sprag sprocket source? and 2 speed jackshaft idea

[Masonisgreat35]

i am working on an idea for a two speed jackshaft based off of other 2 speed jackshaft setups and am wondering where to find sprag sprockets or one way sprockets witchever u call them

i cant seem to find any online that are either 3/4" or 5/8" bore, 20 teeth, pitch 35
anyone know of any manufacturers or a way to make one myself, i can have it welded together where needed but i cannot fabricate the components so i would need links to the peices that can then be assembled

also am i correct that the ratio from clutch 1 to sprag would be 2:1 so 6000rpm on crank will be 3000rpm on jackshaft?
when googling the formula to calculate it says as an example

the sprocket ratio is simply the number of teeth on the driving sprocket divided by the number of teeth on the driven sprocket
if the front sprocket has 20 teeth, and the rear sprocket has 80 teeth, the sprocket ratio is 20/80 = 1/4 = 1:4 so 4:1

following this formula as i understand it, they divided 20 by 80, witch would give u 0.25, instead of the 4 that they have as an answer.
but dividing 80 by 20 gives the correct answer of 4 instead of 0.25
am i not understanding the formula correctly?

as simplified as possible how would i calculate the ratio of two sprockets, and am i correct in thinking 10tooth to 20 tooth is 2:1 ratio or is it 1:2 ratio

attached is a picture of the idea, teeth count, and ratios, because the jackshaft is 5/8" ill be using a 3/4" to 5/8" steel keyed adapter so i can use 3/4" clutchs and sprockets
any feedback on the idea aswell as how to properly calculate ratios is welcome
thanks

 

[Master Hack]

also am i correct that the ratio from clutch 1 to sprag would be 2:1 so 6000rpm on crank will be 3000rpm on jackshaft?
when googling the formula to calculate it says as an example

the sprocket ratio is simply the number of teeth on the driving sprocket divided by the number of teeth on the driven sprocket
if the front sprocket has 20 teeth, and the rear sprocket has 80 teeth, the sprocket ratio is 20/80 = 1/4 = 1:4 so 4:1

2:1 ratio means the driver sprocket turns 2 revolutions for every time the driven sprocket turns one revolution.
Your example: 6000rpm crankshaft = 3000 at jackshaft is correct

 

[Masonisgreat35]

2:1 ratio means the driver sprocket turns 2 revolutions for every time the driven sprocket turns one revolution.
Your example: 6000rpm crankshaft = 3000 at jackshaft is correct

thanks for the reply, thats good to know, but am i correct that my ratio from crankshaft to jackshaft is 2:1 though?
because this idea relies on the jackshaft spinning slower than the crankshaft so it gives time for first clutch to be engaged, then when jackshaft reaches a high enough rpm it should engage the second clutch with a differant gear ratio

 

[Master Hack]

thanks for the reply, thats good to know, but am i correct that my ratio from crankshaft to jackshaft is 2:1 though?
because this idea relies on the jackshaft spinning slower than the crankshaft so it gives time for first clutch to be engaged, then when jackshaft reaches a high enough rpm it should engage the second clutch with a differant gear

No, 20 teeth on the crankshaft and 80 on the jackshaft is 4:1
so 6000 crankshaft = 1500 jackshaft RPM.

 

[bob58o]

21 Tooth
5/8” bore
#35 chain

not sure HP or RPM rating

and it takes me a few minutes to think about and understand the Fairbanks two speed set up so not sure if this is what you are looking for (or could be used in a slightly different configuration).

From your diagram, it appears this is what you want.

One Way Sprocket Type P Bore 5/8" Pitch 35 – Lowell Corporation

Lowell Corporation One Way Sprocket For original equipment manufacturers and plant operation.Economical to buy, easy to apply, simple to use. Pick the size of the sprocket needed and we’ll build it into an assembly. Or: substitute a pulley, etc. for the sprocket.

lowellcorp.com

 

[bob58o]

This is best publication I found describing the Fairbanks set up

https://www.parduebrothers.com/minibike/twospeedfairbanksminibiketransmission.pdf

 

[bob58o]

If both clutches are set to engage at 1500 rpm and the jackshaft spins half as fast as the crankshaft…

Then 3000 engine rpm is 1500 jackshaft rpm and that is when high gear clutch engages. Right?

if high gear clutch is set to engage at 2000 rpm, then you’d hit high gear at 4000 engine rpm.

