Build Your Own Combat Robot

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F batteries are the source of power for a robot, and motors are the source of
movement and locomotion, you might consider the electronic speed controller
(ESC) the “ringmaster” of all robot systems. The ESC is the device that controls
the amount of voltage that goes to the motors and the direction in which the motors
turn in your robot. Without an ESC, you cannot control your robot.
The ESC is probably the most critical component in the entire robot, so you
must select it carefully. An improperly selected controller will usually result in a
short life for your robot and can damage the motors or the batteries. If the ESC
fails during a competition, you can pretty much count on losing the match.
This chapter will explain several different approaches to implementing electronic
speed and direction controls, including simple relay controls and solid-state
electronic variable speed controllers. Each approach has its advantages and disadvantages
and should be selected according to the application.
Relay Control
A relay is an electric device used to switch a high-powered electric circuit with a
low-powered signal. Inside a relay is an electromagnetic coil and a set of movable
electric contacts. When power is sent through the relay coil, it creates a magnetic
field inside the relay case. The magnetic field then pulls a piece of metal connected
to a set of movable electrical contacts into contact with stationary set of contact
points—thus making an electric circuit and allowing power to flow to the load.
When the power to the coil is interrupted, the magnetic field disappears and a
spring pushes the movable contacts back into their original position, breaking the
circuit. Figure 7-1 shows a schematic of a typical single-pole double-throw
(SPDT) relay (see the next section for a definition of relay types).
Poles and Throws
Relays contain one or more circuits. The number of circuits in a relay are referred
to as poles. A relay with one circuit is called a single-pole (SP) relay. A relay with
two circuits is called a double-pole (DP) relay.