# CVTs Revisited



## PhantomPholly (Aug 20, 2008)

No opinions on this???


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## major (Apr 4, 2008)

PhantomPholly said:


> No opinions on this???


Hey Phant,

I've seen it tried a couple of times and it worked for crap. I think the problem is that the speed/torque characteristic of the series motor conflicts with the way the ratio changing mechanism of the cvt acts. I'm not saying you could not get it to work, but the guys that tried it ending up scrapping it for the standard tranny or direct drive.

My opinion.....not worth the trouble.

major


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## Dalardan (Jul 4, 2008)

I've been working with a CVT this year, tuning one for a Formula SAE race car. Well... I've put the right person with the right tools at the right place...

There is quite a mechanical challenge to place one in a car that isn't designed for it at the beginning. The clutches alignment must be really precise, and the whole assembly pretty stiff to keep this alignment.

For sure, stock settings won't work for whatever CVT you'll find. You'll need to play mainly with the ramps that sets the ratio change (there are fixed ratio ones, double ratio, slope ratio, and if you've got money even custom machined ramps that fits exactly with your motor). Another thing that comes into play is rivets in the main clutch that produces the centrifugical force that allow the ratio change. Those also need to be tuned. Also, the belt tension will affect the clutch RPM and the Shift RPM.

The clutch RPM is the RPM where torque is beginning to be applied to the wheels. Shift RPM is the RPM where the CVT tries to stay when applying full power.

CVT tuning is somewhat of a black science where self experience helps a lot because a lot of factors (that I didn't mention you because I don't know them) all affect the same things at the same time. I you still wanna consider that thing, you should talk with a snowmobile drag racer (They get 0-60MPH in 1,2s if I remember), clutch tuning is almost more important to them than motor tuning... We've got a snowmobile drag racer with our FSAE team. Without him, never we would have considered to tinker with a CVT.

Continue to gather information, maybe with permanent magnet motors (with a narrower torque band) it might be usefull. But it'd be a lot of work.

My 2 cents,

Dalardan


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## PhantomPholly (Aug 20, 2008)

Thanks for the replies. I didn't expect it would be automatically easy.

I already figured I'd need to build a "cage" to mount the motor with the drive clutch and a shaft with a driven pulley. On the site I linked they had some stock mods which seemed pretty straight forward - just lighter or heavier weights and a lighter or heavier spring.

I was hoping that these were simple enough that at a nominal power setting the motor would stay in low gear until it spun up to around 3000-3500 rpm. I can see why it would behave differently than a gasoline engine since there are no equivalent power pulses which would keep driving the clutch to a lower gear, so my suspicion is that I would need lighter weights but a "normal" spring.

The one thing I can't know without playing with one is if it is possible to reconfigure them so that they never slip into "neutral." If that is possible then it seems like it will just be trial and error to find the right weight / spring combination.


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## rallyshark (Sep 19, 2008)

the 2010 subaru outback and legacy have a self-contained CVT transmission which bolts up to any EJ series subaru engine. It might be worth looking at. I drove the 2010 outback and the power delivery was excellent and smooth. The CVT is also meant to go up to 100k miles without any service whatsoever.


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## kittydog42 (Sep 18, 2007)

The Subaru Justy also had a CVT for an automatic.


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## PhantomPholly (Aug 20, 2008)

rallyshark said:


> the 2010 subaru outback and legacy have a self-contained CVT transmission which bolts up to any EJ series subaru engine. It might be worth looking at. I drove the 2010 outback and the power delivery was excellent and smooth. The CVT is also meant to go up to 100k miles without any service whatsoever.


Hmmm, I currently drive an old Legacy (2000). It's a bit heavy for a conversion though, and only gets 21mpg.

There are several newer cars with CVT transmissions - I just don't want to use a new car for a conversion!

I would guess that buying a new "real" transmission would be very expensive. The snowmobile units are only a couple of hundred bucks, and VERY light.

I'll keep researching, but I think that it might be worth experimenting with. Using two CVTs off a single drive shaft (one to drive each front wheel) would negate the need for a differential, saving more weight. As little as they cost, I may dummy up a unit for testing and just sell it at a small loss to real snowmobilers if it doesn't work out.


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## rallyshark (Sep 19, 2008)

kittydog42 said:


> The Subaru Justy also had a CVT for an automatic.


Yep, i think it was the first production car with a CVT if i'm not mistaken.

The only advantage to getting one of the new subaru CVT transmissions is that they are probably built for more torque and abuse than what snowmobile versions are.


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## Dalardan (Jul 4, 2008)

I've seen with my own eyes 1000cc Turbocharged Artic Cats going over 300hp... it should be ok for a small conversion. 

Artic Cat main pulleys are well used in drag racing because you can easily change ramps and springs without removing the clutch. Also, there not really expensive when compared to some others (Yahama...)

Again for drag racing purpose, Team Industries secondary pulleys are well used around where I live. They are an aftermarket brand that performs well.

If you want to do a decent job, you should do what we did : put your motor on a dyno bench and get your torque/RPM chart or efficiency/RPM chart. Then, calculate the maximal ratio reduction of the CVT you choose you'll use (the two extreme limits of ratio adjustment are very inefficient in a snowmobile CVT as well as tend to burn belts). You'll maybe need to do another ratio adjustment after, a CVT doesn't provide a really huge ratio change. After all that, you can begin clutch (pulleys) tuning, where I know a lot less stuff...

You should ask South Dakota School of Mines, they've made an electric snowmobile with a CVT :
http://www.go-ev.com/SDSM_Album_files/Finished_Snowmobile 011.jpg

If it happens that I can talk with our CVT guy this summer, I might be able to give more help.

