if you put a 12toothed sprocket on the engine, you would need a 
60toothed sprocket for the rear axle.
As for types of sprockets, motorbike sprockets and chains are best. Chains 
off bycycles are extremely light and come off very frequently.
It might be possible to get old sprockets from a motorbike repair shop, 
and these can be used on a kart. As it is difficult to choose an exact 
drive ratio (size of sprockets), it is possible to cut the rear sprocket 
and reweld it to facilitate removal and changing of sprockets. See:
http://www.kartbuilding.net/gallery/v/Kart_Clearance_and_Memories/DSC01027.JPG.html
http://www.kartbuilding.net/gallery/v/Kart_Clearance_and_Memories/DSC01028.JPG.html
http://www.kartbuilding.net/gallery/v/Kart_Clearance_and_Memories/DSC01028.JPG.html
http://www.kartbuilding.net/gallery/v/Kart_Clearance_and_Memories/DSC01026.JPG.html

But as a rough estimate a ratio of 5:1 should work ok for the 70cc engine 
and a general purpose kart.

Lastly, I definately suggest you look into getting and using a 
"centrifugal clutch" as it gives much more flexibility when starting and 
stoping the kart.

If you have any further questions etc. just email them on.

Best of Luck,
-steve


On Sat, 28 Apr 2007, parag jafar wrote:

> hey,
> i m from pakistan. we some friends r making a go-kart. we've got a 70cc
> 4-stroke bike engine. i m doing the transmission portion.
> would kindly tell me about sprockets? we've got 3in dia space for mounting
> sprocket on engine. how many teeth should be there in motor sprocket and in
> axle sprocket? and what is the criteria for choosing teeth no.?
>
> parag jafar
>
>