 

[bob58o]

Ratio…
Driven : Driver

If the crankshaft has 10 teeth and the jackshaft sprocket driven by the crankshaft has 20 teeth,

then the driver is 10
And driven is 20

The ratio is 20 : 10
Or 2 : 1

the jackshaft spins half the speed of the crankshaft so it is underdriven.

Overdrive is a situation where the driven spin faster than the driver.

for example if you had 10 tooth on the crank and 8T on the jackshaft

the ratio would be 8 : 10
Or 4 : 5

the jackshaft would turn 5 times for each 4 turns of the crankshaft.

I think about gear ratio as speed reduction and TQ multiplier.
If gear ratio is greater than 1, the driven moves slower with more TQ.
If gear ratio is less than 1, the driven spin faster with less TQ.

 

[Masonisgreat35]

No, 20 teeth on the crankshaft and 80 on the jackshaft is 4:1
so 6000 crankshaft = 1500 jackshaft RPM.

I meant am i correct its 2:1 for 10t to 20t, witch looks like i am so thats good

 

[Masonisgreat35]

21 Tooth
5/8” bore
#35 chain

not sure HP or RPM rating

and it takes me a few minutes to think about and understand the Fairbanks two speed set up so not sure if this is what you are looking for (or could be used in a slightly different configuration).

From your diagram, it appears this is what you want.

One Way Sprocket Type P Bore 5/8" Pitch 35 – Lowell Corporation

Lowell Corporation One Way Sprocket For original equipment manufacturers and plant operation.Economical to buy, easy to apply, simple to use. Pick the size of the sprocket needed and we’ll build it into an assembly. Or: substitute a pulley, etc. for the sprocket.

lowellcorp.com

View attachment 145096

I couldent find a way to order these from them, i found these exact sprockets before making the post, but ive been talking to someone whos built the exact idea i have and he pressed a one way locking needle roller bearing clutch into a sprocket and it works as intended, i asked how long it lasted and he said multiple bikes/karts and still is alive and functioning, although he said he hasent used it with motors over 6hp, the specific bearing he chose is rated at 35ft-lb of torque, im planning on using the same style but rated at 60-80ft-lb depending witch i can get with a inner diameter of 1"

 

[Masonisgreat35]

Ratio…
Driven : Driver

If the crankshaft has 10 teeth and the jackshaft sprocket driven by the crankshaft has 20 teeth,

then the driver is 10
And driven is 20

The ratio is 20 : 10
Or 2 : 1

the jackshaft spins half the speed of the crankshaft so it is underdriven.

Overdrive is a situation where the driven spin faster than the driver.

for example if you had 10 tooth on the crank and 8T on the jackshaft

the ratio would be 8 : 10
Or 4 : 5

the jackshaft would turn 5 times for each 4 turns of the crankshaft.

I think about gear ratio as speed reduction and TQ multiplier.
If gear ratio is greater than 1, the driven moves slower with more TQ.
If gear ratio is less than 1, the driven spin faster with less TQ.

Thank you for this explanation thts perfect

 

[msrfan]

I made a two speed trans for a bicycle about 10 years ago. https://motorbicycling.com/threads/two-speed-automatic-transmission.46564/

 

[bob58o]

I made a two speed trans for a bicycle about 10 years ago. https://motorbicycling.com/threads/two-speed-automatic-transmission.46564/

Nice project.
Nice work.
Nice write up.

it seems you press fit the sprag bearing into the “hub” for the low gear sprocket after boring the sprocket (hub) to fit the sprag bearing.
Very cool stuff!

Is this the type of sprag bearing used?
The first one I found was $50 on Amazon, but you mentioned them being inexpensive on eBay. Maybe 10 years of inflation has played a part?

 

[bob58o]

eBay is gold. $10 seems more reasonable.

 

[msrfan]

Nice project.
Nice work.
Nice write up.

it seems you press fit the sprag bearing into the “hub” for the low gear sprocket after boring the sprocket (hub) to fit the sprag bearing.
Very cool stuff!

Is this the type of sprag bearing used?
The first one I found was $50 on Amazon, but you mentioned them being inexpensive on eBay. Maybe 10 years of inflation has played a part?

Thanks. Yes that's exactly how I installed the sprag bearings in the sprockets. I bought my sprockets from McMasterCarr and my bearings from ebay. Took a long tome for me to figure it out. I had to actually build it to understand it. Especially with the extra sprocket to enable me to pedal start. Of course I pressed the one way bearings in backwards at first and had to start over. It was a rewarding project that I'm in the process of getting back on the road after sitting for a few years.