Gearing help for tracked kart

[java230]

Im building a tracked sort of kart. Could use some help with gearing and clutches.

So its a snowmobile track and tunnel, the drivers are 7", which as far as I can tell we can use as 'wheels' to determine speed. Ideally I would like to hit ~20mph.

For power I have a Honda 13HP.

Will be used mostly offroad, and in snow. So a higher ratio is probably better. I have not removed governor so 3600 is max RPM's on the motor, im not opposed to removing it at this time, but its more work...

Now one Idea is to use the CVT from the snowmobile, but its designed for an engine that gets to 8000 Rpm's, engages at ~4500. So I would need to rig a JS that would multiply the engine speed by about 2.5. Would this motor have the torque to even be able to spin that?

Or run a simple chain and centrifugal clutch, I don't want to spend $200 on a Comet right now. Would a 6:1 have enough torque to get the track moving? It would give me 12mph, which I maybe able to live with for simplicity.

Thoughts?

 

[OzFab]

First, are the drive wheels 7" with or without the track? Using such small diameter drive wheels, you can afford to drop the ratio a bit to gain more speed; with that setup, you could probably get away with 4:1 (I said probably!) which, if the tracks are, in fact, 7" should give you around 20mph...

Second, you're using a 13hp Honda which, with a few easy mods, you can get 15hp out of; the last thing you need to worry about is not having enough torque!

Chinese knock-off torque converters can be found for around $120 & we haven't heard any horror stories yet...

Unless you plan on using the engine from the snowmobile as well, leave it intact, don't remove the drive assembly from the engine...

 

[java230]

Thanks for the help!

They are 7" without the track, the lugs are about 3/4"-1" so that would add 1.5-2" to the diameter.

You really think I can go that low on the ratio? Im worried about getting the heavy track moving, its 136"x15", and not exactly low friction.

I know I can get more out of the engine, but I don't want to stress the valve springs. And replacing is not in the budget right now, can be done later.

Why do you say not to use the snowmobile primary? Do you have a name or link to the Chinese torque converter? I see a lot of different things searching, but no 40 series equivalent. Would a TC be far better for this application?

 

[itsid]

here's a series40 clone for example:
http://www.ebay.com/itm/40-Series-G...her_Vehicle_Parts&hash=item2c758e038f&vxp=mtr

you need a belt as soon as you know the center to center mounting distance as well

and yes, that is much better than a clutch...

'sid

 

[anderkart]

Jave, some of the snowmobile CVT's can be modded to a lower RPM engagement suitable for use with your 13hp. You might research the brand/model of your CVT to see if its possible.

Then you could ask this shop: http://www.cartpartsplus.com/if they have the correct shaft adapter for your application.

 

[java230]

It's a skidoo cvt. I can get it down to about 4k rpm with the stock hyfax, I am not sure it's worth it. Designed for 100hp...

Thanks for the link Sid, so if I am seeing it correctly, Any of them with a 1" shaft on the driver should be a "40 series"

 

[itsid]

NOPE!
the series 30 is available for 1" shafts as well.. and although it alone is rated up to 13hp,
it's a bit of a stretch... the ones with belt and backplate are rated 8hp max (IDK why to be honest)
Anyways.. make sure it's the driver with the prominent nut in the center

'sid

 

[firemanjim]

NOPE!
the series 30 is available for 1" shafts as well.. and although it alone is rated up to 13hp,
it's a bit of a stretch... the ones with belt and backplate are rated 8hp max (IDK why to be honest)
Anyways.. make sure it's the driver with the prominent nut in the center

'sid

I think the back plate is the weak link.....

 

[itsid]

I think the back plate is the weak link.....

it appears to be for sure... but the casted backplate isn't exactly flimsy either, and considering an engine torque of ~30Nm (that'd be three kilos or 6.6lbs or something like that)
I'm not sure it'll fold under such forces *shrugs*

Anyways.. it's not meant to be powered by a 13hp engine for whatever reason, and to make sure the kart is in fully working condition for longer than just a minute or two, it shouldn't be used

'sid

 

[OzFab]

They are 7" without the track, the lugs are about 3/4"-1" so that would add 1.5-2" to the diameter.

Cool so, now we're at 9"

You really think I can go that low on the ratio? Im worried about getting the heavy track moving, its 136"x15", and not exactly low friction.

(I said probably!)

6:1 just seems a little low to me; stick with it if it makes you feel better, you can always change it later...

FYI: 5:1 will give you 19mph...

 

[java230]

Thanks guys, now is cvt worth the cash? Or should I try a clutch first and see if it burns out? It will mostly be used in the snow which helps a little with cooling.

 

[java230]

OK guys, Im a newbie, bear with me.

Step down clutch? Im looks for a budget 1" option, does that simply mean that the 1" spindle section does not carry all the way through? Is that a problem?
This one http://www.bmikarts.com/Stepdown-Clutch-1-to-12-Bore_p_2985.html

 

[itsid]

NO!

and before you ask, YES, that means you need a Torque Converter!

'sid

 

[java230]

Arrrg Sid. Trying to stay away from the TC. Just adds a ton of cost with the Jack shaft and whatnot.... Teardown has started... This is the track doner.


20140919_160319 by Java_230, on Flickr

 

[itsid]

Sorry.. in that case.. bulk order the clutches, since you will go through them faster than through gasoline

'sid

 

[java230]

OK OK I think in getting the memo.... Just doubles my build cost.

Edit: so what would you suggest for gearing with the TC?

 

[itsid]

well.. again; I'm sorry...
but I can't help it, you wanted to use the heavy tracks, not me

there is a reason sleds come with powerfull engines and CVTs

'sid

 

[java230]

well.. again; I'm sorry...
but I can't help it, you wanthigh o use the heavy tracks, not me

there is a reason sleds come with powerfull engines and CVTs

'sid

This is true.... Maybe I need to look at the oem cvt again. Just needs such high rpms.

 

[landuse]

Excuse me if I missed it.....but why don't you use the sled engine

 

[java230]

Excuse me if I missed it.....but why don't you use the sled engine

Doesn't run. I think it needs a Stator and coil, which is a few hundred $$. I would have kept it as a sled if I could have gotten it running!
Here's what I'm building.