Dalardan


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## PhantomPholly (Aug 20, 2008)

Thanks for the picture and the notes.

I'm not sure why you think the gear ratio variation isn't wide enough - the Comet 94C (good for up to 40hp, or a bit more than 1/2 of the hp of a 9" motor) has ratios from 3.49:1 to 0.78:1. Maybe the bigger ones don't get such a good range? In any case, I'm not looking for a dragster!

I did realize, though,that there is something I overlooked. Or, maybe I don't have enough info. Do the front drive axels drive the front wheels at 1:1 on a FWD vehicle? 

My goal would be that in "top gear" I would be somewhere in the 70-80mph range at max theoretical rpm. Given the example above and wheels with an 18" outer (road) diameter, that equates to about 1500 wheel RPM at 80mph. At a 1:1 axel to wheel ratio, that would only be a motor speed of about 1100-1200rpm @ 0.78:1. Thus I would need about a 4:1 stepdown AFTER each of two CVTs to achieve that speed at 4800-5000rpm motor speed. I suppose I could use a single CVT and a differential, but that's adding back in the weight I thought I was going to save...

Well, this may just be yet another not-so-brilliant idea...


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## 2cycle (Jul 2, 2009)

I think the CVT is a great idea that's why I'm using it on my project EV. I have been tuning CVT's for a long time so I understand what they need. If you haven't been tuning them for years or can call on someone that has you will not figure them out. Not to turn you away from them but to let you know they are not easy and there are very few indiviuals who can "calculate" where to start with for parts.
I'll give you an idea of where to start for parts and it will soon sink in that it may not be cheaper than a tranny. First, the CVT drive clutch you will want to use is an aftermarket one. These cheap ones you found will not take the kind of torque that will be put into it from the dc motor. The Micro Belmont 4 or 6 cam arm clutch will have the strength you are looking for. The reason I say maybe a 6 cam clutch is you may want the clutch to engage the belt at a very low rpm and to do this it takes lots of weight and a fairly light spring. You can not run a weak secondary pulley spring or the belt will slip and you go nowhere and just wreck parts. The belt of choice will be the Polaris racing belt that the grag racers are using as it takes the squeeze better than any other. 
The shift curve of the CVT will be very different than a snowmobile. With a snowmobile we have huge amounts of hp at the peak in the higher rev ranges but in the low rpm ranges there is not much there. That's why the clutches don't even grab the belt until the drive clutch reaches 5000 rpm or even higher. 
Not to throw you a curve but the other option is the CVT combined with the centrifugal clutch. This is what is used in the 4 wheeler and UTV world and has proven to be very good at shifting those lower rpm and higher torque 4 stroke engines. For a street going vehicle I would do this method. The main difference is the clutches don't even start moving until the throttle is hit and the centrifugal clutch engages. The belt also has full tension (squeeze) at all times, no slack in the drive clutch like a snowmobile. These types of systems have a limit to the amount of torque put into the centrifugal clutch so it may need to be put on a shaft that runs 2x motor speed to reduce torque. So basically in the output to the rear diff you will have the same torque as direct drive during accel but you can make use of the 20% overdrive of the CVT to net more speed. 
For drag racing the snowmobile clutch would be my choice because you double your torque with the CVT ratio and gain an overdrive on top.
If and when you decide to set it up with the CVT I would help you out as much as I can.


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## bbbowden (Apr 13, 2009)

I'm currently building something along these lines. I have a direct drive set up with two motors driving the rear wheels independently via a chain drive. I set the gear ratio so that at max motor RPM, I should get 60 MPH (if I did the math correctly). However, I'm concerned that my launch is going to be VERY slow. I have looked at those belt CVT and think that I might try that if my current set up doesn't work.


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## 2cycle (Jul 2, 2009)

When figuring out max speed for a given set up use a 1:1 ratio at top speed for efficiency reasons. These pulleys will shift out past 1:1 but only with everything correctly set up. There are 20 different things that can stop it from fully shifting out into the overdrive ratios. 

You mention 80 mph top speed. That seems pretty high for a mild set up, how much hp are you making with your set up. Remember when figuring top speed torque means nothing by itself. Hp is the variable needed to figure top speed and if you don't have enough hp all the torque in the world will do nothing for you.


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## PhantomPholly (Aug 20, 2008)

Ok, I do understand that the way these clutches are designed by default they will not engage the belt until sufficient RPM is developed.

Is there a way to circumvent that so that it is 100% engaged but just the drive ratio changes? Given such a setup I wouldn't need to do any special tuning - clutch rpm would keep it in "low gear" until sufficient rpm was reached to overcome the driven pulley spring.

Has anyone got a link to an exploded view?

Oh, and I don't think I'll typically cruise 80mph on the highway. My thought process was to make the low end gearing as low as possible while still ensuring that if I had a nice down-hill run on the freeway I wouldn't overspeed the motor.


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## 2cycle (Jul 2, 2009)

PhantomPholly said:


> Ok, I do understand that the way these clutches are designed by default they will not engage the belt until sufficient RPM is developed.
> 
> Is there a way to circumvent that so that it is 100% engaged but just the drive ratio changes? Given such a setup I wouldn't need to do any special tuning - clutch rpm would keep it in "low gear" until sufficient rpm was reached to overcome the driven pulley spring.
> 
> ...


yes, the system that keeps belt tension is the one I explained for the ATV's and UTV's. That would likely be what you would want. At first I was thinking about needing the internal centrifugal clutch but that wouldn't be needed. Suzuki, Arctic Cat and Yamaha are users of this style of CVT so just go on any online microfiche from many ATV dealers and take a look at the pictures. Before buying anything let me know because I may be able to save you some cash. 
You still did not answer how much hp will you be producing at what rpm.


