Bicycle Mechanics - Nupace infinite gears- Anyone?

I was just wondering if anyone already have a formed opinion about this new product (http://nupace.com/product.htm)

It's been done, and done better.
http://www.rohloffusa.com/frame.htm

It's been done, and done better.
http://www.rohloffusa.com/frame.htm

I don't think the Rohloff is stepless like the Nupace claims to be. In any case, why do you think the Rohloff is better?

Wait, this isn't a CVT, is it?

I don't think the Rohloff is stepless like the Nupace claims to be. In any case, why do you think the Rohloff is better?

The Rohloff 14-gear version has 13.6% steps, AFAIK.

What a deal, only $995. Something about that website just says scam to me though.

-jon

I don't think the Rohloff is stepless like the Nupace claims to be. In any case, why do you think the Rohloff is better?It is a 14 speed, planetary geared hub instead of a mere 7. It's gearing range is the same as that of a 27-speed mountain bike drivetrain, and has a 526% increase in gear ratio between the lowest and highest gear. Couple this up with a larger ring up front and you could more than duplicate a typical road bike range.
The quality of the unit is basically unmatched. I'd equate it to a Chris King product in terms of the precision involved.

The Rohloff 14-gear version has 13.6% steps, AFAIK.
To be more accurate it's between 13 and 14% depending on the specific gears

It looks like the real deal to me. I've been anticipating a CVT for bicycles for several years.

I think that it'll be awhile before it makes it's way into the mainstream. At around $1,000, it isn't cheap and it isn't going to be as efficient as a derailleur drive train. That's two fairly significant strikes against it.

It looks like the real deal to me. I've been anticipating a CVT for bicycles for several years.

I think that it'll be awhile before it makes it's way into the mainstream. At around $1,000, it isn't cheap and it isn't going to be as efficient as a derailleur drive train. That's two fairly significant strikes against it.

what is cvt and how does it work?

what is cvt and how does it work?

I believe it means continuously variable transmission, this thing looks pretty cool but too damn expensive. The 2120 gram weight of the system sounds huge, until you think about being able to lose the weight of your entire rear cluster and one or two front chainrings....

B'Dog

I believe it means continuously variable transmission, this thing looks pretty cool but too damn expensive. The 2120 gram weight of the system sounds huge, until you think about being able to lose the weight of your entire rear cluster and one or two front chainrings....

B'Dog

And FD and RD. Still, seems a bit heavy. I hope it's not a scam or vaporware, as it sounds like a really nifty piece of hardware.

I wonder how it works.

Looks cool enough. I'd expect poor efficiency and weight scaring off performance-oriented riders.

What if you controlled the gearing ratio electronically? You could have a auto transmission that maintained your favorite cadence!

I wonder how it works.

Me too. I can't make out the shifting mechanism from the cut-away.

After staring at their CAD rendering and also a couple of the pictures from their patent for a few minutes, I understand how their mechanism works. I will try to describe it to you.

The relevent US patent is 05971877.

Explaining the mechanism from the axle outwards, and neglecting literaly hundreds of bearings, we have:

1. A fixed axle and associated torque arm. They don't clearly show the torque arm in their diagram, but it must be there and it wouldn't be very interesting if it was. The axle is eccentric in the middle section, standard in the portion that joins with the frame. The axle only moves when your torque arm rattles loose and beats the hell out of your rear triangle.

2. One Eccentric sleeve with engages the axle in the portion where it is itself eccentric. This is reminiscent of an eccentric bottom bracket. By turing this sleve relative to the axle (By having the stop for a boden cable on the torque arm and the cable clamp on the sleeve), the amount of eccentricity of the outer diameter of the sleeve can be changed relative to the axis of the axle. The sleeve only moves when you shift "gears", and it does so continuously rather than being indexed.

3. Four pawl holders, which are concentric about the outer diameter of the larger eccentric sleeves from (2). They do not engage with anything except the pawls they are holding. Each pawl hoder has two sets of pawls oriented in opposite directions.

4. Pawls. Each pawl is held in by a spring mechanism, rotates about the end in the pawl holder, and has teeth on the outside, which engage with (from chain side to drive side):

5. An outer toothed ring that is fixed to the rear cog.

6. Three more toothed rings. Each toothed ring engages with two sets of pawls, one from each pawl holder. The two sets of pawls associated with each toothed ring are oriented in opposite directions.

(Parts 3 - 6 are all moving whenever you are pedaling.)

7. The hub shell, which engages a single set pawls, i.e. the leftmost set. This set of pawls freewheels when you are coasting. The hub shell rotates axially about the center of the axle.

To understand how the pawls work, imagine a very flexible person standing on skis that are parallel, one slightly forward. Now assume said person passes out. Gravity pushes said flexible person down and he/she does the splits, pushing one ski forward and one back.

Analogy:
Gravity <--> Eccentric sleeves acting as a cam relative to the hub shell / toothed rings.
Skier <--> Pawl Holder
Pawls <--> Legs
Skis <--> Two adjacent toothed rings

So on one side, say the front, of the hub you have pawls engaged with teeth and expanding, and on the other side, say the back, you have pawls contracting and engagine with new teeth. The more eccentric the outer diameter of the outer sleeve, the farther down the pawls "squish" during each cycle.

