While reaching high speeds is a concern, that’s not really why we don’t have more gears.
The two gears we get from a Schlumpf are great, especially given the alternative of just one. But if the technology existed to give us more gears, many of us would be very excited… assuming it was reliable, not too heavy, affordable, and user friendly.
I’d love to be able to downshift to a super granny gear. My 24" is close, but still a few gears higher than the granny on my 24 speed mtb. And with the current Schlumpf, it’s quite a jump from 1:1 to 1:1.5. Having some options inbetween would be great.
at the moment, I am thinking of some pretty crazy stuff. like a drive shaft going up one leg of the frame driving a small gear near the top, with a locking derailleur mechanism feeding to a thin cassette. uneven weight distribution is an obvious downside, though I’m not sure how much of a problem that is on a unicycle. another is the narrower spoke profile, but i don’t think that would be a huge problem for a road uni.
my crazier idea is building a transmission that rests inside a hub. weight and complexity aside, I think it would be really damned cool. when I have a solid idea, I will sketch it out and let you guys tell me why it wouldn’t work. I just really like thinking of design ideas for things
@steveyo : I still can’t even ride my darn 20", so i really have no idea how a uni handles at high speeds. on clean tarmac, what sort of dangers does high speed bring? I would imagine the inability to brake fast could be a problem at times, but that doesn’t really bother me (I used to live in the country, and ride my 10 speed ditch bike that had no brakes down the rolling drumlin hills. a bit scary, but not crazy as long as you know that there isn’t anything that will get in your way :). does a uni exhibit speed wobble at high speeds? that is one thing that TERRIFIES me. I’ve only ever been in a speed wobble once, and that was flying down a hill on a skateboard at a good 40K. I thankfully bailed onto a looong stretch of grass, but the fear of speed wobble has haunted me to this day.
@redwelly: I didn’t know unis were capable of hitting 40kph right now. if that is the case, then you just rendered this entire thread pointless.
NEW QUESTION
why not make shifting cranks, so you could change crank length on the fly? that seems a lot more practical now that I think about it!
My top speed is pretty much limited to how fast I can run - if I fall I want to be able to run it out. Anything faster than that is scary, and I personally don’t want to take that kind of risks.
You will probably find this thread interesting: Fastest speed on a unicycle
Note that 3 in the top 10 are ungeared.
Changing crank length is not really the same as gears, as it would still be 1:1. I seem to remember hearing about cranks where the pedal position could be shifted on the fly, but unfortunately I don’t remember where anymore.
I know it would still be 1:1, but being able to adjust the torque on the fly would be pretty handy, wouldn’t it? anyhow, I don’t even know what I just looked at looking at those pdfs, lol. I was thinking a pretty simple cable pull system that pushes a cog out when the cable is pulled. the cranks would be sprung, so that when the cable is pulled, they will slide into the shorter position automatically. if you want a longer crank, pull the cable and push the pedals away from the hub. really pretty basic design in my eyes, and would fit on any frame with an isis hub. if I’m no explaining it well enough, I’ll draw a picture
Well, Dakoroman was a bit… special. I miss that guy.
Check this post in that thread to get an idea of how it would work.
Sure would! The one I’m thinking about shifted depending on your speed I think, i.e. faster = shorter cranks. Maybe it was just an idea, as said I don’t remember clearly anymore.
Tholub, I agree with you, my concept is of course with cable shifting; one under-gear, one direct-gear, one over-gear; distance between 2 gears is shorter than on Schlumpf because too large according to my opinion and I’m not interested by very high speed.
Last summer I had the opportunity to show a drawing to Kris, Roger and Nathan, they liked the idea. Since that, I did a lot of modifications, hope to realize a prototype one day, if possible with Florian support has he has a huge experience on such uni hubs.
I do want a little speed, but the main reason I’m interested in gearing is the same reason as on a bicycle - to be able to achieve and maintain a convenient speed at a comfortable cadence.
Yeah, I hear motorcycles are pretty safe…
Does it really need to be hard direct-drive in both directions? Has anybody tried a setup that drags instead of freewheeling?
I’ve tried such a thing. It’s like a unicycle as long as you’re accelerating, then it’s like and impossible wheel, only harder because the foot platform isn’t stationary.
alright, I’m home from school. I’m going to sketch out my idea for a derailleur based uni. it will require a custom tabbed frame, hub, and will absolutely need to be used with a bar, as there is a pretty basic clutch involved as my work around for the direct drive limitation of a bike derailleur. I will post it shortly
alright, here is a dirty mspaint drawing of the lower half. I didn’t bother adding much detail in the frame part, since that isn’t really important. the bearing between the spindle and the hub is not actually where it should be, so ignore that one bearing. the hub would mount to the frame itself via a larger bearing, just like on current frames. the hub would be entirely free from the centre spindle, driven by the chain.
on the top half is where I think I have a good idea. throwing the cassette up top has some huge advantages, one being that the shape of the cassette fits nicely into the outer edge of the wheel, keeping the spokes free at the hub.
the derailleur will be assisted with a clutch as I’ve said. the first 1/4 stroke of the clutch will disengage the cassette from the driveshaft, and the last 3/4 of the stroke will actually slide the entire cassette down a few inches. this will take the chain tension job away from the ill equipped derailleur, eliminating the main problem that derailleurs have with direct drive.
one significant downside to this is that it will take a good 1 second to fully disengage/reengage the clutch, plus the amount of time it takes to shift gears, which will leave the rider coasting for the time it takes.
anyhow, I am going to go make some food then draw the derailer/clutch mechanism. I probably won’t be done it for a while ,since it will require a few separate drawings to explain.
