Need advice

[buggyman]

Hey! I am making a mini go kart (for a 30 lb driver). I am using a very small engine from a feather like weedeater (21cc) not sure about the hp but 2 or less for sure. I am having a hard time finding a clutch for such a small engine. Could anyone recommend a place that would have a clutch for such an engine? Also, I am wondering what type of gear ratio would give me the most power so that the thing will move (do not mean fast I mean move at all: for clarification). I would like a top speed of no more than 5mph. Thanks.

 

[RobertD]

wow, that's a small rider! be careful with this idea.

i'm putting up a new speed calculator later -- that should help.

 

[buggyman]

Well, he will be about 4 when I get the thing finished and might be heavier by then. It will not be used without supervision either. The problem is, I am not sure if the engine will be powerful enough to move the kart. I have finished designing the engine mount and will hope to have that done by end of week. Also, trying to find tires less than 10 inches in diameter is a challenge I'm finding.

edit: I'm using your "one seater" as a basic design for the frame. I'm using about 75% of the width and about 50% of its length, so it will be a pretty small kart.

I called the engine company and they said that the engine is roughly 1/2 hp and around 5000rpm. Would that even move, say, a 45-50 pound Kart with 10 inch wheels? Thanks.

 

[cojaro]

((5000rpm/gear ratio) * 60 * (10 * 3.14)) / (5280 * 12)

You're going to need a pretty high gear ratio. I put the gear ratio in at 1(drive):5(driven) and got a theoretical top speed of 30mph. You're probably looking at a 1:8 ratio or greater if you want only 5mph. Either that or go with smaller diameter tires.

Go to gokartnminibikeparts.com, they have some tires that might suit your needs. They have a few between 7.5" and 8.8" in diameter (but much more at 10" or larger diameters).

 

[buggyman]

Thanks guys for the speed calculator, gear ratio esitmates and the lead on the tires. I'll get some photos within a couple of weeks. Starting the engine mount today.

 

[jrjulien1]

i think that an engine that small would have no problem pushing a small kart even with a bigger rider and as for the top speed i would suggest a gear ratio that is around 9 to 1 or so with some 10 or smaller inch tires also keep in mind that with a gear ratio that low the engine will be stuck right at 5000rpm almost all the time at wide open so you might want to put a govenor on it to limit the rpms some


hope this helps

 

[buggyman]

Another question for you. I have some people who can help me out but I would like to understand for myself in a bit more depth before talking to them. I plan on using a live axle set up (just ordered the tires today).

This site does a nice job of explaining the difference between live and fixed axles but doesn't go into much detail on how the parts all fit together.

How exactly does the live axle drive the wheel? I am making a 1 inch axle stepped down to 3/4 inch at the end. I see that the components for the back wheel assembly is wheel, bearing hub. How does the axle attach to the wheel? Won't my axle just spin in the bearing? Is there a keyway in the wheel similar to the hub? I'm a bit confused.

Like I said, I have help but would like a better understanding before I even think about talking about it.

Have the engine mount cut out and will weld it next week. Thanks in advance.

 

[jrjulien1]

first of all a live axle usually uses a keeyed hub or a flange to bolt the wheels to you cant use wheels with berings in them for the rear but for na kart this small i think you should consider single wheel deive as it will greatly improve handling and where this kart goes so slow it may turn so little that youd have to do it later anyways but theres an easy way to do this all you have to do is insted of using a keyed hod or flange on one wheel use a wheel with a bearing on itso it spins independantly from the axle

hope this helps

 

[buggyman]

Great, thanks. You've convinced me, I'll us a fixed axle (ordered wheels with bearings). Starting in on the frame this week. Got wheels, steering wheel, sproket all ordered up.

 

[buggyman]

Progress Update

Got the frame all cut out and sandblasted, going to do some mig welding on it Thursday! I'm pumped about this. Also am considering ordering a new honda engine for it instead of the weed whacker one, we'll see.

 

[jrjulien1]

if you order a new honda good luck finding something that will be small enough to go that slow {note a honda spins at 3900rpm instead of the 3600 turned by tecumesh/briggs}