# Motor Torque required for 4 wheel drive electric car

• Sandesh_10
In summary, the conversation discusses the calculation of the motor torque required to move a car with a weight of 14 kg on a chassis with 2 identical rear wheels and 2 steel caster ball wheels at the front, all coupled to a 1:1 DC motor-gearbox. The wheels have a diameter of 80mm and are made of rubber, with an adhesion coefficient of 0.85. The calculation is based on the traction force required, which is determined by multiplying the adhesion factor by the weight of the car. The resulting torque is 4.67 N-m, assuming a constant velocity and the need to overcome the adhesion force. However, without information on rolling resistance or drag, there is no lower
Sandesh_10

## Homework Statement

There is 14 kg of mass kept on a chassis (consider chassis weightless). Chassis is having 2 identical rear wheels and 2 Steel caster ball wheels at front. Consider the weight distribution to be equal on each of the wheel. All wheels are coupled to a DC motor-gearbox (1:1) each.The Rear Wheels are having 80mm diameter and made up of rubber and the chassis car is to be moved on a dry vinyl flooring. Adhesion coefficient,μ = 0.85.
Find the motor torque required if the car is to be moved at 1.2 m/s.

## Homework Equations

Torque, τ = F * D/2
F : traction force required
D: diameter of wheel

Traction force, F= β * W
W : weight

## The Attempt at a Solution

F = 0.85 * 14*9.81 = 116.74 N
and thus
τ = 116.74 * 0.080/2 = 4.67 N.mm

Are these formulations and method correct?
Where and how does the velocity comes into picture?

Last edited:
It seems to me that you have computed the maximum torque that can be applied without skidding. Since no rolling resistance or drag data have been provided, there is no lower limit to the torque required to keep the vehicle moving at a steady speed.

I think your calculations are correct but your units should be N-m not N.mm.
I (we) assume the velocity is constant and that the torque is merely to overcome the adhesion force.

barryj said:
I think your calculations are correct but your units should be N-m not N.mm.
I (we) assume the velocity is constant and that the torque is merely to overcome the adhesion force.
That assumes 'adhesion coefficient' means that the wheels are tending to stick to the floor, resulting in a constant drag as the vehicle advances. The term was unfamiliar to me so I did a little research before posting (above). As far as I can make out, it is just another term for static friction. This led me to conclude, as I said, that what has been computed in the OP is the maximum torque that can be applied without skidding.

Yes, your formulations and method are correct. You have correctly used the equations for torque and traction force, taking into account the adhesion coefficient and weight distribution on the wheels. The velocity is incorporated into the calculation through the traction force equation, as the velocity of the car affects the amount of force needed to overcome the friction and move the car at a constant speed. This is represented by the β (adhesion factor) in the equation. As the car moves faster, the adhesion factor may change, resulting in a different traction force and torque required.

## 1. What is motor torque and why is it important for 4 wheel drive electric cars?

Motor torque is a measure of the rotational force produced by an electric motor. In 4 wheel drive electric cars, torque is important because it determines the ability of the car to generate enough power to move all four wheels simultaneously, providing better traction and control on the road.

## 2. How is motor torque calculated for 4 wheel drive electric cars?

The motor torque required for 4 wheel drive electric cars can be calculated by multiplying the weight of the car by the desired acceleration and dividing the result by the radius of the wheels.

## 3. What factors affect the motor torque required for 4 wheel drive electric cars?

The motor torque required for 4 wheel drive electric cars can be affected by various factors such as the weight of the car, the type and number of electric motors used, the terrain, and the desired speed and acceleration.

## 4. How does the motor torque impact the performance of a 4 wheel drive electric car?

The motor torque plays a crucial role in the performance of a 4 wheel drive electric car. A higher torque allows the car to accelerate faster and climb steep inclines with ease, while a lower torque may result in slower acceleration and reduced control on rough terrain.

## 5. Can the motor torque be adjusted in 4 wheel drive electric cars?

Yes, the motor torque can be adjusted in 4 wheel drive electric cars through various methods such as changing the gear ratio, using multiple electric motors, or adjusting the motor controller settings. This allows for customization of the car's performance based on the driver's preferences and the driving conditions.

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