How to calculate the tipe of DC motor you need?

Question

How to calculate the specs of a DC motor to be used to propel a small car.

Given:

mass of the car

max speed the car should be able to achieve

max acceleration

From this data how do you figure out what DC motor will be able to provide the above parameters?

How to calculate the power required?

How to calculate the torque?

Answer 1

Well, we all know that you have to start with physics.

F=ma

So you know the mass of the car, and you know the acceration.  From that you can find the force that you will need to have the engine make.  (scaled by any gears, and size of your tires)

As for max speed, This will be related to the max RPM's of the motor.

For the power reqired... well power is Energy per second.  That will give you the power.

Torque, that is just the rotational eqivilent of force.

It should be pretty easy, this should give you a good idea of where to start.

Answer 2

15 kg car, max speed 30 km/h, and max acceleration 3- 3.5m/s. 15-20cm wheels (diameter).  2 electric motors.

Torque = F x d = Power/rps

F = mass x acc = 15 x 3.5 m/s^2 ~53 N(ewton)

Torque = 0.1m x 53N ~ 5.3 Nm

rps = distance/circunf /time = 30,000m / (0.2 x pi) /3600 ~ 14

Power = T x rps = 53 x 14 = 742 Watts ~ 1 HP

Answer: ~0.5 HP / motor

You can get them cheap at ebay.com. You should have/ask for a torque/speed curve

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Friction will depend, in addition to the weight,  on the width and  material of the tires. You'll have to look it up yourself.

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