Kv and Kt
Kv and Kt are important concepts. Those constants affect all motor parameters, including motor efficiency and torque. The following video explains those concepts.
To help illustrate the concept of Kv and Kt, we worked with a student from Carleton University, @juandadelto. He developed a web page demonstrating how the motor parameter affect the Torque-Speed graph. Don't hesitate to play with the motor parameter to understand intuitively how changing them will change the mechanical power output, the heat losses, and the total power used.