The design does have some elegant properties:
- You don't have to change the dimensions of any of the parts relative to each other to change the gearing range of the hub. This is in contrast to the much seemingly difficult to design and dimension gears in a traditional gear hub.
- While there is a rediculous number of parts, there are not really very many types of parts.
- It may not be as difficult to service as it seems; It seems like each pawl holder and associated two sets of pawls stays together when you pull the mechanism apart.
- I could imagine it being very smooth when in good working order and at lower speeds. I imagine the pawls whining a bit at higher speed, i.e. not when they are engaging, but when they are slipping to new teeth.
- It is, IMHO, easier to understand than a rohlhoff.
- Does not rely on friction like many other continuous gearboxes.

So no, they don't seem to be a hoax, yes, it seems that have a workable mechanism, and no, I wouldn't recommend buying one until they bring the price down by a factor of ten or so and hire a competent marketing department.

So on one side, say the front, of the hub you have pawls engaged with teeth and expanding, and on the other side, say the back, you have pawls contracting and engagine with new teeth. The more eccentric the outer diameter of the outer sleeve, the farther down the pawls "squish" during each cycle.

The design does have some elegant properties:
- You don't have to change the dimensions of any of the parts relative to each other to change the gearing range of the hub. This is in contrast to the much seemingly difficult to design and dimension gears in a traditional gear hub.
- While there is a rediculous number of parts, there are not really very many types of parts.
- It may not be as difficult to service as it seems; It seems like each pawl holder and associated two sets of pawls stays together when you pull the mechanism apart.
- I could imagine it being very smooth when in good working order and at lower speeds. I imagine the pawls whining a bit at higher speed, i.e. not when they are engaging, but when they are slipping to new teeth.
- It is, IMHO, easier to understand than a rohlhoff.
- Does not rely on friction like many other continuous gearboxes.

So no, they don't seem to be a hoax, yes, it seems that have a workable mechanism, and no, I wouldn't recommend buying one until they bring the price down by a factor of ten or so and hire a competent marketing department.


Almost sounds like that one from Honda I saw in DirtRag last year, only their's, I believe, didn't "step" at all.

[QUOTE=awagnerSo no, they don't seem to be a hoax, yes, it seems that have a workable mechanism, and no, I wouldn't recommend buying one until they bring the price down by a factor of ten or so and hire a competent marketing department.[/QUOTE]

Actually, with no gear-to-gear drive, that sounds to me like a pretty efficient power transmission. It's a little pricy, but it's still in the early stages of it's development. They'll get cheaper. Actually it's not that far off of the price of a Rohloff hub. Keep in mind that it replaces the rear hub, cassette and both derailleurs so it's cost, while still high, isn't too far out of line. I think that it'd be fun to build up a bike with one to see how it rides. I wonder what the OLD is.

Oh my gosh, there goes my screen name again!

After looking at the cutaway drawing and reading the above description of operation, I find it amusing that the company refers to the conventional derailleur as a "contraption".

It's funny that the company failed to mention the efficiency of their transmission and how it compares to the derailleur and chain contraption.

For those who think they got the thing figured out: If it's a true CVT, then it has to have a friction-based transmission somewhere. Period. If not, it's a pseudo-CVT with many gears and microscopic gearing steps, which means something somewhere has a very large number of very small teeth, which isn't exactly the most mechanically reliable thing.

In short: either the hub is real and it's no wonder they don't publish any efficiency figures, or it's a scam. Given how childish and unconvincing some of the mechanical explanations are on the webpage, I vote for the latter.

By the way, I keep wondering why cyclists are so obsessed with CVTs: CVTs are desirable to compensate for engines that have a narrow range of working rpms, typically internal combustion engines that have a very narrow band in which they can output power efficiently. Human legs however, work efficiently from 0 to 120 rpm with standard cranks, and can even spin much higher if needed. A cyclist may want some gears to protect his knees in the long term, and for comfort, but really he can ride on a single gear bike without any problem, so what's the big deal with wanting CVTs on bicycles so bad? Heck, even car engines make do with only 5 speeds.

Yeah, a real CVT would use opposing cones with a belt that slid up and down the cones as their spacing changes. Effectively you're changing the diameter of the gears in smooth, continuous steps. None of this 13-14% steps, you can vary gearing by 1% at a time or 0.5% or 0.01% if you wanted.

One cool application would be a sprint. You'd start the sprint in a low-gear for maximum acceleration at say... 100rpms. Then as your speed increased, the CVT (computer-controlled of course) would smoothly increase the gearing so that you'd stay at 100rpms the entire time you're accelerating... Then once you've reached the highest gear you're gonna use, the tranny would lock and you'd spin up that final gear to 130rpms for top-speed... Pretty nifty...

The main "problem" with the current chain/cog/derailleur bicycle drivetrain is that it has set the bar so high it's extremely difficult to improve on. It's very efficient, light, reliable, simple in concept and inherently low cost (Campy Record and Dura Ace notwithstanding. Status always costs a lot. :) ) Therefore, every shade tree inventor just has to try to "improve" it.

