# Do we still need transmissions with todays motors?



## Duncan (Dec 8, 2008)

Hi Loa

We still need geared transmissions - the only difference is that we can get away with one gear rather than several

The reason is that motor torque is (roughly roughly) proportional to weight - if the motor runs a wheel rpm it has to be heavier than if it is smaller running at 8 times wheel speed and geared down

If you are using a motor with a lower max rpm you can still get away with it but your top speed may(will) be effected

I'm running an 11 inch DC motor without a gearbox driving a 4.1:1 diff
Great acceleration but top speed is limited to 130kph


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## Matej (Dec 4, 2015)

It depends on what your priorities are.

For a home-built conversion, using a transmission will probably always be slightly more efficient when it comes to getting more range out of it, even with the extra weight of the gearbox.
On the other hand, direct drive is mechanically simpler and much more robust if you are going for a high power application.

Even Formula E teams still cannot seem to decide which is more advantageous.


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## dcb (Dec 5, 2009)

but to your question, we don't *need* a multi-speed transmission, as long as you get enough torque and rpm for your needs with one speed. That is a function of budget and/or resourcefulness.


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## Loa (Apr 5, 2015)

Thanks for the inputs. 

I am planning on using a 11" motor for my conversion, and I know I could find a ~4.1:1 rear end for my car. 130kph is enough for me. 

But as Matej said, I'm worried about range. Which is more efficient at 115kph?
-No tranny, so motor at very high rpm)
OR
-Using 3rd or 4th gear (on old 1970's car), so motor at lower RPM but with added weight of the tranny. 

I'm guessing electrical motors don't have flat efficiency curves?

Loa


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## dcb (Dec 5, 2009)

you have to interpolate for different voltages/current capacities but this is the general idea:









too much/too little torque and efficiency suffers. too much/too little rpm and efficiency suffers. And you are trading torque and rpm with gear changes, so there is no pat answer, it is situational.

And there are a few extra losses in a constant mesh multi-speed transmission to consider as well.

My limited understanding leads me to believe that a sepex motor is better for partial load conditions (i.e. cruising at 60) as is any field oriented AC motor. But Series motors handle overloading better (partly why you usually see them in drag racing).

But it isn't a huge difference as far as I know, i.e. http://www.ijeit.com/Vol 3/Issue 1/IJEIT1412201307_101.pdf

And multiple gears also don't result in a large efficiency gain either (usually trading rpm inefficiencies for load inefficiencies).

edit: also it is worth knowing that you can often tweak your driving style to avoid inefficient modes of operation.

edit2: I usually think of multi-speeds when the motor system is weak and/or when the vehicle is heavy. When the power to weight means I have to choose between being able to climb a hill vs going the speed limit were I to use a single ratio.


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## Duncan (Dec 8, 2008)

Hi Loa

_-No tranny, so motor at very high rpm)
OR
-Using 3rd or 4th gear (on old 1970's car), so motor at lower RPM but with added weight of the tranny. 

_In an older gearbox 4th gear is normally 1 to 1 - which is exactly the same as not using the gearbox at all!

The advantages of using a multispeed gearbox are more wheel torque at lower speeds because you are in a lower gear_. - _which means that you can use a smaller motorThere will be little or no efficiency gains

The big reason (IMHO) for doing away with the gearbox is that you can then put the motor where the gearbox used to live freeing the whole engine bay for batteries


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## Loa (Apr 5, 2015)

Hello, 

I hadn't considered that the 1:1 4th gear was in fact the same thing as no transmission. Interesting. This mean that I will be able to test with my set-up and my car if a no transmission option is acceptable. If I can drive all day long (in city and highway) on 4th gear, I could consider removing the transmission. 

Dcb: one information I haven't been able to find on the netgain webpage is this: are there more efficient RPM bands on an electric motor. For example, is the motor going to use more or less juice if I drive at 115kph on my transmission's 3rd gear rather than on the 4th? Or is the electric motor's efficiency the same regardless of RPM at a given speed and car weight?

Thanks for the answers!


