# EV motor vs Open differential?



## Zer0 (May 9, 2008)

One of the big problems here is you're not just talking about direct drive. In most direct drive setups, you're still running the power through the axle gear which has a ratio anywhere from about 3:1 to about 4.77:1 (usually only small and/or high performance cars). if you ran the motor directly to the half-shafts (or CV shafts, if front wheel drive) you don't get the benefit of the torque multiplication that axle gear provides. Not saying it can't be done, but you better have a monster motor(s) and lightweight car.


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## major (Apr 4, 2008)

Whitey_87 said:


> Did the EV1 have something similar?.


Hey ******,

The GM EV1 was direct drive with about a 10 to 1 reduction ratio and a differential. A great system where the drive motor could reach 12,000 RPM.

Regards,

major


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## joseph3354 (Apr 2, 2008)

use a ford 9 inch differential and you can get gear ratios as low as 8 to 1.


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## ww321q (Mar 28, 2008)

I built a gocart with 4 wheel independent suspension. I striped the differential , axles ect. from an old honda car . Removed the ring gear and replaced with sprocket and chain drive . You could use a belt drive to . Would be a lot of fabricating but can be done. J.W.  ps had a 750 Kawasaki 4 cyl. motor


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## Whitey_87 (May 30, 2008)

Thanks for the responses.



joseph3354 said:


> use a ford 9 inch differential and you can get gear ratios as low as 8 to 1.


My current final drive is ~3.5:1. If I wanted to direct drive to it does that steer my project more towards AC or DC? Does that ratio also require minimum motor size so that I don't burn it up? I am not looking for insane acceleration - just want to know if I need to add the cost of a new differential.


Would this ford differential fit on a nissan? 

Much Thanks


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## Manntis (May 22, 2008)

With the weight of an automobile, as opposed to a flyweight like a go-kart, the differential is a lightweight and efficient way to give you proper handling and save your tires. "direct drive" typically refers to losing the transmission, not the diff.

The other option is to use 2 motors, one for each drive wheel, with sophisticated controller programming that monitors what you're trying to do (cornering, f'rinstance) and varies their relative speeds accordingly.


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## Whitey_87 (May 30, 2008)

So is there any negative aspect to searching out or having fabricated, a 10:1 ring and pinion set? Or should I stay somewhere below 10:1?


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## major (Apr 4, 2008)

Whitey_87 said:


> So is there any negative aspect to searching out or having fabricated, a 10:1 ring and pinion set? Or should I stay somewhere below 10:1?


Hi ******,

Answer to question #1.....cost.

Answer to question #2.....For starters, I suggest you calculate the wheel RPM for your desired top speed. And divide that into the maximum speed you want for the motor.

Regards,

major


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## Whitey_87 (May 30, 2008)

Thanks for the advice major.


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## VDubber (Jun 2, 2008)

Manntis said:


> The other option is to use 2 motors, one for each drive wheel, with sophisticated controller programming that monitors what you're trying to do (cornering, f'rinstance) and varies their relative speeds accordingly.


Actually, you simply need to hook the two motors up in series to a single controller. The electrical characteristics of the motors will work as an "electric differential":



EVDL said:


> With 2 series motors connected in series to the controller you do get a differential action. Good in one respect, but beware. One wheel on ice or off the ground will cause a twice voltage light load condition on the motor connected to it. This will cause that motor to overspeed very quickly resulting in damage.


Sounds like a RPM limiter on each motor would be needed.

Another problem is you cannot run the motors at wheel RPM, waaaay to slow. You would need a gear setup for each motor with a 5:1 ratio or higher. Something like this, perhaps:

http://www.casadelgato.com/RoyLemeur/medshop48.jpg


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## Coley (Jul 26, 2007)

Quote:
"The GM EV1 was direct drive with about a 10 to 1 reduction ratio and a differential. A great system where the drive motor could reach 12,000 RPM."

No. 1. direct drive would mean NO reduction.

No. 2 How did the EV1 hit over 180 MPH with a setup like that? The motor would be turning 40,000 rpm!!!

Just curious....


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## MrCrabs (Mar 7, 2008)

Coley said:


> Quote:
> "The GM EV1 was direct drive with about a 10 to 1 reduction ratio and a differential. A great system where the drive motor could reach 12,000 RPM."
> 
> No. 1. direct drive would mean NO reduction.
> ...


1) I guess technically you would say it had a single speed gearbox, or a single reduction unit... but most times I've seen it called direct drive.

2) The EV1 was electronically limited to 80 mph, not 180 mph.


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## Manntis (May 22, 2008)

^ Crabs is correct. "Direct drive" _technically _refers to no gears in between, but commonly refers to no transmission gearset between motor and diff.

