That’s interesting, I hadn’t thought about that particular issue with the Schlumpf, but it certainly accounts for some of the reason why the only way to recover from being off-balance in high gear is to pedal faster.
The other thing which I think is a significant factor in MUni is the slop. Slop doesn’t wind up being a huge factor on the road, as once you’re solid you can spend most of your time “pegged” on the front of the slop envelope, but when you’re doing MUni you’re constantly having to adjust, and every adjustment back and forward has to go through the slop twice.
Of course something 1/4-1/3 the price would be more affordable. So would something that is free. But how about something that is reasonably priced? I don’t think you have a grasp of that for perhaps the same reason that you won’t be submitting plans for one: it’s not your area of expertise.
You’re right, there is a market out there. It just happens to be a very small market that supports the current price of the existing product. I’ve had a lot of people approach me with “really great ideas” in the past thinking that their “really great idea” can not only be realized, but realized for next to no cost, with no effort on my part, and will be supplying a huge market with limitless funds.
I have a couple of designs for hubs that you are welcome to that are two-speed shiftable by simply moving a bolt and a spacer. One of the designs has been posted on my website for several years. For you to take that design, which is simpler than the Schlumpf, and have one manufactured would certainly cost you more than the Schlumpf itself and the Schlumpf is the superior and more flexible product. I’m not convinced that Florian is making Euros hand over fist with this item even at the current price.
Finally, to go into production with a less flexible, inferior product would be risky to say the least. You could try to convince UDC to undertake this for you but UDC is accustomed to taking other kinds of business risks. I seriously doubt that this would be the horse they would bet on.
It was more of an over reaction than totally freaked. I was out of line.
The title more than what was posted caused me to think Schlumpf product was being singled out, rather than the benefits of a fixed geared uni being emphasized. I paraphrased it in my head as “let’s dump that in favor of this” and It’s like someone that picks on another to further their own agenda. I know the OP wasn’t intending to do that, but that’s how I read it. What I can only aspire to emulate (Schlumpf) seemed to be challenged, and it struck me personally. I shouldn’t have let it.
I just don’t think Schlumpf needs dumping on, in favor of something that doesn’t exist in production. Such a production hub may have it’s own failings, and the reality is we’re putting an ideal against a real product and my sense of fairness was incensed. Also, it seemed the merit of a fixed gear uni is greater than the need to simply overcome Schlumpf issues.
Lots of folks have ideas, some cause those ideas to exist, and few produce them for the rest of us… each step is a major undertaking especially the envelope that Schlumpf has defined in manufacturing such intricate machines. The one off fixed geared systems are generally more exposed, delicate, are stressed by heavy torsional loads, and are likely inferior to a Schlumpf in real world MUni. So the stuff that doesn’t yet exist in practice shouldn’t be postulated as superior. I felt it was falsely discrediting the product and discouraging the manufacturer.
The reaction force is trying to rotate the frame backwards isn’t it?
In general, I think a cheap single-speed (not “fixed” - Schlumpfs are fixed gear) geared unicycle would be nice for some situations (easier to transport than a big wheel), but not terribly practical in most cases, as tholub said.
In my limited guni experience, I’ve ridden a Schlumpf 29er and a KH/Schlumpf 24. The 24 in high gear certainly did not feel just like a 36er - not extremely hard to ride but took more concentration, and that was just around a smooth gym floor. I find a G29 very hard to ride, but I’ve only tried a few times.
All the people I know (and know of) with Schlumpf hubs do use both gears.
No it isn’t, in the situation I described. Try the following with a Schlumpf uni in high gear: put the wheel on the ground, vertically, and the frame lying to the rear. (Position of seat drag but stationary.) Now hold the wheel still (maybe against a wall), while pushing the front pedal down hard. The whole frame will rotate upwards, because of the reaction force.
If you’re good, you can mount the uni like an ultimate wheel in said “seat drag” position, and then bring the seat under your butt by pushing hard. I know Irene Genelin did this successfully in her first ever session with a geared unicycle.
