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# DC motor with 30nm torque and more than 3000 RPM Answered

Hi I need DC motor with 30nm torque and more than 3000 RPM how to build this or form where I can buy this in India please guide me on this also tell me what should be battery specifications to run this for 100km with the total load of 250kg?

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## 3 Replies

Jack A Lopez (author)2017-11-17

Is 30 N*m (newton*meters) the stall torque (torque at zero speed), or is it the torque at 3000 RPM?

If its the second one, then this is kind of a beefy electric motor. I mean how much mechanical power is 30 N*m torque, multiplied by 3000 RPM?

Convert RPM to radians per second, by multiplying by (2*pi rad)/(60 s), so

So torque multiplied by speed, in SI units, is

P = (30 N*m)*(314 rad/s) = 9420 watt = 9.42 KW

Divide by 746 watts/horsepower, to get 9420/746 = 12.6 horsepower

Basically, you are asking us how to build an electric car.

Coincidentally, there was someone else on this forum, this week, asking us how to build an ultralight airplane.

I think your idea to build a car is more realistic, and, if you'll forgive the pun, more uh, "grounded".

XD

Back to what I was saying before, about torque and speed, I do not think an electric motor is fully characterized by just those two numbers. Rather, every motor has a characteristic torque-speed curve; i.e. the graph that you get when you plot the torque for each speed over a range from 0 RPM, to whatever the maximum speed is. Also the integral of this curve is a power-speed curve.

I was looking for a kind of tutorial on torque-speed curves. I could not find one I liked, but I am going to point you towards an example of one. It is on this page,

https://www.osvehicle.com/osv-platform/

under the tab labeled "Powertrain", and that is a page I wanted to point you towards anyways, because it is basically an open-source electric car.

I am kind of guessing the usual plan for an electric car uses a motor with a flat, or downward sloping, torque-speed curve, so that the motor can give you its maximum torque at zero speed, so that you can easily get the car rolling from a complete stop, and also you can do this without the need for a transmission with different gears, like is typically needed for an internal combustion (IC, ICE) engine.

All the nitty-gritty details of this OSV "TABBY" design are available for download, I think, here,

although I have not downloaded anything from them myself, because I was stymied by a lack of social credentials. I think they want me to "like" them via Facebook(r), or "tweet" or "retweet" them via Twitter(r), or something-something, them via GooglePlus(r), and I just cannot be bothered with any of that.

I also noticed there was a user here on instructables, named "bennelson",

https://www.instructables.com/member/bennelson/

who seems to have written a bunch of 'ibles on the subject of electric cars.

You'll see his username in many of the results that appear in a Let's make: search for "electric car".

https://www.instructables.com/howto/electric+car/

Downunder35m (author)2017-11-15

Once the people get over running in front of a TV they throw them out.
Usually they have 180V DC motors in them, plus of course the required electronics.
Going low voltage means using scooter motors, quite cheap on Ebay.
Some mobility scooters these days already come with 48V battery systems, they are better than the 24V types as they require less amps.

iceng (author)2017-11-14

30nm = 22ftlb torque

So you want a 12 HP 3000 RPM DC motor..

ebay sells this 10 HP

https://www.ebay.com/itm/FUJI-ELECTRIC-189-200V-10...

You probably want a PM lighter DC motor