automatic 2 gear jackshaft

[Frankenstein]

Thank you for all the tips here.

I want to start after my first reduction because I don't want to build a full transmission box with two shafts, I love my 4G transmission and I would like to keep it and just adding 1 more shaft (the jackshaft), will add less power loss (bearing, chains, etc).

Let me give you some of the calculations I've being doing, having you telling me what can fail based on your experience is priceless:
HS motor has an engagement RPM of 3k and a max RPM of ~6.8k, so the output shaft of the 4G transmission will spin at ~750 RPM when main clutch engages and at ~1700 RPM at full throttle.
My idea is getting a clutch that engages at ~1200 RPM and install it on the output shaft of the 4G, based on your affirmation that lockup happens aprox 1.3 RPM later than engagement, it will lockup at ~1560 RPM. First speed will run from 750 to 1200 RPM, transition between 1200 and 1560 RPM and second speed from 1560 to 1700 RPM. Max torque is at 4500 RPM on the motor, 1125 RPM on the shaft.
Now talking about the two gears, the first one will be around 3:1 reduction and the second 2:1 reduction, still doing numbers bout this.
Talking about speeds, right now I do 29mph with a total reduction of 8:1 (40T sprocket), second speed has exactly that reduction ratio, so I expect the max speed to be a little bit lower, due to more chains and bearing, but will be a good test to see how much power is being lost on the jackshaft. First speed will be like having a 50T sprocket (9:1 reduction), I didn't try that sprocket, but I tried a 44T and it was quite quick.

Well the bearings will probably fail first if you keep the chain lubricated and don't use cheap chain, the cheaper the faster the stretch and the quicker you loose sprockets to wear.

You will need 2 shafts or you will need to press the 4g shaft out and put a longer one to accept the extra hardware, you basically illustrated that on the first page however so I think you understand that.

The idea you are presenting is sound and has been demonstrated as a working idea, if you build it true then you won't have a problem, just use quality parts, I would suggest an adjustable rail or swinging hinge to remove slack in the chains without adding the friction or additional complications of 2 idler pulleys along with a third on the final drive.

 

[dmopedMA]

Well the bearings will probably fail first if you keep the chain lubricated and don't use cheap chain, the cheaper the faster the stretch and the quicker you loose sprockets to wear.

You will need 2 shafts or you will need to press the 4g shaft out and put a longer one to accept the extra hardware, you basically illustrated that on the first page however so I think you understand that.

The idea you are presenting is sound and has been demonstrated as a working idea, if you build it true then you won't have a problem, just use quality parts, I would suggest an adjustable rail or swinging hinge to remove slack in the chains without adding the friction or additional complications of 2 idler pulleys along with a third on the final drive.

I know about the longer shaft. I'm now looking for all the parts and how to build it in a way that fits my bike. I'll keep you all posted and please, if you see other flaws or points of failure, let me know, all feedback is welcome!

 

[Deleted member 26224]

If you are running 26" wheels, then 29mph at 6800rpm means you have a 18:1 ratio, not an 8:1. I'm running an 8:1 right now on my 212 and I top out around 56mph at almost 6000rpm. Use that magic number .078 which is MPH per 26" wheel RPM. rpm*.078/reduction = speed

The 1.3 engagement/lockup is only for max torque clutches used in 2-speeds. When you go on a karting shop site and read that the yellow spring will engage at 1650rpm, my 1.3 rule is that IN A 2-SPEED it will lockup fully when the output shaft is spinning 1900. you need to design for 2300rpm or so lockup so that you have some adjustment.

There's 2 reasons this is not going to work: you will not find a clutch that will lockup less than 1900rpm, and the hs50 doesn't have the power to drive all that complexity.

You also need a lot of space for this transmission. If your bike isn't stretched, you simply won't have anywhere to place it. For longevity you also need to run sprockets with a minimum size of 11t.

As a person with experience trying every transmission out there and putting thousands of miles on each, I can say with certainty that unless you really know what you are doing, the single speed with single jackshaft is your best bet.