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## dcb (Dec 5, 2009)

well, if the motor operation is optimized, it will look something like this (nissan leaf shown):











so yah there is a most efficient rpm (speed) and torque point, but efficiency goes down in both directions from there, though nothing like in an internal combustion engine. Here it is roughly in the middle of the max torque and max rpm, coincidence?

edit: aerodynamics is likely to be a much bigger factor fyi


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## Loa (Apr 5, 2015)

Very interesting!

I think that I'll have to look at my gages to see which gear is most efficient at any given speed. Also, the 11" warp motor I'm looking at tops at 5500, so the curve will be different. 

As for aerodynamic considerations, it will be in part 2 of my project, so probably 2018!


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## Sunking (Aug 10, 2009)

For DIY EV you are going to likely need a transmission. Reason is you are likely going to use a DC motor with fairly low RPM's and narrow Power Band similar to an ICE. 

Tesla and Nissan use AC Induction motors custom made for the EV. AC motors can operate at much higher RPM's with wide power bands. When you have a motor that turns 13,000 RPM, you do not need a Transmission, just a fixed differential ratio. 

Example at 10,000 RPM, with a Differential Ratio of 7:1 with 24 inch tires is 104 mph

Bottom line here is you will not likely not have access to a AC motor like manufactures use. There is one company that makes AC Induction motors for the DIY EV market call HPEV Motors. I use the AC15 motor on my racing golf cart, with a fixed differential of 6:1 with 20 inch tires gets me 70 mph scary fast at 7050 RPM's. You do not see a lot of AC motors in DIY EV's because they are very expensive and require expensive Inverter motor controller. 

Bottom line is your budget dictates what you can do. Additionally motor RPM is dictated by Voltage. DIY EV's are typically 72 144 volts while commercial EV's today use up to 600 volts at 13,000 RPM. 

Kind of off the subject and hijacking the thread I would love to find a 2-speed differential. Low sped for climbing trees, and high speed for the road. My buddy copied me but used a 12:1 ration gear. Only goes 35 to 40 mph, but you have to be real careful accelerating from a standing position as the motor torque is enough to flip the cart over backwards. He put Wheelie Bars on it. That sucker does great doughnuts .


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## Duncan (Dec 8, 2008)

Hi Sunking
I'm using a stone age DC motor - 11 inch Hitachi
And the Device can now unstick the rear tires and accelerate strongly up to the highest speed I dare (currently 115Kph) - 

http://www.diyelectriccar.com/forum...dubious-device-44370p13.html?highlight=duncan


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## Loa (Apr 5, 2015)

Hello Sunking, 

You just confirmed what I thought when I saw the Leaf graph that Duncan posted: the motors I'm looking at don't rev up to 11000 RPM! And while I did check the possibility of doing an AC conversion, the price turned me off pretty quickly. 

Guess I've found many good reasons for sticking to the original transmission. 

Thanks a lot for the info guys. 

Loa


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## dcb (Dec 5, 2009)

Loa said:


> Of course, I'd still like to have decent performance (let's say a bit more than the Leaf).


So with the assumption of "todays motors", i.e. what you can reasonably find in the boneyard, the most straightforward way to improve a leafs performance is to take a leaf driveline and remove maybe a couple thousand pounds and make it streamlined (and muck with the gear ratio, i.e. taller tires) and set it up for better acceleration traction (i.e. rwd).

edit: no, I take it back, forcing more amps into the motor would be the *most* straigtforward way, but you are limited by weight and drag still, and the limitations of the existing system.

but DIYers have access to 400 volt packs these days, and motors and controllers, again using "today" as the criteria.


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## Sterling2015 (Jun 24, 2015)

For WarP 11HV, Zilla 2k, 300v LiFePo

Hi- decided on transaxle with racing clutch for a street/track road race car.
Clutch for reasons, extra safety, allows for quick/emergency mechanical decoupling of the motor , 2) I want a reference to compare to traditional manual gear shift sports cars, 3) Do not want to destroy the synchros and need quick reliable shifts. A test bed to establish best gearing if I go to single gear (+ reverse) trans.