So far the only, even slightly, successful competator is the geared multi-speed hub. These are heavier, mechanically complex and less efficient but have a few minor advantages of their own such as shifting while stationary and allowing a perfect chain line and/or an enclosed chain. For certain utility uses these advantages are worth the trade-offs. The ultimate extension of this type so far is the 14-speed Rohloff with it's large gear range and even steps at the cost of some weight and a very high price plus the shifter is not intended for drop bar applications.

ppc is correct that a true CVT has to have friction surfaces to allow continuous, non-stepped ratio changes so the object of this thread doesn't seem to fit this design criterium. If it is a series of very small steps then its strength and durability are suspect. Bicycle riders can genetrate very significant torque values so robust parts are a necessity. That plus a 2000 gm weight disadvantage will be a tough sell even if it's legit.

Well, even if it work flawlessly and does what they claim, a 14-speed Rohloff is probably way better. The greater range is a bigger advantaage then being stepless. The Rohloff is probably more effective as well, although still way worse then my singlespeed:D (or a derailleur bike, for that matter)

Phantoj: Automatic shifting does exist, but it's useless for anyone but the few people who have more money than riding skill. Shimano Nexus 3-speed.

ppc is correct that a true CVT has to have friction surfaces to allow continuous, non-stepped ratio changes so the object of this thread doesn't seem to fit this design criterium.

Nope. That's like saying that an internal combustion engine has to have pistons. Sometimes things that used to be true (as any Mazda owner will tell you) are invalidated by new designs. In this case the continuously changing part is the eccentric pivot for the prawls. It has neither friction driven nor gear-to-gear components so it should be a significantly more mechanically efficient design than conventional internal hubs.

This thread is a joke because I'm the one whose supposed to be the retro grouch.

I'll retract my comment that a CVT has to have friction surfaces as your description of the ecentric as the gear ratio control is probably correct.

However, saying this hub isn't an improvement in weight, simplicity, cost or efficiency over the current standard drive train isn't being a Luddite. It's pointing out mechanical facts.

Your comparison to internal combustion engines is similar. No they don't have to have pistons but, so far, that system works best. Wankle engines, as Mazda has returned to in a very limited usage, still fall behind their piston counterparts in several respects including seal problems and fuel efficiency. Note even Mazda only uses it in one specialty car.

However, saying this hub isn't an improvement in weight, simplicity, cost or efficiency over the current standard drive train isn't being a Luddite. It's pointing out mechanical facts.

Actually, I 100% agree with your earlier comment that modern derailleur drive systems are so efficient, both mechanically and costwise, that it sets a pretty high bar to improve upon. In some previous threads I've even commented that I couldn't understand the attraction of hub gear systems - a comment that drew a LOT of response from the hub gear crowd.

I'm attracted to the Nupace because it's a design that I hadn't seen before. I think that it might be interesting to see how it's use might progress in the near future. I suspect that efficiency wise it might already come close to rivaling a derailleur drive system. Weight and especially cost, however, are another matter but they both might well improve with a little bit of development.

I'm attracted to the Nupace because it's a design that I hadn't seen before. I think that it might be interesting to see how it's use might progress in the near future.

I also find the whole thing fascinating and would like to see how well it works in real world use. Indeed, if it proves durable enough and the cost penalty can be reduced it may be a sufficient improvement over hub gears that it replaces them in many bikes. As someone noted, the 14-speed Rohloff isn't exactly given away either.

I really hope they succeed and my previous point was only that it isn't magic and isn't going to transform or reduce the effort to ride a bike. We'll see.

By the way, I keep wondering why cyclists are so obsessed with CVTs: CVTs are desirable to compensate for engines that have a narrow range of working rpms, typically internal combustion engines that have a very narrow band in which they can output power efficiently. Human legs however, work efficiently from 0 to 120 rpm with standard cranks, and can even spin much higher if needed. A cyclist may want some gears to protect his knees in the long term, and for comfort, but really he can ride on a single gear bike without any problem, so what's the big deal with wanting CVTs on bicycles so bad? Heck, even car engines make do with only 5 speeds.

Are you serious? Car engines make do with five speeds because they can put out plenty of power (whether efficiently or not) within quite a broad range of RPMs. Cyclists like having lots of gears because human legs and bicycle cranks produce very low power and high torque at a very low (and small) range of RPMs. We certainly can produce power from 0 to 120 RPM and up, but it sure isn't fun to have to pedal very slowly with a lot of force or to be spinning our legs off - at least not for most people. SS and fixed-gear riders probably aren't the target market for this product, though!

I suspect that this product is mechanically a distant relative to the power-split device used by the Toyota Prius hybrid automobiles: a geared CVT that works through various mechanical thingies and doo-hickeys that seem rather complicated (at least to a lay person like me), rather than friction. I'd be willing to bet that the efficiency is about on par with a conventionally-designed internal geared hub. If we're going to criticize it mechanically, the only thing we can know is that, if something goes wrong with it down the line, who's going to know how to fix it? There are precious few bike mechanics that know anything about conventional internal gears, let alone something like this! Durability and reliability depend upon the quality of the materials, tooling and specific design of this product, not the general concept, which I think is demonstrably sound.

I'm really tempted to dismiss this as a scam or simply a poor product, in large part because of the marketing - focusing on the faults of the system you're "competing" with, rather than the benefits of the system you're producing. This could be nothing more than poor advertising, however. It seems likely that they are new comers to bicycles and the bicycle industry, or very naive. The derailer drive is not going to disappear. It is incredibly efficient, works effectively and without much fuss (we're talking about modern derailers here), and still has a wider range of possible gears than any other system out there, with the possible exception of hybrid systems. If these guys want to compete with another product for a place in the market place, they should look at internal-gear hubs, especially for city or recreational, bike path riding, or even commuting and other utility use. Another factor that is strongly against them is the price of the device, which occupies the same stratospheric territory as the Rohloff 14-speed hub. The Rohloff, of course, has an established reputation for quality and a wider range of available gears.