Yes you’re right now I think about it more (pedals drive the planet assembly, sun is attached to frame, ring gear held still by the wheel). Sounds wrong but is actually true :o
Well that’s the first time anyone has suggested an off road guni is not desireable. I sincerely hope you are mistaken, otherwise I just spent a whole bunch of money on something that I’ll have to resell
So if it’s the slop and/or too tall gearing, why wouldn’t it make more sense to have a fixed gear ratio at 1:1.25 or similar, esp for a 24" which is the most manageable wheel size for muni, but suffers from being way to slow for XC? Yeah, yeah, that’s why folks buld up a guni, but then didn’t I just read a couple posts suggesting that an off road guni is not that viable. It seems like some folks on this forum disagree
I agree that a 36" equivallent on technical trails could be a challenge, but at the same time a smaller wheel is more easilly maneuvered both on the ground and when hopping. I do not find a 36" wheel, with it’s weight, high center of mass, and centrifugal momentum to be all that great for off roading. It’s a chore to manage and it’s a long way to the ground when it become unmageable.
I didn’t say I was uneducated, my undergraduate major was engineering for a couple years, and I already do a fair amount of monkeying around with tele gear, so I know welding and machining. I just don’t have time to be the guy who builds stuff, maybe someday…
In terms of UDC taking on a project, I’m pretty sure they’d need a protype before they’d consider being the producer, more likely they’d sell it for the producer. It woud be a major undertaking for sure, likely not that profitable, probably a lot like what Florian is doing; which explains why he takes so long
The whole purpose of the offroad KH/Schlumpf Hub was to be used as a sort of road/trail hybrid mechanism. I for one live near trail systems that have easier paved/gravel roads that widely separate various single track sections. Before I owned my KH/Schlumpf Hub my range of trails that I could cover in a certain fixed amount of time was extremely limited. With the geared hub it is now practical to link these various trail sections that I couldn’t before on my single speed unicycle. For that reason alone I know it was $$$ well spent. While riding in high-gear on single track isn’t as “viable” as say riding a geared up fixed gear bicycle, it is still doable if you are very apt at up/down shifting and know your trail system very well. While I’m not quite at that level of skill yet, I’ve gotten better at recognizing what sections of trail I can upshift to and when I need to downshift. It’s quite fun! Going with the shorter cranks for my small feet really helped my shifting proficiency. Anyhow, it’s the ability to have TWO gears that make the KH/Schlumpf a worth while investment, a fixed, geared up mountain unicycle would have very little value IMHO.
This is a quote from the write-up on my website after the uni.5 was built and tested so about 9 or 10 years ago.
“The tab that you see is screwed to the sun gear assembly and attaches to the fork. One of the technical problems that concerned me was the torque applied to the frame by the sun gear assembly which must remain stationary around the axle. I thought this would tend to push the seat in the direction pedaled making it essential for the rider to keep his or her weight on the seat. Since it is attached to only one side of the fork it should also have applied a slight torque around the seatpost axis tending to make the seat rotate as the rider pedals. As it turned out, these effects were insignificant enough to be unnoticeable.”
Now that there is a substantial amount of distributed experience with geared unicycles do you think that this effect is in general quite noticeable? At one time, JC even told me that he was able to sense the rotation about the seatpost which I never felt.
Staging the seat drag mount with Irene was really fun. It was done in the Northbend gym where the Panther Pride team practices. Connie and Andy Cotter were there with Irene to give a performance-related seminar for the Panther Pride riders. I think Irene was 16 years old at the time. I explained to her what was expected to happen and the idea was alien to her. Why should the unicycle rotate? She was pretty surprised when the seat popped up off of the floor but with practice she was able to time it correctly and mount from the seat drag position. “With a little practice” usually means two tries for Irene.
The other astonishing thing was my first real comprehension of how good really young riders can be or, conversely, how totally inadequate I was as a rider. The kids there immediately picked up a geared unicycle and were riding it backwards, one-footed, idling, doing pirouettes, riding seat out, seat dragging, all things that I thought would be at least very difficult if not impossible. Of course I was the chief proponent of the impossibility of a shift on the fly unicycle so Bob’s your uncle.
I definitely think that the rotating tendency of the frame in the fore-aft direction, as a result of the reaction torque from the hub, is noticeable. I cannot explain otherwise why a geared unicycle feels so much more unstable than a nongeared unicycle, even if they have a similar Total Gear Ratio.
Nowadays I ride an approx 50/50 mix of geared and nongeared unicycles. I have gotten quite a bit better at ‘anticipating’ the required level of corrective forces to stay in the stability envelope on my Schlumpfs. Still, for me the nongeared unicycles are really more intuitive to ride.
