# Is it too much waste "The direct drive"?



## Genius Pooh (Dec 23, 2011)

Is it too much waste "The direct drive"?

I know high RPM from higher voltage....


So.. without transmission is it too much wates of electricity?

I don't understand why people do "direct drive"

Can you tell me about it?


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## Jordysport (Mar 22, 2009)

depends on the application. eg if you had an average road car 1,000kg with dual warp 11's, you will be spinning the wheels all day long in 1'st 2nd 3rd and most likley 4th aswell. 4th gear is typically a 1:1 ratio, so if your loosing traction whats the point of a transmission. 

most of the time people on here will use a gearbox rather than DD but the people that do run DD will have a Diff ratio typically 2-4:1. 

I will be using DD with a GR of 1.5 - 2 : 1 but i will be using Dual K9 220V in a 330kg car. 

The issue with DD is mainly prolonged amps on the motor, the driving force required is much greater than with a gearbox. 

It entirely depends on your application.


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## Genius Pooh (Dec 23, 2011)

Jordysport said:


> depends on the application. eg if you had an average road car 1,000kg with dual warp 11's, you will be spinning the wheels all day long in 1'st 2nd 3rd and most likley 4th aswell. 4th gear is typically a 1:1 ratio, so if your loosing traction whats the point of a transmission.
> 
> most of the time people on here will use a gearbox rather than DD but the people that do run DD will have a Diff ratio typically 2-4:1.
> 
> ...


Yeah you are right...if car is under 60 Km/h 

DD is good choice but if 0-130 km/h?

It's too waste I think ...( DD mean also fixed gear ratio..in my mind)


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## Jordysport (Mar 22, 2009)

Genius Pooh said:


> Yeah you are right...if car is under 60 Km/h
> 
> DD is good choice but if 0-130 km/h?
> 
> It's too waste I think ...( DD mean also fixed gear ratio..in my mind)


yes 0-37mph DD will generally be fine, but you might as well use a gearbox and speed up the acceleration. 

The issues with gearbox's come in when you get up to 60mph+ as electric motors don't have the high RPM's ICE's have so the gear ratio's are not long enough after 80mph or so, if you have 5th gear it will be an overdrive 0.87 ish and then the Diff ratio 2.5-3.5 typically your ratio will be around 2.5 : 1 . and a wheel radius of 0.20m you will be doing 95mph MAX. 

Unless you have a custom gearbox DD is the way to go if you want to go faster than that!

Tbh, there are too many variables to say DD is good or bad or likewise with gearboxes, each persons conversion is dependent on their needs and their vehicle, a broad statement cannot be made about the subject.


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## Genius Pooh (Dec 23, 2011)

Jordysport said:


> yes 0-37mph DD will generally be fine, but you might as well use a gearbox and speed up the acceleration.
> 
> The issues with gearbox's come in when you get up to 60mph+ as electric motors don't have the high RPM's ICE's have so the gear ratio's are not long enough after 80mph or so, if you have 5th gear it will be an overdrive 0.87 ish and then the Diff ratio 2.5-3.5 typically your ratio will be around 2.5 : 1 . and a wheel radius of 0.20m you will be doing 95mph MAX.
> 
> ...


 
Yeah I seriously think about 3 stage manual trasmission. 

BTW what is your battery module's capacity? in Kw/h

and what is maximum range and car's weight?


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## Jordysport (Mar 22, 2009)

Genius Pooh said:


> Yeah I seriously think about 3 stage manual trasmission.
> 
> BTW what is your battery module's capacity? in Kw/h
> 
> and what is maximum range and car's weight?


6 kwh , range: 10km hopefully , 400kg with driver


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## Genius Pooh (Dec 23, 2011)

Jordysport said:


> 6 kwh , range: 10km hopefully , 400kg with driver


 
OMG really? do you know other's mileage? at 6kw with transmission?

400kg just 10km OMG


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## Jordysport (Mar 22, 2009)

Genius Pooh said:


> OMG really? do you know other's mileage? at 6kw with transmission?
> 
> 400kg just 10km OMG


nope, i'm after speed not range, its a race car.


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## PStechPaul (May 1, 2012)

Jordysport said:


> nope, i'm after speed not range, its a race car.


A very good example of the need to define exactly what you expect, and then determine how (and if) the conversion can be done. A fixed ratio direct drive may be ideal for both extremes of a high speed racing car at one end, and a powerful low speed tractor or forklift on the other end. For a typical passenger vehicle, especially when low cost and high efficiency are paramount, a transmission with at least two speeds seems to be the way to go. 

The torque requirement is not only for quick acceleration, but also needed to negotiate a steep incline or speed bump. Ideally you probably need enough thrust to climb a 50% grade which means 1000 lb for every 2000 lb of car weight, and at a minimum 25% grade or 500 lb thrust. For the OP, an "executive sedan" is probably 4000 lb, so assume 1000 lb thrust. For 24" diameter tires and a 2:1 differential ratio, the motor needs 500 lbft torque. To run at 60 MPH the wheel turns at 840 RPM so the motor will turn at 1680 RPM. So the motor will need to be at least 80 HP. A typical EV of that size will probably use an average of 350 Wh/mile and at 60 MPH that is 21 kW or about 16 HP. 

So for DD you need a motor roughly 5 times bigger than actually needed, although the minimum size for such an EV is more like 25-30 HP. The difference in weight between a 25 HP and 80 HP motor (based on about 5 lb/HP) is 275 lb, while a transmission is probably about 100 lb. So you may have almost 200 lb less with a transmission, which would be about 20 kWh of batteries and about 60 miles of range.


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## EVfun (Mar 14, 2010)

The highest powered EVs often go direct drive because it is hard to keep clutches or transmissions together with the kind of low end torque a series wound motor can make. Going direct drive requires more motor and more controller than would be needed otherwise. You need to be able to handle high peak motor currents. On the other hand, you don't need a transmission. Since most cars come with a transmission for free it is usually cheaper just to keep it. 

I can easily drive my EV around in 3rd gear all the time. It is a little slower from 0-20 mph, but my controller has a peak motor current of only 1000 amps (battery amps limited in software to 300 amps.) I top out at about 70 mph in 3rd, so it does take 4th to hit 85 mph. I usually choose to drive in 2nd around town and 3rd on the freeway. 4th is only used to prove I can go that fast and 1st is only good for chewing up tires. I wouldn't want to try driving only in 3rd gear in the hills of Seattle. I would have to buy a larger motor that made more torque per amp (less rpm per volt), raise my system voltage about 20% to get back the rpm (5000 rpm at 70mph), and install a better controller cooling system for those time I do have to pull downtown hills at low speeds. 

An 11 inch motor at a Zilla Z2k-HV would be a decent combo for direct drive with about a 4.5:1 final drive in a 2500 lb. car. See -- that is kinda big and expensive, but a 9 inch motor and a Z1k-LV would likely be inadequate as a direct drive setup in hilly city driving. You pays your money and you takes your choice.


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