>jb (the real jb), this "Martin Skank" is being pedantic. If you refer
>to the assemblage of cogs as a cassette, then yes there are no pawls in
>it. What I'm after is a freely rotating assemblage of cogs, and the
>outboard bearing of a cassette hub may be an advantage.
>
>Yes, it's for a multi-speed idler, for an in-line tricycle.
You can do it and it works. I have done it. Here is a photo of my
bike:
http://tinyurl.com/7wvns
I embedded a rear wheel hub in the frame and use a free-spinning
free-hub body and restacked 8-speed cassette as a mid drive and I use
the hubs original wheel axle as the suspension pivot.
There are a few things to watch out for when using a casette this
way...
1) The cogs of a typical cassette are designed to be driven and to
shift easily, not to drive. In order to make this type of mid-drive
work, you must restack the cogs, with the one that drives the rear
wheel flipped over (that means about 3 minutes of work with a hand
file to make it fit back on the free-hub body). If you don't flip the
rear wheel drive cog, you'll find as I did, that when you pedal hard
the rear chain will just slip over the teeth of the drive cog.
2) The chain line will require careful attention. On my bike the
rear wheel cassette and mid drive cassette are in exact alignment
because I used parallel stays and a rear wheel axle as the suspension
pivot. The rear drive cog is the largest on the mid-drive and is
closest to the bike frame. This works fine for driving all 8 cogs at
the rear wheel but there is one bugaboo. When the rear chain is on
any but the largest 3 cogs at the rear wheel, if I pedal backwards (as
one might do to adjust pedal position when stopped at a traffic
signal) the chain will throw itself off the drive cog at the mid-drive
(it is doing what it was designed to do- trying to shift gears). I
have solved that problem by adding a plastic disc about 7" in
diameter, cut from the lid of a plastic bucket and installed between
the rear drive cog and the next one on the mid-drive. The plastic
applies just enough side pressure to the chain to keep it from coming
off when I pedal backwards. I have since come to realize that if I
try to start the bike up from a stop on level ground in any but the
largest 3 cogs on the rear wheel I am in trouble anyway, so if you
develop the habit of downshifting the rear derailleur before stopping
(which is sort of normal anyway), you may not need to bother with such
a disc. A better solution would be to buy or make a rear wheel drive
cog without and easy-shift ramping. You might also try offsetting the
mid drive so the rear drive cog lines up with the middle of the rear
wheel cassette.
Some bike dealer in Wisconsin was selling off a bunch of Trek R200
mid-drives on ebay a while back. Those units had a plain, unramped
cog to drive the rear wheel.
3) Instead of using a rear wheel hub to hold the thing in place you
can use a standard bottom bracket shell (with a freewheel- NOT a
freehub body/cassette). A little known fact is that the threads that
mount a freewheel on a rear hub are exactly the same as the threads in
a BB shell. You can mount a mid-drive by attaching a BB shell to your
frame. Screw a BB end cap part way into the shell, then screw the
freewheel onto the the exposed part of the end cap. Use an alumnum BB
shell instead of a steel one to save a bunch of weight. If you want
to shift gears you'l have to figure out how to mount a derailleur in
the right position, of course.