# PGO 500 conversion with CVT



## scooby555 (Apr 26, 2013)

Hell evryone ,

After reading many things and still not able to make up my mind ( ps many links in the wiki page dont work ). 
It is time to ask advise before i do anything really stupid 

I choose the PGO for mainly the following reasons : 

no homologation issues as its registered as a motorcycle and those do not have to go yearly to a tech inspection....BUT the goverment wants to change the legislation on that  pfff

its lightweight

And it has a CVT altough I'm not sure I'll be able to salvage that part from the main motor block.....

But the idea is to use the CVT , cause I THINK it has the following huge advantages : centrifugal clutch and variable gearing SO for DC motors there is no issue of stall currents ( which are a huge loss again I THINK meaning I DO NOT KNOW )

The idea is to lower the clutch bite point to a suitable RPM ( ANYONE experience with this )

Then choose a motor , the buggy weighs less then 350Kg currently , so i guess after fitting batteries and engine and controllers and a proper windscreen we will have a 500Kg weight incl driver/passenger ( max 600Kg )

So I looked at DC motors
AGNI or LEM and KOSTOV K9 seems nice to me

If there are better options , please feel free to discuss

As for a controller I am thinking of building my own.....not sure this is the way to go......
As for BMS also not sure this is worth the cost.....
A charger will be necessary.....how about having 2 plugs ? is there an industry std ?

Any tought on rolling resistance ? should I go for less wider tires ?
Should I think on changing bearings for lower overall friction , anyone used ceramic ones on bikes or small vehicles ?

Also where can I get the best deal on batteries , offcourse Li P types
The target is a min of 120Km range and ideally 220Km range
But also some fun so a bit of power would be nice , no quest for high topspeeds but a good accelaration is very much appreciated.
Regen i'm not sure this works with DC........but its not a must.

What is a must is budget friendly


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## scooby555 (Apr 26, 2013)

here would be a few pictures of this buggy if i could att these.....


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## major (Apr 4, 2008)

scooby555 said:


> It is time to ask advise before i do anything really stupid


CVT and electric motors do not go well together. I've seen it done a number of times on various size EVs and all have resulted in undesirable performance. In every case, the EV has been redesigned and the CVT removed.


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## scooby555 (Apr 26, 2013)

Hi Major,

Thx for the bad news  ahh well before i resell this ( its supposed to be a winter project should be ready come may ) I'd appreciate if u care to explain to me why this is such a bad idea ? or ( and I have looked ) where I can find someone who has gone the road before me.

Cause I really cannot see  why this is not good  , it "seems" to me the perfect solution.....maybe not for a big car , but for a buggy that originally has a 500cc 4stroke engine and drives like a cart with a modest 30hp.

So if u, know of any links to such even failed projects i'd certainly look and read.

I can always resell and buy something else.


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## major (Apr 4, 2008)

scooby555 said:


> Hi Major,
> 
> Thx for the bad news  ahh well before i resell this ( its supposed to be a winter project should be ready come may ) I'd appreciate if u care to explain to me why this is such a bad idea ? or ( and I have looked ) where I can find someone who has gone the road before me.
> 
> ...


I was afraid you'd ask  What do they say? A smart man learns from his mistakes: A wise man learns from the mistakes of others. Unfortunately others don't often document their stupid failures and when then do, it is nearly impossible to locate. I've explained the reasons before but searching for _CVT_ comes up empty. It's been a while. I don't recall what I said before.

The typical CVT is designed to overcome the weakness of the ICE, namely the inability to self start (produce torque at zero RPM) and to produce meaningful torque at lower RPM. The electric motor excels in these areas.


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## scooby555 (Apr 26, 2013)

Funny forum search engine u got  , doesn't even find my own CVT thread....So googled it and guess what 

http://www.teslamotorsclub.com/showthread.php/9982-CVTs-for-Electric-Vehicles

read the whole thing torough and guess what , its not clear , there is pro and contra as usual , but for AC it clearly is a no go ( which seems logical to me ) but since i was planning on going DC ( seems a lot cheaper ) it seemed logic to me to go to a CVT for some advantages ( I most fear the stall current when starting and the very low efficiency at very low RPM )

I would adjust the CVT to engage at 300-400 Rpm

From that tread :
Pros:
Faster acceleration
Higher top speed
Longer range

Cons:
Cost
Weight
Complexity
Reliability
Traction Response
Regen (?)