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## PhantomPholly (Aug 20, 2008)

2cycle said:


> yes, the system that keeps belt tension is the one I explained for the ATV's and UTV's. That would likely be what you would want. At first I was thinking about needing the internal centrifugal clutch but that wouldn't be needed. Suzuki, Arctic Cat and Yamaha are users of this style of CVT so just go on any online microfiche from many ATV dealers and take a look at the pictures. Before buying anything let me know because I may be able to save you some cash.
> You still did not answer how much hp will you be producing at what rpm.


Oh, at this point I'm looking at a typical 9" or 11" motor. The specs I've seen say 70hp / 5000-5500 rpm max; info I've found on line about a Honda Civic sedan suggests even freeway cruising only uses 15 hp continuous @ 70mph. Thus, if I were looking at the Comet line listed earlier I would probably opt for something that can handle a bit more, perhaps one of their models rated for 120hp - that would strictly be for better belt life.

For the differential I have a couple of options - either look for a traditional differential, or get two planetary gear stepdowns with about 4:1 ratio and two CVTs (which could then be rated at lower power). I've heard a rumor that some FWD vehicles actually have a differential which separates from the transmission - that would be an ideal approach if I identify the right vehicle since I wouldn't have to do anything funky to mate the drive shafts.


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## 2cycle (Jul 2, 2009)

PhantomPholly said:


> Oh, at this point I'm looking at a typical 9" or 11" motor. The specs I've seen say 70hp / 5000-5500 rpm max; info I've found on line about a Honda Civic sedan suggests even freeway cruising only uses 15 hp continuous @ 70mph. Thus, if I were looking at the Comet line listed earlier I would probably opt for something that can handle a bit more, perhaps one of their models rated for 120hp - that would strictly be for better belt life.
> 
> For the differential I have a couple of options - either look for a traditional differential, or get two planetary gear stepdowns with about 4:1 ratio and two CVTs (which could then be rated at lower power). I've heard a rumor that some FWD vehicles actually have a differential which separates from the transmission - that would be an ideal approach if I identify the right vehicle since I wouldn't have to do anything funky to mate the drive shafts.


If you want to save a little money and get a better CVT clutch than a Comet for your EV let me know your plan and I may be able to save you $100 or so. The Comet line of clutches are fine for little ICE engines with little torque. If your running a 9" or 11" motor I would never use the Comet line of clutches. If I were running even a 9" motor I would run the Micro Belmont clutch. Yes it's $1800 or so, but after you grenade a couple Comets you'll wish you just took my advice, and hopefully nobody gets hurt in the process. I have friends with permanent injury from exploded drive clutches that threw pieces.


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## PhantomPholly (Aug 20, 2008)

2cycle said:


> If you want to save a little money and get a better CVT clutch than a Comet for your EV let me know your plan and I may be able to save you $100 or so. The Comet line of clutches are fine for little ICE engines with little torque. If your running a 9" or 11" motor I would never use the Comet line of clutches. If I were running even a 9" motor I would run the Micro Belmont clutch. Yes it's $1800 or so, but after you grenade a couple Comets you'll wish you just took my advice, and hopefully nobody gets hurt in the process. I have friends with permanent injury from exploded drive clutches that threw pieces.


Well first I believe you - but, ACK! For $1800 I'll skip the experiment and just use a manual tranny!

It's easy to daydream until you have to open your wallet...


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## Amberwolf (May 29, 2009)

Speaking of daydreaming: 2cycle, what would you think might work as a CVT for an ebike like my Crazybike2:
http://evalbum.net/2691 
or a similar design in a trike version (tadpole). 
They're both heavy bikes (120+ pounds), and are designed to haul cargo and/or a trailer as well as themselves plus me (150 pounds). So whatever transmission I use has to be able to take that torque. 

I don't need or want a clutch, as the electric motor can run as low a speed as necessary. Also, I'd need to be able to change ratios on the fly by an automated system eventually, and I want to be able to do it even if I'm stopped (or nearly so), since sometimes traffic forces me to stop so fast that I have no chance to shift down first. Right now that's a big problem with the bicycle type chainring/shifter setup, as I have to either get off and manually move the chain to the lower gears (sometimes necessary with a heavy load or on a hill) before I can startup, or simply waste power and suffer pain in my knees as I try to get going and shift down as fast as I can. I'd really really like to be able to shift down even when stopped if at all possible. 

If there is already a clutch in the CVT(s) you suggest, then is there an easy way to defeat or remove them?

Currently the motor I'm using has it's own gearbox, converting whatever the ~350W motor RPM is down to around 120RPM, and the ~650W motor I will be using shortly is geared down to 135RPM. I use a chainring size on each to give around 100RPM typical at the input to the drivetrain, where pedals and motor powertrains meet. Both of those are from powerchairs, and they provide an assist to my pedalling. 

I would like to eliminate the existing bicycle shifters and chainring cassettes (which are exposed to weather/dirt/etc), converting it to an enclosed CVT, driving a single chainring on the rear wheel. Ideally, both pedal and motor drivetrains would run thru the same CVT. 

I would like to have at least 3:1 to 0.5:1 ratios available, for hill climbing and for speed. Even if it does not have those exact numbers but does have a wide range, I can still gear it's input or it's output differently to achieve what I need, which is mostly the hill climbing abilities (there's not many in Phoenix, but the ones there are cannot be ridden up by my existing system). 

The NuVinci wheel-hub-based-CVT would be great to use, but it can't be driven by any kind of motor without voiding it's warranty (even though someone from NuVinci contacted me via the Electricle blog to suggest using one on my ebikes!). So that's out. It's price is too high for me anyway, at $400 and up, depending on where I would get it.

