What is a brushless motor?

A Brushless DC (BLDC) motor is a rotating electric machine where the stator is a classic three-phase stator like that of an induction motor and the rotor has surface-mounted permanent magnets. In this respect, the BLDC motor is equivalent to a reversed DC commutator motor (or brush motor), in which the magnet rotates while the conductors remain stationary. In the DC commutator motor, the current polarity is altered by the commutator and brushes. On the contrary, in the Brushless DC motor, the polarity reversal is performed by power transistors switching in synchronization with the rotor position. Therefore, BLDC motors often incorporate either internal or external position sensors to sense the actual rotor position or the position can be detected without sensors. The BLDC motor is driven by rectangular voltage strokes coupled with the given rotor position. The generated stator flux interacts with the rotor flux, which is generated by a rotor magnet, defines the torque and thus speeds of the motor. The voltage strokes must be properly applied to the two phases of the three-phase winding system so that the angle between the stator flux and the rotor flux is kept close to 90° to get the maximum generated torque. Due to this fact, the motor requires electronic control for proper operation.

What advantages do brushless electronics have over glow engines?

Previously, only glow engines could achieve the performance now available from brushless motors, ESCs and accessories. Brushless technology, however, has benefits that glow power can’t match.
Cheaper - Only a charger and batteries are required…no fuel, glow plugs, starting equipment, or maintenance accessories to replenish over time. 
Simpler - Just connect the battery to the ESC and go! 
Cleaner - No fuel spills and exhausts residue to clean, and no fuel odor. 
Quieter - An important consideration with non-modeling neighbors. 
Maintenance-free - Compared to glow engines, which require maintenance and tuning.

When I use a brushless motor, do I also have to use a brushless ESC?

Yes. Brushless motors will not work with non-brushless ESCs - the two technologies are completely incompatible. A brushed ESC just pumps out current like a fire hose pumps out water. A brushless ESC spreads current in a precise pattern to different places in the motor.

How does motor choice affect my model's performance?

In electric motors, an increase in winds means an increase in top end speed. A decrease in winds means an increase in torque, or acceleration. Conversely, more turns means more torque/acceleration, while less turns means more top end speed.
Pinions and spur gears work the same as turns—more teeth, more torque, less teeth, less torque but more speed.

How do I break in an electric motor?

Ideally you'd like to run the motor at about 1/3-1/2 it's rated voltage with no load (without prop) for an hour or two—long enough to wear the brushes down without arcing.
R/C car modelers have special transformers for optimum breakin on high performance motors. If what you're working with is a typical 05 can motor, you can make your own system that works fairly well. Start with 2 alkaline D cell batteries and some spare 12 gauge wire. Simply hook the batteries up in series so you have a 3 volt power source and hook the wires to the appropriate terminals on the motor. Let the motor run until the batteries are dead.