# Why not use a clutch and Gearbox?



## martin_b14 (Oct 17, 2011)

Hi Everyone,

I am new to this forum and am yet to build my first EV.

I have a general question about transmissions so please forgive me if it has been addressed before.

Most builds I have seen on the Internet have connected the motor directly to the gearbox as a direct drive. The Flywheel, clutch and Gearbox are therefore redundant. I understand this is a simple maintenance-free system.

But can someone please explain to me why the motor is not used in a similar way to an Engine and runs all the time with the flywheel acting as a load and the revs restricted to say 3000rpm.

Possible pros

- The high start up current draw would be reduced with the flywheel providing momentum. The motor would instead draw a constant current.

- The gearbox can be used providing a higher speed range.

- The gearbox doesn't require any additional work.

- Ancillary equipment could be attached.

- The driving experience would be the same.

Forgive me if I missed something obvious or my mechanics / physics are too simple - but i'm here to learn.


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## piotrsko (Dec 9, 2007)

flywheel provides negligible power for the car. for the conversion, all things being equal, a very light flywheel is desired.

gear box provides lower torque (and current) demands from the motor, and can provide less back EMF in the higher gears. SEE also thread under Why automatic transmissions will work in..... Most people opting for a clutch wish to replicate the ICE experience for the masses that cannot fathom the difference.

Generally not necessary to idle the electric motor, UNLESS you are powering the alternator, power steering, or vacuum brake boost pump.

finally, no the experience won't be the same, it will be better. Permagrin is hard to remove from a satisfied DIY'er in their conversion.

I would suggest a wander through our extensive WIKI, and welcome to the forum.


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## dtbaker (Jan 5, 2008)

martin_b14 said:


> Most builds I have seen on the Internet have connected the motor directly to the gearbox as a direct drive. The Flywheel, clutch and Gearbox are therefore redundant. I understand this is a simple maintenance-free system.



I think you will find that most folks DO end up using a transmission. DC motors are great but cannot provide enough torque in a high enough gear to accelerate from stop and reach desired top speed at less than 5000 rpm.

There is lots of room for discussion as to how you want to couple the motor to the tranny though! clutched, or clutchless is a grand debate.


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## tomofreno (Mar 3, 2009)

To add to what dt said, AC motors generally can be run to higher rpm than DC series motors but they run out of poop (torque) at higher rpm, so generally also work better with a transmission as far as maximizing acceleration unless a very powerful AC motor is used. Those cost about as much as you would pay for a new subcompact car, so most of us use transmissions with AC or DC, unless we are satisfied with top speed limited to around 65 mph or less (depending on gear ratio chosen), taking longer to get to that speed, and having anemic acceleration around that speed.


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