I'd like to use something I could reasonably expect to find used, possibly even in a junked vehicle/etc that I could adapt to this.
________
Avandia Law


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## 2cycle (Jul 2, 2009)

PhantomPholly said:


> Well first I believe you - but, ACK! For $1800 I'll skip the experiment and just use a manual tranny!
> 
> It's easy to daydream until you have to open your wallet...


I said it would be pricey to do it right with a CVT. For heavy vehicles they are not the best choice I guess. Snowmobiles and ATV/UTV's only range from 500 lbs to 1200 lbs (the biggest UTV's) and they seem pretty under engineered at times in these units. I really believe a tranny with the proper ratios and 3 speeds for high speed cars and 2 speeds for a 70 mph and lower car is what I would put my money on. 
My wife's car, Ford Five Hundred, uses a CVT built by ZF ( a heavy equipment drive line manufacturer) and the ironic thing is even though it's built by a heavy equipment man. it's so fragile that if one tries to pull a trailer even a small one it will destroy the CVT. I thought that was odd, but it just goes to show you a CVT is not really tough like a standard tranny.
Amberwolf, You have a totally different type of set up and all those pieces would likely have to be custom made, unless you just fork up the $400 to buy the already made one and hope it doesn't break. Sometimes it doesn't pay to reinvent someone elses mouse trap because you'll spend more time and money in the end without any real assets over the original. 
I'm sure I could design a tougher one and machine all the pieces for you but it would cost 1000's of dollars. Just not worth that kind of money.


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## Amberwolf (May 29, 2009)

If I could afford it, I would buy all sorts of things for my main ride, but at the moment even rent and utilities are a month-to-month gamble.  So I build my transportation from recycled junk others don't want anymore (a lot of it has come from Freecycle). 

I was just wondering if you already knew which ones might take such a light load and low speeds, that would be something commonly available enough to find in scrapped equipment. Apparently not, but that's ok, I may eventually find it on my own.

I'm not truly worried about the NuVinci breaking due to anything I would do to it, but if there were a factory defect already and it did break, then simply because I am using it in a motor-assisted drivetrain they would not warranty it. 

They also will not warranty it unless it is used as the rear wheel's hub itself, so I cannot use it for another idea I have for a front-wheel drive, even if I only used pedal power. Nor would I want to use it and ~9lb weight in my actual rear wheel, as that adds even more startup rotating mass to the wheel itself, and more rotating mass to stop when I brake. (though that might not really matter since its' still mass on the bike). I'd rather use it in the middle of the bike and have it drive the rear drivetrain. That way if I find that I do not have low enough gears, I can still put a regular bike drivetrain back there again, so that I can shift down to lower ratios without rebuilding the whole rest of the drivetrain.

They just have too many limitations in how the NuVinci can be used and still be covered under warranty, even though the specifications for it's capabilities certainly exceed the puny limits of the applications they limit it to.

Since warranty would not matter for something I find in scrapped equipment or junked vehicles, etc.,  then I could do whatever I wanted to with that. NuVinci hubs are not something I'm likely to ever find like that--I haven't even found a junked bike with disc brakes, or the old Sturmey Archer 3 speed hubs, or any of the Shimano Nexus hubs, etc, so I don't think I'd be finding something as expensive and high-tech as a NuVinci. People that have bikes with these things on them seem to know what they are and that they are worth money even if the rest of the bike no longer is. 

If any kind of CVT was common enough to find in junked/scrapped stuff, though, I'd be able to search for that type of stuff. 

I did look into building my own pulley-based CVT, but I don't have all the knowledge or equipment to do it from scratch yet. I have a lathe I could turn or modify pulleys on, but no mill or drill press (which I could also build but might have to borrow someone else's to do certain parts of!). Everything else I have is hand tools or small hand-held electric power tools. Eventually I'll get there, but if I had a working junked CVT, it'd just be that much faster. 
________
new condos in Pattaya


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## 2cycle (Jul 2, 2009)

The biggest problem I see is most CVT pulleys are too big for an Ebike and require at least 2000 rpm to operate properly. A perfect mini motor and CVT might be something like a 3600 rpm setup. If I think of something I'll let you know. I did look at the NuVinci and it's really slick but I can see why they don't want motors hooked to it.


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## Amberwolf (May 29, 2009)

2cycle said:


> The biggest problem I see is most CVT pulleys are too big for an Ebike and require at least 2000 rpm to operate properly. A perfect mini motor and CVT might be something like a 3600 rpm setup. If I think of something I'll let you know.


Most of them definitely are too large, of the ones I've looked on the web for. But I'm sure some of them are small enough. I think I've seen some on a go-kart that would work, in some videos from the UK on youtube a while back, but I don't know how expensive that one might be, or how common it is. 

As for the RPM, what little I know of them is simply that they have clutches on them designed to prevent damage or stalling of an ICE hooked to them (since that's the most common power source on CVT-equipped machines I know of). Those clutches have minimum RPMs to engage them, but if bypassed I see no reason why the CVT itself would not operate at much lower speeds, if the shifting mechanism(s) are not operated by rotational speed, but rather by lateral mechanical motion (cables, etc). 

I don't really know the mechanical engineering details of how they work, but that's my layman's grasp of them. Please correct anything I have misunderstood! 

If it werent' for the shifting mechanism, I probably could design an extremely basic one myself (I tried, but couldn't work out something I could actually build out of the parts I have around here). 



> I did look at the NuVinci and it's really slick but I can see why they don't want motors hooked to it.


Me not being a mechanical engineer or knowing enough technical bits about it, what specifically do you see?