There's no need to dismiss the Nupace like this. I'm willing to bet that it works pretty much the way they say it does, the open question of quality notwithstanding. There are plenty of issues to overcome, which I've discussed at length above - marketing and pricing being the most obvious and clearly known problems, in my opinion. If it can overcome these obstacles, we'll know that there's something to it. If not, then we know that it was a failure.

The short story is, there's no way I would buy this without hearing several corroborating positive reviews, but that goes for any expensive product. I'd love to hear how it works from someone who's ridden one and gotten an idea of how the Nupace holds up, but until then, I see no reason not to give them the benefit of the doubt.

Are you serious? Car engines make do with five speeds because they can put out plenty of power (whether efficiently or not) within quite a broad range of RPMs. Cyclists like having lots of gears because human legs and bicycle cranks produce very low power and high torque at a very low (and small) range of RPMs.

This is incorrect, you got it backward. This subject has been rehashed at least a million times on rec.bicycles.tech and on the bicycle science mailing list. I suggest you look up the archives. Here's one from the faq for starters: http://www.faqs.org/faqs/bicycles-faq/part4/section-30.html



I suspect that this product is mechanically a distant relative to the power-split device used by the Toyota Prius hybrid automobiles: a geared CVT that works through various mechanical thingies

Geared CVTs don't exist by definition, just as overunity doesn't exist. If you want a mechanical device that has an infinite number of gears, somewhere inside you need a pair of gears with an infinite number of teeth and a variable diameter (i.e. two smooth surfaces coupled by friction), or a pawl that engages with an infinitely small amount of slop, that is to say, a perfectly-made roller clutch, but again a friction device. There's no way around it. If you don't have a friction linkage in it, then it's a pseudo CVT with many gears perhaps, but it's not a CVT. In fact, I believe all patent offices in the world look for a friction device first off when they receive an application for a purely mechanical CVT design, and if they don't find one, they throw away the application.

The best proof that friction-less CVTs can't exist is that they don't :) The few CVTs in existence on cars (be it the old DAF system, or the new fancy-schmutzy Audi one) all rely on belts. If it was possible to do otherwise, you can bet car makers would have done it.

It looks like the real deal to me. I've been anticipating a CVT for bicycles for several years.

I think that it'll be awhile before it makes it's way into the mainstream. At around $1,000, it isn't cheap and it isn't going to be as efficient as a derailleur drive train. That's two fairly significant strikes against it.

Here's a link posted from the Dahon forum pertaining to the Nupace Hub (http://www.freeridehubs.com/Contact_freeridehubs.html) . This hub was quoted as having an efficiency range from mid-80% to mid 90% last year by one of the design team.

Bruce

I think the one thing that no one seems to be talking about on this hub is that it really doesn't have a very wide range. 300% is no better than the current 8spd Nexus and 7spd SRAM. This isn't improving upon what we currently have out there by much and it is less than the Rohloff. Now lets say it was 600% then I'd be more interested.

Geared CVTs don't exist by definition, just as overunity doesn't exist. If you want a mechanical device that has an infinite number of gears, somewhere inside you need a pair of gears with an infinite number of teeth and a variable diameter (i.e. two smooth surfaces coupled by friction), or a pawl that engages with an infinitely small amount of slop, that is to say, a perfectly-made roller clutch, but again a friction device. There's no way around it. If you don't have a friction linkage in it, then it's a pseudo CVT with many gears perhaps, but it's not a CVT. In fact, I believe all patent offices in the world look for a friction device first off when they receive an application for a purely mechanical CVT design, and if they don't find one, they throw away the application.

The best proof that friction-less CVTs can't exist is that they don't :) The few CVTs in existence on cars (be it the old DAF system, or the new fancy-schmutzy Audi one) all rely on belts. If it was possible to do otherwise, you can bet car makers would have done it.

Is there a proven theorem in mechanical engineering that says a frictionless CVT cannot exist? One that does not assume anything more than solid frictionless parts? Any references?

I have been unable to convince myself either way regarding the smoothness of the output (i.e. perfectly linear or even differentiable relationship between input angle and output angle). I am similarly unsure about whether the variability is continuous, or how you would even define that if the output is not smooth. I can't fully analyze the timing of the engagement of the pawls with a finite number of teeth. I believe the output would have to be at least piecewise smooth, i.e. while you have one "scissor" fully engaged. Anyone feel they understand the engagement of the pawls to the point where they could write out full equations of motion of the parts if they were motivated to?

Note: this distinction is purely academic; It is pretty clear that a device like this could ideally give an arbitrarily close approximation of smoothness and continuity in the gearing. Time will tell if the tradeoffs all ballance out favorably.

It's been done, and done better.
http://www.rohloffusa.com/frame.htm

Afraid that's not true Raiyn, Rohloff do not do a variable gear hub. The Rohloff has 14 speeds, one that Rafael highlighted does not have set gears, it can be set anywhere in the gear range. Look forward to hearing about how it will perform in comparison to my Rohloff.

