For the past 8 months one of my fabrication projects has been a geared 36". Today I finally completed the first version and took it for a short spin. The 150 cranks seem fine with the 1:1.5 ratio. I used a double 22/18 cog reduction, with a std. 3/32" chain. The hub is a PW track hub & cog. The jackshaft is a couple of track hubs cut & just the cog portions welded together. Adjustment via dropouts & std. chain tensioners. The basic frame was brazed up by Rick Hunter per my “V” design, and I welded on the jackshaft housing. The bars are another custom design of mine. All components are still unpainted, and will likely remain so until I’m satisfied with the workings.
Pete Perron
And for what it’s worth, I’m calling this a Geared 36" (tho I do like the “Uber-36” moniker), 'cause the only Coker product here is the tire (not even the tube). I don’t see why we keep referring to these as Cokers, some day there will be another tire choice anyway and no Coker products will be involved… Just my .02
You should paint it green. Green is the color of envy.
It will be interesting to find out if it rides better than the internally geared hubs like the Uni.5 and the Schlumpf hub. The jackshaft drive type of gearing definitely has potential. The other advantage with the jackshaft gearing is that you can gear it higher than you can with an internally geared hub.
Now we need some fast riders to come to Seattle and try to break the 1 hour distance record and the 100 mile speed record using your unicycle.
That seems very reasonable to me: to call that a coker would be very
misleading, or more probably an untruth. You might be tempted to conjure up
your own brand name, to be applied to the genre of all unis following the
pattern. A KH unicycle is merely a (good) modification of a standard
pattern, yours deserves a wider recognition, in the way that Blue Shift now
defines that particular geared unicycle . I think your gearing concept
would be a nice addition to a smaller wheeled machine, if it could be done.
It looks a mean machine and I like it, especially how, with the double
gearing, the pedal axis remains in line with the wheel centre. Nice simple
concept, not sure how difficult it was to fabricate. Look forward to
hearing some road reports.
What I can’t figure out is how the two cranks manage to stay in sync. Is there another gear system on the other side, or are the two cranks connected directly? Or is there something else I don’t see?
Pete is going to have to explain the details of the design.
The basic design is that the hub body is on bearings and rotates around the spindle. It is a one piece spindle and the cranks attach to the spindle. That keeps the cranks in line. The trick is that the hub body is on bearings and is able to rotate faster than the spindle.
On Thu, 11 Nov 2004 23:18:53 -0600, “unisk8r” wrote:
>For the past 8 months one of my fabrication projects has been a geared
>36".
Great concept! I notice two chain tensioners. Can the tensions be
adjusted separately without the drive getting out of true? Maybe that
is not needed because both are 22/18.
You probably have to adjust chain tension to hit a compromise between
friction losses and backlash, maybe you can comment on that?
Klaas Bil - Newsgroup Addict
“Deflating pi does not reduce calories, it just concentrates them. - billham”
I used twin dropouts and chain tensioners ala giraffe. Only here there are 2 chains. In a perfect world, there would be no chainline issues. But here, even though I did my best to get the cog separation on the jackshaft equal to the separation between the hub and the crank cogs, it seems that so much tension is required to avoid crank play, that the stress results in a ever-so-slight bend of the jackshaft housing. Those that have peered down the chainline of a giraffe know what this means. You want it perfect. I think this arrangement is fine, and I suspect that the inferior chain has more to do with the necessary tension than the cogs. I’ve adjusted so much tension that there’s friction at the wheel.
As for the ride, I will confirm Harper’s and Childs’ assessment that it is less forgiving. I think that because your inputs are magnified at the wheel due to the gearing, that you have a smaller “sweet spot” of controllability. Crank length is definitely much less of an issue. I think it will just take practice to “get the feel” of it. But it’s definitely smoother overall than a direct drive, and the lower cadence was a big motivator for me; I still don’t spin well!
I’ll report more later after I become more familiar with its potential…
Daino, John is correct. The cranks are attached via std. square tapers to the 180mm axle (spindle), which is otherwise a smooth and solid stainless steel rod. The Phil Wood company kindly (but for a price) made the longer-than-normal axle for me. The hub rotates faster than the axle due to the gearing.
Pete
Stevyo, no shifting…think 1 wheel track bike. The jackshaft is a solid piece that connects the 2 top cogs as one. Drive pressure goes from the crank up to the jackshaft, then back down to the hub.
I rode it again briefly today, and it seems to magnify any input. You step on the pedal and it accelerates. You backpressure the pedals and it slows down, alot more than direct drive. I also notice that the side-to-side effect of pedal pressure is pronounced, not too bad, but maybe that’s more to do with the 9" spread of the pedals. That’s not much more than a wide-hub direct drive, but there’s definite Q-factor. As I pedalled smoother it was minimized. And starts are a bitch, I’m learning all over again!
Bottom line is that with less room for pilot error, I’m still working my way up to go fast. I’m doing about 15 (only on the flats so far) with much less pedal effort, but more balancing effort.
Open it up, you sissy. That’s what protective gear is for. I know at least ONE of the axle threads is done correctly. How much does the assembled unicycle weigh? Have you determined a way around the tensioning problem yet?
On Fri, 12 Nov 2004 19:14:30 -0600, “unisk8r” wrote:
>it seems to magnify any input. You
>step on the pedal and it accelerates. You backpressure the pedals and
>it slows down, alot more than direct drive.
Isn’t that unexpected? I would have thought that your input effects
would be reduced. If I ride on a bike in high gear, the effect
of more power on the pedals is slowly translated into more
speed.
Another question: can you swap the cogs relatively easily? It might
then be worthwhile to temporarily convert it do a geared DOWN 36",
effectively 24". People have talked about the virtues of such a
machine for MUni (great rolloverability but still low gearing) but
no-one has ever tried it. Or they didn’t tell me.
Klaas Bil - Newsgroup Addict
“Deflating pi does not reduce calories, it just concentrates them. - billham”
That’s just because you need more force to turn the wheel in a high gear.
Gearing up in this way effectively has the same effect as putting an even bigger wheel on it, except that the wheel is still only as heavy as a 36" wheel, so you don’t get as much of a flywheel effect as you would on a 42" or whatever its equivalent to.
I think its probably the same feeling as when you put shorter cranks on your unicycle, or, more like it, when you get on a bigger wheeld uni.
Congratulations to an interesting design. I hope you will continue telling us about how well it works on the road. But let me pose a dummie’s question: Why did you not go for a single chain design à la giraffe? Would placing the cranks 15 cm above (or below) the hub’s axle make the uni behave much different? Or were there other reasons?