I usually prefer technical terms to remain unobfuscated but single motor converstions requiring a diff for cornering are so prevalent compared dual motor diffless drives that the use of this common term doesn't confuse most people.


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## joseph3354 (Apr 2, 2008)

Whitey_87 said:


> So is there any negative aspect to searching out or having fabricated, a 10:1 ring and pinion set? Or should I stay somewhere below 10:1?


search the drag racing sites for parts,the ford 9 inch is a very popular item.they can be machined and welded to fit almost any vehicle with leaf suspension.summit racing has a 7.33 ring and pinion set for under $350.with a 15 inch tire and 10k rpm you would hit 115 mph top speed(roughly).so i would guess an AC motor would be the ticket for that setup.a DC motor pushing 5k rpm would get you around 60-65 mph.of course using smaller or larger tire diameters would change these numbers a lot.


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## Whitey_87 (May 30, 2008)

Thanks for the responses. I'll check out that summit site. I would like to just get a new pinion and ring gear so I can keep the fabrication/modification to a minimum.


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## major (Apr 4, 2008)

Coley said:


> Quote:
> "The GM EV1 was direct drive with about a 10 to 1 reduction ratio and a differential. A great system where the drive motor could reach 12,000 RPM."
> 
> No. 1. direct drive would mean NO reduction.
> ...


Hi Coley,

Direct drive may include a reduction ratio. Most often does. Just no ratio changing mechanism, like a multispeed shifting transmission.

And the GM EV1 that did 180 mph was extensively modified. Although I think it did use the stock motor.

Regards,

major


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## Whitey_87 (May 30, 2008)

I checked summit - they had nothing for nissans. I do not know if some of the stuff they had would be interchangable on a nissan diff.



VDubber said:


> Actually, you simply need to hook the two motors up in series to a single controller. The electrical characteristics of the motors will work as an "electric differential":


This has got me thinking. I was going to do a dual motor setup anyway (like that 300ZX conversion - forget where I saw it, I think the link is in a thread somewhere on the site). Won't I be using a lot of amps to get the vehicle going from a stop if there is no reduction? Would AC or DC work best when connecting the motor right to the wheel?

Thanks.


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## joseph3354 (Apr 2, 2008)

hey ******,what model nissan are you converting?


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## VDubber (Jun 2, 2008)

Whitey_87 said:


> I checked summit - they had nothing for nissans. I was going to do a dual motor setup anyway (like that 300ZX conversion - forget where I saw it, I think the link is in a thread somewhere on the site). Won't I be using a lot of amps to get the vehicle going from a stop if there is no reduction? Would AC or DC work best when connecting the motor right to the wheel?
> 
> Thanks.


It's a question of heat.

It would have to have reduction. Any electrical motor that will fit into the car will burn up at that low of RPM with those torque (current) levels. Maybe it was a drag car? They spend very very little time under 60MPH...

DC will get you by with a lower ratio, they are made much more 'grunty' then a smooth running AC system. AC works better with a higher ratio, since they will RPM to no end.


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## Whitey_87 (May 30, 2008)

VDubber said:


> It's a question of heat.
> 
> It would have to have reduction. Any electrical motor that will fit into the car will burn up at that low of RPM with those torque (current) levels. Maybe it was a drag car? They spend very very little time under 60MPH...
> 
> DC will get you by with a lower ratio, they are made much more 'grunty' then a smooth running AC system. AC works better with a higher ratio, since they will RPM to no end.


Thanks for the info.

Joseph3354 - If I do not decide to to go with an older ZX, I am basing all of my searching on converting my 07 350Z. It is a weighty little beast...shame on nissan for making a 3,300 Lb, 2 person sports car. Some may say that I should not do it, but I read in the wiki or somewhere else that (to paraphrase) you should enjoy the car you want to convert and not be embarassed to be seen in it. 

My only other choice is my total rust bucket of a honda. But I want to convert the Z because I only drive it in the summer anyway so I wont have to worry about performance in the winter.

I am thinking any kind of lead battery will put me over the GVW. I will probably have to go with LiFePo4...but I should have the money for it. Once I start the conversion I will make another thread to track the status. I plan to start this next winter and have it ready for summer 09.

Not to derail my own topic or anything.


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## joseph3354 (Apr 2, 2008)

i think the 350z is an awesome car to convert,a little heavy but so what?its your money,its your car. check around with gear manufacturers and tell them what you are doing,you might get a sympathetic ear(or gear).
i don't know the costs of custom gear manufacturing,but it has got to be easier to install a set of gears as opposed to building a differential from scratch,just my insignificant opinion.


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