So there is some sort of belt that runs between the two spools. How are you shifting? Is the green thing a tensioner?
This is a very interesting idea, can you give us an idea of exactly how this is going to work?
Im going to attempt to describe how this works in words…bear with me. I’m not sure how familar you are with a snowmobile transmission works but this is on variation of it. What I’ve done is have the motor spin the cone shaped object. This cone will spin a timing belt. and depending on the power needed by the robot the belt will slide up and down the cone. The spool shaped object is the output shaft to the wheel/track/etc. This whole system works of the tension of the springs and the belt and is mechanically automatic. The green thing is the tensioner on the belt. Currently this is my last ratio only because I don’t believe a belt could handle the high RPM of the atwoods(my team only uses the atwoods in the drivetrain).
Please keep the questions coming…
-Thanks
Pat
editthere are some more design views being uploaded soonedit
This is called a CVT (continuely variable transmission), a torque converter uses hydrolic forces to chagne torque in automatic transmissions.
there are designs all over these forums of them! Yours looks nice though!
Strangely enough, they also call snowmobile-type CVTs “torque converters”. I was also very confused at this the first time I heard it. Someone on my team asked me, “why don’t we use a torque converter for the transmission?”
I said, “because we would lose power because to fluid coupling is not very efficient.”
Then we both thought each other were idiots for a little while. Little did I know that these CVTs were called “torque converters” and the other guy didn’t know that the fluid coupler in an automatic transmission was also called a “torque converter”.
Anyway, the point of the story is that they both share the same name.
I plan to make a white paper if I can test it and whatnot. I also will have some more detailed drawings eventually. Can anybody see any problems with the current one (other than theres no motor)
-Thanks
Pat
What keeps the belt from slipping. Does just the friction keep the spool and cone in sync? Also, what would be the efficiency of a contraption like this?
Thats correct that the friction of the belt and cone cause the spinning action. The spool looking object will be a timing pulley and will have teeth. As for the efficiency not sure havent done any testing.
-Pat
How do you keep tension in the belt when it slides down to the right side where it is smaller?
If this device is actually built like a mini torque converter from a snowmobile (I’m from northern Canada and have three snowmobiles, and the assemblies in them don’t look the same.) then it will have very low efficiency, especially with an electric motor. Because the Troque converter in a snowmobile uses high RPMs to shift the belt ou farther and gain a higher ratio. The faster the motor spins the more torque you get. This is fine for a gas engine that is designed where the maximum torque output is very close to the redline RPM, but in an electric engine the max torque is a 0 RPM, so it would be impossible to get even close to your maximum torque out of a that sort of design with an electric engine.
Then again I have lots of snow machines, and spend most of my free time fixing snowmobiles, and that device doesn’t look the same as whats under the hood of my Mach Z.
here is a pic of team 494’s cvt, using 2 cones to control the ratio. much better than one in my opinion.
noremorse, how does the ratio changing happen? I can’t see how the timing belt can move anywhere or how either of the pulleys change size unless maybe the two halfs of the cones move closer to each other…
The tensioner is on a spring it constantly is having a force acting on it to create tension.
-Pat
The 2 cones move toward eachother, effectivly increasing the diameter of the conact area of the belt and cone. The other side does the opposite to componsate for tension.
Noremorse,
I see what your saying in why two is better. For simplicity though I thought that one would work. This is still obviously being developed. My next step is to get the details worked in and hopefully build a working model. I think that a problem that I may have to solve is increasing the distance between the two pulleys. Any comment on that?
-Pat
http://www.andersoncvt.com/
This is what I was trying to emulate on a smaller scale and with one cone. I couldnt find the supplies (chain) to actually do it the way the anderson is setup but I will try to find a way to do it like it. The site you posted was awsome.
-Thanks
Pat
edited
If you use oposing cones, you can use standard v-belt. the only problem is your limited to a certain range of ratios due to the width of the belt, and the travel of the cones.
Although it is hard to see because the tranmission is moving, there are counterweights on the nearest pulley that are meant to push the two halves together. The counterwieghts are similar to those found inside a governor and the force they apply to the pulley varies according to the rpm of the shaft.
494 had the weights on one end, but they also had a torque converter on the other end.
The way they explained it to me was that the counterweights changed the ratio based on RPMs and the torque converter would change it based on load.
Sounds interesting.