Here's a link posted from the Dahon forum pertaining to the Nupace Hub (http://www.freeridehubs.com/Contact_freeridehubs.html) . This hub was quoted as having an efficiency range from mid-80% to mid 90% last year by one of the design team.
Bruce
If that's the case then this hub's efficiency is at the low end for internal geared hubs and significantly below a derailleur system. Also, the hub's efficiency has to be combined with a single chainring/chain/single cog drive at about 98% so the overall efficiency is even lower.

A bit off-topic but this was posted a bit further down the linked page:

"Sorry, but as the Canadian Distributors of Rohloff Speedhubs and other Rohloff products we will not be allowing any more Rohloff products to enter the country due to the serious cases of fraud they have committed."

Does anyone know what that's all about? I was under the impression Rohloff is a good quality, reliable company. Why this comment?

Is there a proven theorem in mechanical engineering that says a frictionless CVT cannot exist? One that does not assume anything more than solid frictionless parts? Any references?

There's no need for a "theorem of frictionless CVTs" anymore than there's a need to prove that 1+1=2, it's just obvious to anybody who understands mechanics.

Think about it: the only two ways you could create a true geared CVTs is

1) with a variable geometry cog: that would be a complicated mechanism inside a cog that add or subtract teeth on the outer diameter of the cog. Perhaps something with a chain full of teeth on the outside, around a cone, and when you slide the chain up and down the cone, the chain and its teeth are rolled back in and out of the cone. Regardless of the mechanism, if you add or subtract teeth on the fly, there'll always be only a finite number of configurations where the mechanism would work, and that's when there's a integer number of teeth out. If you have a fraction of a tooth out, the whole thing fails with a bang.

2) with a lever-action mechanism where you turn the rotating motion at the input into a reciprocating motion, feed that into a lever with a mechanism by which you can slide the lever's pivot point closer to or further from the input rod, recover the amplified or diminished motion at the other end of the lever with an output rod and turn the reciprocating motion of the output rod back into a rotary motion that goes to the output shaft. Of course, since you can't use a fixed crank on the output rod because it has a linear motion of variable amplitude, you need to use pawls and teeth on the output shaft. And since teeth only mesh at integer numbers of their sizes,... back to point 1. If you use a roller clutch instead of pawls/teeth to convert the linear motion into a rotary motion, assuming the roller clutch is perfect (no slop), you're using a friction linkage.

Any other form of geared CVT mechanism, reduced to its working principle, will either fall in category 1 or 2, and will be either a pseudo-CVT with lots of gears, or a friction device. Pseudo-CVT with lots of gears are so obviously complex, and therefore unreliable, for the service they render that they are simply never built or used in any application.

Assuming the hub in question isn't a scam (which I'm convinced it is personally), from what I've read so far in this thread, it would be some form of mechanism #2 with pawls and teeth, maybe not with levers but with excentrics, but essentially working on the same principle. Perhaps it has a lot of micro-steps in the gears, making it close enough to a true CVT in practical terms, but it's not a true CVT.

As a side note, In the case of bicycles, there would actually be a form of CVT that would work very well and for almost no efficiency or weight trade-off, and that would be variable-length cranks :) Since a bike converts a piston action from the legs in the first place, and human legs can cope with variable amplitude without any problem, it would work quite well. The best proof is that some unicylists who ride cokers sometimes adopt cranks with two or three pedal holes, so they can either go fast with less control (short cranks) or have more torque and go slower (long cranks) simply by unscrewing and moving the pedals.

This is incorrect, you got it backward. This subject has been rehashed at least a million times on rec.bicycles.tech and on the bicycle science mailing list. I suggest you look up the archives. Here's one from the faq for starters: http://www.faqs.org/faqs/bicycles-faq/part4/section-30.html

Well, then I stand corrected. Begging your pardon. Nonetheless, a cyclist is still very clearly better served by many gears, if they wish to maintain an optimum cadence under all conditions. Singlespeeds and fixed-gears are fun to ride, but who would argue that the gear ratio is ideal for all conditions? It isn't.


Geared CVTs don't exist by definition, just as overunity doesn't exist. If you want a mechanical device that has an infinite number of gears, somewhere inside you need a pair of gears with an infinite number of teeth and a variable diameter (i.e. two smooth surfaces coupled by friction), or a pawl that engages with an infinitely small amount of slop, that is to say, a perfectly-made roller clutch, but again a friction device. There's no way around it. If you don't have a friction linkage in it, then it's a pseudo CVT with many gears perhaps, but it's not a CVT. In fact, I believe all patent offices in the world look for a friction device first off when they receive an application for a purely mechanical CVT design, and if they don't find one, they throw away the application.

The best proof that friction-less CVTs can't exist is that they don't :) The few CVTs in existence on cars (be it the old DAF system, or the new fancy-schmutzy Audi one) all rely on belts. If it was possible to do otherwise, you can bet car makers would have done it.

I am well aware of the fact that "true" geared CVTs do not exist. My question is, so? Such a system has enough gear ratios, all close enough together, to effectively act as a stepless transmission. I considered noting that the CVT power-split device used in the Toyota Prius (which, as you recall, I compared functionally to the Nupace) is not, in fact, a true CVT, but I decided not to. I figured that it would muddy the waters, and that no one would be pedantic enough to really care. Apparently, I was wrong :rolleyes:.

