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Electric vehicle motor selection Answered

As any one who has looked at my instructables knows whilst a school teacher I built a full sized electric racing car.


This had a 250 watt DC motor over run to 500 watts - 20 amps at 24 volts .

It was capable of running the car up to 25 - 30 MPH and using 2 car batteries drive for a couple of hours on the flat.

Nowadays electric vehicles are all the rage. Looking at a few motores as small as 4000 watts are in use for city use where high speed isn't necessary.

Now the question:


This motor intended for model cars is rated at 4000 watts RPM 26,100 100 amps at 45 volts. that's about 5.5 Hp.

Suitably gears down could such a motor be a power unit for a light weight electric vehicle.

The DC motor I used was, by comparison, huge and weighty. It seems to me that HP is HP and 5.5. Hp is plenty for what I have in mind.

My concerns as always is I see no other commercial manufacture doing this - or anyone else for that matter, only electric bikes use small motors.

There has to be a reason I am not catching.

Experts out there you opinion please.


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1 year ago

I had a chat with a guy who did electric racing karts down here some years ago.
His theory to make BLDC motors work for more than RC models goes like this:
Take a motor with a moderate kv rating.
Calculate though the wheel diameters and chain or direct drive system the required RPM for a motor to get the desired top speed.
Said top speed should be at about 90% of max speed of the motor to leave some safety margins.
The key then is to select a motor that has a far high max RPM than what you need, preferably 6 to 10 times, more if you can.
Keep the supply voltage in mind when doing this ;)
As it was just karts the guy then used sprockets and a chain to get the desired reduction.
For the motor usually these tiny sprockets the BMX guys on the back wheel when converting them to something more suited for tricks.
He claimed getting a kart up to 60km/h this way was no problem, with a runtime that is still acceptable to make it through 5-7 "races" around the track before the battery needs to be changed over.

Appearently, for better performance, it is best to modfiy the rear axle to a swing arm system like on motorbikes.
With a motor system per wheel and an "electronic torque converter" the handling and acceleration would drastically improve.
He did not want to go into details though how this electronic torque converter is supposed to work as that design of his is still used in licensed race karts - go figure...


Reply 1 year ago

Very useful and interesting and thanks for taking the time. More food for thought.


1 year ago

What I know about EVs could be expressed in one paragraph but I have been looking at converting a lawn tractor to electric. I can't answer your question about the motor you posted but you might be interested in this site. https://www.evdrives.com/Default.asp


Reply 1 year ago

Many thanks for replying, Golf cart motors will work well for your application where torque is more important than speed.

Thanks for the link.