# direct drive plan is it sane?



## onegreenev (May 18, 2012)

What car are you doing? 144 volts and that motor seem a bit on the weaker side for doing a direct drive. You might just be better off buying a rebuilt tranny and utilizing the leverage that the transmission will give you over doing directly drive. With enough power you could do the direct drive. I know of a vehicle right now that looks at first glance to be a direct drive but it actually has a small auto transmission and the motor controller combo would most likely work as direct but utilizing the leverage a transmission will give you is just the smart thing to do. Gives you reverse without all the hassle of electronic reverse contactors and extra junk to contend with. 

Simply use the transmission and be done with the conversion and go have fun driving your electric car. 

Pete


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## davidmillin (Dec 14, 2013)

Hi Newbie I think your plan is feasible plenty of others have done direct drive but I am wondering if it isn't easier to get another transmission out of a wreck. it saves finding a coupling solution for the driveshaft, wiring a reversing contactor they are about $200 dollars before you even install switches and interlocks in the cabin and you won't need to source and install a different differential. Maybe I'm missing something perhaps your gearbox is hard to come by.In my case I had to replace the gearbox before I had even received my motor it was $250 secondhand and included clutch and clutch pedal assembly.


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## dougingraham (Jul 26, 2011)

I am with the other guys on this. Find a replacement transmission and save the headaches.

You will need three high power contactors in order to do reversing of the motor. At current Ebay prices that is over $200 and you can probably find a used transmission for that. Also it is hard on the motor to run it in reverse. Since you undoubtedly have the timing advanced for forward operation, when running backwards the timing is retarded and this will cause brush and comm issues although they can be minimized by limiting power in reverse. You need to make certain that no current is flowing when you switch directions. I think the Zilla has hardware to facilitate reversing. The Soliton does not have hardware to sequence the contactors but has some software awareness of the operation. I don't know about the Open Revolt. If you have a contactor hang up during the transition the result will most likely be a damaged motor controller.

Unless you go to a 1000 amp controller your acceleration will be pretty limited. At 1000 amps I think it would be acceptable up to 45 mph (although not great). Not sure how the motor would handle 1000 amps all the time.

Best Wishes!


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## EVfun (Mar 14, 2010)

More voltage, a bigger motor, and more motor amps would be needed for decent drivability and to prevent things from overheating. More like an 11 inch motor, 240 volts, and a Zilla Z2k-HV. 

I can drive my buggy around in 1 gear, third. That is a 1200 lb. car with a 5.77 to one drive ratio, a Zilla Z1k-LV and 122 volts with a 7 inch motor. Smaller motors typically make more rpm per volt. I run a peak of 900 motor amps (300 battery amps.) The performance in 3rd is fine, but not exciting. 

You're looking at about 2x what I have and I'm glad I have my gears.


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## Newbiee (Feb 16, 2011)

hey guys thanks again for the help! 

i dont mean to have this post about direct drive vs transmission for ev's but instead what someone would need to know to accomplish this direct drive plan and what kind of end result i could be looking at if others have experienced an ev like this. 
Its because there were unfortunate circumstances that happened to my specific EV build when i was having parts made to couple the transmission and motor, which resulted in leaving me without the option to simply buy a replacement transmission and drop it in like most other conversions.

-I wont be needing to replace my differential, i will just be changing the ring gear and pinion inside of it to get a 4.9 final drive ratio, this wont be costing me much when i go find the vehicle to take them from at a pick your part junkyard.

-ok i will now need a reversing contactor, understood.
-limiting power in reverse with the controller or my foot?
-what are the ways to make certain no current is flowing before switching to reverse?
-how have other conversions accomplished coupling the electric motor to the driveshaft?
-if i were to encounter a small hill, is there a mathematical way to compute if i could make it over the hill with these parameters? lol


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## stealthhack (Aug 18, 2011)

The boy says that he don't want high top speed but will need BIG motor for direct drive to transfer many NM to the pavement, or a good reduction ratio on the diff. something like 5-6-7:1.
Overall to move a car with that weight don't cost so much neutons but the grades eats a lot of them for sustaining speed.


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## Newbiee (Feb 16, 2011)

hey evfun do you have to pull 900 amps from stopped in 3rd to accelerate?


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## EVfun (Mar 14, 2010)

I don't have to pull 900 amps, but 500 would be pretty weak. I've dialed the controller around a little bit and find that 600 amps is pretty much the minimum if I want to take off in 3rd, and that wouldn't be any good taking off up a hill. It should be about 3.3 seconds to accelerate from 0 to 25 mph on level ground. It would quickly get worse if trying to climb a hill. 

Here is a back of the envelope calculator. It only applies when the EV motor is in the initial constant torque range. Note that ft-lb of torque at the ground is only equal to ft-lb of torque at the axle if the tire height is 24 inches (1 foot radius.)

ft-lb of torque at the ground / weight in lb. * 32.18 = acceleration in feet per second per second

I don't think the 9 inch motor can survive the required motor amps (torque) in city driving without lower gearing. You might be able to make a city only car with about 7:1 gearing, but that would give up the ability to reach freeway speeds. I'm a big fan of direct drive, but it takes a big controller and lot of motor brush area to pull off.


