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Old 11-21-2004, 03:17 PM   #1
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Default Variable speed Transmission Question

I've not been into RC cars for some time. I've just recently sold all my electric RC airplane stuff probably to get back into cars.

I work in industry where a number of machines are driven by variable pitch pulley systems. This is where one or both pulleys effectivly vary in diameter by seperating the halves of the pulley. When this happens the belt slips down farther into the groove changing the gear ratio. One such device does so based on RPM via a hinged/weighted mechanism that seperates the pulley as the RPMs goes up. It does this automaticly and its continiously variable.

I've read a little and it seems most electric companies ditched the idea of 2 speed transmissions due to little gain and other problems. But what about one that is continiously variable, It should give a good top end with out sacrificing acceleration.

I'm just in "hmm..I could make that" stage and I wanted to run it by some more currently avid RC guys to get any feed back.

I apreciate any input

Gigaah
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Old 11-21-2004, 03:34 PM   #2
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Default Re: Variable speed Transmission Question

Quote:
Originally posted by Gigaah
I've not been into RC cars for some time. I've just recently sold all my electric RC airplane stuff probably to get back into cars.

I work in industry where a number of machines are driven by variable pitch pulley systems. This is where one or both pulleys effectivly vary in diameter by seperating the halves of the pulley. When this happens the belt slips down farther into the groove changing the gear ratio. One such device does so based on RPM via a hinged/weighted mechanism that seperates the pulley as the RPMs goes up. It does this automaticly and its continiously variable.

I've read a little and it seems most electric companies ditched the idea of 2 speed transmissions due to little gain and other problems. But what about one that is continiously variable, It should give a good top end with out sacrificing acceleration.

I'm just in "hmm..I could make that" stage and I wanted to run it by some more currently avid RC guys to get any feed back.

I apreciate any input

Gigaah

I had a Mini bike when I was younger that ran on the same principal and I have seen machine's like those you speak of....

I too have wondered why the RC industry doesn't do the same....
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Old 11-21-2004, 03:48 PM   #3
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My guess is the the loss in efficiency would out weigh the gains in speed or acceleration. I think regular two speeds would work fine with brushless motors since they have so much more torque. Just my guess.
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Old 11-21-2004, 09:24 PM   #4
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One of the reasons why variable speed stuff doesn't work too wel in our application is the amount of strain it puts on the motor. With the motor on full load accelerating, adding more load to it when it changes gears just makes it hotter, and makes the brushes arc the hell out of the comm.
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Old 11-21-2004, 09:32 PM   #5
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well this wouldn't really "change gears" it would effectivly always be changing gear as the gear ratio is continously variable depending on the rpm. At a dead stop your gearing would be easy and allow it to spin up faster, as the rpms come up the gear ratio gradually changes to allow a higher top end. In theory if it was well engineers it could work like that.

I've heard snowmobiles work with similar transmissions.
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Old 11-21-2004, 09:37 PM   #6
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I believe Kyosho did manage to come out with a 2 speed for EP TC.
Cant confirm this cos i havent seen the thing before and it was just a saying.
Anyone able to confirm this?
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Old 11-21-2004, 11:19 PM   #7
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Yokomo and HPI both used to have a 2 speed option for their TC's(many years back) but it was illegal for racing in most parts of the world....
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Old 11-22-2004, 12:06 AM   #8
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The system you are talking about is used in snowmobiles and works great...but.... gas engines make their max torque closer to the top of their power range and electric motors make their peak torque at zero RPM, and it drops as RPM rises. So this system would put more load on the motor as RPM rises and the torque falls.... dont think it would work.
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Old 11-22-2004, 02:58 AM   #9
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sorry guys, but i can't quite picture the transmission in question here. I can understand what it will do, but i can't quite picture how it is achieved. Anyone with a site or a picture?
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Old 11-22-2004, 03:05 AM   #10
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I know Willams did this in F1 and it was banned before it hit the race track. But I know it had big time gains. I think Honda made a road car with it, very strange to drive.

Bascially the motor revs don't change.

So many things in F1 are banned in fear of it becoming too good to fast. Look no further than active suspension and ground effect skirt cars.

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Old 11-22-2004, 08:47 AM   #11
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I'm pretty sure you can just about as easily make it function to keep it shifted so the RPMs stay lower thus keeping the motor in its torque band..where ever that may be or if you even want to do that.

I don't particularly care about "Race legal". I used to race with a local group and they had a class where most anything goes.
They believe it keeps the inovative spirit going. Some of these guys are running 14.4+ volts lithium packs. Its just as important to have bleeding edge setup with some unique inovation as it is to be a good driver. I think they cap the number of consecutive wins before you have to sit out, They toyed around with the idea of making the winner set up a class to disclose the secrects if they won X years.

I'm mainly fishing to see if A: anyone has done it and it sucked
Bone it and it worked well C: Never been done to most peoples knowledge. D: See what input people have if they have some ideas about its potential.

So far I'm ready to buy a new Car and start working on it. I'm working on trading my Xbox for a Mini-T and I also have a old vanessa's Lunch Box RC Van that is larger and easier to work on.

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Old 11-22-2004, 09:17 AM   #12
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Do a search on "CVT", there are a lot of them out there and many finding their way into new cars coming out, especially their electric cars....

Here's some interesting reading....
http://cvt.com.sapo.pt/


It could very well be applied to the RC industry and have a dramatic effect on EP cars...
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Old 11-22-2004, 09:42 AM   #13
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Ahh CVT..I was searching variable speed transmission. Thank you for that link very much! It gives me several variations of a CVT that I can work with as well as some extra solid information.

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Old 11-22-2004, 10:29 AM   #14
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The Anderson CVT seems to be the most promising.... It's less reliant on friction and less moving parts.... I'm a big advocate of the KISS principle....

The thing I don't understand on the Anderson system is how he'd have the belt/chain move under its own? You'd still need a cetrifugal system of sorts to vary where the belt is along the cones.... I'm not sure if you could get the gearing correct isn the small spaces we deal with either....

The type used in snowmobiles would probably make the most sense but the amount of moving parts would make it expensive to produce on our scale....
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