Why don’t we have more gears? The engineering problems are only challenges, I wouldn’t call them barriers. I think the reason we don’t have them is purely economic. If I could know the answer to one question on this topic, it would be, why hasn’t Schlumpf put out a 3-gear hub? No one knows the market and tech better than him, so I think he’s probably got the best insight of anyone as to where we are on this and where we’d need to be to get more.
Another thing I find interesting, that tells me there isn’t enough of a market to support speed-oriented setups is the lack of any single-speed geared unicycles on the market. Can’t remember all the details… wasn’t there going to be someone putting out unicycles similar to the “Purple Phase” or whatever, some time ago? That was a really cool setup.
Very neat idea, I haven’t seen or thought of quite that one before. Looking forward to the other drawings!
You may want to search the forum for geared unicycles and geared hubs. There are a number of threads which will describe the complexities and limitations with designing and riding geared unicycles. I’m always astounded at how easy people who have not done this think that it is.
The semi-jackshaft design is almost workable. A full jackshaft design is a proven system. The top half, where you intend to employ a clutch to 1.) transmit the full drive torque and 2.) do some so-far undesigned camming operation to 3.) disengage and re-engage the driveshaft and finally 4.) translate the cog cassette is where you may run into some difficulties.
A friction clutch to handle this kind of transient torque requires a large surface area and large release spring force. It would necessarily be a large and heavy component. Spline or rachet systems are better suited to this.
Designing a cam system to perform multiple functions is tricky business. I don’t think you’re going to be able to pull this off in the real estate available. I did, however, predict incorrectly that no one would be able to shift a unicycle on the fly.
The driveshaft as shown uses some kind of miter or bevel gear transfer. This has no travel. In order to accommodate a vertically moving cog cassette the driveshaft would have to be telescoping and splined in the telescoping region. This is heavy, cumbersome, and it is difficult to make a component like this move freely.
The idea of translating the cog cassette vertically while maintaining tension in the chain and shifting from one cog to another with a very short overall chain length seems far-fetched to me at best.
Aye, there’s the rub to most of these types of devices. While it’s one thing to make a functional multi-speed unicycle (I’ve seen several), it’s quite another thing to make one that’s actually “useful” to ride. Or even enjoyable. Useful, as in not so heavy that you wouldn’t want to lug it on a ride of any length, or not reliable enough to be comfortable to take on a long ride.
…In any gear. Before you invest too much time in building a gear-changer, try taking a ride on a geared-up unicycle. Any type will do; maybe someone in your area has one? I used to put big sprockets on my Giraffe and ride it at nearly 2:1. I learned early on the drawbacks of being geared up. Essentially, it’s faster, but much harder to ride. Net gain is pretty minimal, even with a Schlumpf.
Mostly the clean tarmac, though that would be better than dirty tarmac. The main “danger line” is crossed when you exceed the speed at which you can run out of a dismount. Ouch.
Speed wobble is probably not an issue, since you have to be pedaling the whole time. If you can learn to spin high enough RPMs, that will negate the types of wobble that seem to affect other types of vehicles at really high speed. Mostly because the speed won’t be as high.
Smart man! Though I can ride with very good stability at speeds up to 18mph, at that point nervousness comes in and inhibits me really pushing it. And even at 17mph or so, nobody’s perfect…
Mostly to win the race.
Yup. Nobody seems interested in making them at this point, since they would probably cost most of the price of a Schlumpf, but be much more limited. A unicycle that only has a high gear would really suck on hills. On a 36", the size of my Schlumpf, it would be basically useless for me.
the clutch isn’t friction based at all, but is the most questionable aspect of my idea that I have so far. it is either fully engaged or fully disengaged, but I fear that it would degrade quickly. the vertical driveshaft spins a horizontal bevel gear. that bevel gear is bored with grooves. the hub of the cassette has the same grooves, and the shaft that connects the cassette to the bevel gear slides in and out of the bevel gear. I’m not sure if the grooves will wear down in no time flat, but this is my fear. if there is a way of making this pull-pin engagement system work, then I think that the rest will work pretty well. when the chain is on the largest sprocket, the chain will be directly connecting the hub sprocket with no slack in the chain, and the derailing cog will be out of the way. the derailing cog engages while shifting to the smaller sprocket, but is not sprung at all. the cassette is sprung while disengaged to enable shifting, but when re engaged, it is firmly mounted. the derailing cog can only shift between its gear positions, which means that it’s rigidity is not affected by the chain going forward or backward.
anyhow, I have zero plans of building this, so no worries there. if you can’t tell by my terrible drawings, I don’t know anything about design, much less a machine shop
I do have an alternate idea for a derailleur that would eliminate the need for a clutch and let the cassette remain stationary, yet still handle force from both directions, though it would leave up to 3mm of play depending on which gear you are in, and would have to be built pretty strong
