# transmission or no transmission



## serge1951 (Nov 22, 2015)

Hi,
I am new to this group, so please bear with me if I ask silly questions. I am about to convert to electric power an ICE Lotus seven which I built from scratch and I am exploring my options. One question that popped to mind today was transmission. My rig runs on a 1991 Suzuki Samurai 5 speed transmission , which I fear may not like the high torque of an electric motor, in particular if I choose DC.

My question :what are the pluses and minuses of a direct drive.

Thanks.


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## dcb (Dec 5, 2009)

a multi-speed transmission allows you to have selectable gear ratios, but adds some weight and losses.

my 3400lb leaf is perfectly fine without one (imho), and about 100hp peak.

power to weight is probably your best first approximation if one is "necessary". My leaf would be driveable at 50hp I'm sure. But much less than that and I might be wanting more than one gear to climb hills/accelerate better, and have ok top speed. I'm sure other people would have different perceptions on power to weight vs needing multiple gears.

Aerodynamic load will be a factor as well.


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## Duncan (Dec 8, 2008)

Hi Serge
My car is a Lotus 7 thing - with direct drive

http://www.diyelectriccar.com/forum...-dubious-device-44370p2.html?highlight=duncan

I used Subaru suspension and overbuilt the chassis a bit so its quite heavy

Thoughts
I put the motor where the gearbox would normally live
This leaves the entire engine bay for batteries
I'm using a DC (forklift) motor
I have an 11 inch motor - a 9 inch would have been lighter and had a higher maximum rpm

With my heavy car (and I'm too heavy as well) I can beat a Ferrari off the line but I can't quite break traction on good tarmac - that is with 1000amps - if I turn it u to 1200amps I expect to be able to break traction

My motor and diff combination limits me to about 140Kph (somewhere above that I expect to grenade the motor)
Currently with 130v I an voltage limited to 100Kph
I have just bought a second hand Chevy Volt battery pack - I'm hoping for more power and speed


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## serge1951 (Nov 22, 2015)

Duncan said:


> Hi Serge
> My car is a Lotus 7 thing - with direct drive
> 
> 
> ...


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## Moltenmetal (Mar 20, 2014)

Give up the tranny and you will compromise on either off the line performance or top speed. Keep it and you have options for greater fun, at the risk of a weak link in the reliability. Like a particular gear ratio? Stay there and don't shift gears.

The clutch is optional for sure.

Yes you can go transmission- free with the right differential ratio and a huge DC motor in a vehicle like yours- Duncan's device is proof of that. But most people keep the gearbox and don't regret it. If you intend to drive rather than race the car, you might appreciate the opportunity to spin the motor a little slower. And if you want to go AC, you will be disappointed without the gearbox. Depends on your goals.

Word of warning: in Ontario, don't buy anything for a conversion until you have insurance sorted and a firm quote in hand. You may be surprised that whoever insured your Lotus build will not insure it if converted to EV drive- seems bizarre but it was my experience with my Spitfire conversion. The same companies that would insure it if I put a huge ICE in it, wouldn't touch it as an EV. If you're comfortable going on the don't ask don't tell basis, be prepared for a hell of a fight if they ever have to pay out on your policy. Work with a broker and get it sorted first.


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## Sunking (Aug 10, 2009)

It depends on the Motor Power band and RPM's. If you use a low RPM motor will most likely dictate you use a gearbox. OTOH use a high RPM motor with a wide power band like constant current up to cruise RPM and you can go direct drive.

Have you calculated Motor RPM required to get your desired top speed? If not click this link and punch in your numbers.Hint to use the calculator if you plan to run Direct use 1 for transmission Ratio.


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## serge1951 (Nov 22, 2015)

Word of warning: in Ontario said:


> Thanks for the warning,
> 
> It looks like Hagerty insurance will not want to hear about electric conversions, at least in kit cars. That may ring the end of my project.


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## ferd (Dec 1, 2015)

Our EV club experimented with this question (transmission or no transmission) using several converted cars on 96V to 130V DC. Our cars were heavier than the one you describe (mostly small pickup trucks, a Suzuki Samurai, and a full sized pickup truck) but our results should be applicable.

We found that we could increase battery range by installing a transmission. Yes it makes the car heavier and yes there is energy lost in the transmission, but it allowed enough load relief on electrical system to more than make up for it. We were able to extend battery range by about one third - from about 25 miles (direct drive) to 40 or so. The transmission also made it easier to drive different road’s speed limits. 

It's hilly around here so most of our gains were probably due to being able to downshift to go up hills. We saw the ammeter drop from about 425 amps load to about 150 amps load. Note that our goal was to increase range rather than break traction.


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## fatmanfatworld (Dec 8, 2015)

Hi very interested in this thread and grateful for the replies so far.
I was looking to do a conversion myself and wanted to go clutchless and transmissionless in a mk1 Ford Focus.
Are the any motors you would suggest? I was going to look for dc forklift motors but if there are any suggestions of type or power ETC then that wold be much appreciated.


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## evnz (Jul 24, 2010)

i have the clutch and manual trans in 4 gear ( amost 1:1 at 200 amp out of the pack) it is slow of the line but i also am 1400 kg in weight so to keep up with the other car in town i use 3 rd and out of town 4 th 
heat is somthing to think of to if your rpm's are to slow the motor will heat up to 
so do your sum's on what your going to do a round town car or a show off car 
i do not regret keeping the gearbox

owen


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