ROBOT . HEAD to TOE
Product User’s Manual –
Shield-Servo
1.2 How RC Servo Motor Works
RC Control hobby Servos are small actuators designed for remotely operating model vehicles such
as cars, airplanes, and boats. Nowadays, Servos are become more popular in robotics, creating
humanoid robot, biologically inspired robot, robotic arm and etc. This is because its ability to
rotate and maintain at certain location, position or angle according to control pulses from a single
wire. Inside a typical Servo contains a small motor and gearbox to do the work, a potentiometer to
measure the position of the output gear, and an electronic circuit that controls the motor to make
the output gear move to the desired position. Because all of these components are packaged into a
compact, low-cost unit, Servos are great actuators for robots.
Besides signal wire, a RC Servo has other two leads for power and ground. The control signal is a
continuous stream of pulses that are 1 to 2 milliseconds long, repeated approximately fifty times
per second, as shown below.
The width of the pulses determines the position to which the Servo moves. The Servo moves to its
neutral, or middle, position when the signal pulse width is 1.5 ms. As the pulse gets wider, the
Servo turns one way; if the pulse gets shorter, the Servo moves the other way. Typically, a Servo
will move approximately 90 degrees for a 1 ms change in pulse width. However, the
exact
correspondence between pulse width and Servo varies from one Servo manufacturer to
another
.
Shield-Servo is designed to simultaneously generate 8 independent Servo control signals. The
Servo controller can generate pulses from 0.5 ms to 2.5 ms, which is greater than the range of
most Servos, and which allows for a Servo operating range of over 180 degrees.
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