 

[dmopedMA]

If you are running 26" wheels, then 29mph at 6800rpm means you have a 18:1 ratio, not an 8:1. I'm running an 8:1 right now on my 212 and I top out around 56mph at almost 6000rpm. Use that magic number .078 which is MPH per 26" wheel RPM. rpm*.078/reduction = speed

The 1.3 engagement/lockup is only for max torque clutches used in 2-speeds. When you go on a karting shop site and read that the yellow spring will engage at 1650rpm, my 1.3 rule is that IN A 2-SPEED it will lockup fully when the output shaft is spinning 1900. you need to design for 2300rpm or so lockup so that you have some adjustment.

There's 2 reasons this is not going to work: you will not find a clutch that will lockup less than 1900rpm, and the hs50 doesn't have the power to drive all that complexity.

You also need a lot of space for this transmission. If your bike isn't stretched, you simply won't have anywhere to place it. For longevity you also need to run sprockets with a minimum size of 11t.

As a person with experience trying every transmission out there and putting thousands of miles on each, I can say with certainty that unless you really know what you are doing, the single speed with single jackshaft is your best bet.

Running 20in on the back wheel.

Worst case scenario I see, I'll have a 1 fix gear jackshaft and some spare parts around, still worth if I have some fun, I lear about gearing and spend some time on my hobby.

Let's see if I can find all pieces I need on my budget.

 

[Frankenstein]

If you are running 26" wheels, then 29mph at 6800rpm means you have a 18:1 ratio, not an 8:1. I'm running an 8:1 right now on my 212 and I top out around 56mph at almost 6000rpm. Use that magic number .078 which is MPH per 26" wheel RPM. rpm*.078/reduction = speed

The 1.3 engagement/lockup is only for max torque clutches used in 2-speeds. When you go on a karting shop site and read that the yellow spring will engage at 1650rpm, my 1.3 rule is that IN A 2-SPEED it will lockup fully when the output shaft is spinning 1900. you need to design for 2300rpm or so lockup so that you have some adjustment.

There's 2 reasons this is not going to work: you will not find a clutch that will lockup less than 1900rpm, and the hs50 doesn't have the power to drive all that complexity.

You also need a lot of space for this transmission. If your bike isn't stretched, you simply won't have anywhere to place it. For longevity you also need to run sprockets with a minimum size of 11t.

As a person with experience trying every transmission out there and putting thousands of miles on each, I can say with certainty that unless you really know what you are doing, the single speed with single jackshaft is your best bet.

Ooo, that means the nuvinci is a better idear depending on legislation language.

 

[dmopedMA]

Guys, I've being thinking about how to reduce the complexity of the 2 speed transmission jackshaft in order to avoid what Tony01 is saying, that the small engine is not gonna be able to move all that properly.

I got a new design idea is to skip the jackshaft all together, running two chains to the wheel, one on each side using a longer shaft directly from the 4G transmission.

Here a diagram:

Explaining it:
- First gear will be on the right side of the wheel using a freewheel 44T sprocket (SBP has the freewheel adapter and sprocket), maybe a 48T if 44 is too small.
- Second gear will be on the left side of the wheel using a regular 40T sprocket.
- Centrifugal clutch will be as before on the shaft and will act as "freewheel" when on first speed.
- I'll use bike chains well lubricated and avoiding tensors as much as I can.
- Longer shaft will be hold on the right side with a jackshaft bearing to keep it in place.

Question for the audience: Will that be "lighter" on the motor that the previos idea with the jackshaft?

 

[curtisfox]

You might want to mount a extra bearing on the long shaft, other wise it looks good, basically what the mini bike shaft does..........Curt

 

[dmopedMA]

You might want to mount a extra bearing on the long shaft, other wise it looks good, basically what the mini bike shaft does..........Curt

Sure thing, thanks for the feedback

 

[Deleted member 26224]

Not gonna work either. The 2nd gear clutch has to be on the driven axle when side by side with a first gear chain. It needs to shift based on wheel speed, not engine speed.

 

[curtisfox]

Here is what he is trying to accomplish, and i think it will work, sorta backwards clutch...........Curt

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