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Post by 2stroked on May 2, 2016 15:26:35 GMT -5
Technically, the CVT is an ingenious design, with near limitless design implications. The Honda Helix CVT, the Variomatic is a beautiful example in its pure trim. The Variomatic will keep the Helix engine near dead center of its power band till it's run out at top speed. 6.5 k at close to eighty miles an hour.
It's easy, too easy, to mess up the operation of a CVT during tuning. The continuously variable transmission wasn't designed for high performance, at first, but rather for efficiency and simplicity of operation. They CAN be tuned for high speed purposes, but they are highly inefficient when set up for high speed, due to the required heavy weights, slowing the climb to higher rpms. If set up for fuel efficiency, high speeds are still possible, just harder to obtain. Most CVT setups are happiest when in a neutral setting, neither for HP nor pure efficiency.
Just my .02¢, any thing I missed?
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Post by tiny on May 2, 2016 16:35:57 GMT -5
Well said. Works for me
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Post by Fox on May 2, 2016 18:01:09 GMT -5
One time I used a wine cork for a float. I thought about coating it with epoxy once I had it on the rod end but it was for some cheap-ass customer so I just left it bare. Worked good but I have no idea how long it lasted.
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Post by FrankenMech on May 2, 2016 21:05:56 GMT -5
I have spent most of my life designing machines, mechanisms, etc. Everything from heavy equipment, production equipment, machine tools, hydraulics, to aircraft instruments and even industrial electrical and electronic devices and controls. When I say the scoot CVT is a bad design I mean it. I have had to 'fix' many bad designs over the years. Many where design limits had been stretched or exceeded. The CVT in a car or industrial machine can be quite reliable, simple, efficient, and sometimes robust. The 'CVT' applications in industrial equipment have been largely replaced with electronic variable speed drives or hydraulics. The 50cc 4T CVT in our scoots is not reliable at all, -a very very poor design. The clutch and contra mechanism is not too bad but the variator itself, -is crap. There is a better way to build the variator but I have not seen any examples. The belt limitations remain also.
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Post by SandStorm on May 3, 2016 7:36:16 GMT -5
I don't mind the CVT system on scooters, and this simply because I'm a n00b on this motorized 2 wheel world. For starters a CVT is ok because of the ease of use. No need to fiddle with a hand operated clutch, or fiddle with feet up-down for gear changes. all of this for a newbie can be terrifying. (because now, everyone with a car license can drive motorbikes up to 125cc where i live, without the need to go to driving school again...)
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Post by 2stroked on May 3, 2016 10:22:53 GMT -5
I have spent most of my life designing machines, mechanisms, etc. Everything from heavy equipment, production equipment, machine tools, hydraulics, to aircraft instruments and even industrial electrical and electronic devices and controls. When I say the scoot CVT is a bad design I mean it. I have had to 'fix' many bad designs over the years. Many where design limits had been stretched or exceeded. The CVT in a car or industrial machine can be quite reliable, simple, efficient, and sometimes robust. The 'CVT' applications in industrial equipment have been largely replaced with electronic variable speed drives or hydraulics. The 50cc 4T CVT in our scoots is not reliable at all, -a very very poor design. The clutch and contra mechanism is not too bad but the variator itself, -is crap. There is a better way to build the variator but I have not seen any examples. The belt limitations remain also. Okay, point. I have NO experience with the 4t 50cc stuff. The 2t 50cc varis seem alright, but just alright. The variators on my two 250's are a different story all together. The wider ramps won't wear as fast cuz of the added surface area. The boss journals hold grease, and have seals on each end to keep it there. Even the boss itself, has a grease journal on each side. The guides ramps are beefier, and the plastic guides themselves have metal clips that hold them in place and add strength. The big bikes stay right in the center of their power band all the way through to top speeds. The bigger CVT's are stronger and better built. As for the belt limitations, their always going to be there. Even with the wider thicker belts in automotive applications, the belts are going to be a weak point.. For the most part though, as long as we don't expect too much, or try to exceed the limitations, the CVT is the best option for these heavy bikes with underpowered engines. I read at another forum, about a chain driven CVT setup, for industrial and automotive apps. I can't remember the name of them at the moment, but if you Google " chain driven CVTs" I am sure you will find it.
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Post by mclark999 on May 3, 2016 11:11:23 GMT -5
Don't know about the cheap Chinese 4t scooters, but the variator in my wife's Honda Metropolitan is dead on reliable. The weights provide an easy way to tune for acceleration.
I think if there was a much better system, some manufacturer would be using it already. It certainly meets my needs for cost, reliability, and ease of maintenance.
