The purpose of the motor is to spin the propeller. It is the power-plant of the airplane.
There are two types of motors used for electric RC airplanes:
brushed motors and brushless motors.
These motors were the first type of motors to be used in electric RC airplanes. While they are still used in a few airplanes today they have largely been replaced by the newer brushless motors.
Brushed motors get their name from the fact that they have brushes inside them. They require a brushed ESC to work. They are generally less efficient and heavier than an equivalent brushless motor. Brushed motors are often found in “Ready to Fly” airplane packages but even those are slowly moving over to using brushless power systems.
Brushless motors are the latest development in electric RC motor technology. They are lighter, more powerful and more efficient than their brushed equivalent.
Brushless motors get their name because they do not have brushes inside of them. Brushless motors require a brushless ESC to work.
There are two main types of brushless motors: Out runner and In runner motors. On an Out runner motor the outer casing (or bell) is the part that rotates. With an In runner motor, on the other hand, the core of the motor rotates while the casing remains stationary.
Terms related to motors:
Speed: This usually refers to the different brushed motors eg. Speed 400, Speed 250 etc. The different Speed values imply motors of different sizes and capabilities.
This value indicates the number of revolutions per minute (RPM) that the motor can produce, when not under load, per volt of input from the battery. Example: If you have a 2000Kv motor and are using a 12 volt battery the total RPM that the motor would theoretically produce, while not under load, would be 12 x 2000 = 24,000RPM. This is a theoretical value and in reality will differ based on quality of manufacturing and definitely by your choice of propeller.
Input Power Rating:
This value measured in watts refers to the maximum input power that can be supplied to the motor without it overheating. The actual input power is relative to the choice of propeller and throttle stick position. The input power can be calculated for any given combination of these factors by multiplying the input voltage and current. This value should be equal to or smaller than the motor’s power rating.