I don’t think a 15cm offest is an option for a single chain design. It would have to be more than 46cm (in which case it would be a giraffe). With a 15cm offset, the cranks could no longer be connected via an axle, and thus each would would require it’s own chain.
Actually that is what I meant; one chain on each fork leg. The cranks would be attached one ‘bottom bracket’ each side of the wheel. From there a short chain to a sprocket on the wheel’s axle. Just like a giraffe but with a split bb.
Here’s a picture of a big wheel unicycle with that style of chain drive. In this case it was done so that shorter people could ride a wheel that big. It does take two chains with one chain on each side of the unicycle.
It would be interesting to ride a 36" wheeled unicycle with the cranks below the center of the wheel. An inverted giraffe. It would be interesting to see how that affects the ride. Would it be more stable or less stable? What would it feel like while riding at speed? What would it feel like when climbing?
The big question here is: Why the big wheel if you have gearing? He could have done the same thing on a Coker and had a much more comfortable ride.
Because a big wheel that big looks really impressive, especially in parades. Put a large big wheel next to a Coker in a parade and nobody will remember the Coker.
It looks really interesting, I have been meaning to do this for ages and have not got around to it. I had thought of inverting the stub axle and complete axle so it gave a lower centre of gravity… but it also makes it harder to make and I have my short legs to think about.
I do love the frame, I bet it is really rigid. But I would love to know how you get on with your handle though. It is of a similar size to the one that Joe made for me but I could not use. I had several problems with them; they poked me in the eye when I mounted (not a nice experience) and when you actually sat on the seat as a unicycle it was too low. I also found that the extra weight away from the centre was not good for off-road. I had hoped it was going to help, but did not for me. I ended up shortening mine to be only 5" in front of the Miyata saddle.
Ah! I have just had a better look at your chains, you are keeping the same centres aren’t you by using 2 chains… my idea only used one per side, not as robust as your’s I guess. I think I got my idea from a picture of a guy in the UK who did one a few years ago on a 26" wheel.
Ah, of course. I was thinking practically. Not a good thing when talking unicycles.
Greg (& all), this one weighs 19.5 lbs. The extra weight due to the steel jackshaft box, cogs & chains, etc.
As for the slight chain slop on the cogs (a minor distraction, yet enough to want to eliminate), these are 3/32" cogs, which are supposed to take a 3/32" chain. But I’m finding most 3/32 chains are flexy (they’re meant to shift well). A 2nd brand of 3/32 chain was also sloppy in the cog teeth. Today I installed a 1/8" chain, and that seems to reduce the slop almost entirely. I talked with some LBS employees who told me about “single-speed” 3/32 chains, which are tighter tolerances and less flex. I’m gonna try an ACS or similar brand.
If anyone out there wants to build a chain gear on each side, lowering the crank axis with stub axles on each side, have at it. But I’m not going there, I don’t see any advantage at this time.
My next area of interest is replacing the chain drives with 1/4" cogged belts and pulleys. Big Harleys only use 1 1/4" belt drives. This should result in even less driveline friction.
Another note on the ride: I said that the pedal inputs felt magnified, and I think that’s because indeed it pedals like the 54" wheel it’s geared to, but does it on a smaller size. So despite the overdrive and 150mm cranks, pushing on the pedals makes the wheel shoot out in front more, and backpressure makes the wheel go out the back more. With both these effects, you have to have better balance to stay over the wheel as it moves about more under your body.
But I have to say that the more I ride it, the more I like it. I have no interest in under-gearing it, or taking it off-road. I’m just trying to go as fast as I can on one wheel, and I think the current records are woefully lagging our true capabilities.
Edit: Seattle riders, I installed an adjustable seatpost clamp today, so you all are welcome to try it. And Greg, shouldn’t you test your tibia with some freemounts before that sissy-cast comes off and you have to do it for real??
Re: Re: Re: Geared 36
I understood that. I asked my question because unisk8er seemed to state the contrary. Now that he has explained it, I think he means that pushing on either front or back pedal pushes him out of the balance envelope quicker on the geared 36" as compared to a non-geared 36". That is then caused by the fact that the balance envelope shrinks more than the gearing factor itself. Ummm, am I making that any clearer now?
(posted directly on forum because of technical hitches)
I don’t know much about this, if anything at all, but if one geared up something smaller, like a 24 or 26, could one not have the maneuverability of the small wheel the speed a a much larger one?
Very nice looking machine. I was over at Rick Hunter’s today and told him you posted the photo. His first question was, “How fast can he go?” Can’t wait to hear more about it after you’ve got more miles under your belt.
Good luck and don’t crash!
i like the design. i’ve always liked the idea of a chain gear unicycle. a few months back i came up with a similar design, maybe some day i can actually put it together here is the drawing
That looks cool. It looks like alot of chain (weight) with no tensioning, though. It appears to be an up-down drive with a crank connected to one cog, two cogs connected to a freewheeling axle at the crown, and a smaller cog connected to the hub. Another problem, absent in Pete’s design, is potential snagging at the crown level (pants, legs, etc.) All these cool ideas emerging.