We've established that you know something about mechanics. That's wonderful for you. Do you have anything to say about the Nupace, and/or mine and other posters' comments on it?

Anyway, Wavshrdr, that's a good point, and of the major obstacles to success of this product I was referring to. You can cover a similar or greater gear range with a hub for less than three hundred dollars. Sounds like they've got a long way to go.

It seems like these guys are really in the same trap as most of the other people who've been pushing for bicycle CVTs. They assume (quite wrongly) that it will sell simply upon the merit of being stepless, or effectively stepless, without much regard for other factors. They are of course completely wrong - what's so great about a stepless transmission on a bicycle? If this device covered a gear range of, say, 600%, and cost $500, they'd be on to something. But it doesn't, and so they're really not. Are the benefits of "stepless" operation worth something like six or seven hundred dollars over the cost of a Nexus-8? Not so much.

I wouldn't dismiss the idea itself, since I think it has some merit - the design of the Nupace is probably pretty sound. But I don't see it taking off until they can demonstrate that it's really worth the price.

As a side note, In the case of bicycles, there would actually be a form of CVT that would work very well and for almost no efficiency or weight trade-off, and that would be variable-length cranks :) Since a bike converts a piston action from the legs in the first place, and human legs can cope with variable amplitude without any problem, it would work quite well. The best proof is that some unicylists who ride cokers sometimes adopt cranks with two or three pedal holes, so they can either go fast with less control (short cranks) or have more torque and go slower (long cranks) simply by unscrewing and moving the pedals.

Doesn't sound like such a good idea to me. Playing with crank length for gearing purposes would be playing with what is arguably the most biomechanically critical part of the bicyle. Playing with Sheldon Brown's Gear Calculator (http://sheldonbrown.com/gears/) reveals that a range of crank length from 150mm to 190mm would have a total gear range of less than 20 inches. That would be in exchange for an enormous amount of changing forces and pressure on the cyclist's knee. Nope, just because it works for some unicyclists doesn't mean it's good idea for anyone else.

EDIT: Apparently I just like to play :rolleyes:.

I think the one thing that no one seems to be talking about on this hub is that it really doesn't have a very wide range. 300% is no better than the current 8spd Nexus and 7spd SRAM. This isn't improving upon what we currently have out there by much and it is less than the Rohloff. Now lets say it was 600% then I'd be more interested.

Agreed. It's still too high for touring cyclist and even recreational riders like myself will struggle up hills because it drops only to 40 inches!

After staring at their CAD rendering and also a couple of the pictures from their patent for a few minutes, I understand how their mechanism works. I will try to describe it to you.

The relevent US patent is 05971877.

Explaining the mechanism from the axle outwards, and neglecting literaly hundreds of bearings, we have:

1. A fixed axle and associated torque arm. They don't clearly show the torque arm in their diagram, but it must be there and it wouldn't be very interesting if it was. The axle is eccentric in the middle section, standard in the portion that joins with the frame. The axle only moves when your torque arm rattles loose and beats the hell out of your rear triangle.

2. One Eccentric sleeve with engages the axle in the portion where it is itself eccentric. This is reminiscent of an eccentric bottom bracket. By turing this sleve relative to the axle (By having the stop for a boden cable on the torque arm and the cable clamp on the sleeve), the amount of eccentricity of the outer diameter of the sleeve can be changed relative to the axis of the axle. The sleeve only moves when you shift "gears", and it does so continuously rather than being indexed.

3. Four pawl holders, which are concentric about the outer diameter of the larger eccentric sleeves from (2). They do not engage with anything except the pawls they are holding. Each pawl hoder has two sets of pawls oriented in opposite directions.

4. Pawls. Each pawl is held in by a spring mechanism, rotates about the end in the pawl holder, and has teeth on the outside, which engage with (from chain side to drive side):

5. An outer toothed ring that is fixed to the rear cog.

6. Three more toothed rings. Each toothed ring engages with two sets of pawls, one from each pawl holder. The two sets of pawls associated with each toothed ring are oriented in opposite directions.

(Parts 3 - 6 are all moving whenever you are pedaling.)

7. The hub shell, which engages a single set pawls, i.e. the leftmost set. This set of pawls freewheels when you are coasting. The hub shell rotates axially about the center of the axle.

To understand how the pawls work, imagine a very flexible person standing on skis that are parallel, one slightly forward. Now assume said person passes out. Gravity pushes said flexible person down and he/she does the splits, pushing one ski forward and one back.

Analogy:
Gravity <--> Eccentric sleeves acting as a cam relative to the hub shell / toothed rings.
Skier <--> Pawl Holder
Pawls <--> Legs
Skis <--> Two adjacent toothed rings

So on one side, say the front, of the hub you have pawls engaged with teeth and expanding, and on the other side, say the back, you have pawls contracting and engagine with new teeth. The more eccentric the outer diameter of the outer sleeve, the farther down the pawls "squish" during each cycle.

