I was searching today for some pics of 494’s cvt from 2004…they pop up on google but the links to the website are busted.
Can anyone help me get the pics? I’d also be curious to discuss tuning and other cvt related things.
Thanks.
http://firstrobotics.uwaterloo.ca/gearboxesgallery.php
Scroll down about 2/3’s of the way. Theres 4 or 5 good pics.
I just discovered today that my 1978 Peugeot 103 SP moped that I bought a little less than a week ago has a CVT type mechanism they call “the variator” The whole engine is mounted on a pivot and pushed with a spring to keep the belt tight. It is really quite mesmerizing to rev up the engine and watch the pulley slide over and essentially become larger and watch the engine shift backward to take up the slack in the belt. 
I have very little idea how it actually works, but it is quite fascinating.
Here is the owner’s manual: http://www.mopedriders.org/html/manuals/peugeot/ownersmanual.pdf
And here is the service manual: http://mopedriders.org/article_view.php?faq=2&fldAuto=36
These are the pics of it that were on 1114’s database for those who don’t want to scroll.
http://firstrobotics.uwaterloo.ca/resources/galleries/gearboxes/gearboxes76.jpg
http://firstrobotics.uwaterloo.ca/resources/galleries/gearboxes/gearboxes78.jpg
http://firstrobotics.uwaterloo.ca/resources/galleries/gearboxes/gearboxes79.jpg
http://firstrobotics.uwaterloo.ca/resources/galleries/gearboxes/gearboxes80.jpg
http://firstrobotics.uwaterloo.ca/resources/galleries/gearboxes/gearboxes81.jpg
http://firstrobotics.uwaterloo.ca/resources/galleries/gearboxes/gearboxes82.jpg
http://firstrobotics.uwaterloo.ca/resources/galleries/gearboxes/gearboxes83.jpg
Our website is being rebuilt and the pictures haven’t been moved yet. :o
Thanks for such a great program 1114.
What are the points of the brass fin-thingies? I remember seeing it at IRI in 2004, and having the full system explained to me, but I can’t recall what the brass fins do. No other CVT’s I’ve seen has anything like them.
The brass fins are weights that are used to shift the cvt from a high ratio (high input to low output) to a low ratio. When the input spins fast they pull out causing the pulley they are on to close making the radius of the pulley higher this causing the ratio to get higher. When the input slows du to a larger amount of torque being need the weights are pulled in by a spring and opening the pulley making the ratio lower.
At least that is what I get from the pictures.
So is this an automatic CVT or do the weights simply aid in shifting?
So is this an automatic CVT or do the weights simply aid in shifting?
CVT stands for Continuously Variable Transmission. This means that technically there is no “shifting” meaning no actual going from 1 gear to another. However the “shifting” in gear ratios happens in the variating size of the pulley.
To get an idea of what it does ( not how it works ) you can look at many off road dirt or dune buggy style cars. Also Nissan ( I believe ) has a new national advertisement of a CVT in one of their new cars. Motor revs up and no shift jerk, pretty neat.
Anyways, this is a sharp transmission I’m kinda bummed I didn’t get to see this in person this year.
I am going to try to give you the best explanation i can. ok here we go, it is a continuously variable transmission and as the motor thats connected to it’s rpm’s raise the brass weight move inward towards the belt, when that happens the “gear ratio” changes making the power transfer much more efficient.
centrifugal force makes the weights go in?
Saw this in a Motor Trend article and decided to check it out.
Its quite a nifty idea and could definitely be implemented on a robot (they even mention robots as one of its applications).
Not only are they relatively small (bicycle hub) but they are also driven by chains!
INERTIA would make the weights change position, and help “shift” the gear ratio (although I’ve seen other CVT’s, rather they use motors or other actuators to control the positioning of the pulleys).
Actually, to be completely accurate, it’s a centripetal acceleration that causes the weights to exert a force outward, which operates the shift. Higher RPM means higher centripital acceleration, a higher force pushing outwards, and a different ratio.
More importantly, I had been ogling the available pictures of this transmission over about the past year, and when I glanced at it walking through the pits in Atlanta, myself and Cody from our team immediately ambushed the only kid in their pits. I actually apologize for that, I think I scared him a bit. “Can you demonstrate your CVT to us? Please?! We really want to see it! Please!”
Anyways, the thing is really, really cool, if it is a bit noisy. It shifts really smoothly, but it does seem to offer a lot of internal resistance to movement. But really, really slick!
Well, I was just trying to say that centrifugal force doesn’t really exist :rolleyes:
Besides, centripetal acceleration wouldn’t exist without inertia. 
(well, little of physics would exist without other fundamental physics principles…)
Thanks for the correction. However, centrifugal force does exist, it the force that keeps the citizens of a country in the country or some such like that. I learned this in my geography class 4 years ago so its a little fuzzy and I was afraid that last night a 11:30 I would get them mixed up and of course, I did.
This CVT is a one of a kind that I designed on my dining room table with paper and pencil, so no CAD drawings are available at this time. I had never designed a transmission before this one. I used a book on tuning snowmobile clutches as my reference for my design. Unfortunately this book is out of print. If someone were interested in converting the paper drawings to CAD and making them available to the CD community, I might be able to fine a complete set and mail them to you. If there were more time, this could also make an interesting white paper.
Here’s a brief description of the function:
The drive side of the CVT responds to RPM and belt tension. One sheave is fixed to the shaft and the other is allowed to slide along the shaft but not slip. The faster the input shaft spins, the more the brass fly weights push the movable sheave toward the fixed sheave. The flyweight force is proportional to the square of the RPM and directly proportional to the mass of the weights. This device was designed to operate at about 1450 RPM. A snowmobile clutch operates at speeds up to 10,000 RPM. For this reason, the flyweights had to be rather large.
The driven side of the CVT responds to belt tension and torque on the output shaft. One sheave is fixed to the shaft and the other is free to slide and spin. The moving sheave is held against the fixed sheave by a spring that is inside of the aluminum cup with the cam surfaces. The movable sheave is kept from spinning on the shaft by three rollers that ride on the angled cam surfaces.
If the drive side is at full RPM and there is little or no load on the output shaft, the belt will be pulled down and the driven sheaves will be open. At this point, the CVT will be in high gear. If there is a load applied to the output shaft, the moving sheave will want to slip and will bear against the cam surfaces. The rollers will ride up the cam surfaces and push the sheaves back together. This will tighten the belt and pull the belt back down into the drive pulley and force the drive sheaves to open back up. This is known as “back shifting”
This CVT can function in either direction and does not have a neutral position. A snowmobile clutch only works in one direction and does not begin to bring the drive sheave together to contact the belt until the shaft is spinning about 2000 RPM.
The width of the V-belt and the angle of the side walls will determine the gear ratio change that is available. Because we wanted to use a small belt to keep parasitic losses to a minimum, we have a range of about 60% change from low to high gear.
We fitted this to one of our old robots and put the robot on our dynamometer to do some tuning of flyweight size and shape, cam profile, and driven clutch spring force. More development would would be required, but we are not pursuing it at this time.
Jay
My goodness. I’m glad you understand that. Nice work.
That sounds interesting. I’d like to do that, maybe during winter break in the last week of December. PM me if that would work.
nice we should all have a transmission like that