Have you measured the backlash at the 150mm point on the crank. I used that as a figure of merit with the geared hubs. It was easy to measure repeatedly. I had hoped for 0.5mm but got about 1.0mm after wear. Uni.5 was a bit worse than BlueShift because it experienced more abuse. BlueShift stands at about 0.75-0.80mm backlash measured at 150mm from the axle. The best was uni.5 at assembly which was slightly under 0.5mm.
My tibia is fine. I broke my fibula. It doesn’t matter…I could one-foot that sissy cycle of yours. With that frame it looks self-riding.
For those who don’t clearly understand Pete’s design, it doesn’t depend on the frame to support a split axle. Split axles have been tried in the past with moderately disastrous results. Pete’s design is strong.
the chain tension was something i thought about, my initial thought was to use some sort of shims under the upper drive but the problem i saw with that was that the two chains will be at different tensions so one would always be more loose then the other. the snagging aspect was another thing i noticed, the problem is that the upper shaft has to be wide enough to be inline with the hub so it’s pretty wide already and any sort of chain guard would be even more bulky. the nice thing about a drawing is that it’s just an investment of time and not money
That’s a really clever and interesting design- can’t wait to hear how it fares after you’ve put a few km’s on your machine. It looks pretty robust- kind of reassuring at high speed knowing that your wheel isn’t suddenly going to lock up.
Just a few Questions:
-Does it offset the wheel at all to have the gearing on one side? Or is the wheel pretty centred in the frame? Did you have to widen the Q factor to accomodate this?
-What are you going to call it? You need a better name than “Geared 36” surely!
-How heavy is it? Overall and just the gear system?
-How fast does it go? OK, well stupid question…maybe, but how much faster are you going on it compared to a regular coker?
Aw man, I so want to have a go!
Hope to hear some updates over the coming weeks!
One question for HAndyAndy: if you’re using a wide hub in your Coker wouldn’t the upper chainring have to sit a long way out from the frame (possibly hitting your leg with every pedal stroke)?
Greg, if you’re measuring only 1MM of play at the pedal (i.e. 150mm out), then you’re doing better than me. That’s just a bit more than what I have now, with the 1/8" chain I installed and rode briefly today. I can just feel the play when riding, and I have ordered a single-speed chain which should eliminate the problem entirely. It’s a problem only because of the odd-brand track cogs I used. I don’t think most riders would even notice it.
And you’re right about the low transmission, I set it below the pedal height because the last thing you’d ever want is to get a pant leg or shoelace caught in the chain!!
>-Does it offset the wheel at all to have the gearing on one side? Or is the wheel pretty centred in the frame?
>Did you have to widen the Q factor to accomodate this?
The wheel is perfectly centered in the hub, and in the frame. The spread between the cogs (both sets) is 1.25". The frame bearings center-to-center is 135mm, which is the same as my wide-hub direct drive. The Q-factor is mostly due to the offset cranks, to clear the jackshaft box with the right crank.
>-What are you going to call it? You need a better name than “Geared 36” surely!
Still don’t know, but I’d be glad to take suggestions!
>-How heavy is it? Overall and just the gear system?
Overall, 19.5lbs. Just the transmission, don’t know. I suspect 2.5 lbs, which is the difference between my direct drive model at 17.0 lbs.
>-How fast does it go? OK, well stupid question…maybe, but how much faster are you going on it compared to a regular coker?
Today I was able to cruise easily at 17. I’m still getting the hang of it, and like it better each time out (tho each ride has been very short). It seems to me that you ride this with less input, that it’s kinda-sorta like a “moving stillstand”. I’m certain that top speeds will be 25+ with a talented rider. (KH, how fast do you think you’ve gone on yours?)
That is possible. Harper has put his internally geared hub on a 24", a 26", a 29er, and a Coker. The smaller wheels are more maneuverable.
However, the internally geared hub is limited in how high it can gear up. The internally geared hubs have a theoretical maximum of a 1:2 ratio (or is it 2:1? I can’t remember which way the ratio goes), but that results in a infinitely small planet gears. In real life the internally geared hubs are limited to ratios of 1:1.5 or 1:1.6something.
The jackshaft style gearing is not limited to those constraints. You could gear that up to 1:2, 1:2.5, 1:3 or anything that you want. A 29er geared up 1:2 or 1:2.5 would also be neat to try. A 29er geared up like that would have a bigger virtual wheel size than the 36er geared up 1:1.5.
What would really be interesting would be to try the internally geared 36er and the jackshaft geared 36er side by side to see how they compare. They’ve both got the same gear ratio so the main difference would be in the style of gearing.