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## scooby555 (Apr 26, 2013)

waooow and some very useful links and reading for me ( and for anyone interested in cvt for ev 

"Here’s some evidence:
1)	This article validated the improvement in torque off the line and vehicle top speed by modifying a two-wheeled EV with a CVT. Note the negligible range impact in Table 1.
2)	The upcoming Lito Sora has successfully applied this concept to a high-performance E-Bike
3)	The 2012 Nissan Maxima (290 hp / 261 ft-lb) has specs similar to the Tesla Roadster, and utilizes CVT technology. The 2012 Toyota Highlander Hybrid (280 hp / 215 ft-lb) isn’t quite as similar, but incorporates electric motors and a CVT.
4)	This article talks about a 2-speed gearbox can reduce battery consumption 5-10% by keeping the operating range nearer to its sweet spot. A properly-tuned CVT should have further benefit."

hope i'll be wiser


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## major (Apr 4, 2008)

scooby555 said:


> Funny forum search engine u got  , doesn't even find my own CVT thread....So googled it and guess what
> 
> http://www.teslamotorsclub.com/showthread.php/9982-CVTs-for-Electric-Vehicles
> 
> ...





> ( I most fear the stall current when starting and the very low efficiency at very low RPM )


The motor controller solves this for you. In fact, much better than the stupid CVT


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## major (Apr 4, 2008)

scooby555 said:


> waooow and some very useful links and reading for me ( and for anyone interested in cvt for ev
> 
> "Here’s some evidence:
> 1) This article validated the improvement in torque off the line and vehicle top speed by modifying a two-wheeled EV with a CVT. Note the negligible range impact in Table 1.
> ...


The Toyota Synergy Hybrid is not a CVT. And then you get into the whole EV transmission argument. There are a number of threads devoted to that. And many of the pro EV tranny articles you find on the web are authored by those in the transmission business attempting to justify their existence in the EV future.


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## scooby555 (Apr 26, 2013)

Well its very appreciated , cause I have 0 experience.....

I'll sleep a while on this, there is still the question for this what engine ?
LEM is in britain and I also read the fiat 127 agni driven project , another very nice peoples project and I'd actually have to find out how he is doing with his agni......

Was thinking about the Kostov K9 , any thoughts ??? Probably not very popular in the states....


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## tylerwatts (Feb 9, 2012)

Major, forgive me contradicting, but the desired benefit of the CVT is the changing gearing and amplified torque at low speed. If we exclude the clutch, the electric motor benefits are still present, and the CVT maintains ideal gearing proportional to the road speed so immediate drive and minimizes overloading the small motor with current. Alternatively you would use a bigger motor (kostov) that allows short periods of high current to give the needed higher torque at different speeds. 
So I feel the CVT supports using a smaller motor and improved efficiency and does not require the clutch. The larger motor won't benefit and needs current to provide a broad amount of torque with fixed gearing.


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## tylerwatts (Feb 9, 2012)

Benny, you can upload pictures directly to the forum as an attachment. Use the advanced reply view. Or if on tapatalk you need to log in with a tapatalk id and then you can attach photos again in the advanced reply window. Please show us the offending CVT. I know the vehicle a little bit and am sure the CVT would suit you well with a Lynch or Agni motor! 
Thanks
Tyler


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## major (Apr 4, 2008)

tylerwatts said:


> Major, forgive me contradicting, but the desired benefit of the CVT is the changing gearing and amplified torque at low speed. If we exclude the clutch, the electric motor benefits are still present, and the CVT maintains ideal gearing proportional to the road speed so immediate drive and minimizes overloading the small motor with current. Alternatively you would use a bigger motor (kostov) that allows short periods of high current to give the needed higher torque at different speeds.
> So I feel the CVT supports using a smaller motor and improved efficiency and does not require the clutch. The larger motor won't benefit and needs current to provide a broad amount of torque with fixed gearing.