Looking for advice on ratio calculators: here's one I use based on my project that uses a racing transaxle with torque bias differential and high gears. 
http://ranchotransaxles.com/calculators/


My 4th gear is .70 but the calculator only goes to 0.82, but seems close enough I think. Shift point for WarP11HV is 4000-5000 rpm. 200mph car?
Yes, body is aerodynamic, based on 200mph KemarkGT kit.
My actual gears are: (3.88 ring and pinion)
1st 2.70, 2nd 1.86, 3rd 1.35, and 4th .70 

Or on paper:
3.88*0.7= 2.72 (final drive)
Drive Rot = 1
Driven = .37
5000 RPM * .37 = 1850 RPM
Dia 26" = 66cm = 207cm circumference
1850 rpm *207cm = 382950cm / min
2.4 mi/min = 144 mph

I have the main parts on hand and building now: (2000 lbs est car weight)
WarP11HV - Zilla 2K - MD4-2D transaxle
Planning on 300v LiFePo battery


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## AdamAnDrone (Mar 23, 2017)

Not really, efficiency can suffer a bit but to me the increased simplicity is definitely worth it in a passenger car.


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## taoofbean (Apr 23, 2017)

@Sunking - You can personally convert your transmission to be a 2 gear setup, discarding the other gears, or you can order one premade, like EVWEST's 2 gear modified VW transmission gearbox. They discard the reverse and extra gears, replacing the setup with two that accommodate high torque start, and then cruising speed.

I am considering whether the expense of them modifying it is worth the weight savings in my own build.

Kind regards.


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## nucleus (May 18, 2012)

Loa said:


> Of course, I'd still like to have decent performance (let's say a bit more than the Leaf).


You are going to have to be significantly faster than a Leaf to get to "decent".

Car and Driver has the Leaf at 10.4 seconds 0-60 which is very slow. Corollas are faster than that.


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## Karter2 (Nov 17, 2011)

nucleus said:


> You are going to have to be significantly faster than a Leaf to get to "decent".
> 
> Car and Driver has the Leaf at 10.4 seconds 0-60 which is very slow. Corollas are faster than that.


 But this is a DIY conversion forum isnt it ?
So just do the controller mods as Arlo did (or similar) and boost that Leaf motor up to 200+ kW


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## nightrider (Jun 4, 2017)

im interested in this subject with regard to using a chevvy spark drive(gear reduction removed), direct to tailshaft for rear wheel drive.
i think the diff ratio i have is 3.58/1..


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## brian_ (Feb 7, 2017)

nightrider said:


> im interested in this subject with regard to using a chevvy spark drive(gear reduction removed), direct to tailshaft for rear wheel drive.
> i think the diff ratio i have is 3.58/1..


The Spark was originally announced with a reduction ratio of 3.17:1, and later changed to 3.87:1, so 3.58:1 is certainly a reasonable ratio between this motor and the wheels.


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## nightrider (Jun 4, 2017)

great. thanks for that.
i really need to confirm what the diff ratio actually is. if its not 3.5:1, it may be 4:1.
is a 94 hilux dual cab diesel, 2wd. iv looked for specs, but it seems there are several ratios available for that model.
i read somewhere they print the ratio some where in the engine bay..will check


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## brian_ (Feb 7, 2017)

nightrider said:


> ...
> i really need to confirm what the diff ratio actually is. if its not 3.5:1, it may be 4:1.
> is a 94 hilux dual cab diesel, 2wd. iv looked for specs, but it seems there are several ratios available for that model.
> i read somewhere they print the ratio some where in the engine bay..will check


According to OffRoad.com, Toyota Differential Identification:


> One way of determining your axle type and stock gearing is to look for an Information Plate on your truck, on the firewall (prior to 1989) or door jamb (1989-current). It will look something like this:
> 
> C/TR/A/TM 138 HR11 G282 A130H or C/TR GJ7/KQ41 A/TM G251/R150F
> 
> ...


In the article, this is followed by tables giving a more detailed breakdown of the coding, translating code values into ring-and-pinion gear ratios.


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