They didn't try to explain any of their reasons, just simply said it's how their warranty is written, and that they'd someday consider changing the warranty to not restrict it in the various ways they do. What bothers me most is that they actively go out there and suggest people use these things in applications that they know they won't warranty.
________
Web Shows


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## 2cycle (Jul 2, 2009)

That's right you don't need a clutch to engage the belt you want the belt engaged at all times.  Give me an idea of what kind of size drive and driven pulley you can fit on your buggy and I'll give it some thought. I also have an idea for a one way bearing (sprague) that may be able to incorporate the rear wheel axle. Maybe I can see something working here, and I have all the tools needed to build most anything.


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## Amberwolf (May 29, 2009)

As for the freewheel/rear axle/etc, that's already taken care of with the bike's existing drivetrain. Even if I simply remove the derailers/shifters and use just a fixed chain length on the rear wheel, I can still leave the rear cluster/freewheel. To reduce weight I can simply take off all the chainrings not being used, and put small spacer rings in their places. Alternately, if I can get it off the other wheel it's on right now, I have a fixed-gear freewheel but it has a small number of teeth (16, I think) and I will likely want a larger one.

Speed is not very important in this project, as 20MPH is the max legally allowed for ebikes in AZ anyway (the law doesn't say if that's while the motor is running or not, only that it is considered bicycle class "when it is operated at or less than 20MPH"). It's startup and hill climbing power that are important, since that's also what is used to fight headwinds (which I run into a fair amount at the times of day I end up going to work, especially). 


Now, for the amount of space, I'd have to measure it, but in this pic:








the entire middle triangle from the front seatpost to under the seat is currently available. It's not much space, but it's all that I have in this design. In the pic, the (white) battery is a 12V7Ah SLA mounted end-up, and is going to be moved, probably to the space in the front triangle, and then eliminated entirely once I finish a DC-DC converter to give me a regulated 12V(13.6V, really) for the lighting system, running from the traction batteries. 

The bike uses 24" wheels, so a guesstimate without going outside in the heat and measuring it  is 14" across the base of that triangle from front to back, and 10" from the apex of it vertically down to the base. For the width, at the narrowest it is the same as that front seat post, less than 2". At the widest rear part, it is around 8". 


In the trike version still being designed, there is a large box area under the seat that will hold the motor and whatever intermediate drivetrain I use, which I hope to be a CVT of some type by then. I expect that box area to be 6" to 8" high, and at least 14" to 16" wide and from front to back. There may be additional room behind the seat depending on what rear suspension system ends up having to be used. 

Keep in mind that I really *am* looking to get this thing as a scrapped unit from something else, especially since I'd guess one thing that commonly breaks is the clutch, probably in a way that keeps it from engaging automatically, and thus would leave it eminently useable for me, since I can then just either remove the clutch entirely (if possible) or fix the clutch in place so that it is always engaged. As long as the shifting mechanisms still work, or are repairable with what I have on hand, I could probably use something junked like that. 

It just has to have a wide enough ratio spread that I can use it for a sufficiently wide range of "gears". Even if it doesn't, I can still use it for the constant gear changes I normally have to do, and then use just a rear shifter/derailer/cluster on the bike wheel itself for any other ratios I need to get out of the system. That way I don't have to worry about being stuck in the wrong gear after a sudden stop, and wasting power and/or hurting myself just to get going again. 
________
XKandyX live


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## 2cycle (Jul 2, 2009)

When trying to keep tension on the drive belt full time all you need to do to the drive clutch of the CVT is mechanically keep it from opening back up wider than the belt. On an Arctic Cat or Polaris style drive clutch it's very easily done with about 2 minutes of machining on a lathe. Normally we use shim washers to precisely set belt to clutch sheave clearance to about .020", in your case take out all shims and if there were not at least enough to take away all belt side clearance than machine a little off the post that holds the washers. 
You don't have much room so likely they would need to be less than half the size of a normal CVT pulley, that's why I think machining your own would work better. The only CVT drive clutch that is small enough would come on those small scooters or buggies. 
Where in Phoenix do you live. When I was in school in Phoenix I remember a motorcycle shop on the east side I think the name was Edwards Cycle. A place like that would sell small clutches like that off from old junked mopeds, scooters, and buggies. Maybe take a look at one of those and see if that may fit, if it does then figure out how to keep the belt in tension at all times.


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## Amberwolf (May 29, 2009)

That all sounds fairly doable. 

I'm in the Metrocenter area of Phoenix, a long stone's throw from I-17 and Northern. It looks like Edward's Cycle is now called Cycle Gear, if it is the one I could find in a quick search at 13220 N Cave Creek Rd. http://www.cyclegear.com/store_locations.cfm?State=AZ 
That puts it just about on top of one of those hills I was referring to having insufficient low gearing to climb. 


The idea I originally had to build myself was to have two center-split expandable pulleys, so that as the sides of one are moved apart slightly, the sides of the other are moved together. It would have been shifted by a cable-operated spring-loaded lever on each side of the pulleys that would see-saw one direction or the other depending on which pulley was to be expanded or contracted. A spring and set screw system would push the pulleys apart to keep belt tension. 

It sounds fairly simple, but actually building it isn't. When I started working out what parts I'd need to have (or make) to do it, I realized that I probably could not do it with my current knowledge and tools. So I had a simpler idea:

Make two equally-sized pulley cones, one installed inverted on one shaft, and one normal on the other. Original tension would be created by simply bolting down the shaft ends in slotted boltholes, rather like setting the chain tension on a fixie bike. A cable-operated shifter rather like the rear derailer on a bike (but with a guide pulley instead of a guide sprocket) would hang between the cones and pull the belt laterally as needed, and would be kept in tension by a spring and set-screw on the hanger. 

This should be much easier to machine, and I might end up making this for the trike. But it's physically larger than the other one, and requires a flat belt instead of a v-belt, and I can imagine the belt slipping or refusing to shift "up" a cone at some point. 