I must admit that I have never thought about the rotation around the vertical axis that you point out. I’ll check it out on one of my next rides, to see if I can feel it now that I know. I think though, based both on physics and on my never having noticed it, that this effect is at least an order of magnitude smaller than the fore-aft rotation - although I’m not sure how to express an objective ratio between the two.
I’ve thought about this a little more…probably incorrectly. The sun gear attachment to the frame causes a torque reaction that tends to rotate the frame in the direction pedaled. This is equivalent to applying a force on one and only one of the fork legs (the side to which the sun gear is attached) at some distance from the axle. The force applied will of course vary with the distance from the axle and I want to pick the point at which the fork leg meets the crown to apply this force.
To counteract this force, the seat is held firmly in place by the rider. The seat pushes against the rider causing the disturbances that you notice. The counter force is not applied at the connection between the fork leg and the crown. Instead, it is applied at saddle and translated down to the connection between the seat post tube and the crown, right in between the forks.
These are two unbalanced forces causing a shear between the points on the crown where the seat post tube and the fork of interest attach. I think that the two disturbances are roughly related as follows:
1.) A counter torque is applied at the saddle that reacts to pedaling. The saddle is located one seat post length above the crown (L2) plus the crown height above the axle (L1) away from the torque axis. The force required to counteract the torque is F1 applied at L1+L2.
2.) The force applied at the point where the seat post attaches to the crown is F2= F1(L1+L2)/L1.
3.) F2 is balancing the equivalent force being applied at the fork-crown connection but the two forces are not co-linear. This causes a torque equal to 2F2C/4=F2C/2 where C is the width of the crown.
The counter forces are then related by the distance from the saddle to the axle, the distance from the crown to the axle, and the crown width. Considering how narrow the crown is, I think your order of magnitude guess must be reasonable.
In order to compare the torque reactions felt they must be compared at the same point, the saddle. This must be independent of the height of the crown above the axle which I gave as L1. Picture instead the force being applied at saddle height to a point off the rigid structure to the left or right by a distance equal to half the crown width. The torque arm is then L1+L2, the distance from the saddle to the axle.
The torque reactions to this force are in two axes, one through (co-linear with) the axle and one through (co-linear with) the seat post. Their ratio is 2(L1+L2)/C. The first one is felt as a force pushing the saddle fore-aft, the second is a twist rotating the saddle under the rider.
If the fork spacing (crown width) is around 10cm and the saddle to axle distance is about 60cm then this ratio would be 12 making the effect of the rotation seem quite small. This would also agree with your original estimate of one order of magnitude.
This twist, in order to be felt as a force, would have to be scaled in a way that is unclear to me depending primarily on where the saddle contacts the thighs of the rider. It should be much more clearly noticeable on the arms of a rider on a unicycle with a long handlebar setup.
Now that I have muddied it up for you, can you clarify it for me?
Hi Greg, everything until the last few sentences of your second post is comprehensible. The contact between seat and rider is not very simple in physical terms, since butt and thighs, as well as the seat, are no simple geometrical shapes, and the legs are constantly moving at that. And then again, the movements are not exactly periodical since the rider is making small “random” corrections all the time. This complexity was probably the main reason for my statement that I was unsure how to express an objective ratio between the two torques in question. Alas, I still cannot clarify that any further.
I’m not sure that the effect “should be much more clearly noticeable on the arms of a rider on a unicycle with a long handlebar setup”. Granted, with a greater distance from the axis of rotation as is the case at the end of a long set of handlebars, any movement would be larger. But conversely, the forces on the rider’s arms will be smaller, and hence are perhaps more easily counteracted by the rider without him/her noticing.
One more thought. In your treatise, you state that the reaction force from the gear is applied to one fork leg only, and you conclude that this results in a torque rotating the frame sideways (poorly reworded by me). I agree that this would be the case if this force were applied externally on one fork leg only. However, in this case, the reaction force is somehow generated within the system of unicycle + rider. I wonder if somehow in the interplay of all the force transmissions, a countertorque is generated such that there is no net tendency of the frame to rotate about its vertical axis. I don’t feel like working this out in detail, maybe you do.
Hey, we’ve effectively jacked this thread, haven’t we?
Yes it’s true that the force at the end of a long handlebar would decrease with length. I think that I introduced some confusion because long is not important here. It’s just, as you said, that the butt/thigh/saddle interface is very difficult to characterize whereas a hand/handlebar interface is very clear.
