ideal tractor transaxle for karts?

[tractor guy]

In lawn tractor racing the Peerless 700 seems to be the most popular trans. Its and independant gear box that transfures the vetical belt drive to a horazontal chain drive creating the need for a kart axle. This is popular for a reason, it works really well. BUT, like most tractor trans setups, it does not do well with shifting on the fly.
I have three tractors (a '90 Montgomory Ward, a MTD tradesman, and a '94 troybuilt bronco) that are all from MTD. All of them use a variable speed pully system. (pictured) The way they work is they use two drive belts instead of one. The rear belt runs from the transaxle to the variable speed pully, then the front runs from the bottom of the pully to the engine pully. There is a shifter that locates the speed pully forward to back. When the pully is in the forward position the rear belt is pulled to the center forcing the center of the pully down, inturn forcing the front belt to the outside of its seat resulting in higher speeds. This makes shifting from low to high speed on the fly possable. Going from high to low speed requires pushing in the brake/clutch since the speed pully doubles as the clutch pully.
The other advantage to this setup is the transaxle itself. Two of mine are single speed with nuetral and reverse and an off center input shaft. These are resonably light whieght and use 1/2" belts. The other has high and low range with nuetral and reverse and a pretty much centered input shaft. This one is pretty heavy with 1" axles and uses 3/4" belts. The offset input of the two smaller ones is so much the the engine could be placed centered nearly directly over the transaxle if smaller pullys are used on both and a fancy clutch is made to maxxumize the contact area of the belt to the pullys when ingaged.
The main setback for the variable speed pully is that the belts have to be strait across from eachother. Since transaxles are not that wide, the speed pully would have to go in front of the trans with room to move forward and back, and the motor located in front of it with room for the speed pullys movement. That would place the motor a good ways forward of the wheels making a very long kart.
I have racked my brain tryin to work out the kinks in this idea but every idea i come up with creates more complications then it fixxes. I am open to ideas and would like to know what you think of this idea.
Thanks for readin.
The tractor guy

 

[Doc Sprocket]

Any of the Peerless offerings that I am familiar with, are not shift-on-the-fly friendly. Some folks will tell you that you can- and indeed at low speeds they seem to tolerate it. However- having been inside these gearboxes and intimately familiar with the operation, I wouldn't- especially at speed.

The variator idea is a cool one, but how much ratio range does it offer? Is it even worth it?

 

[tractor guy]

is it worth it?

Im a crappy judge of speed but i would guess its the same as the diffrence between first and top gear on any other type tractor. I would say it would be worth it if speed is top prioraty. Like gearing it to to start off at the most the motor can handle and using the speed pully to max out once your momentoms up. My brother guesses it to go be a 10mph diffrence maybe.
Im mostly just a fan of the lighter single speed transaxle and how the input shaft is so offset. The simple shift setup is nice to (just side to side, no H pattern) but im pretty shore many others with multible gears have that same advantage too.

 

[Doc Sprocket]

In the absence of shift-on-the-fly with a normal tranny, I'm awfully tempted to try a combination of a CVT with a manual gearbox. It's very tempting. You still don't have the shift on the fly, but it would broaden the range of each gear- to the point where even if you gear for a higher speed, you could still take off in 5th without breaking a sweat.

 

[machinist@large]

In the absence of shift-on-the-fly with a normal tranny, I'm awfully tempted to try a combination of a CVT with a manual gearbox. It's very tempting. You still don't have the shift on the fly, but it would broaden the range of each gear- to the point where even if you gear for a higher speed, you could still take off in 5th without breaking a sweat.

I'll have to get you some photo's of the system on my combine; it uses a hydraulically actuated variable speed pulley set with a three speed tranny and an automotive style clutch. It works very similarly to the way you just described, only you have total manual control over the pulley speed. The belt is always under tension, and runs constantly when the engine is running; the clutch and transmission are after the belt drive. I'll try to get photo's tomorrow, if you want them.

 

[Doc Sprocket]

Sure- I'd be interested in seeing them!

 

[machinist@large]

Sure- I'd be interested in seeing them!

I'll see what I can do.

 

[tractor guy]

Toystory said... ", I'm awfully tempted to try a combination of a CVT with a manual gearbox."
Thats a kick a$$ idea!
I know im gettin off subject a lil but anybody ever tryd using a chain drive on a vertical shaft? I saw a racin mower build that used a jackshaft to make lowering the rear using the stock transaxle possable. I liked that he used a disc brake mounted on the jackshaft but didnt like the idea on loosing brakes if the belt broke. I thought it would work great if a chain was used from jackshaft to transaxle and the diff was welded (locked). I saw another tractor build that used a chain on a vertical shaft but it never menchend how it did long term.
Btw, this site is awsome. I have been poppin in and readin up on stuff for months but only recently signed up and posted a couple ideas. Lovin this place.

 

[Doc Sprocket]

I don't think it would be too much of a problem using a chain drive on a vertical shaft application. If the chain is fairly long (and it probably would be) I'd want to rig a spring-loaded idler sprocket as a tensioner to keep the slack under control.

As for the CVT/gearbox combo- the more I think about it, the tastier it gets. I have a Comet 40 sitting around gathering dust, and some ideas for my UTLTV project. I'd like to lay my hands on another Peerless 700 (I have one on my racer).

I'll bet I could adapt the 40 driven unit onto the 700 input shaft, and do away with the factory clutch. Install a live axle, and use chain components between the 700 and axle to dial in the gear ratios.... Hmm...

The only thought I don't like right now is the fact that the 700 input shaft is pretty short (maybe 1 1/2") and only 5/8" diameter, IIRC. The 40 requires about 3" of 3/4" shaft. Not a huge hurdle. One could use a 5/8"x3/4" sleeve to tie together an extension shaft, with a bearing to support the other end.

 

[tractor guy]

I saw an idea on youtube by fearlessfront to that effect (the extention). He thought of conecting a universal joint to the output going strait out to a bearing with a sprocketon the other side of the bearing. The bearing would have its own mount on the frame. This would releave the pulling stress on the 700s housing. As far as i know he did not use this idea but i liked the idea. Be and interesting way to extend a transaxle to be wide enough for a two seater kart.

 

[machinist@large]

Photo's; you want them, you got them!!!!!!

Hey guys!!!

Here's some photo's showing one way you could use a belt drive with a mechanical gearbox; while not a CVT in that it has a separate mechanical clutch like a car or truck, it does validate you guy's idea's of using a variable drive of some sort to let you spread out your gear ratios.

OK, from left to right; photo #1 shows the vari-drive' with a ballpoint pen for size reference, pic #2 is a close up of the hyd. cylinder that mechanically changes the pulley ratio (taken from our parts machine outside), pic #3 is a B&W of the clutch input shaft with the fixed and moveable shiv's; the inside one is the spring loaded one (heaven help you if you have to take it apart- been there, done that), photo #4, LH bottom row is a close up of the gear shift handle w/ shift pattern, photo #5 is an overall of the machine so you can get a sense of scale, and #6 is one of the dashboard w/ the hyd., ground speed and engine controls and gauges.

So if anyone thinks that you can't run a belt drive on anything bigger than a go kart, think again; this was old technology when this machine was new. That was back in 1969.


Pat

 

[Doc Sprocket]

Fantastic! Thanks for that....

I keep looking over at the UTLTV and thinking, Comet 40, Peerless 700, live axle... *drool*

 

[tractor guy]

Toystory said "I keep looking over at the UTLTV and thinking, Comet 40, Peerless 700, live axle... *drool*".
Go for it man! Thats an awsome idea!