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Post by 2stroked on May 3, 2016 15:43:53 GMT -5
Don't know about the cheap Chinese 4t scooters, but the variator in my wife's Honda Metropolitan is dead on reliable. The weights provide an easy way to tune for acceleration. I think if there was a much better system, some manufacturer would be using it already. It certainly meets my needs for cost, reliability, and ease of maintenance. Thank you. The Honda Variomatic CVT is friggin amazing! The Helix has flat spots on the rollers that make them in usable in mist scoots. The Helix isn't fazed at all. She climbs smoothly, stays in the power band, and has a good top speed. On teg other end of the scale, my Roketa Cyprus has nearly the exact same cvt, but is MUCH touchier about the flat spots. I noticed a few months ago when the vari started acting odd. Still, I HAVE to take the stand on the side of the CVT. IMHO the CVT is a perfect option for these bikes. The Honda version is near perfection, the cheaper clone if the same cvt is as good or better than could be expected from Chinese quality items.
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Post by 2stroked on May 3, 2016 15:45:51 GMT -5
Oh, there is a different version if a CVT, that relies on the same principal, called an IVT. Infinitely Variable Transmission. It does require some human interaction to function.
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Post by FrankenMech on May 3, 2016 20:34:51 GMT -5
I am hoping the CVT on a 150cc gy6 works better. The units I have seen don't give me much hope though. There are belt and chain combo CVT units from Comet that are used on some go carts etc. They look more robust but they still rely on that belt friction. Friction produces heat The heat causes more slippage and heat. Wider belts don't help a lot, surface is the limitation. There is a limit to how much surface area one can get against the pulleys. Belt flexing also causes heat. The thicker the belt the more heat. The belt is a big limitation. The CVT concept is OK it is just the 50cc 4T GY6 rendition that is not so good. It is operating beyond its limits which results in rapid wear and failure. Especially if the load is increased by weight, hills, or power transmission. Automotive CVT units often use metal segments on a steel band for a belt that actually pushes instead of pulling like rubber belts. There are also cone drives for industrial use. mclark999 "I think if there was a much better system, some manufacturer would be using it already. It certainly meets my needs for cost, reliability, and ease of maintenance." There is a stronger system in production by Comet but it would be difficult to adapt to a 50cc 4T GY6 unless it was designed in by the OEM. It is probably not as tuneable also. When I figured out what the major problem was with the variator I sketched out a better design (that is what I do). I have searched all over and I have not found anyone using it. I would buy one if found. It would cost more, probably about 1.5x due to 3 more parts and assembly. I can't do anything about the rubber belt limitation though. I should probably use one of those 3D printing machines to make one out of plastic hahahaha! A NC milling machine would be required to make the pulley side prototype but it could be cast in production. A better casting alloy would improve things also. The back plate would require modified tooling somewhat similar to what is used now. I should probably take the design to DR Pulley but then lawyers would be needed and all that BS. Naw, the design will die with me like many others.
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Post by 2stroked on May 3, 2016 22:29:20 GMT -5
FrankenMech,
Copyright your design before the next mofo gets around to it.
I do agree that the little 50cc systems are very weak, and prone to failure. Part of that's our faults, trying to turn multi purpose engine into a high performance machine. We expect too much from these little things. The big brands have better quality casting machines, and use a better alloy. I would think an alloy with added silicone would be good for a CVT material.
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Post by Fox on May 3, 2016 22:53:13 GMT -5
It really boils down to maint. If you take the cover off every couple/three weeks and clean/inspect/replace as necessary then your CVT is gonna last and don't wait til your belt breaks to order a new one. Those little U-shaped guides are crucial. No need to wait til those break to order a few sets just to have on hand. Clutches amd belts are gonna wear out so it behooves everyone to do regular inspections to avoid "surprises".
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Post by FrankenMech on May 3, 2016 23:01:09 GMT -5
A design has to be patented and that is a major PITA and costs $$$$$ and lawyers etc. Then if you don't have major bucks to defend a patent it gets copied in China/Asia. Even with $$$$ they still thumb their nose at you and flood the market with knockoffs. I have had ideas stolen by US firms also so IP theft isn't all happening in Asia. We do push our scoots hard but then a little 50cc or even a 75cc can only do so much. There is no replacement for displacement My 50cc gets pushed real hard. My neighbor scoffed at me for saying it weighed at least 250#. I weighed it tonight, 293# plus add me for another #250 with riding gear and that poor little motor and CVT is trying to push 543# I do maintenance and I have extra parts for everything. Two weeks is not often enough. You guys push your CVTs to the limit to where it fails every few weeks and constant maintenance is required. I push mine way beyond the limits but in doing so I was able to ID the failure points and limitations. A more robust design is needed. Something that will last 2-3 months even under abuse like mine gets.
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Post by Fox on May 3, 2016 23:08:40 GMT -5
Yep, "Made In China" is the key phrase that should be in the forefront of your mind when deciding on your maint. schedule. These aren't "gas-and-go indefinitely" machines.
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Post by FrankenMech on May 3, 2016 23:10:14 GMT -5
The trouble is, with a new design even the Chinese could make a good one.
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