About me briefly:
I live in Oakland CA, where the weather is currently gorgeous. I
started riding a uni at age 38, 7 years ago. My wife, bless her heart,
noticed the longing in my gaze at the uni in the bike shop, and got it
for me for Christmas. I proceeded to teach myself by trial and much
error, having no source of instruction. I've ridden on and off since,
getting better only slowly due to lack of practice.
I recently jumped at the chance to buy a used giraffe from a fellow
nearby. I have been practicing much more lately, and have been making
rapid progress. I can now do a curb mount on the giraffe, soon it will
be a freemount!
NOTE: Anyone live in my general vicinity? Gimme a holler - let's ride!
Anyhow, lately I have been in the process of trying to figure out
whether it would be possible to adapt a Sturmey-Archer 3-speed hub to
a giraffe. (Yeah, I guess you could say I've really got it bad!)
I have done some analysis of the hub, and after scratching
my head for quite a while, I don't see how it could easily be made to
work. I have heard things mentioned here about people using geared
unis, and I would like to either find out how someone has already
solved this problem, or to engage other unicyclists' ingenuity in
arriving at a workable solution.
The problem is this: to enable the ratio of crank revolutions to wheel
revolutions to be changed on the fly, yet to prevent all free-wheeling
while a gear is engaged, that is, any time except when shifting between
gears. It is in preventing freewheeling while still permitting shifting
that I need help.
Here's what I have so far. I got a used Sturmey-Archer model AW (very
standard) hub from a bike shop. I found a Glenn maintenance manual in a
used bookstore with a pictorial procedure for overhauling my exact hub.
(BTW, as a kid, I used one of these for years, so I understand exactly
how it works from the user perspective, such as when it ticks, when the
pedals spin free between gears, the order of gears, etc.).
OK, so I began taking it apart little by little, peering into holes,
pulling the chain and moving things as I went, in order to begin to
understand how the thing works from the _internal_ perspective. To
make a long story short, I now understand how it works _as designed_.
(Aside: it's no wonder these hubs are still in use around the world.
I don't think I know of another mechanism that packs such complex
function into such a relatively simple package. It is fiendishly clever!)
>From this point on, it's kind of technical. I originally wrote
quite a bit more, but deleted it for brevity. If anyone wants more,
I still have it.
It comes down to two problems:
1 If we could find a way to lock the hub for one gear's
power path, that would be great, though no better than
having no gears, I guess. The problem is changing gears.
We might find a way to lock one gear, but we must be
able to _unlock_ it to use _other_ gears.
2 There is quite a bit of slack movement of the driver when
power changes from pushing to coasting. This, I think,
permits the clutch to move easily among the three gears,
and was not a problem for the original designers
because they _wanted_ it to freewheel, and there's no
difference from the user perspective between slack and
freewheeling. But it's a problem for us because, even
IF we can figure a way to lock and unlock gears to the hub,
it still won't be acceptable unless we ALSO find a way to do
it with little or no slop.
BOTTOM LINE: Does anybody know how this is done?
Thanks ever so much for reading and head scratching. To misquote W. C.
Fields, "Everybody has to believe in something: I believe I'll have
lunch".
>> Mark
Mark Schecter
3735 Maple Avenue
Oakland, CA 94602
510-482-2094 home
510-645-3466 work