Lend me your brains

Prime.

Sukkah!

am i gettin' yer goat yet?

Nope. I just wanted an excuse to count to the next prime number whilst using a prime counting system for the number of dots.

.....................................................................................................................................................................................................^^

•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••

@object, 126 is not prime, FAIL

Although, fruitbat, you will be glad to here that 131 is prime as is 127, Fred must be pleased

come on object, don't you know these things? :-DDD

^ that is different though mate... it has a split BB spindle and is designed to train your pedal stroke in a similar manner to PowerCranks..

but its has two cranks so it would look similar.

Jos & Keith have got double drive fixed at Tour de Ville - Jos said it handled erratically, so more of a show-piece.

Not the same as 100's idea, of course.

.

Absolutely 100% WILL NOT WORK.
Take a piece of paper and draw a simple representation of a freewheel like this:

or print mine

Now, hold your paper up so that the drawing is on the right hand side of the paper, representing a "normal" right hand drive freewheel and notice how the outer bit with the teeth which is driven by the chain engages the pawls on the inner part and drives the hub/wheel.
Now flip the paper around to represent the left hand freewheel and you will notice that the inner part with the pawls will drive the outer part with the teeth and in turn the chain and cranks. Neither side of this system will ever freewheel, when you pedal forward on the right side crank/chainring you drive the right side rear cog which turns the hub which turns the left side rear cog wich turns the left side crank. Unless the same gears are ran on both sides as soon as you move the bike the two cranks and the two sides of your hub will be trying to move at different speeds.
Sorry if iv repeated myself there but its hard to explain.

With respect to all posters I'd like to see this attempted- being British I admire engineering that could end in a) heroic failure, or b) self effacing success.

Whilst most have gone in on (a) seeing a bit of (b) would be top drawer.

Sorry, i dint mean to be defeatist. I could be wrong.

unless you run both free-wheelss on the same side, with a double chainring, 2 chains with the both free-wheels running in opposite directions.

that would means dishing the wheel and sorts but that surely is feasible.

I think the whole thing will just catch fire and explode in protest, before you even get on it :)

hehe would be a fitting end

Absolutely 100% WILL NOT WORK.
Take a piece of paper and draw a simple representation of a freewheel like this:

Now . . .

. . . Unless the same gears are ran on both sides as soon as you move the bike the two cranks and the two sides of your hub will be trying to move at different speeds.
Sorry if iv repeated myself there but its hard to explain.

Fuck me, you are quite right, and fuck me this is a big reply, but you got me thinking . . . .

First up - thanks for saving me from wasting time and money playing around with this - I was going to pick up the pieces in the week as I was convinced it would work. It took me a while to visualise what you had said - and to confirm it I sketched the system out on my computer - and you are 100% right!

With a 16t freewheel and 24t freewheel (chosen for the easy maths) and two equal tooth count chain rings - so the system is pulling the same amount of links off each freewheel at the same rate (again for easy maths) - the following happens . . .

Assuming a certain starting position, you turn the cranks - which pulls the chain - which turns the rear small freewheel (left hand side in illustration below) - this freewheel's drive notches connect with and then pushes it's pawls - which are fixed to and so turn the hub - the hub then turns the the pawls on the bigger freewheel mounted on the other side.

But . . . the freewheel on the other side has it's centre (hub/inner freewheel/pawls) and it's outer (teeth) turning at different rates. . . .

Assuming a 16t small freewheel and a 24t big freewheel, when you turn the cranks and pull 24t worth of chain off the rear of the drive chain (half a revolution of the cranks on a 48t chain ring - for instance) then the 24t freewheel will turn one full revolution while the 16t will need to turn 1 and a half revolutions to 'supply' the chain ring with 24t worth of chain.

So the inside of the 24t freewheel (driven by the smaller 'drive' freewheel through the hub) will be turning faster than the outside - as the outside of the 24t will turing at 1 revolution per half crank turn (assuming a 48t chain ring) while the inside will be turing at 1.5 revolutions per half crank turn (assuming a 48t chain ring), this means the 24t freewheel's own pawls will quickly catch up with and then push it's drive notches (normally it is the notches that push the pawls) - and when they do the whole system will bind and come to a standstill as it's pawls can't move any further forward, which mean the hub can't continue to rotate.

Making the chain ring smaller on the 24 freewheel side (my initial intention to give two different ratios) only makes matters worse (grinds to a halt quicker) - making the chain ring bigger only transfers the problem to the other side.

It's totally fucked. :) The only way it would work would be as mechanical_vandal says, to have the same size freewheel on each side, which defeats my initial reason to try this.

In this illustration I have 'glued' the pawls down, out of the way of the drive notches on the 24t freewheel (right hand side freewheel), so it can turn and you can see the system moving smoothly, notice the inside of the 24t and specifically that it's pawls are turning faster that it's drive notches/outside/teeth.

Now imagine we unglue the pawls on the 24t and let them spring out into position, you can quickly see that they would meet the slow moving notches and the curtains would come down on this whole sorry mess. (ignore that the chain is not wrapped around the freewheels, it is just there to show that both sides are pulling the same amount of chain).

Anyhow, mechanical_vandal you are officially the winner of this thread !!! :) Cheers once again, you saved me a few quid and a week of oily hands - and well done for working this out in your head (!) - it's hardly intuitive stuff!

Right then, anyone ever tried two 650c wheels on the front on their bike?

That animation is cool as, where did you get/make that?

Fuck me, you are quite right...

+1
And a great animation 100. it made things clearer!

So basically, in other words:

"I think the whole thing will just catch fire and explode in protest, before you even get on it."

Do I not get points for that? :)

Glad i saved you the effort/expense and btw your animation is 100 x better than my shitty paint drawing.
I was thinking about this a bit more though and came up with a few things, Would it be possible to make a double sided freecoaster hub? Freecoasters are a clutch mechanism rather than a ratchet and they eliminate the problem of the wheel/freewheel centre driving the chain and cranks. Primarily used for bmx stunts so that you can roll back with the cranks held still but seeing as the left hand drivetrain is effectively running in reverse it might work.
Also, i remember seeing an old school bmx freewheel on ebay that had a button on it which turned it from a standard freewheel into a freecoaster somehow. Or possibly it just shut off the ratchet mechanism so that itd coast but you would get no drive from it.
I think the button was on the face of the freewheel where itd normally carry the branding ie dicta acs etc. No idea how it worked but if it could be rigged up to have the button activated via cable from a handlebar mounted lever etc.
Or just run two of them in freecoaster mode on either side of a flip flop hub thus creating the above mentioned dual sided coaster.