Questions on building a go kart

Question

I am wondering how the whole transmission thing works on a go kart. I want it to be automatic but i dont really know how. What should I buy beside the motor to make it automatic? Is it just an automatic clutch I need? Where to buy?

Answer 1

Most home built go karts don't have a transmission at all.  They use a small engine and a centrifugal clutch.  The centrifugal clutch just slips a bit until the engine rpm gets up a bit and then spins and drives a chain which drives the big sprocket located on the drive axle.

Answer 2

There are usually two different kinds od transmission used in a go kart.

First is a Centrifugal Clutch.  This is an older simpler design.   It is a clutch that engages or disengages depending on engine RPM.  Once the clutch is engaged, there is a direct drive with no changes in gear ratio.  These are relatively inexpensive costing about $30.

The other is a torque converter setup.  This is a belt drive system.  The system engages and disengages based on engine RPM like the other setup.  The difference is that the pulleys can change diameter depending on load and can change the final drive ratio.  These are more complicated and expensive.  These cost between $150 and $250.  

Answer 3

I think you're talking about a torque converter.  Go to Northern Tool or go online and look up "Torque converter variator."  That's the kind of continuously-variable transmission you're looking for.

A variator works by pressing the sides of the pulley closer together as speed increases.  On the driveshaft pulley, this makes the pulley present a larger radius for the belt, and the tension forces the belt to ride lower on the axle pulley.  So you start with a low ratio and work up to a high one.  Usually this thing also works as a clutch, so you can idle without any creeping.

Most will have to have a chain rather than connecting directly to the axle; you'll still want to step the drive down off the second pulley.

Google Comet Variator to learn more.