# Interested in building my own CVT...



## Clyde (Jun 11, 2010)

I've been looking around the internet and I've gotten the general idea of how Continuously Variable Transmissions work from watching some YouTube videos of them running.

My knowledge of how they work still isn't precise enough to just skip along merrily to the shop and spin up the lathe and magically churn out a CVT though. 

Has anybody got closeup pictures of important CVT details, or maybe a CAD model? I have a knack for reverse-engineering but what I could find on YouTube wasn't really enough to go on-


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## major (Apr 4, 2008)

Clyde said:


> I've been looking around the internet and I've gotten the general idea of how Continuously Variable Transmissions work from watching some YouTube videos of them running.
> 
> My knowledge of how they work still isn't precise enough to just skip along merrily to the shop and spin up the lathe and magically churn out a CVT though.
> 
> Has anybody got closeup pictures of important CVT details, or maybe a CAD model? I have a knack for reverse-engineering but what I could find on YouTube wasn't really enough to go on-


Hi Clyde,

What does this have to do with Electric Vehicles? EVs don't need CVTs.

major


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## Clyde (Jun 11, 2010)

Really? I was under the impression it would help with my torque problem, since my bike/moped/thing currently has no way to change gears...

Also I'd seen them mentioned elsewhere on these forums for a similar project:
http://www.diyelectriccar.com/forums/showthread.php/electric-moped-conversion-13766.html


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## major (Apr 4, 2008)

Clyde said:


> Really? I was under the impression it would help with my torque problem, since my bike/moped/thing currently has no way to change gears...


It's your project. Do what you want. But if you have a properly sized motor and the appropriate battery and controller, there is no need for a CVT. 

Just my opinion,

major


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## Clyde (Jun 11, 2010)

Hmm... thanks for the info-

I take it this means a controller will give me an increase in torque then?
My understanding of mechanical speed control is a bit better than my understanding of electronic speed control, but I can certainly look things up.


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## major (Apr 4, 2008)

Clyde said:


> I take it this means a controller will give me an increase in torque then?


I don't know what motor you have, or battery. And it sounds like you don't have a motor controller. But for most EVs, the motor is rated for nominal power needed for cruising, say that comes out to 100 amps. Most DC motors rated for 100 amps can do 3 to 5 times that for short periods, like needed for accelerations. And since torque is proportional to current, that means 3 to 5 times nominal torque. The PWM motor controller will do current multiplication at lower motor speeds, so that low speed extra torque does not have to tax the battery with excessive current.

Get a decent motor and electronic PWM controller and it serves the function of a CVT without the messy mechanical stuff. 

major


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## Duxuk (Jul 11, 2009)

[

Get a decent motor and electronic PWM controller and it serves the function of a CVT without the messy mechanical stuff. 

major[/quote]

Or the up to 25% lossof energy which CVT canstealfrom you. They usually come with fan cooling to watse this as heat.


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## aeroscott (Jan 5, 2008)

for the greatest flexibility in a transmission look to the Mars Lander drive system . It's 2 motors driving a planetary reduction gear one motor on the sun gear the other on the ring gear . Prius , GM , MB, are using this to some extent in hybrid form . A buddy put this system on a boat for driving the prop . It was 8k for 4 hp. controlling two motors , modifying a gearbox , lots of work .


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## Clyde (Jun 11, 2010)

Well my main goal here is to be actually buying as little as possible- and using materials I can scrounge or already have as much as I can...

Are CVT's that inefficient in general? I was looking at the Comet Torq-A-Verter and other similar devices and none of those appeared to have cooling fans...

Also- wouldn't a controller also generate some amount of heat?



I don't mean to come off as being defensive or anything, just curious.
A variable belt-drive like on most scooters out there I could likely throw together over a weekend... but a PWM controller I'm not so sure about. 

Are there any well-documented schematics out there for creating a motor controller?


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## major (Apr 4, 2008)

aeroscott said:


> for the greatest flexibility in a transmission look to the Mars Lander drive system . It's 2 motors driving a planetary reduction gear one motor on the sun gear the other on the ring gear .


You might find this thread interesting. http://www.diyelectriccar.com/forums/showthread.php?t=41164&highlight=planet


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## major (Apr 4, 2008)

Clyde said:


> Also- wouldn't a controller also generate some amount of heat?


I'd figure a good PWM controller to be 95% efficient for a low voltage system. They can get up in the 98% range. 



> Are there any well-documented schematics out there for creating a motor controller?


I'm sure there are.

Like I said before, I have no idea what motor you're talking about. But whatever, you should have a system for current limiting, which the motor controller will do, and a CVT or mechanical speed controller will not. 

Regards,

major


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## aeroscott (Jan 5, 2008)

Major , thanks for the link . I missed it or forgot it . I'm looking it over .


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