The benefits you mention come from a multi ratio transmission, not necessarily from a CVT (continuously variable (ratio) transmission). And yes, if you choose to use a wimpy motor drive additional ratios can be useful. The CVT is a poor choice to get the 2 or 3 ratios which you might need. The CVT will likely cause more problems than it solves and overall subtract from performance instead of aiding it.

But WTH, it is his DIY project. Go ahead and use the CVT. Let us know how that works out.


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## scooby555 (Apr 26, 2013)

I uploaded 3 pics of the same vehicle , mine is in a warehouse of a friend.

No need to drive there down yet 

The gut feeling is that the CVT as is is not good , it needs definetly a mod on the centrifugal automatic clutch. The Rpm for ICE engines where u use the clutch is way too high compared to Emotor , but for Emotor a clutch is also beneficial cause even if the controller limits the stall current , its still lost current. Thats what i think  but no experienced means much to learn.

Tyler many thx for your input , I'm still digging info and appreciate all tips given , Major also many thx even if u are pointing me in another direction , I'll look into it


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## major (Apr 4, 2008)

scooby555 said:


> .... but for Emotor a clutch is also beneficial cause even if the controller limits the stall current , its still lost current. Thats what i think  but no experienced means much to learn.


There is no "lost current" and the clutch is pointless with the electric motor. Even those who retain the clutch and standard transmission in their conversions do not use the clutch to launch from standstill. They leave it fully engaged. That's the beauty of EVs. There is no wasted energy in slipping clutches at launch. You can get full torque at zero RPM or any amount you desire.


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## steelneck (Apr 19, 2013)

With a K9, a Soliton Jr. controller and a battery pack above 190V and a total of 15kWh to get range, in a 500kg car, you will probably have a city screamer capable of making smoke of your tires anytime you want, with one single gear within city speeds. Add a second gear and you reach freeway speeds quite quick too. The second gear could be made out of the overdrive unit from an old Volvo, or many other brands from the seventies using the same or similar units (many did). That OD unit is not much bigger than a grapefruit, contains its own hydraulic pump and can easily handle the torque in this very light case.

The beauty of CVTs is the ability to keep the ICE engine at its best torque RPM or fuel efficiency RPM at low loads, and its best power RPM at high load. Low RPM at low loads and higher at high loads, quite the opposite to an EM that on low loads are more efficient at high RPM, add to this that the beauty of electric motors is their ability to produce torque at almost whatever RPM, still with good eff. over a quite broad range. So, the beauty of electric motors get lost with CVT transmissions.

I do have a lot of experience with the CVTs used in snowmobiles, those do handle a lot of power in very light vehicles (not so much mass to get moving). Though i have not any experience with the CVTs made for cars, except the old implementation that was used by DAF (DAF 66) in the seventies, that was terrible inefficient even for the ICE. It is the snowmobile industry that in the eighties and nineties developed the CVT concept into the very efficient and reliable transmisson it is today. But this concept is the perfect match for engines with a very narrow power band, like two-stroke engines and small highly tuned turbocharged fourstrokers in light vehicles with a small mass. CVTs do not handle high torque at low RPM very well, the part that electric motors excel at.

I wrote more about it here:
http://www.diyelectriccar.com/forums/showthread.php?p=361234#post361234


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## Duncan (Dec 8, 2008)

steelneck said:


> With a K9, a Soliton Jr. controller and a battery pack above 190V and a total of 15kWh to get range, in a 500kg car, you will probably have a city screamer capable of making smoke of your tires anytime you want, with one single gear within city speeds. Add a second gear and you reach freeway speeds quite quick too. http://www.diyelectriccar.com/forums/showthread.php?p=361234#post361234


I would agree with that except - why would you need a second gear?

My 710Kg car (40% heavier!) with an OpenRevolt controller and a forklift motor will almost spin the back tires and is geared for 135Kph

It is about 7 seconds to 100Kph (60mph) 

With a 9 inch motor and the same gearing it would reach 190Kph
A Soliton Junior would probably not spin the tires in mine with a 9 inch motor
I lust after a Soliton!

But the PGO is over 200Kg lighter!

So why bother with the complexity (and weight) of a gearbox??