The hanger/guide pulley I would likely start off with for experiments is the tensioning pulley from a serpentine belt arrangement off a car. It's very large, though, at about 2.5 to 3" diameter and an inch or more wide, and heavy because of the steel mounting bracket it's on that I don't think I can remove it from with my tools.

The cones I could make from a number of things, and the shafts I can use bike wheel axles. Then I can use the bike hubs and bearings to support the cones. I'm not sure what angle would be best to use on the cones, but for a wider belt (which would transfer torque better, right?) it'd need a shallower angle, I think. So this system will almost certainly be much larger than the first idea I had. 

The shifter arrangement can be made from either derailer or pull-brake parts, most likely.
________
Laguna Heights Condo


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## Jimdear2 (Oct 12, 2008)

Amberwolf said:


> That all sounds fairly doable.
> 
> The idea I originally had to build myself was to have two center-split expandable pulleys, so that as the sides of one are moved apart slightly, the sides of the other are moved together. It would have been shifted by a cable-operated spring-loaded lever on each side of the pulleys that would see-saw one direction or the other depending on which pulley was to be expanded or contracted. A spring and set screw system would push the pulleys apart to keep belt tension.


 
What you are describing here is called (one of the names) a variator transmission found on many garden tractors. Usually the ones with 6 or 7 speed with out low range or 12 or 14 speeds with low range. MTD, who builds about half of the garden tractors sold in the U.S. under all of the Private Brand names uses it a lot. 

This is a three sheave setup on a single shaft. The middle sheave is double sided. When you force the drive belt into the upper sheaves with the shift lever that squeezes the lower spring loaded belt out on the lower sheaves, changing ratios.

Usually you will see a tractor with a High range , (sometimes a ) Low range and reverse on a shift lever goining to a geared transaxle. Then on a separate lever you will find a multi step slot with a lever that positions the idler/clutch pully. This positioning pully forces the belt into the variator pully sheaves to change ratio. You can also control speed with the clutch pedal, the further you depress the pedal the wider the pully sheaves are forced, the slower you go until the sheaves no longer contact the belt.

I think that once you look at a couple of these you will find what you need for a manually shifted CVT.


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## order99 (Sep 8, 2008)

The Endless Sphere Forums have been thrashing this idea out for awhile:

http://endless-sphere.com/forums/viewtopic.php?f=28&t=9342

http://endless-sphere.com/forums/viewtopic.php?f=28&t=10998

http://endless-sphere.com/forums/viewtopic.php?f=28&t=8644


Not to sound like an ignorant fool (too late! ) but could you rig up a mini-derailler with say, three short chains, three gears of your favorite ratio and a salvaged shifter? Or does even that small motor have too much torque and speed for that to work? Even if it worked I could see it being awkward-accelerate, cut power, shift, accelerate, cut power, ad nauseum...

Mind you, if you COULD make it work, it would fit your condition of 'easily found salvage' pretty well!


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## Amberwolf (May 29, 2009)

order99 said:


> The Endless Sphere Forums have been thrashing this idea out for awhile:
> 
> http://endless-sphere.com/forums/viewtopic.php?f=28&t=9342
> 
> ...


I have not read the entire threads for the first or last of those, but they all start off with what look to me to be very definitely *non*-CV transmissions--each has specific ratios they would shift between. The middle thread doesn't have a CVT in it's (single page of) discussion. 

Is there something about CVTs in those other two threads somewhere? They're at least 10 pages long and I don't relish digging thru them only to find nothing CVT-related. 





> Not to sound like an ignorant fool (too late! ) but could you rig up a mini-derailler with say, three short chains, three gears of your favorite ratio and a salvaged shifter? Or does even that small motor have too much torque and speed for that to work? Even if it worked I could see it being awkward-accelerate, cut power, shift, accelerate, cut power, ad nauseum...
> 
> Mind you, if you COULD make it work, it would fit your condition of 'easily found salvage' pretty well!


That it would, but if I understand what you are describing, I could much more easily use my existing bike drivetrain for a much simpler way to shift, exactly as it already is, for even more ratios, since the idea of a CVT is to have smoother shifting (and easier shifting) between ratios, by being continuously variable between the upper and lower ratio limits it's designed with. 

Having *less* gears doesn't really make much sense to me, to try to accomplish those goals, nor to increase the ratios available (for my case) to allow better hill climbing and still have speed available. 

I'm also confused how the three chains would be able to work, since they couldn't all fit on there at once. Only one chain can be used if shifting between all the various gears is to be possible. 





Jimdear2 said:


> What you are describing here is called (one of the names) a variator transmission found on many garden tractors. Usually the ones with 6 or 7 speed with out low range or 12 or 14 speeds with low range. MTD, who builds about half of the garden tractors sold in the U.S. under all of the Private Brand names uses it a lot.
> 
> This is a three sheave setup on a single shaft. The middle sheave is double sided. When you force the drive belt into the upper sheaves with the shift lever that squeezes the lower spring loaded belt out on the lower sheaves, changing ratios.


Pardon my ignorance of the CVT you're describing, but that does not sound at all like what I was describing, since you are describing a single shaft with multiple sheaves that a belt is physically switched between, and what I am describing is a pair of pulleys each with a single (set of) sheave that are on separate shafts, with a single belt that always stays between them, simply changing the sizes of the pulleys (simulaneously) by separating the cones of one while closing the cones of the other, forcing the belt to ride farther out circumferentially on the one being closed, and farther in on the one being separated. 

What you describe sounds to me more like a simple three-speed belt-driven transmission, instead of using meshed gears or chain/sprockets. 

What I am describing is a CVT, to be continously variable in ratio between the upper and lower bounds of the pulley sizes. 

