3 speed tranny??

[freakboy]

well i was thinking about as when i get my engine fixed and running puting it in my gokart. its a 20 hp briggs and straton and instead of making a 1:1 gear ratio 90* transfer then going into a torqe a verter. i was thinking about making a simple 3 speed gearbox out of gears from a lawnmower transaxle.

I made a rough drawing of it but am to tired to scan it and its not final because i dont have gear sizes or ratios. but here is where i got the idea from and i even made a mock up with a vex kit i have but again im to tired to up load anything so here is the link. http://www.nxtprograms.com/transmission/steps.html

I was also thinking if im making one from scratch i can have it so it bolts directly on the output shaft of my vertical shaft briggs. the way im going to lock the gears in is the linkage is going to go up front and its just going to go back and forth and when its in gear its going to have a small grove to fall in and hold it in.

would there be a simpler way to do this then i put? mabey one that will work better? anything i over looked about this? and for a clutch i havent decided what to do about that yet. probaly just a shift fork that pulls the one pinion gear up and put it back down.

 

[Kaptain Krunch]

Wont work, the gears will just grind, they wont actually grab. You would have to completely remove power from the gearbox in order to shift, and lifting the pinion gear wont work, because like i said it would just grind and never re-engage. Now you could use a dirtbike style clutch (basket, plates, etc), and mount that on the input shaft of the transmission, but then it starts to get very complicated, takes up space, and time, and may still not work.

On a side note, i took a lego robotics class last year and made a car with full independent suspension, rack and pinion steering, 2 speed transmission/w manual clutch, all fully remote controlled with bluetooth. If i had more time to work on it i would have done 4wd.

 

[freakboy]

lol wow. i was just wondering. and is there a much easyer way to make a simple 3 speed that will work? or a easyer more compact way?

 

[mike75925]

there're always easier ways, easy means tons of money

 

[freakboy]

ok let me re prase my question. Is there a simpler easyer, cheaper way?

 

[mike75925]

there was a guy who took and removed the crank from a bike engine, replaced it with a shaft of the same size. he attached the crank gear to this shaft and then connected the lawnmower type motor to the bike trans. i would go for an atv engine/tranny, they have reverse. usually.

 

[freakboy]

but then it would need to be sideways.

 

[mike75925]

sideways is better than longways, or do you want it longways?

 

[Rotore]

is this for a vertical shaft? if so i can post pictures on how to make it work horz. worked for my old briggs. really simple and then u can adapt a mc gearbox to it.

 

[freakboy]

well i am cheap and i really dont wana by anything ahhah. i have gears and stuff in a transaxle and i need to do something for a gradproject so whats a easyer way to get a A then to make a freaking transmission?

 

[Rotore]

showing your ability to build an engine for another purpose then what its for got me a 98 in school but transmission would do.

 

[frederic]

Just some ideas...


----- relating to attached pictures -----
Two gearstacks from a mower transaxle. Gears on left have splined hubs to mate rigidly on the splined shaft partially showing in the picture in the upper left.

Gears on right slip over a slotted shaft in reverse order of the other gearstack and are engaged to the shaft with sliding woodruff keys machined so that the ends of the woodruff key sticks up above the shaft and the remainder of the woodruff key is flush with the axle surface.

This is probably the easiest way of making a transmission, and you can easily change the number of gears.

------------------------------------------

Another method of creating gear changes is to use a bicycle bicycle derailleur, gears and chain. One could make this with larger, kart-sized parts of they want as it's a very simple mechanism. Just make sure the derailleur mechanism is on the slack side of the chain and you're good to go.

Yet another method to make a three-gear setup is to put three clutches with a different sized sprocket on a shaft side by side, having each sprocket driving a chain and another shaft. Engage the clutch for the gear you want to be in. Automatic transmissions do this very thing using hydraulic pressure to activate planetary gearsets, but you can do it with chains and clutch plates.

The question is how are you going to shift on the fly, and how fast do you need to shift?

 

[toofarnorth]

I was thinking of doing a three speed tranny by putting three different sized pulleys on the crankshaft then three corresponding pulley on a jackshaft then selecting the ratio you want by tensioning one of the belts, it would be easy enough to make three tensioners but I was also thinking of using one tensioner that would slide from one belt to another the plus side to this setup is the tensioner acts as a clutch.

 

[freakboy]

I think i am going to go with using the gears out of my lawnmower transaxle. two reasons, first i need the miter gears in there anyway to be able to use a vertical shaft engine, second after i do that i have all these gears laying around and stuff. so i will put the gears to good work and mabey sell or scrap the housing.