With a light car you are limited by tire grip - 
As soon as you can spin the tires in top gear a gearbox is just a hinderance


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## scooby555 (Apr 26, 2013)

steelneck said:


> I wrote more about it here:
> http://www.diyelectriccar.com/forums/showthread.php?p=361234#post361234


well i'm going to read it , many thx for all the info i can get my hands on


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## steelneck (Apr 19, 2013)

A more simple way of looking at this. If you run the car with the ICE, just keeping a steady speed, what RPM are you running at? Now if you instead floor it, full throttle acceleration, what RPM do you get? I know you will get quite a difference in RPM. You do not want this with an electric motor. It runs more economical at high RPM, but has strong torque already at low RPM. An ICE is just the opposite.

What happens in the CVT when you suddenly give full throttle, is that the helix cam controlling the movable half of the secondary is resisting this change, thus resisting upshift when RPM increases by rising belt force. By this you get more belt pressure as load increases, this is what made CVTs more reliable when the Swedish snowmobile maker Ockelbo started to make use of this some 40 years ago. 

When driving around and the CVT is engaged, this helix cam have more influence on the shift _pattern_ than any other single component in the CVT, it is what makes the CVT dynamic over different loads, all other components in both the primary and secondary have a much more static influence, quite linear to RPM, not load.


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## tylerwatts (Feb 9, 2012)

Ok folks. I'll concede that in larger applications a bigger motor with fixed ratio is prefered. I'm treating this application as a lightweight vehicle where we don't want more than 100kph (60mph) and have a smaller pack so efficiency over ultimate tire shredding power is needed. Plus this suits a tight budget that Benny suggests he is on. 

So Benny, let's set some performance and driving condition parameters. What are you going to use the vehicle for? How are you going to use the vehicle? This will help us suggest specific specs and components. Also what budget do you want us to work in?


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## Duncan (Dec 8, 2008)

tylerwatts said:


> Ok folks. I'll concede that in larger applications a bigger motor with fixed ratio is prefered. I'm treating this application as a lightweight vehicle where we don't want more than 100kph (60mph) and have a smaller pack so efficiency over ultimate tire shredding power is needed. Plus this suits a tight budget that Benny suggests he is on.


Hi Tyler
It is in SMALLER applications that a bigger motor with fixed ratio is preferred,

Only if you have a small motor for your application would you want multiple gear ratios

_so efficiency over ultimate tire shredding power is needed_

The most efficient, least energy sapping gearbox - is the one you don't use! - guaranteed 100% efficient!

Electric motor efficiency does change with speed and load - but nothing like the differences you see on a petrol engine


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## PhantomPholly (Aug 20, 2008)

I asked these same questions when I first joined this forum. I think the biggest issue is that a CVT would need a different algorithm to work well than an ICE engine, and as Major points out you don't need any "neutral" - the CVT should always be engaged with the motor even at zero rpm.

The goal of a CVT for an electric motor should be to do its best to hold a particular RPM (either most efficient rpm for that amp load, or based on ability of air-cooled motor to remain cool under load, etc.) given a particular throttle (or current) setting. This approach would probably yield the best acceleration for a given current setting, but would require a sophisticated CVT.

Where you could likely see some real gains would be in a golf cart, both by upgrading to batteries that aren't the original lead and by adding a CVT for simplest operation. This would yield better acceleration, hill climb, and top end at the cost of some inefficiency in the drive train.


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## tylerwatts (Feb 9, 2012)

Ok, Phantom, this PGO is like a big offroad go-kart, in weight and cost. So this is why I am saying to Benny the CVT is useful for his application. Again I concede this is my opinion.


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## steelneck (Apr 19, 2013)

So far i have written arguments against CVT, but it can be done even if other solutions would be better. Now i am going to write a bit how to alter the CVT to better suit an EM.



scooby555 said:


> The gut feeling is that the CVT as is is not good , it needs definetly a mod on the centrifugal automatic clutch.


No, it is not the centrifugal part that is in most need of change, the change needed is mainly going to be about the helix cam in the secondary. The primary is controlled by its spring, the spring preload, the centrifugal weights and the cam angles on the weights. All this is about engagement RPM and the cruise RPM. The primary do not alter RPM depending on load, though the primary is all about things linear to RPM.