The gears are all kind of floating around in the backlash space in the hub. The planets are connected to the axle, the ring is connected to the hub, but the sun gear is attached to a lever arm or a knurled connection on only one side and that part is in turn connected to the fork on that side. The torque produced on the sun gear by the rest of the gearing system is applied only to one fork. Granted, the system is pretty rigid, but it is far from perfectly rigid.
And, no, I don’t feel like working this out in detail either.
I feel that is our duty as old-timers. I’m pleased with the parts we have played in commandeering this discussion.
I would think that most riders of geared unicycles also ride with significantly longer cranks than ungeared. They also tend to apply significantly more force to the longer cranks at a slower cadence. This tends to move the center of gravity as the weight transfers from seat to pedal to seat to other pedal to seat , etc. It is especially noticeable to me when climbing a long slight incline.
When riding “Blue Shift” this transfer combined with gear torque and my riding style would contribute to a lope similar to pedaling on a galloping horse. It was pronounced enough that I seemed to bob up and down and sway back and forth several inches with each half pedal revolution. I never managed to video capture this. Does any one else notice this while riding in high gear on long cranks?
I do not experience this same galloping lope on a geared 36. But I have never ridden a geared 36 with long cranks.
The torsional torque effects seam most pronounced to me when approaching still stand speeds as when waiting for a traffic light to change while in high gear and then standing on the pedals to accelerate when the light changes to green.
Do you suppose we could use this torsional torque and sun gear orientation to help compensate for road camber?
I did love to put those blue Kooka 165s on BlueShift. It sounds to me that your galloping gait is crank length related from the way it doesn’t transfer to a geared 36 without long cranks. My legs are a lot longer than yours and, as such, they are more forgiving to long crank spinning. I don’t notice this motion.
Do you actually experience the torsional reaction torque? That’s one of the things we’re trying to determine. If the sun gear is on the correct side of the unicycle then this effect could be used to counteract road camber which you would really like until you got back onto a flat surface. Have you had it on both sides?
As someone who (also) has not ridden a 24" Schlumpf offroad in high gear, I tend to agree with Tom. This based on my experience with 29" and 36" Schlumpfs, mostly on pavement. This makes my opinion of similar worth to anyone else who hasn’t ridden a 24" Schlumpf offroad.
If you ask me, I’d say that the vast majority of this effect is simply from the drag/friction inherent in the gearing system. Though that torque effect is there, I’d guess it’s more of a background thing in relation to pushing the gearing. The other effect that is probably a factor is the “disconnect” between pedal rotation and wheel rotation. Not sure how to communicate this, but it’s the fact that the wheel doesn’t act the same way as it does when your pedals are going around at the same speed as the tire. Not sure if I’m imagining that effect or if it really is a factor in handling and control.
While acknowledging that a twisting force is probably present, I would guess it to be undetectable if you are actually pedaling at the time. The simple act of pedaling puts on so much twisting force, it probably covers up any of that torque completely. People tend to be unaware of the amount of twisting torque that a uni frame gets, but I developed an appreciation for it when those forces broke my Roger Davies carbon MUni frame many years ago. It had a small defect, that Roger repaired, but it was still way stiffer than I ever thought would have been necessary, and the twisting effect of (steep, uphill) pedaling caused the joint with insufficient glue to pop.
Maybe. We’re pedaling harder, and as you said on longer cranks than an ungeared uni. This contributes more to that twisting force being applied as we pedal. And we have to compensate as we are able, due to the single point of contact a unicycle has with the ground. In other words, an increased tendency for “wobble” when cranking hard on a geared uni. I find a handlebar helps to compensate for this, but it’s still only a single contact point with the ground.
Back to the original topic, I agree that a less-expensive, non-shiftable geared hub (or uni) would be desirable for people who can’t afford the investment in a Schlumpf. The most useful form of this is probably the shift-not-on-the-fly type that Harper has built, but this one would probably have manufacturing costs pretty similar to the Schlumpf (assuming an equally high standard of build quality). And the lest-expensive approach would probably be a jack-shaft type design, with a little chain on each side. The advantage on a jack-shaft model would be an ability to change gears by swapping out the sprockets. If there’s adjustability there, you wouldn’t have to change the length of the chain each time you switched to a different number of teeth.
But like anything else, creating a niche product for an already-niche market would be expensive, so don’t hold your breath…
