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# How do you measure torque required for an electric motor in an EV weighing 250kg.?

I found this link on the net. **http://www.ehow.com/how_5009233_calculate-required-torque-vehicle.html**.It is quite informative.Is this the correct way?

## Discussions

Yes that is the correct way to do it.

Ok .But How much will it vary when the torque generated by the motor is quite equal to or less the torque of the vehicle.The variables i meant are speed and acceleration to be set.

Torque is simply how strong the twisting action is of the motor. You need how strong that 'moment' is in conjunction with rotor speed to come up with the useful value of 'power' or 'work' in HP or Watts.

Total power to weight ratio will determine your acceleration.

Total power with some fancy math will determine maximum speed based on frontal area and rolling resistance (Total friction + drivetrain losses) "coefficient of friction"

Total energy storage in conjunction with the above will determine your range...So, virtually any motor will work - its just what is in the 'workable range'.

http://en.wikipedia.org/wiki/Power_to_weight_ratio

look at the 'examples' section.

Note how the space shuttle Hydrogen rocket motor has the highest power to weight ratio? That's because weight was one of the biggest concerns building the thing.

Alternately, looking at a aircraft carrier engine, it can afford to weigh a lot more because acceleration is not such a big deal, so long as you keep floating :)

There is no mention in there about torque because you pick a motor based on its total power and ideally the torque will fall in line based on the required rpm.

Are you talking about the resulting torque from the motor, through the drive train, and to the wheels? The amount of overall torque will depend on the drive train you use. A motor's torque can be increased with the right set of gears but at the cost of RPMs. So long as the motor itself has the enough RPMs to maintain the desired speed the right set of gears can give the torch you need. You may not need a very strong motor just a high speed motor. But all the math for that is beyond me. You'll have to look into gear ratios and how they affect overall torque and speed.

If your building an electric car then have a look here The motor is 250 watts

continuously ratedThis would drive the car at around 28 to 30 MPH on the flat no wind.

The car + battery + motor etc + driver weighed about 150 pounds

You can drive about 60 miles on the flat on 2 car batteries if your careful.