The secondary is controlled by its spring, rotational pre-load of the spring and the helix cam. What you want is to vastly reduce the rate of downshift upon load. With the ICE you want low cruise RPM for economy, and high RPM for power when you floor it. With the EM you want as little downshift as possible upon load, you want to keep the RPM quite constant independent of both speed and load, but you still want to get a higher belt pressure upon load to avoid slip. All this is about getting the right helix cam in combination with spring pressure and its torsional preload. There are no helix cams with the right angles for an EM, you have to find a metal working shop that can custom-make one for you. Expect a quite hefty price for this, and expect that you have to make a couple of them with different angles to experiment with. You will also need some different springs for both the primary and secondary, maybe also a couple of different centrifugal weights. Adjusting a CVT is a highly cut and try process, even for very experienced people. Expect a lot of testing and changing parts, and a couple of drive belts..

Those who have the best knowledge and hands down experience adjusting CVTs, you will find on snowmobile forums.


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## PhantomPholly (Aug 20, 2008)

tylerwatts said:


> Ok, Phantom, this PGO is like a big offroad go-kart, in weight and cost. So this is why I am saying to Benny the CVT is useful for his application. Again I concede this is my opinion.


I think you are right all the way around - it depends on the scenario. I was disappointed a few years back to find out they weren't the magic bullet I had thought they would be, and I'm still a bit disappointed that some enterprising person hasn't come out with a line of CVTs geared (pun intended) specifically for use with electric motors.

The problem, as always, is that while in theory "theory and practice are the same" in reality they hardly ever are...

So - I hope someone actually does a CVT conversion so they can tell us how it works out!


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## major (Apr 4, 2008)

PhantomPholly said:


> So - I hope someone actually does a CVT conversion so they can tell us how it works out!


It sucks; so they don't talk about it much  

http://www.squarewaveracing.com/The_Machine.html 

In the second photo you can see the guts of a CVT on this electric motorcycle. They raced it once. Admitted it was a big mistake. Removed it and went to direct drive. But they don't talk about it 

That is one example of about 4 or 5 failed attempts I've seen.


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## PhantomPholly (Aug 20, 2008)

major said:


> It sucks; so they don't talk about it much
> 
> http://www.squarewaveracing.com/The_Machine.html
> 
> ...


Interesting. Is the issue that the CVT cannot be made to seek optimal RPM rather than over-respond to torque demand (i.e. the motor has so much torque that it forces the CVT to a ratio that overspeeds the motor)? Belt slippage? Too easy to break the back wheel loose? Something else?

A motorcycle is an challenging platform because it is easy to deliver too much torque for the rear wheel. I can see how on a racing cycle with an over-powered motor a CVT might actually work against you (breaking the rear wheel loose too easily). 

For ordinary vehicles, however, it seems like you could get peppier performance out of an "average" motor without forcing it into realms where it starts creating too much heat (that torque multiplication thing really makes an under-powered motor feel bigger than it is). On the other hand, based on everyone's comments it still seems like you would need an advanced CVT (electronically controlled to more accurately control rpm) to get the full benefit - otherwise the ratios would spend so much time changing that it would make driving feel "funky."


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## major (Apr 4, 2008)

PhantomPholly said:


> Interesting. Is the issue that the CVT cannot be made to seek *optimal RPM* rather than over-respond to torque demand (i.e. the motor has so much torque that it forces the CVT to a ratio that overspeeds the motor)? Belt slippage? Too easy to break the back wheel loose? Something else?
> 
> A motorcycle is an challenging platform because it is easy to deliver too much torque for the rear wheel. I can see how on a racing cycle with an over-powered motor a CVT might actually work against you (breaking the rear wheel loose too easily).
> 
> For ordinary vehicles, however, it seems like you could get peppier performance out of an "average" motor without forcing it into realms where it starts creating too much heat (that torque multiplication thing really makes an under-powered motor feel bigger than it is). On the other hand, based on everyone's comments it still seems like you would need an advanced CVT (electronically controlled to more accurately control rpm) to get the full benefit - otherwise the ratios would spend so much time changing that it would make driving feel "funky."