Perhaps I need to create a set of drawings to explain it, since two different people appear to have misunderstood my goal (though another seems to understand it). Or perhaps I am totally misunderstanding both your replies. It is possible. 



> Usually you will see a tractor with a High range , (sometimes a ) Low range and reverse on a shift lever goining to a geared transaxle. Then on a separate lever you will find a multi step slot with a lever that positions the idler/clutch pully. This positioning pully forces the belt into the variator pully sheaves to change ratio. You can also control speed with the clutch pedal, the further you depress the pedal the wider the pully sheaves are forced, the slower you go until the sheaves no longer contact the belt.


With this part of the description, in the last sentence, I *think* I understand that it might still be a CVT you are describing, but I am not sure. I may have to find one to see it in operation to be sure. 



> I think that once you look at a couple of these you will find what you need for a manually shifted CVT.


I might find something I could use, so I'll look around and see if any scrapped ones are in my area.
________
E-CIGARETTES


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## grayballs (Aug 27, 2008)

Amberwolf said:


> .
> 
> 
> The NuVinci wheel-hub-based-CVT would be great to use, but it can't be driven by any kind of motor without voiding it's warranty (even though someone from NuVinci contacted me via the Electricle blog to suggest using one on my ebikes!). So that's out. It's price is too high for me anyway, at $400 and up, depending on where I would get it.


I remember the initial drawings for the Nuvinci Hub. They showed an 'industrial strength' model with 8 internal balls rather than the 3-4 they use for the bicycle hub. I wonder, what ever happened to that?


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## order99 (Sep 8, 2008)

Amberwolf said:


> I have not read the entire threads for the first or last of those, but they all start off with what look to me to be very definitely *non*-CV transmissions--each has specific ratios they would shift between. The middle thread doesn't have a CVT in it's (single page of) discussion.
> 
> Is there something about CVTs in those other two threads somewhere? They're at least 10 pages long and I don't relish digging thru them only to find nothing CVT-related.
> ......
> ...




I missed the point entirely? didn't I ? Sorry.  I was posting just before bed and forgot the whole "continuously variable" bit once people started talking about manual shifters and such!!

You're right about the paucity of actual CVTs in those threads-they mostly debate Nuvinci CVT vs the standard Sturmey-Archer with shifter vs homemade multi-speed belt drives(efficiencies, costs etc). Good for transmission ideas, bad for CVT alone...

And God only knows why I typed 'three-chain' rather than 'three-gear'.  I was talking about three gears of choice, a derailler and a short chain joining the motor to the side of the wheel opposite your other chain-and a separate shifter. The more I think about it though, the more I believe even a weak motor would turn my idea into shrapnel in less than an hour.

Lesson to my fellow Posters-never post late at night once the coffee runs out.  Please ignore the funny monkey hitting the keyboard with his feet and carry on...


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## Jimdear2 (Oct 12, 2008)

Amberwolf said:


> Perhaps I need to create a set of drawings to explain it, since two different people appear to have misunderstood my goal (though another seems to understand it). Or perhaps I am totally misunderstanding both your replies. It is possible.
> 
> 
> 
> ...


 
Maybe this sketch will help. Excuse my poor hand at drawing.

The way it works is one belt has a spring loaded idler that pulls the belt into the center forcing the movable sheve to move down. This squeezes the other belt out to the edge of the sheves This second belt has a idler connected to the clutch pedal and shift lever that will tighten the second belt moveing it into the movable sheve and forcing the spring loaded first belt out thus you have a continious variation of ratios.

I hope my description is clear. I just had a brain fart. I'll googlr Variator and see if there is better information. I'll post a link if I find anything.


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## Jimdear2 (Oct 12, 2008)

Amberwolf,

Do a google search on US Patent 6932730.


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## Amberwolf (May 29, 2009)

Jimdear, even just your sketch makes it make sense.  It makes more sense than the patent does! It is still different in physical construction from what I describe, but it would probably create the same result. 

The issue I would have with it is that it requires two belts, and thus has more potential for slippage than what I wanted to do, which only has one. It also requires two tensioning mechanisms, where mine only needs one. Might be more friction losses because of the two belts vs one, too, but I dont' know how to figure that part out. (me and math don't get along very well  )

However, mine would be more mechanically complex, because it requires two pulleys with expandable sheaves, and the mechanism to control them simultaneously. 



order99 said:


> I missed the point entirely? didn't I ? Sorry.  I was posting just before bed and forgot the whole "continuously variable" bit once people started talking about manual shifters and such!!


That's ok, I just wanted to make sure I understood whether *you* understood, or were trying to redirect me to another type of transmission for a specific reason. 



> You're right about the paucity of actual CVTs in those threads-they mostly debate Nuvinci CVT vs the standard Sturmey-Archer with shifter vs homemade multi-speed belt drives(efficiencies, costs etc). Good for transmission ideas, bad for CVT alone...


I've had lots of transmission ideas for this project, many of them from other people or forums or just project blogs/etc. I certainly don't mind seeing even more of them. 

If I could get a 9-speed Nexus or similar using internal planetary gears or whatever, I'd settle for that for now just because it is still better than the chainring/derailer system I have now, as far as maintenance goes, and for overall installation/design simplicity (even though internally it's more complex, it makes my part of the design simpler, because I don't have to ). 

But my goal is to get or build a CVT that will give me a high ratio range, yet won't add too much weight to the bike (which is already far too heavy as it is) and isn't too large. That's why the NuVinci looked like such a good idea, until I saw the warranty terms and verified via discussion with them that I can't use it in my projects. (Especially since I hope at some point to have a cargo trike design that could be built and sold to various people around the valley in need of such things, but if I can't get warranty coverage on one of the most expensive parts of it, I can't possibly give any warranty on it either, and to most customers I'm sure that'd be unacceptable--it certainly would be true for me!). 