The design does have some elegant properties:
- You don't have to change the dimensions of any of the parts relative to each other to change the gearing range of the hub. This is in contrast to the much seemingly difficult to design and dimension gears in a traditional gear hub.
- While there is a rediculous number of parts, there are not really very many types of parts.
- It may not be as difficult to service as it seems; It seems like each pawl holder and associated two sets of pawls stays together when you pull the mechanism apart.
- I could imagine it being very smooth when in good working order and at lower speeds. I imagine the pawls whining a bit at higher speed, i.e. not when they are engaging, but when they are slipping to new teeth.
- It is, IMHO, easier to understand than a rohlhoff.
- Does not rely on friction like many other continuous gearboxes.

So no, they don't seem to be a hoax, yes, it seems that have a workable mechanism, and no, I wouldn't recommend buying one until they bring the price down by a factor of ten or so and hire a competent marketing department.

Wasn't the price about half that a year ago?
Seems price isn't coming down.

I think the one thing that no one seems to be talking about on this hub is that it really doesn't have a very wide range. 300% is no better than the current 8spd Nexus and 7spd SRAM. This isn't improving upon what we currently have out there by much and it is less than the Rohloff. Now lets say it was 600% then I'd be more interested.

But that is a 300% overdrive-the Nupace is a 1:1 in low. None of the Nexus, SRAM, or Rohloff hubs have even a 2:1 ratio, the Nexus-4 (which have been recently discontinued) is the highest overdrive at 1.84:1 other than the new Sturmey-8. Might have some niche applications for small tire bikes such as folders-particularly with greaseless belt drive commuters, but the efficiency penalty and price seem prone to hamper. The Sturmey-8 has a similar range and overdrive, so the elimation of discrete steps at the price and efficiency penalty might make the Nupace a hard sell.

There's no need for a "theorem of frictionless CVTs" anymore than there's a need to prove that 1+1=2, it's just obvious to anybody who understands mechanics.

Think about it: the only two ways you could create a true geared CVTs is

1) with a variable geometry cog: that would be a complicated mechanism inside a cog that add or subtract teeth on the outer diameter of the cog. Perhaps something with a chain full of teeth on the outside, around a cone, and when you slide the chain up and down the cone, the chain and its teeth are rolled back in and out of the cone. Regardless of the mechanism, if you add or subtract teeth on the fly, there'll always be only a finite number of configurations where the mechanism would work, and that's when there's a integer number of teeth out. If you have a fraction of a tooth out, the whole thing fails with a bang.

2) with a lever-action mechanism where you turn the rotating motion at the input into a reciprocating motion, feed that into a lever with a mechanism by which you can slide the lever's pivot point closer to or further from the input rod, recover the amplified or diminished motion at the other end of the lever with an output rod and turn the reciprocating motion of the output rod back into a rotary motion that goes to the output shaft. Of course, since you can't use a fixed crank on the output rod because it has a linear motion of variable amplitude, you need to use pawls and teeth on the output shaft. And since teeth only mesh at integer numbers of their sizes,... back to point 1. If you use a roller clutch instead of pawls/teeth to convert the linear motion into a rotary motion, assuming the roller clutch is perfect (no slop), you're using a friction linkage.

Any other form of geared CVT mechanism, reduced to its working principle, will either fall in category 1 or 2, and will be either a pseudo-CVT with lots of gears, or a friction device. Pseudo-CVT with lots of gears are so obviously complex, and therefore unreliable, for the service they render that they are simply never built or used in any application.

Assuming the hub in question isn't a scam (which I'm convinced it is personally), from what I've read so far in this thread, it would be some form of mechanism #2 with pawls and teeth, maybe not with levers but with excentrics, but essentially working on the same principle. Perhaps it has a lot of micro-steps in the gears, making it close enough to a true CVT in practical terms, but it's not a true CVT.

As a side note, In the case of bicycles, there would actually be a form of CVT that would work very well and for almost no efficiency or weight trade-off, and that would be variable-length cranks :) Since a bike converts a piston action from the legs in the first place, and human legs can cope with variable amplitude without any problem, it would work quite well. The best proof is that some unicylists who ride cokers sometimes adopt cranks with two or three pedal holes, so they can either go fast with less control (short cranks) or have more torque and go slower (long cranks) simply by unscrewing and moving the pedals.

It is also possible to do it:
1) Hydraulically- using a proportioning valve; and
2) Electrically- electric drive.

I actually talked to this guy a while back. I was thinking about options for a tandem build I was doing. I got some feedback from him but it was vague. I remember asking him how much torque it could handle. He did not know! That sent me elsewhere. Seems to me that would be one of the first tests you would run...

Well, then I stand corrected. Begging your pardon. Nonetheless, a cyclist is still very clearly better served by many gears, if they wish to maintain an optimum cadence under all conditions. Singlespeeds and fixed-gears are fun to ride, but who would argue that the gear ratio is ideal for all conditions? It isn't.



I am well aware of the fact that "true" geared CVTs do not exist. My question is, so? Such a system has enough gear ratios, all close enough together, to effectively act as a stepless transmission. I considered noting that the CVT power-split device used in the Toyota Prius (which, as you recall, I compared functionally to the Nupace) is not, in fact, a true CVT, but I decided not to. I figured that it would muddy the waters, and that no one would be pedantic enough to really care. Apparently, I was wrong :rolleyes:.

We've established that you know something about mechanics. That's wonderful for you. Do you have anything to say about the Nupace, and/or mine and other posters' comments on it?

Anyway, Wavshrdr, that's a good point, and of the major obstacles to success of this product I was referring to. You can cover a similar or greater gear range with a hub for less than three hundred dollars. Sounds like they've got a long way to go.

