Bolting a DC motor straight onto a differential?


Ive been toying with the idea on an EV for a while now and decided to enquire about a couple of bits i cannot seem to find out :slight_smile:

ive read somewhere that people like to use the cars gearbox/clutch as the car would be prone to have a jerky start when setting off. i drive an electric forklift truck at work which sets off lovely and smooth so cant understand why a car couldnt be made to do likewise? ive worked out based on the forklift truck that i use, if i was to put the battery in the boot of a small/medium sized car and transform the electrics across it would all still weigh less than the actual forklift (lighter chassis on the car). the forklift is limited to 15mph but if the motor was changed for a larger one with intentions of hitting a max of around 50/60mph then would i need to use a clutch if the motor would sit at that sort of speed with no problems/real strain?

cheers :slight_smile:

No, you don’t need a clutch for smooth starts or gear shifting. My Mitsubishi pickup had the motor direct to the pinion shaft and pulled away very smoothly. Without a gearshift, however, it was limited to about 36 mph. Using the same motor in my 924 Porsche conversion, and going thru the gears (no clutch) I can hit 60 mph in 5th.

if the DC motor does not give a reasonable top speed ie 1500 rpm at 48 volts then just up the volts as it is the current that limits the power of a DC motor and typically i had a 36 volt 1500 rpm forklift motor on 144 volts (70 mph) as long as i did not exceed the 150 amps rating of the motor.
at 6000 rpm the motor was near its limit.

look at any dc motor catalog and you will see 2 identical motors one say 24v 2 hp and the other 48 v 4 hp.
the limit is where the revs are too much for the windings
so direct drive to diff and good controller

Early electric mail jeeps did this