Calculating electric motor efficiency ..
Motor Efficiency - Brush DC Motor Efficientcy | Portescap
Yes, the goal of motor design is different between vehicles and industrial applications. In industry, efficiency and longevity are key design parameters. That's why a 150hp AC motor weights several thousand pounds. In a vehicle, the motor weight plays a big role in the overall system efficiency. It's not just the energy efficiency of the motor that matters, but you also have to consider the weight of the motor that is being lugged around. Thus, they design for weight and power density. A 150hp motor for an electric car only weighs a few hundred pounds.
Efficiency classes for IEC line motors ..
Something that I should have emphasized is that motor designers can't seem to design for peak efficiency. They are always designing for peak power or peak torque. Often, this is known as power density (most power in the smallest volume). When you are choosing a motor for peak efficiency, you will often have a larger motor than you might normally expect for a given load.
Motor Energy Efficiency - Drive Technologies - Siemens
The second way to choose a motor, which applies more to drones, is to look at the efficiency curve and to select a motor/prop combination that puts you just to the right of the peak efficiency point. In this case, a load of about 0.1 oz-in would be ideal. If you select a point to the left of the peak, even light variations in load will cause vast efficiency swings (notice the steep slope) and if you select a point too far to the right, then you will be losing power continually with little recourse.