In radio control, the term motor refers to an electric motor. There are some exceptions to this in the full scale world - for example, the misnomer "outboard motor" - but interchanging the term "motor" with engine in R/C can be very confusing, as R/C models can be powered by either.
Brushed Motors[]
Most surface models are powered by a 540-series brushed motor, or a motor with a length of 54 millimeters. Motors in electric aircraft range from 180-series to 540-series; 370- and 400-series motors are quite common. These use brushes made out of a Hard iron compound to send energy to the commutator.
The brushes require physical contact with the commutator, so they are held in place with springs. These springs keep constant tension on the brushes even as they wear. The commutator is part of the armature, or rotating part of the motor. In racing applications, the copper commutator must be trued or 'cut' with a special lathe when it becomes worn and blackened, preferably before this point as an overly worn commutator cannot be lathed. The brushes and their retaining springs must be replaced as they are worn down as well regardless of the conditions in which the motor operates. Badly worn brushes lead to tremendous loss of power and possible commutator damage.
Motors are characterized by the number of turns and winds they have. 'Turns' refers to the number of times the armature wire is wrapped around the iron core of the armature. In general, the lower the turns, the faster the motor and the higher the turns the more torque the motor has. 'Winds' refers to the number of strands in the armature wire. Motors are available with one to four winds. More winds equal more torque; less winds equal more speed. Turns and winds are denoted in the following format: TURNSxWINDS. For example, a "15x2" denotes a 15 turn, double wind motor.
Such a motor would be an excellent all-around motor in an offroad buggy with its combination of speed and torque. Your specific needs will best determine the type of motor you require.
Brushless Motors[]
Brushless systems are also available. These motors have fixed, radially arranged windings inside the motor can and permanent magnets on the motor shaft. They use special electronic switches to send power to the appropriate set of windings at the appropriate time. They need a special high-frequency electronic speed control to do this.
Brushless motors require much less maintenance than brushed motors because of the lack of brushes and commutator. They are usually very powerful and efficient, up to 87% efficient according to some manufacturers. Such power often requires upgraded transmissions in R/C cars and trucks. The initial cost of brushless systems is higher, but once you factor in the maintenance and other costs associated with low turn, powerful brushed motors, the cost quickly justifies itself. An upgrade to lithium polymer batteries. or "li-pos" is recommended as well when "going brushless," but is not absolutely necessary.
Since the technology is similar to that found in CD-ROM drives, some aircraft hobbyists wind their own brushless motors out of CD-ROM motors. They require a few readily available parts in order to mount them to a model and operate off of the same speed controls as commercially available brushless motors. CD-ROM motors are primarily used in direct-drive aircraft applications since their design is similar to toroidial, or donut-shaped "outrunner" motors.
The following is a partial list of online sites linking to manufacturers of CD-ROM conversion parts and systems:
http://www.aveox.com This site has information about brushless motors including axial design motors: http://web.archive.org/web/20060125012427/http://www.members.cox.net/~rdoctors