Optimal RPM  The electric motor efficiency map typically shows efficiency within a few percent of peak for like 80 to 90% of the area (RPM x load). And the losses of the CVT contraption itself will negate the few percent optimization it might accomplish in that area. In most applications, time periods that the electric motor spends at loads and/or RPM outside the vast "good" efficiency area are of such short durations that the energy that could be gained from "shifting" drive ratio is insignificant. 

The electric motor/speed controller drive is a very good variable speed system unlike the ICE. The electric motor/speed controller also provides torque multiplication equivalency via the current multiplication with PWM.

Having said that, there are situations where multiple ratios are desirable. In most cases 2 or maybe 3 ratios will suffice. The need will depend on the type of drive system and the application duty cycle. The classic case is the DC motor with limited top RPM and the use at low speed traffic encumbered travel vs high speed highway.


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## tylerwatts (Feb 9, 2012)

I fully agree with you Major, but please consider this for a moment. Where I see the benefit for Benny and most times is this: Let's consider the motor to be roughly equally efficient through its power band. Say rated rpm is 3000 where Max torque exists and power is always available (incidentally this is probably peak efficiency also). Now say the motor in use is a smaller 10kw continuously rated unit, and is in Benny's PGO. Ideally you would have about 3 gears for good off-road drive, decent acceleration and a reasonable top speed. Now look at the CVT in this situation where the motor could hold 3000rpm continuously and the CVT becomes a torque multiplier. This means you get the maximum torque possible at each speed, on demand, and always have an optimum gear ratio. Thus you won't get caught out in the wrong gear,or have the complexity of a manual transmission when driving, all nice extras in my opinion. 
So if Benny is on a tight budget and wants modest performance from a smaller motor the CVT makes sense in my opinion. But it could require some tricky modification of the CVT cams, of which I am not familiar. Buy not an insurmountable task, and one should be able to fabricate replacement cams by hand for trial purposes initially. 

What do you guys think?


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## major (Apr 4, 2008)

tylerwatts said:


> I fully agree with you Major, but please consider this for a moment. Where I see the benefit for Benny and most times is this: Let's consider the motor to be roughly equally efficient through its power band. Say rated rpm is 3000 where Max torque exists and power is always available (incidentally this is probably peak efficiency also). Now say the motor in use is a smaller *10kw continuously rated *unit, and is in Benny's PGO. Ideally you would have about 3 gears for good off-road drive, decent acceleration and a reasonable top speed. Now look at the CVT in this situation where the motor could hold 3000rpm continuously and the CVT becomes a torque multiplier. This means you get the maximum torque possible at each speed, on demand, and always have an optimum gear ratio. Thus you won't get caught out in the wrong gear,or have the complexity of a manual transmission when driving, all nice extras in my opinion.
> So if Benny is on a tight budget and wants modest performance from a smaller motor the CVT makes sense in my opinion. But it could require some tricky modification of the CVT cams, of which I am not familiar. Buy not an insurmountable task, and one should be able to fabricate replacement cams by hand for trial purposes initially.
> 
> What do you guys think?


I think if he uses a decent electric motor with a 10kW continuous rating and a matched controller he will have peak power of 30kW and likely 10 times rated torque up to 70% top speed using direct drive. The shifting transmission of any type will just get in the way. He'll be way better off using that space for battery.

Now if he intends to do some steep slope rock crawling he would benefit from a lower gear, weather it comes from a shift or a sprocket change. Other than that, direct drive....IMHO


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## PhantomPholly (Aug 20, 2008)

major said:


> Having said that, there are situations where multiple ratios are desirable. In most cases 2 or maybe 3 ratios will suffice. The need will depend on the type of drive system and the application duty cycle. The classic case is the DC motor with limited top RPM and the use at low speed traffic encumbered travel vs high speed highway.


lol sounds like we all need to start shopping for a Powerglide.


