Go kart pulley drive help

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  #1  
Old 06-15-07, 07:35 AM
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Go kart pulley drive help

Hey guys,
I am currently undergoing a home go kart project and am almost complete but unfortunately i have hit a brick wall in relation to the particular drive i have chosen. Im running a 5hp 192cc engine with a pully centrifugal clutch as the driver pulley that i i have made so it can slide on the engine shaft and a three sized stepped pulleys as the driven. My problem is that i want to make the belt change to the three different sized pulleys. I have successfully been able to change from first (the largest pulley) to third (the smallest pulley) by using a third pulley with a housing to pull the belt to each pulley, the only problem that i cant get my head around is that i cant change from third to first (it seems as though the belt wants to change but there is not enough grip to make the full change from third to second and second to first) Ive tried with more slack and more tension but it doesnt seem to work, ive even tried a couple of different belts
The three stepped pulleys are attached to the axel of the kart, and are fuzed together, (much like the pulleys you find in a drill press). The belt shifter i made can move either up or down to change pulleys, though i have the problem changing from the third pulley back to the first. I can send you guys some pictures if yous want to make it easier to understand!

If there is a way of doing this can anybody help me out? or tell me a way of doin this, any suggestion would be much appreciated!!
Thankyou
 
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  #2  
Old 06-16-07, 11:42 AM
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If I'm understanding the problem - you have three sizes of pulleys on the driven side of things to get three different speeds and you have been able to come with a belt shifter to move the belt from one to the other. But when you go to the smallest pulley the belt doesn't have enough tension to drive the cart.

If this is the case, you need to put a spring loaded tensioner on the belt. Then you would have approximately the same belt tension when you are on any of the three pulleys.

There are probably some store bought jobs that would work or you could fabricate it yourself with an idler pulley on an arm and attach the spring to the arm to apply the tension to the belt.

Hope this helps,

Bob
 
  #3  
Old 06-18-07, 06:23 AM
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Hey bob,
Thanx for the reply. The problem doesnt lie with engaging the third smallest pulley! I made a pulley with a housing which will tighten the belt using springs as well as shifting the belt to each pulley, up and down and this works with all three pulley. The problem is it doesnt want to move from the smallest pulley back up to the largest pulleys no matter how much slack or tension i put on the belt. I tried a rubber flexible belt and it was hesitant but eventually changed back. I dont like the rubber belt, as i asked a mehanic and he said with movement the belt may slip off because of the flexibility. So im still in a situation???
 
  #4  
Old 06-19-07, 09:27 PM
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I see the problem and why it would happen. You'll need to clutch the spring tensioner to release the tension on the belt when you shift. On the underside of the belt just past the driven pulleys mount a rod perpendicular to the travel of the belt so the belt will rest on the rod when you clutch the tensioner.

What will happen (if all goes well) is the belt with no tension will lay on the rod and gather at the pulley nest. This should give you a large enough loop to transfer the belt to the larger pulley. When you release the clutch on the tensioner, the belt will lift away from the gathering rod. Without that larger loop the belt can't climb onto the larger pulley from the smaller.

You don't have the same issue going from larger to smaller because you don't have a climb, but a drop.

Good luck,

Hope this helps,

Bob
 
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