# EV with no geabox



## rillip3 (Jun 19, 2009)

This is possible. It is usually not advised for a couple of reasons:

1) poor acceleration. Even though you have full torque at any RPM, you have a fixed amount of power. Applying your full power with a 3:1 added mechanical advantage from the transmission gearing vs applying full power without that mechanical advantage means you reduced your acceleration by 3:1.

2) mechanical considerations. If you connect directly to the differential, there is very little room for error. Your connection has to be perfect, or the torque on the joints/welds will rip the thing apart. With the transmission, this has already been taken care of for you, you just have to make sure you get a clean connection to the transmission, which is already engineered to allow for an easier, solid connection.

There are probably some other things to take into account, like placement of the motor, weight distribution, but those get a little specific to the donor car. No reason you can't do it, but you can easily take advantage of a lot of years of engineering work by keeping the transmission.


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## carp3 (Aug 5, 2010)

because it's easy for me to do this. i'm planing to convert a Citroen Dyane which is 600Kg and it's very cheap ( under $200,without ICE) i want to put batteries,controller,motor and extra tire and differential in the hood. so i want to save space.


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## TX_Dj (Jul 25, 2008)

Any gear reduction is a mechanical advantage. You trade RPM for torque. Torque is what moves you. Any tractive design can benefit from gear reduction.

Further, the slower you attempt to turn the motor, the more amps it will draw (because of higher torque requirements) and the less efficient it will be, and the more heat it will generate (due to the higher amps/lower efficiency).

In some cars, a single ratio (such as the differential) is good enough, so long as the ratio and motor and weight of the car and performance expectations are in harmony. The Commuter Cars Tango is a good example of this, as is John Wayland's White Zombie.

the typical car-sized tire turns about 600-800 rotations per mile. A true "direct drive" without reduction means that the motor would be 1:1 with the tire, turning 600-800 RPM at 60 mph, far less at lower speeds.

Can it be done? Sure.
Is it practical for most applications? No.


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## Woodsmith (Jun 5, 2008)

If you are getting rid of the Dyane's gearbox and repalcing it with just a diff are you going to be able to sort out the brakes? They were inboard on the gearbox weren't they?

You could use an old Jag rear diff with inboard brakes, bit bigger and more powerful then the Citroen's.


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## peggus (Feb 18, 2008)

carp3 said:


> Hi, I'm a newbie here
> 
> 
> is it possible to build an EV without gearbox ? i mean connecting a PMSM(for example 30kw/440Nm/6500rpm) directly to differential? ( a differential with 4:1 reduction ratio for example )


With 440Nm (~330 ft-lbs) you should have no problem, provided that the motor can supply that for a few seconds without overheating. Performance will be excellent in a light car like that!

It's called direct drive and has been debated to death several times over, try the search function.


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## carp3 (Aug 5, 2010)

I'm planing to buy this:
http://www.uqm.com/pdfs/HiTor spec sheet 7.14.10.pdf


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## JRP3 (Mar 7, 2008)

Where are you getting it from? Last I knew UQM wasn't interested in selling single units to individual.


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## carp3 (Aug 5, 2010)

JRP3 said:


> Where are you getting it from? Last I knew UQM wasn't interested in selling single units to individual.


Eh?! damn!


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## meanderingthemaze (Jan 25, 2010)

Maybe someone could become a vendor and sell them to converters? Any volunteers?


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## meanderingthemaze (Jan 25, 2010)

FYI, contacted them and the price for that system is ~$20K with volume discounts of 4+ units.


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## carp3 (Aug 5, 2010)

With controller ?


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## meanderingthemaze (Jan 25, 2010)

Yes, that's what it sounded like. And the sales rep didn't mention that they will not sell to individuals. Perhaps they have changed their policy. Personally, I think that's a bit pricey. 

It's very frustrating that industry is holding back the proliferation of EVs. It can't possibly cost that much to produce. Don't get me wrong, I know people need to keep a roof over there head and make money as entrepreneurs, but this feels a like gouging.


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## JRP3 (Mar 7, 2008)

They simply don't want to deal with the support issues that come with the DIY crowd. If they can sell 100 motors to one company they probably only need to answer a few questions on the first install. If they sell 100 motors to 100 individuals they have potentially 100's of of support questions and problems. They may not come out and say they won't sell to the general public, they just price it out of range for most. Like ACP quoting $25K for their system and selling it for $11K in quantity to OEMs.


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## trampintransit (Jan 5, 2020)

Given the original question, if direct drive without a box is undesirable, where does one source a replacement reduction box. I don't want to use the car's existing box if I can help it..it's 70 years old and and an unknown quantity. Doesn't need to handle huge amounts of power..it'll probably only be a 70hp motor..max.


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## Duncan (Dec 8, 2008)

trampintransit said:


> Given the original question, if direct drive without a box is undesirable, where does one source a replacement reduction box. I don't want to use the car's existing box if I can help it..it's 70 years old and and an unknown quantity. Doesn't need to handle huge amounts of power..it'll probably only be a 70hp motor..max.


Direct drive to the diff is absolutely fine - IF you have enough grunt!
I bought a ford gearbox when I was building my car - when I calculated that I could spin the tyres in top gear I decided the gearbox was not required!

How big and heavy is the car?
Something Spitfire sized will fly with a 9 inch fork lift motor and a 150 volt 500 amp controller using direct drive


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## pengyou (Nov 21, 2012)

The Leaf and Tesla do not have gearboxes. I think the Porsche also does not.


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## Duncan (Dec 8, 2008)

pengyou said:


> The Leaf and Tesla do not have gearboxes. I think the Porsche also does not.


Nope the Leaf and the Tesla have a single speed reduction gearbox
All EV's have a reduction gearbox!!


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