Thank you Frederic i never really understood how lawnmower transaxles worked. but now im pretty sure i get it so thank you!

 

[motor_head]

you could do something like that but a clutch is a must if the only way i could think to do it would be a belt tensioner like on a lawnmower

 

[frederic]

I was thinking of doing a three speed tranny by putting three different sized pulleys on the crankshaft then three corresponding pulley on a jackshaft then selecting the ratio you want by tensioning one of the belts, it would be easy enough to make three tensioners but I was also thinking of using one tensioner that would slide from one belt to another the plus side to this setup is the tensioner acts as a clutch.

If you want a two speed transmission you could put the two idlers at the ends of a center-supported lever (i.e. a see-saw), this way position of the lever determines which belt is tight and which is loose. This prevents the situation where you could accidentally engage the two gear ratios simultaniously and burn some belts.

stuff. so i will put the gears to good work and mabey sell or scrap the housing.

Mower transmissions are very simple but they are strong for their size and the simplicity offers the opportunity for modification and interesting tangents off the original design. However, with their simplicity, they do have some serious short-comings, the most obvious one being you cannot shift while under load, so that means you have to release the tension on the belt if belt driven or lower the engine RPM so the torque converter "floats" then shift. One can file the sliding woodruff keys a little bit to make the part that slides across the gears a bit more pointy on both ends, so it can slide in easier.

Thank you Frederic i never really understood how lawnmower transaxles worked. but now im pretty sure i get it so thank you!

You are more than welcome, happy to help.

If you want to have a real transmission, use something like this: 5 speeds, 1 reverse, shift on the fly without the clutch (except to change directions and of course into first or second from a standstill), and suitable to 350 ft-lbs of torque from the factory and buildable to about 550 ft-lbs of torque if you like spending serious money. It weighs about 150 lbs.

 

[freakboy]

i dont think a 20 hp engine will turn that transmision ahahah. i would like something using all 6 gears nuetral and reverse in the mower. i think i know how i would do it. just take the gears mount them create the shift arm so it goes back and forth and just run levers and stuff like that to make it work. and if i can do it right its going to be r,n,1,2,3,4,5,6 6th being as far back as it can go.

 

[frederic]

i dont think a 20 hp engine will turn that transmision ahahah

Are you sure? I can put that tranny in any of the five gears (or reverse), and spin the input shaft with my hand, and it, all the gears inside, and the differential will freewheel for a few seconds. The OEM machining is that precise. Though to be fair, it's barely wet.

i would like something using all 6 gears nuetral and reverse in the mower. i think i know how i would do it. just take the gears mount them create the shift arm so it goes back and forth and just run levers and stuff like that to make it work. and if i can do it right its going to be r,n,1,2,3,4,5,6 6th being as far back as it can go.

This is an incredibly stupid question... but with all that effort, wouldn't it be easier to just use a mower transmission and belt/chain it between your engine and your rear axle, or a transaxle that also has the differential to drive your rear axle?

To me, a belt to the engine/clutch/TC and a chain to the rear wheels just seems so much easier than using the guts and making a housing, and getting all the measurements within 1/100th of an inch or better. This is why I haven't built a differential-based live axle yet for my son's kart, as you might have noticed I was pondering on my thread. I'm still debating the work versus the gain, and I have big machines to do this job much easier than most backyard mechanics.

Just a thought.

 

[freakboy]

Well i need to do something for my graduation project and everything else im doing to this kart. the transaxle isnt what i need. im considering re doing that so i can put it on the bottom of the engine. then i can run a chain to a axle and dual a arms in the rear. i cant stand my swing arm in my kart.

when im driving around my yard i get up to like 20 but its bumpy everywhere and at this one spot down hill its like a 500 foot run it gets really bumpy and the rear end always kicks up and one time i almost wasnt able to land it.

Also if i use a differential im going to have hell of a time riding trails.

 

[frederic]

I see, you're doing this for a project rather than because you have to. Gotcha.

Is your entire rear a swing-arm style, or do you have two swing-arms like the original VW's (bug, ghia, thing, etc) or side by side parallel swing arms? Just curious.

Depending on the size of your kart, meaning if it's large enough, you can venture into the world of automobile parts. Many companies make LSD (limited slip differentials) for just about every import car there is, the advantage being they're much smaller than the full-size American car and pickup truck-sized differentials.

And of course there's always more complicated solutions for such problems - an ARB air-locker comes to mind. It's an open differential until you feed it compressed air, at which time it locks as if it were a spool.