Electric motors impart a continuous spinning motion and are used in nearly every combat robot. They work by creating a rotating magnetic field, which is used to spin a shaft or a shell at high speed. Many motors will be attached to a gearbox, generally used to decrease the shaft speed and increase torque.

Maytech Brushless 8085

Brushed (DC) Motors

DC Brushed motors have historically dominated the sport due to their availability and simplicity. These motors have an electrical connection to the spinning part of the motor using contacts called brushes.

DC motors have two wires or connections. Apply a suitable DC voltage to these and the motor will spin; reverse the connections, and the motor will spin in the opposite direction.

While these motors can be operated at full speed by switching power on and off as described, an electronic speed controller (ESC) will allow you to control speed by turning the power on and off in very fast pulses. Most ESCs can also reverse the motor direction while in use, so that weapons, tires, etc. can move both ways. Only ESCs made for brushed motors can be used.

Common brushed DC motors

There are literally hundreds of motors to choose from but certain choices have become favorites over the years due to their availability and suitability for robot combat in terms of output-speed at typical voltages, ease of mounting into designs, and robustness. As with all things in robot combat, there are different choices common to different weight classes.
In 150g to 1-pound classes the most common motors are N20 and 16mm motors from places like FingerTech or BotKits
In the 3-pound classes, 25mm spur gear motors and 22mm planetary gear motors are very common.

Common Brushed DC Gear Motors
Motor Type	Source 1	Source 2	Source 3
N20 Spur Gear	EndBots	ServoCity	DFRobot
16mm Spur Gear	FingerTech	BotKits
20mm Spur Gear	EndBots	ServoCity
22mm Planetary Gear	BotKits	RectifiedRobotics	ServoCity
25mm Spur Gear	KitBots	EndBots	ServoCity
25mm Double Spur Gear	AbsoluteChaosRobotics

Brushless Motors

In recent years DC Brushless motors have become more popular. Brushless motors are often both faster and lighter than an equivalent brushed motor, while experiencing less friction, remaining more efficient and less susceptible to heat related failures.

Brushless motors have 3 or even 4 wires, and they will not operate at all without a brushless electronic speed controller (ESC). This specialized circuit synthesizes the rotating magnetic field by sending waves of power into pairs of wires in sequence. By altering which wires are used, the ESC can also reverse the motor; by adjusting the shape of the waves, it can change the speed and torque of the motor. This gives a builder many options, but can make setup of brushless motors very complicated.