Choosing the best electric motor for a specific vehicle isn’t always easy. With so many variables to consider, it can be difficult to know where to begin. Given the cost of batteries and electric motors, the most cost-effective solution is to find a powertrain that closely matches the required vehicle performance.

In this article, we will go over a few fundamental questions that you should consider before attempting to find the best motor for your project. Essentially, you must determine your vehicle’s most demanding requirements as well as evaluate how various road conditions will impact powertrain performance:

1. Vehicle Specifications

Size, weight, overload, and aerodynamics are important vehicle characteristics that will ultimately determine the speed, torque, and power requirements of the electric motor. These factors will aid in understanding the effects of the vehicle’s operating conditions and are critical in selecting the appropriate powertrain. Keep them nearby for the next steps.

2. Cycles of driving

It is also critical to consider how the vehicle will be used. What are the vehicle’s typical driving cycles? Will it be driven in a city with frequent stops? Will it be able to travel long distances with only a few stops? All of this will influence the vehicle configuration and battery pack size, as well as the powertrain choice.

3. Automobile configuration (electric, hybrid)

Is the car hybrid or all-electric? Is it parallel or series hybrid if it’s hybrid? As a general rule, if the vehicle routes are unpredictable or if it will be driven over long distances, the hybrid architecture is usually preferred.

The full electric configuration is ideal for city driving, where the distance between charging points is short, the speed is low, and the number of stops is frequent.

4. Highest possible speed

What is the vehicle’s intended top speed? How long does it have to last, and is it only used for passing?

What are the available gearbox and differential ratios? What is the wheel’s rolling radius? All of these questions must be answered and used in the calculations to determine the maximum speed that the electric motor in your application can reach.

5. Maximum torque

The maximum torque allows the vehicle to begin moving down a slope. You must determine the highest grade that the vehicle must ascend. Using that grade, it is possible to calculate the maximum torque required by the electric motor while taking the differential and gearbox into account if a gearbox is used! The maximum weight should also be considered.

6. Maximum power

Some grades must be climbed at a certain speed, while others do not. When the vehicle has a large frontal area or travels at very high speeds, the maximum power is sometimes simply found at maximum speed. This translates to having a motor powerful enough to withstand all of the conditions that the vehicle can be subjected to!

The vehicle’s maximum power allows it to reach and maintain a constant speed under difficult slope and speed conditions. To calculate the maximum power, you’ll need a simulator that takes into account the vehicle’s drag and friction coefficients, as well as the forces required for the climb.

Again, the duration of the condition is important: unlike combustion engines, the peak power of an electric motor cannot be sustained continuously, and selecting the electric motor to be able to do the worst hill climb conditions with no time constraints would be overengineered.

7. Capacity of the battery

The battery capacity is typically calculated by running a simulator through a reference cycle typical of vehicle usage. The simulator can calculate the vehicle’s consumption in kWh/km. The capacity of the battery can be calculated by multiplying that value by the desired range.

Voltage of the battery

The battery voltage is proportional to the vehicle’s size. The current output decreases as the battery voltage increases. So, in cases where the vehicle continuous power is high, such as in larger vehicles, you want to increase the battery voltage to keep the size of the conductors manageable.

9. Transmission or direct drive?

Will the powertrain architecture necessitate the use of a gearbox? Do you want to reduce the costs of implementing a transmission while also simplifying your system?

10. Cost

Last but not least, what is your financial situation? In a previous blog post, we discussed the various electric motor technologies on the market, their benefits and drawbacks, and their application in electric vehicles.

To summarise

Once you’ve gathered all of the information mentioned above, you’ll need the right tools to calculate the component requirements based on the vehicle’s performance.