It seems like these guys are really in the same trap as most of the other people who've been pushing for bicycle CVTs. They assume (quite wrongly) that it will sell simply upon the merit of being stepless, or effectively stepless, without much regard for other factors. They are of course completely wrong - what's so great about a stepless transmission on a bicycle? If this device covered a gear range of, say, 600%, and cost $500, they'd be on to something. But it doesn't, and so they're really not. Are the benefits of "stepless" operation worth something like six or seven hundred dollars over the cost of a Nexus-8? Not so much.

I wouldn't dismiss the idea itself, since I think it has some merit - the design of the Nupace is probably pretty sound. But I don't see it taking off until they can demonstrate that it's really worth the price.


Here's a reference page someput together on CVT basics and some interesting approaches. One approach includes a CVT combining planetary gears with a gyroscope.

http://www.gizmology.net/cvt.htm

The Rohloff looks really good with 13% gear changes and 526% overall ratios. Does anybody know how much the hubs cost and how much they weigh?

What is an AFAIK?

What a deal, only $995. Something about that website just says scam to me though.

-jon

No one needs that many gears ... really

If that's the case then this hub's efficiency is at the low end for internal geared hubs and significantly below a derailleur system. Also, the hub's efficiency has to be combined with a single chainring/chain/single cog drive at about 98% so the overall efficiency is even lower.

A bit off-topic but this was posted a bit further down the linked page:

"Sorry, but as the Canadian Distributors of Rohloff Speedhubs and other Rohloff products we will not be allowing any more Rohloff products to enter the country due to the serious cases of fraud they have committed."

Does anyone know what that's all about? I was under the impression Rohloff is a good quality, reliable company. Why this comment?

SCAM to make you want to buy thier stuff. There was post a while back about a company that started slamming Rohloff in order to promote thier product. Maybe the same folks?
If you have any doubts about the Rohloff hub check out: http://www.mtbr.com/reviews/Hub/product_68271.shtml
I spoke the Rohloff rep early this year, yes he actually called me back, and returned my emails as well. Had a tech question about frame building and thier hubs.
Has anyone thought to talk to the Rohloff rep about this slam? I might do that tonight and update when I get a reply.
Read what real riders say about the Rohloff, talk to a few. I did before I bought one.
Next try to find somebody using this new hub and talk to them or email them. See what response you get.
If you can not find one, and talk to them on the Phone, or get a personal email back, guess what that says.

No one needs that many gears ... really

I hear you. Hopefully I'll get my fixie by this weekend. Woo, yellow bike!

-Jon

The Rohloff looks really good with 13% gear changes and 526% overall ratios. Does anybody know how much the hubs cost and how much they weigh?

What is an AFAIK?

The're about $900 dollars new. They are heavier than other internal gear hubs-those 14 gears take up weight. The Rohloff is more efficient than other hubs, particularly its higher gears, and has a longevity that goes on and on.

The're about $900 dollars new. They are heavier than other internal gear hubs-those 14 gears take up weight. The Rohloff is more efficient than other hubs, particularly its higher gears, and has a longevity that goes on and on.

I've spoken with a person who removed the Rohloff and returned back to the derailluer because of the weight. My Nexus 7 weights a ton and is not free rolling. I was pedalling and felt like the bike just slowed down too much. My eight year old Univega that weights close to 28 lbs is more free rolling than my Bianchi Milano Nexus bike. I can just imagine putting an even heavier hub on the back of my rear wheel.

I was surprised at the slam against Rohloff too which is why I questioned that web site's statement. I know of two or three very satisfied customers, one of whom has the 14-speed hub on a Tandem. It doesn't come much more demanding than that.

The net weight penalty for a Rohloff 14-speed hub is about 250 grams or slightly over 1/2-pound which will enrage the weight-weenies but isn't that bad really. One problem is that the shifter is designed only for flat bars. I know of riders who have adapted it to drop bars but it's a kludge.

The Rohloff is most efficient only in its single direct drive gear (6th or 7th gear, IIRC) This is true of all internally geared hubs. The non-direct drive ratios suffer similar losses to other internally geared hubs.

snip... If you want a mechanical device that has an infinite number of gears, somewhere inside you need a pair of gears with an infinite number of teeth and a variable diameter ...snip

Quick question for you ppc: would "infinite teeth" be a necessity?

What I'm envisioning is a device with a variable diameter, as you mention, but instead of adding teeth, it would just expand. It might sort-of look like a 1-inch pitch device at larger diameter and something more conventional at smaller diameter. (make sense?)

I have no idea how you'd get a chain to mesh with it at anything other than a perfect ratio (1:1 teeth, 2:1 teeth) but I digress... ;)

BTW, I've heard the Rohloff Speedhub "breaks in" and becomes quieter and possibly more efficient after "x" miles.

There's no need for a "theorem of frictionless CVTs" anymore than there's a need to prove that 1+1=2, it's just obvious to anybody who understands mechanics.

After reading the description what I envision is a planetary gearset in which the planet gears have been replaced by several pairs of prawls that engage the sun and ring gear. The prawl carrier is on an eccentric that allows it's position to be infinitely variable over a limited range. By moving the position of the prawl carrier it can act like planet gears that have variable diameters.