> And God only knows why I typed 'three-chain' rather than 'three-gear'.  I was talking about three gears of choice, a derailler and a short chain joining the motor to the side of the wheel opposite your other chain-and a separate shifter.


I'm still not quite sure what this would do, other than give me more gears than I already have, but also another shifter to have to operate in addition to the regular two. I have considered doing essentially that in a few different methods, but the only one I really would try if it is not a CVT is to use a multi-speed internally-geared rear hub somewhere within the drivetrain path (in the rear wheel itself if I had no other choice). 



> The more I think about it though, the more I believe even a weak motor would turn my idea into shrapnel in less than an hour.


I doubt that. I run my regular bike drivetrain via the motor, and it's pulling my whole 120 pound bike plus my 150 pound person plus whatever other stuff I have on it at up to around 15 MPH by itself, and it's not falling apart or showing signs of strain. The freewheel palls in the rear cassette will probably fail faster under this load, but that'd be a problem with any drivetrain I use. 

The motor I use now is about 350W at a guess from the person that provided it to me, and the one I will shortly be using should be around 650W. I don't think even something more powerful than those would destroy the drivetrain I have. If I tried to do instant-starts and run up to fast speeds with it, maybe, but I don't ride that way.
________
Live sex


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## farmerpj (Jun 16, 2009)

before hydrostatic transmissions, skid steers and combines used a 2 sheave setup and one belt. one pulley (sheave) has one side of the pully spring loaded. the other pulley has its width varied with a small hydraulic cylinder. they transmitted a lot of power. 

paul


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## grayballs (Aug 27, 2008)

farmerpj said:


> before hydrostatic transmissions, skid steers and combines used a 2 sheave setup and one belt. one pulley (sheave) has one side of the pully spring loaded. the other pulley has its width varied with a small hydraulic cylinder. they transmitted a lot of power.
> 
> paul


Generally refered to as a 'Reeves Drive'. I'm guessing that any belt drive is in the neighborhood of 80% efficient (average),,, the Reeves Drive would be somewhat less. They're prone to vibration, wear and slippage,, tough to keep the belts in constant adjustment,,,, I'm guessing that most adjustable drives are in that range


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## eriq9 (Dec 3, 2008)

i seem to remember a few years back, a bicycle on late-night infomercials that boasted an automatic (ie:self shifting) transmission, if you could find one of them for parts maybe. don't remember the name though...i know it's not a cvt, but it'd shift itself...landrider i think...
~E


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## Amberwolf (May 29, 2009)

There was one, no longer made, designed by Ruger (the gun company) that had a folding section of the sprocket, electromechanically controlled, which could automatically shift. However, it is still sprockets, and still has distinct gears. It would also be impossible to get repair or replacement parts for it, since no one bought their IP and continued the business when they gave up on it. It certainly was a neat idea when they came out with it, and I wanted one after I heard about it but it was too late. Nowadays I have other ideas of what I want. 

It also still cannot shift when stopped, and would from what I have seen of it's mechanisms be just as hard to shift across many gears to get down to a low one if I had to stop suddenly when in high gear. 

A CVT (at least a belt driven one or one made from balls and rings like the NuVinci) would be able to do that kind of shifting relatively easily, if designed properly. 

Also, the CVT means I have every gear I need available, within the limits of it's upper and lower ratios, so I'm not stuck with gears that are in many cases just a bit too low or a bit too high for a particular situation (forcing me to pedal too fast or too slowly for comfort). It isn't that I actually need every possible ratio within the range, but that whatever ratio I *do* need is already there. 

That's not possible with a sprocket/chainring based transmission (or a gear-based one), without manually stopping the bike, taking things apart, and changing out chainrings constantly (it's impossible to fit enough of them for every possible situation on a bike's normal clusters unless one has multiple stages of reduction, as some recumbents do, and as mine does (in it's motor portion)). But then if multiple stages are used, one must then have a shifter for each one. It's difficult to keep track of more than two, and impractical after three or four. Too many of the possible shifting combinations become identical, and one must memorize which ones are and are not, and begin orchestrating shifting as not just a single lever move, but instead to shift first one and then another and another and so on until all are at the right sprockets to generate the right ratio.

Way too complicated to use, even though it's simple in principle and setup. 

If I can make or get a CVT, I can easily enough shift once to get the ratio I want, and have done with it.
________
Prilosec class action lawsuit


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## Drew (Jul 26, 2009)

order99 said:


> I missed the point entirely? didn't I ? Sorry.  I was posting just before bed and forgot the whole "continuously variable" bit once people started talking about manual shifters and such!!
> 
> You're right about the paucity of actual CVTs in those threads-they mostly debate Nuvinci CVT vs the standard Sturmey-Archer with shifter vs homemade multi-speed belt drives(efficiencies, costs etc). Good for transmission ideas, bad for CVT alone...
> 
> ...



The second of your posted links was for an epicyclic CVT, its the same system used in the toyota prius and a few other japanese cars. The idea is that the epicyclic has a set base ratio which is usually something like 4:1 and you drive both the sun and the planet gears to get an output to the ring gear, the variation is handled by the torque and speed differences between layers which allows you to vary from base ratio ro 1:1, you can get higher speed ratios than this by driving in the reverse direction, but not higher torque ratios.


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## order99 (Sep 8, 2008)

Okay, let's try a little more Search-Fu now that I remembered my coffee:

http://www.motoredbikes.com/forumdisplay.php?f=116

A whole Sub-forum dedicated to CVTs! Mostly commercial units though-haven't seen any DIY CVTs yet.


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