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## Duncan (Dec 8, 2008)

_Say rated rpm is 3000 where Max torque exists and power is always available (incidentally this is probably peak efficiency also)_

NO
You are confusing an IC engine with an electric motor

The normal torque curve for a series DC motor is much simpler
Constant torque from zero rpm until the controller tops out then the torque reduces with revs

Effectively constant torque

A gearbox is only useful when you have to gear it down at low speed and change gears at high speed
For a light weight machine with limited top speed - direct drive - is the way to go


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## DavidDymaxion (Dec 1, 2008)

I have a successful EV with a CVT. It is a lawn tractor, so that doesn't necessarily extrapolate to a successful street or off road vehicle. The reason to use it was it was already there, and saved having to buy a controller (sepex motor runs constant speed like the gas motor did). Another reason is the drive motor also spins the mower blades, they need to spin fast even if the mower is moving slowly. So yes, I do have to use the clutch to start moving. I pull back on the CVT lever to slow for hills, and push it forward to speed up on flat ground. Yes, I'm giving up some efficiency. I estimate it would take 200 years of savings in electricity cost to financially justify buying a controller for its higher efficiency.

tylerwatts: If you look at the constant power region of an AC or sepex system, that is just like a CVT: The torque falls off inversely proportional to rpm, just like with a CVT.

I had the old Kostov 11 incher in my electric Porsche. It worked fine for me, until I damaged it in an overcurrent event -- I don't blame the motor -- I blame a controller failure and racing. I bought a new Kostov 11 to replace it. The new one looks to be better made, and I like the large fan that blows right on the brushes (that might have saved my old motor).

If you want to do it on the cheap, and you are quite the tinkerer, I personally would find it fun to try to get the CVT to work. If you can afford it, and want a less risky approach, a controller with direct drive or a conventional tranny is the more proven route.

You can get regen with a DC motor. With a series motor regen is inherently unstable and I don't know of anyone that has reliably tamed that beast. With a sepex motor regen is easy. My Porsche with a sepex motor does great regen. My electric lawn tractor regens down steep hills, or if I yank the CVT lever and slow down quickly. While sepex sounds great, it is a less trod path, so you'd be more on your own. The only commercial setup I know about is a Kostov sepex motor with a Kelly sepex controller. I heard someone was going to do a sepex version of the open ReVolt controller, but don't remember hearing if that worked out. You can just turn on a sepex with a big contactor -- it'll start with a spark and a jerk and then spin constant speed. You can then add a starting resistor... and a protection circuit so the motor doesn't get hurt... So you need to know what you are doing even for a "simple" contactor controller. My tractor works with a constant speed sepex, but I control the CVT with a lever. Your CVT might need the motor to vary its speed.



tylerwatts said:


> I fully agree with you Major, but please consider this for a moment. Where I see the benefit for Benny and most times is this: Let's consider the motor to be roughly equally efficient through its power band. Say rated rpm is 3000 where Max torque exists and power is always available (incidentally this is probably peak efficiency also). Now say the motor in use is a smaller 10kw continuously rated unit, and is in Benny's PGO. Ideally you would have about 3 gears for good off-road drive, decent acceleration and a reasonable top speed. Now look at the CVT in this situation where the motor could hold 3000rpm continuously and the CVT becomes a torque multiplier. This means you get the maximum torque possible at each speed, on demand, and always have an optimum gear ratio. Thus you won't get caught out in the wrong gear,or have the complexity of a manual transmission when driving, all nice extras in my opinion.
> So if Benny is on a tight budget and wants modest performance from a smaller motor the CVT makes sense in my opinion. But it could require some tricky modification of the CVT cams, of which I am not familiar. Buy not an insurmountable task, and one should be able to fabricate replacement cams by hand for trial purposes initially.
> 
> What do you guys think?


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## tylerwatts (Feb 9, 2012)

Duncan. I am not confusing drive types. Simply setting an example where torque is maintained until this rpm before dropping off, and this would be the rated rpm which is ideal for continuous operation with a CVT. 

Benny. Can you give us a clear set of performance goals and types of use and we can calculate and probably agree on the type of motor needed and the budget required. 
Regards


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## PhantomPholly (Aug 20, 2008)

major said:


> Optimal RPM  The electric motor efficiency map typically shows efficiency within a few percent of peak for like 80 to 90% of the area (RPM x load). And the losses of the CVT contraption itself will negate the few percent optimization it might accomplish in that area. In most applications, time periods that the electric motor spends at loads and/or RPM outside the vast "good" efficiency area are of such short durations that the energy that could be gained from "shifting" drive ratio is insignificant.