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## Duncan (Dec 8, 2008)

Hi Newbee

I am running direct drive
http://www.diyelectriccar.com/forum...-dubious-device-44370p2.html?highlight=duncan

The Device is a bit lighter (710Kg) and I have an 11 inch motor,
Using the OpenRevolt 500 amp controller its a bit faster than most road cars
Slower than most track cars but not disgracefully slow

Reverse
You will need a reversing contactor - I got one off an old forklift
I have an extra brake light switch that shorts the throttle pot when you brake,
just put your foot on the brakes when switching to reverse

The certification authorities here don't like you to be able to go from forwards to backwards with one switch - so the forward/reverse lever from the forklift was out.

A reversing contactor has two 12v coils, F and R
With both F & R energized or neither - no power to motor
You need to switch F on and R off to go forwards
and R on and F off to go backwards

I have a big hill - and its on gravel
My wife's Mercedes SLK struggles, - the Device flies up it


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## Woodsmith (Jun 5, 2008)

Hi Duncan, could you remind me what your axle ratio and tyre diameter is please.

Thank you.


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## Duncan (Dec 8, 2008)

Woodsmith said:


> Hi Duncan, could you remind me what your axle ratio and tyre diameter is please.
> 
> Thank you.


Hi
I have a 4.1:1 diff ratio and about 24inch tires


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## Woodsmith (Jun 5, 2008)

Duncan said:


> Hi
> I have a 4.1:1 diff ratio and about 24inch tires


Thank you, that gives a 17.4mph per 1000rpm.

My build is 3.91:1 with 21" tyres giving 16mph per 1000rpm. 

If our 11" motors produce a similar torque then, with a slightly lower overall ratio then your set up, I should have a little more torque to the road and a lower top speed. That is good for me.


Newbiee's set up, 4.9:1 with 25.5" tyres, would give 15.5mph per 1000rpm. With a similar motor and controller that might give a reasonably similar performance weight for weight, though the additional weight would hit acceleration and hills though.


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## stealthhack (Aug 18, 2011)

Woodsmith said:


> Thank you, that gives a 17.4mph per 1000rpm.
> 
> My build is 3.91:1 with 21" tyres giving 16mph per 1000rpm.
> 
> ...


How to calculate a tyres with dimmensions 205/75/R15 to inches.
And to ask: can i mount AC24LS on a 4,3:1 differential with the tyres above to move in the city 2250lbs jeep?


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## EVfun (Mar 14, 2010)

27.1 inches tall. 205 is the width in millimeters. 75 means the sidewall height is 75% of the width. Of course, a mounted tire has a 2 sidewalls. 205 * .75 * 2 = 307.5mm You convert millimeters to inches by dividing by 25.4, resulting in 12.1 inches. To that you add the diameter of the wheel, for a total of 27.1 inches. 

Oh, and 1135 Kg (about 2500 lb.) is a lot more weight than 710 Kg. Also, they spell tire funny in the U.K.


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## Woodsmith (Jun 5, 2008)

stealthhack said:


> How to calculate a tyres with dimensions 205/75/R15 to inches.


I often use a tyre size calculator online to check and compare.
This is one I found just now.
http://www.etyres.co.uk/tyre-size-calculator

205/75/15 is 27.11"

The way it works is this:
205 is the tread width in mm.
75 is the aspect ratio, the tyre side wall is 75% of the tread width. That gives 205x75%= 153.75mm

Convert the side wall height to inches. 
153.75/25.4=6.05"

Add two side wall heights to the rim diameter.
6.05+6.05+15=*27.1"*

No idea about the second part of your question, sorry.


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## stealthhack (Aug 18, 2011)

EVfun said:


> Oh, and 1135 Kg (about 2500 lb.) is a lot more weight than 710 Kg. Also, they spell tire funny in the U.K.


Lets say more arround 800kg(no engine, transmission, fuel tank, cooling system, radiators, etc.) 
Li-ion as traction pack. but for simplicity i want direct drive.


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## few2many (Jun 23, 2009)

Mizlplix has gone from a transmission, to a direct drive. He has detailed both, though he is using a 3 phase ac motor to your dc. Search the forum, he has a lot of good info.
http://www.diyelectriccar.com/forums/showthread.php?t=59659&highlight=mizlplix


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## stealthhack (Aug 18, 2011)

Hi guys, recently i made some calculations for direct drive city car, but i want to ask can i manage to run a suzuki wagon R+ on direct drive(with AC24LS motor) to the rear wheels when the differential is 4,1:1(or 4,33 with automatic gearbox) and tyres 135/70/R13 or similar tyres?
I made a comparison with a standard polo with 1.4 MPI 2000y(195/55/R14)
Here are my calculations:


> Wheel force is the acceptable translation of Tractive Effort, which describes what happens between the tire patch and the road. Tractive Effort is a tangential force, a product of prime mover torque and a vehicle's transmission, and can be described as,
> 
> Tractive Effort = (TE * R1 * R2 / r) E
> 
> ...


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