Ok i haven't seen this put together in 1 place so i'll start here.
We will take a deep look at speeds and Rpm's the best way.
Start with the Wheel and work backwards.
In order to hit the speed we want and not kill our motor and not peddle too fast we need to consider all these figures.
I'm still working on the diy Jackshaft but there are actually several topics going on in that thread right now.
We do need that data as well but i think it will be more helpful to break some of this into seperate threads.
I have some math to do here and will post calculations soon.
I will use some standard Sprocket configs to
figure out where we want to start.
So lets say 32T is the largest sprocket we have
on the Rear Cartrige or Freewheel.
This will be our lowest gear we need to get 5 MPH
at just above engine idle.
Wheel speed = 65.91 RPM at 5 MPH
32T Sprocket speed = 65.91 RPM at 5 MPH
For the JACKSHAFT we need to figure the nessessary rpm
of the next sprocket.
Which would be the Crank Sprocket at the Front Freewheel
that the bicycle chain is on.
We will call it sprocket 2 = "S2"
Since it is available we will figure on 44T for "S2"
Gear ratio = 44 / 32 = 1.375 : 1
65.91 / 1.375 = 47.935 Rpm at 44T at 5 MPH
Now lets figure what our jackshaft speed will need to be.
----------------------------------------------------------------------
Now things are a little more complex here because we have
1 speed for the Jackshaft and 2 gears on it.
This means we need to work out 2 ratios that get the
44T sprocket moving at 47.953 RPM.
We cant solve for 2 variables so we will have to pick 1 sprocket.
We will start with the 17T sprocket on the left side of the Jackshaft.
Because it is available.
17T / 10T = 1.7 : 1 ratio.
243.91 / 1.7 = 143.4764 rpm at the 17T and Jackshaft
143.4764 / 47.953 = 2.99 : 1 ratio. so lets say 3:1
We also have another unknow sprocket in the system.
The 2nd front crank freewheel sprocket is smaller than the 44T
For chain interference we want some clearence.
Now the 36T is used
36 / 3 = 12
So a 12T would be optimal with the starting speed of 5MPH
The 12T isn't available.
Chainring sprockets are easy to come by so we could go a little smaller
than the 36T or a little bigger than the 44T.
WITH MOTOR RPM = 1000
10T drive at motor at 243.91 RPM
17T at jackshaft at 143.4764 rpm
11T at jackshaft at 143.4764 rpm
36T at Front Freewheel at 43.8765 rpm
44T at front Freewheel at 43.8765 rpm
32T at wheel at 60.3301 rpm
vERY EASY TO SEE THE EFFECTS OF THE JACKSHAFT.
THE UNANSWERED QUESTION IS HOW MANY RPM DO WE
REALLY GET WITH THE TUNED ENGINE.
AND EVEN AT 4500 RPM THE SPEED GETS PRETTY HIGH.
iTS A MATTER OF HOW QUICKLY CAN WE GET TO SHIFTING SPEEDS
tHE 79.90 WOULD REQUIRE 7 TO 8 SHIFTS.
PLEASE ALSO NOTE IT IS MOST LIKLY INTENDED FOR THE 36T CHAINRING
TO DRIVE THE REAR FREEWHEEL.
I CALCULATED THIS THE OTHER WAY AROUND WHICH MAKES THINGS ALOT FASTER.
TO CLARIFY THE 11t JACKSHAFT SPROCKET SHOULD NORMALLY GO TO THE 44T CHAINRING.
tHAT MAKES A 4:1 REDUCTION.
WITH THE 11T GOING TO THE 36T WE HAVE A 3.27 REDUCTION.
tHAT MAKES A BIG DIFFERENCE.
bUT DEPENDING ON HOW NUTTY YOU WANT TO BE.
I DON'T SEE WHY YOU COULDN'T RUN THE FRONT FREEWHEEL EITHER WAY.
iT'S A MATTER OF HOW YOU PUT THE SPROCKETS ON.
NOW I REALLY UNDERSTAND WHY THESE JACKSHAFTS ARE LIKE GOLD.
LOOK AT WHAT IT ACCOMPLISHES.
GENERALLY IF CONFIGURED CORRECTLY.
YOU WOULD NEVER NEED TO RUN THE ENGINE AT HIGH RPM.
Your maths breakdown are far more impressive than mine - i like it!
With a standard 69cc Happy Time style engine, the rpm zone to keep below is 3500.
Above 3500 the engine starts to vibrate quite a bit and by 4500 you'll need superglue to hold your dentures in place - i've identified a possible manufacturing cause for the problem.
My bike set up with an 11-32T 9 speed cassette and running the optional 11 tooth SickBikeParts sprocket has the bike travelling at 30 miles an hour, turning 3,500 rpm.
Shimano has now brought out a 12-36T 9 speed cassette.
I have found that the 32T is too tall for a 1st gear and the 36T would be much better.
Actiontec sells individual titanium and heat treated titanium sprockets, up to 39T for cassettes - just amazing, scroll down to Titanium Cogsets
Yes there are calculators out there to do the math.
But the brain needs some exercise too.
I really begin to create pictures and thoughts and sometimes the most profound discoveries are made when my brain is runnin 4000 rpm.
The math is stimulating to me and sometimes when i sit and think about the math i need to figure out what i want to know i get a deeper understanding of the MOTOR / CVT / GEARING ect.
Sometimes I have to smile cause you can see they have put some thought int the HT.