Just re-read this with respect to your "confused" emote. To clarify what I was trying to say: While it is true that the electric motor can produce about the same torque over a range of rpm, the same torque at a higher rpm represents a higher total power output (horsepower). Thus if you produce the same torque at a higher rpm and then gear it down exactly to whatever your current speed is, you then take better advantage of torque multiplication. 

Again, you are utterly correct that any power to the wheels that results in spinning is of no benefit; the (theoretical) advantage of the CVT is being able to deliver full "horsepower" to the wheels at any driving speed, whatever that works out to as torque (potential acceleration) at the wheel.

The potential benefit only matters over the range of speeds at which torque is insufficient to break the wheels free for the vehicle / conditions in question - that's why several auto makers matched early CVTs to tiny engines trying to make their performance "acceptable."


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## scooby555 (Apr 26, 2013)

tylerwatts said:


> Benny. Can you give us a clear set of performance goals and types of use and we can calculate and probably agree on the type of motor needed and the budget required.
> Regards


Hi all , yes budgets .....well have to move the buggy from its location....got notified they need the space 
but ok those are small problems 
the idea is to have a sportive buggy , good accelaration , no real off road on the program ( my back is not exactly in the mood for that )
topspeed should be 55-65 MPH for u americanos , so cruising on the high way should be ok. But mostly this is to be used in the city for short commutes.
Budget , i have saved up 4K€ , so thats very tight it seems to me but doable.

Anyway my ex wants the attic done first , and i promised to do that so the kids have an extra bedroom......ah well winter projects .....
chimney needs to be dismantled , roof isolated , electricity , walls , lights , and floor and cupboards and a stairwell ( a lift if i get my way )
so after moving the buggy , will dismount ICE , and post some pics of that , probably the CVT is part of the engine , so the whole discussion will be settled if i cannot use it.....and i dont think i'm gonna make one.....

But please keep the ideas coming


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## tylerwatts (Feb 9, 2012)

CVT is separate and bolts to the engine. It is a generic design most of these types of vehicles use. 
For your budget, what range do you want? You won't get enough batteries to use the car unless you find second hand batteries somewhere. I'd suggest using a forklift motor, not too big, and belt drive (like a Harley Davidson primary drive) to the differential on your PGO. Fortunately this is a separate unit so simple to do I believe. Then build your own controller from a kit. The open revolt controller will give excellent performance in your light vehicle. 

Good luck with the attic!


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## Duncan (Dec 8, 2008)

tylerwatts said:


> CVT is separate and bolts to the engine. It is a generic design most of these types of vehicles use.
> For your budget, what range do you want? You won't get enough batteries to use the car unless you find second hand batteries somewhere. I'd suggest using a forklift motor, not too big, and belt drive (like a Harley Davidson primary drive) to the differential on your PGO. Fortunately this is a separate unit so simple to do I believe. Then build your own controller from a kit. The open revolt controller will give excellent performance in your light vehicle.
> 
> Good luck with the attic!


Yep
I have an 11 inch forklift motor and an OpenRevolt - 
Don't go a big as that for your machine!
a 9 inch or even smaller would be great
Then you need a Lithium pack - as big as you can afford


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## DavidDymaxion (Dec 1, 2008)

The traction limit is a good one. Another limit is heat. You could have a situation where you can briefly spin the wheels, but on a long, slow, uphill climb the motor and/or controller overheats. In this case lower gearing would lower the current and heating. An off road buggy could be subject this to kind of use.

To engineer it, find the max continuous current for your motor. Look up the torque it'll produce at that current. Do the math to see what torque multiplication you need to climb the steepest hill to figure out the transmission ratio you'd need.

Of course, this is presuming the motor is spinning fast enough and/or you have an external fan to keep the motor cool.



PhantomPholly said:


> ... The potential benefit only matters over the range of speeds at which torque is insufficient to break the wheels free for the vehicle / conditions in question - that's why several auto makers matched early CVTs to tiny engines trying to make their performance "acceptable."


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